U.S. patent application number 11/974538 was filed with the patent office on 2008-04-24 for knee joint prosthesis and hyaluronate compositions for treatment of osteoarthritis.
Invention is credited to Andrew H. Cragg, Richard J. Greff, Jonathan Kagan, Rodlofo C. Quijano, Robert J. Socci, Jr., Hosheng Tu, George Wallace.
Application Number | 20080097606 11/974538 |
Document ID | / |
Family ID | 40568059 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080097606 |
Kind Code |
A1 |
Cragg; Andrew H. ; et
al. |
April 24, 2008 |
Knee joint prosthesis and hyaluronate compositions for treatment of
osteoarthritis
Abstract
A medical device and methods to relieve joint pain and adapted
for knee joint repair, replacement and augmentation. The invention
discloses joint lubricant, particularly hyaluronate compositions
and methods for treatment of osteoarthritis.
Inventors: |
Cragg; Andrew H.; (Edina,
MN) ; Greff; Richard J.; (St. Pete Beach, FL)
; Wallace; George; (Coto de Caza, CA) ; Socci,
Jr.; Robert J.; (San Juan Capistrano, CA) ; Kagan;
Jonathan; (Hopkins, MN) ; Quijano; Rodlofo C.;
(Laguna Hills, CA) ; Tu; Hosheng; (Newport Beach,
CA) |
Correspondence
Address: |
GREENBERG TRAURIG LLP (LA)
2450 COLORADO AVENUE, SUITE 400E
INTELLECTUAL PROPERTY DEPARTMENT
SANTA MONICA
CA
90404
US
|
Family ID: |
40568059 |
Appl. No.: |
11/974538 |
Filed: |
October 15, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60852885 |
Oct 19, 2006 |
|
|
|
60919305 |
Mar 20, 2007 |
|
|
|
Current U.S.
Class: |
623/14.12 ;
606/99 |
Current CPC
Class: |
A61F 2/30756 20130101;
A61F 2002/4635 20130101; A61F 2/461 20130101; A61L 27/20 20130101;
A61F 2/3872 20130101; C08L 5/08 20130101; A61L 27/52 20130101; A61L
27/50 20130101; A61L 27/20 20130101 |
Class at
Publication: |
623/014.12 ;
606/099 |
International
Class: |
A61F 2/08 20060101
A61F002/08; A61B 17/58 20060101 A61B017/58 |
Claims
1. A meniscal device comprising a support structure around
circumference of a meniscus in a patient, wherein the support
structure comprises a body with an exterior surface characterized
with enhanced boundary lubrication, the body being made of
biocompatible material selected from the group consisting of PVA
hydrogel, elastomers, polypropylene, polyethylene, PEEK, and
metals.
2. The device of claim 1, wherein said device comprises a meniscal
collar device.
3. The device of claim 1, wherein said device comprises a meniscal
wafer device.
4. The device of claim 1, wherein said enhanced boundary
lubrication comprises means for attracting or adsorbing a
surface-active phospholipid.
5. The device of claim 1, wherein said enhanced boundary
lubrication comprises means for coating a functional phospholipid
on said device.
6. The device of claim 1, wherein said enhanced boundary
lubrication comprises means for coating a reactable phospholipid of
phosphorylcholine.
7. The device of claim 1, wherein said enhanced boundary
lubrication comprises means for coating a reactable acrylate
polymer with phospholipid side chains.
8. A method of meniscal augmentation comprising administering a
meniscal bulking agent to increase a volume of said meniscus.
9. The method of claim 8, wherein said meniscal bulking agent is
administered by injection.
10. The method of claim 9, wherein said injection step is applied
using imaging guidance or arthroscopically under direct
viewing.
11. The method of claim 8, wherein said meniscal bulking agent
comprises a biodegradable hydrogel.
12. The method of claim 8, wherein said meniscal bulking agent
comprises a crosslinkable hydrogel with a first molecular weight,
said crosslinked hydrogel having a second molecular weight higher
than said first molecular weight.
13. The method of claim 8, wherein said meniscal bulking agent is a
liquid with a first viscosity index before an administering step,
said meniscal bulking agent having a second viscosity index after
the administering step, wherein the second viscosity index is
higher than the first viscosity index.
14. The method of claim 8, wherein the bulking agent has a first
volume before an administering step and expands to a second volume
after the administering step.
15. The method of claim 8, wherein the bulking agent further
comprises a scaffold seeded with autologous cells.
16. A method for treatment of osteoarthritis of a patient, the
method comprising injecting a suspension of HA microparticles into
a joint space of the patient, wherein said microparticles have a
hardness number less than the hardness number of a cartilage within
said joint space.
17. The method of claim 16, wherein said microparticles comprise
lyophilized HA, the lyophilized HA reconstitutes in situ after
being injected into said joint space.
18. The method of claim 16, wherein the joint space comprises
bursa.
19. The method of claim 16, wherein said microparticles have plural
concentric layers and plural concentric compartments separated by
said layers, each compartment being filled with said HA, wherein an
outer layer of said concentric layers is configured with a higher
degradation rate than a second degradation rate of an inner
layer.
20. The method of claim 16, wherein said nanoparticles further
comprise steroids.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The application claims the priority benefits of U.S.
Provisional Application No. 60/852,885 filed Oct. 19, 2006 and U.S.
Provisional Application No. 60/919,305 filed Mar. 20, 2007.
FIELD OF THE INVENTION
[0002] The present invention is generally related to therapies for
treating a joint or other body parts of a patient. More
particularly, the present invention is related to a medical device,
hyaluronic compositions, and methods for treatment of
osteoarthritis or relieving joint pain adapted for knee joint
repair, replacement and augmentation.
BACKGROUND OF THE INVENTION
[0003] The knee is very complex and includes many components with
many functions. The knee problems may be related to meniscus, pain,
cartilage, shock absorption, synovial fluids, articular cartilage,
ligaments/tendons and/or preserving normal biomechanics. Available
therapy currently includes chronic synovial lubrication, acute
synovial lubrication, meniscal protection, meniscal augmentation,
partial meniscal replacement, total meniscal replacement, and
partial or total knee prosthesis.
[0004] The menisci are crescents roughly triangular in cross
section, covering one-half to two thirds of the articular surface
of the corresponding tibial plateau. The outer rims of the menisci
are convex and attached to the knee joint capsule. The inner edges
are concave, thin and free. The anatomy of menisci and knee joints
can be found in any anatomy book, for example, Gray's Anatomy of
the Human Body, 20.sup.th edition, New York, Bartleby.com 2000.
[0005] The menisci extend the superior tibial surface, improving
its congruency with the femoral condyles. Both menisci are
fibrocartilaginous and wedge shaped in the coronal plane. The
medial meniscus is crescent shaped, and the lateral meniscus is
more circular. The superior portions of the menisci are concave,
enabling effective articulation with their respective convex
condyles, whereas the inferior surfaces are flat to conform to the
tibial plateaus. Anterior and posterior meniscal horns attach to
the intercondylar eminence of the tibial plateau. The coronary
ligaments provide peripheral attachments between the tibial plateau
and the perimeter of both menisci. The medial meniscus is also
attached to the medial collateral ligament, which limits its
mobility. The lateral meniscus is connected to the femur via the
anterior and posterior meniscofemoral ligaments, which can tension
its posterior horn anteriorly and medially with increasing knee
flexion. The transverse ligament provides a connection between the
anterior aspects of both menisci. The increased stability provided
by the ligamentous attachments prevents the menisci from being
extruded out of the joint during compression.
[0006] The knee joint is innervated by the posterior articular
branch of the posterior tibial nerve and the terminal branches of
the obturator and femoral nerves. Nerve fibers generally penetrate
the joint capsule, along with the vascular supply and service the
substance of the menisci.
[0007] Vascular supply is crucial to meniscal healing. The medial,
lateral, and middle geniculate arteries, which branch off the
popliteal artery, provide the major vascularization to the inferior
and superior aspects of each meniscus. Only 10% to 30% of the
peripheral medial meniscus border and 10% to 25% of the lateral
meniscus border receive direct blood supply. The remaining portion
of each meniscus receives nourishment only from the synovial fluid
via diffusion or mechanical pumping. The latter mechanism derives
from intermittent compression of the tissue during function.
Mechanical pumping through joint flexion may be essential for
continued nutrition.
[0008] The major meniscal functions are to distribute stress across
the knee during weight bearing, provide shock absorption, serve as
secondary joint stabilizers, provide articular cartilage nutrition
and lubrication, facilitate joint gliding, prevent hyperextension,
and protect the joint margins. During knee flexion, the femoral
condyles glide posteriorly on the tibial plateau in conjunction
with tibial internal rotation. The lateral meniscus undergoes twice
the anteroposterior translation of the medial meniscus during knee
flexion.
[0009] Type I collagen fibers provide the primary meniscal
structural scaffolding; this predominance of type I collagen is one
of the major differences between the menisci and hyaline, or
articular, cartilage, which is composed of predominantly type II
collagen. Three collagen fiber layers are specifically arranged to
convert compressive loads into circumferential or "hoop" stresses.
In the superficial layer, the fibers travel radially, serving as
"ties" that resist shearing or splitting. In the middle layer, the
fibers run parallel or circumferentially to resist hoop stress
during weight bearing. Lastly, there is a deep layer of collagen
bundles that are aligned parallel to the periphery.
[0010] Osteoarthritis (OA, also known as degenerative arthritis or
degenerative joint disease) is a condition in which low-grade
inflammation results in pain in the joints, caused by wearing of
the cartilage that covers and acts as a cushion inside joints. As
the bone surfaces become less well protected by cartilage, the
patient experiences pain upon weight bearing, including walking and
standing. Due to decreased movement because of the pain, regional
muscles may atrophy, and ligaments may become more lax. OA is the
most common form of arthritis. The main symptom is chronic pain,
causing loss of mobility and often stiffness. "Pain" is generally
described as a sharp ache, or a burning sensation in the associated
muscles and tendons. Humid weather increases the pain in many
patients.
[0011] OA commonly affects the hand, feet, spine, and the large
weight-bearing joints, such as the hips and knees, although in
theory, any joint in the body can be affected. As OA progresses,
the affected joints appear larger, are stiff and painful, and
usually feel worse, the more they are used throughout the day, thus
distinguishing it from rheumatoid arthritis.
[0012] The primary osteoarthritis is caused by aging. As a person
ages, the water content of the cartilage decreases, and the protein
composition in it degenerates, thus degenerating the cartilage
through repetitive use or misuse. Inflammation can also occur, and
stimulate new bone outgrowths, called "spurs" (osteophyte), to form
around the joints. Sufferers find their every movement so painful
and debilitating that it can also affect them emotionally and
psychologically.
[0013] The secondary osteoarthritis is caused by one or more of the
following conditions or diseases: (1) congenital disorders, such as
congenital hip luxation; (2) cracking joints; (3) diabetes; (4)
Inflammatory diseases, such as Perthes' disease, and all chronic
forms of arthritis (e.g. costochondritis, gout, and rheumatoid
arthritis); (5) injury to joints; (6) ligamentous deterioration of
instability; (7) hormonal disorders; (8) obesity; (9)
osteopetrosis; (10) sports injury; and (11) surgery to the joint
structures.
[0014] Heatley reported that repair of incisions in the central
part of the meniscus on rabbits has demonstrated after surgical
excision of the peripheral rim (J bone Joint Surg 1980;
62-B:397-402). Healing took place via a highly cellular but
relatively avascular fibrous tissue stroma which proliferated from
the synovial margin and invaded along the cut edge of the meniscus.
Suturing facilitated this healing process by providing stability
and possibly by supplying bridges for synovial cells to migrate
onto the meniscus.
[0015] U.S. Pat. No. 4,344,193 issued on Aug. 17, 1982, entire
contents of which are incorporated herein by reference, discloses a
meniscus prosthetic device for a human knee joint so that the
articulating cartilage in the knee totally remains intact. The
prosthesis device translates between the articulating cartilages
during normal knee movement. Insertion of the prosthetic device is
accomplished by applying force on the ends of the device, thereby
elastically spreading them, and placing the device between the
tibial articulating cartilage and one of the femoral condyles.
Prominences on the ends of the device may superiorly extend into
the space defined by the femoral condyles, thereby securing the
device in place.
[0016] U.S. Pat. No. 4,502,161 issued on Mar. 5, 1985, entire
contents of which are incorporated herein by reference, discloses a
prosthetic meniscus that is located between the natural articular
surfaces of the bones of a joint. The prosthetic meniscus includes
a body portion formed of a resilient material and further defines
an extra-articular extension which is attached to the surface of
the bone outside the joint. A reinforcing fabric or mesh is
embedded in the resilient material to give the meniscus strength
and shape.
[0017] U.S. Pat. No. 4,693,722 issued on Sep. 15, 1987, entire
contents of which are incorporated herein by reference, discloses a
prosthetic device for a temporomandibular joint comprising a
prosthetic condyle and a prosthetic meniscus. The prosthetic
condyle comprises two plates that are clamped about the ramus of
the mandible wherein one of the plates extends upwardly into a
convex surface thereby forming the condyle. The prosthetic meniscus
comprising a resilient insert which is inserted into the joint
capsule and has a reinforcing mesh embedded therein, and an
extension for attaching the meniscus to the temporal bone.
[0018] U.S. Pat. No. 4,795,468 issued on Jan. 3, 1989, entire
contents of which are incorporated herein by reference, discloses a
mechanism and method for locking or securing a bearing insert to
the base of a prosthetic implant. The prosthetic implant is for
replacement of a portion of natural bone at the point of
articulation. The implant includes a locking mechanism which
enables the bearing insert to be removably secured to the base
support. The locking mechanism includes a resilient locking clip
which is predisposed on one side of either the bearing insert or
the base support such that when the bearing insert and base support
are assembled together, the clip extends between both the insert
and the support to secure the two components together. To insert
and/or remove the bearing insert from the support, the clip is
caused to substantially fully recede into the component in which it
is predisposed.
[0019] U.S. Pat. No. 4,919,667 issued on Apr. 24, 1990, entire
contents of which are incorporated herein by reference, discloses a
soft tissue implant in the form of a meniscus cartilage replacement
for a patient. Appropriately shaped top and bottom layers sandwich
therebetween at least one intermediate felted layer. A resilient
bonding material coats the layers and holds same in a laminated
condition. The top layer is contoured, to provide a wedge shaped
cross section and a contoured three dimensional shape. A fabric
member is bonded to the thickened edge of the laminant and is
porous to invite ingrowth of patient tissue to anchor the implant
eventually in place.
[0020] U.S. Pat. No. 5,067,964 issued on Nov. 26, 1991, entire
contents of which are incorporated herein by reference, discloses
an articular cartilage repair piece to substitute for a cut-out
piece of damaged articular cartilage on a bone in an articulated
joint. The repair piece includes a backing layer of non-woven,
felted fibrous material which is conformable to flat and curved
surfaces.
[0021] U.S. Pat. No. 5,092,894 issued on Mar. 3, 1992, entire
contents of which are incorporated herein by reference, discloses a
meniscus prosthetic device replacing natural components of a
condylar joint. The body of the device is of biocompatible,
deformable, flexible and resilient material for bearing compressive
loads and for translating the loads to tensile stress. The tail of
the device is also biocompatible material and extends as a
continuation of the body from a first end to a second end of the
body. The tail provides a continuous loop circuit for the
propagation of hoop tensile stresses from the body, and provides
stabilization of the knee joint and proprioceptive feedback. The
prosthesis is implanted in a human knee in a position to take the
place of a naturally occurring meniscus between the femoral condyle
and the corresponding tibia, and the tail is placed into contact
with bone associated with the knee.
[0022] U.S. Pat. No. 5,158,574 issued on Oct. 27, 1992, entire
contents of which are incorporated herein by reference, discloses a
prosthetic meniscus implanted in a human knee where it can act as a
scaffold for regrowth of native meniscal tissues. The meniscus
comprises a dry, porous, matrix of biocompatible and bioresorbable
fibers, at least a portion of which may be crosslinked. The fibers
include natural polymers, analogs, or mixtures thereof. The matrix
is adapted to have in vivo an outer surface contour substantially
the same as that of a natural meniscus. With this configuration,
the matrix establishes an at least partially bioresorbable scaffold
adapted for ingrowth of meniscal fibrochondrocytes.
[0023] U.S. Pat. No. 5,344,459 issued on Sep. 6, 1994, entire
contents of which are incorporated herein by reference, discloses a
prosthetic device which is arthroscopically implantable into a
joint. The device has a ring or a pair of rings sized and shaped to
fit within the joint. The ring or rings are comprised of a
polymeric substance and may contain one or more compartments which
are inflatable or expandable with air, a liquid or a semi-solid,
through an arthroscope coupling means.
[0024] U.S. Pat. No. 6,046,379 issued on Apr. 4, 2000, entire
contents of which are incorporated herein by reference, discloses
an article of manufacture comprising a substantially
non-immunogenic knee meniscal xenograft for implantation into
humans. The invention further provides methods for preparing a knee
meniscal xenograft by removing at least a portion of a meniscus
from a non-human animal to provide a xenograft; washing the
xenograft in saline and alcohol; and subjecting the xenograft to at
least one treatment selected from the group consisting of exposure
to ultraviolet radiation, immersion in alcohol, ozonation, and
freeze/thaw cycling.
[0025] U.S. Pat. No. 5,171,322 issued on Dec. 15, 1992, entire
contents of which are incorporated herein by reference, discloses a
meniscus prosthetic device including a body and a tail. The body is
of biocompatible, deformable, flexible and resilient material for
bearing compressive loads and for translating the loads to tensile
stress. The tail is also biocompatible material and extends as a
continuation of the body from a first end to a second end of the
body. The tail provides a continuous loop circuit for the
propagation of tensile (hoop) stresses from the body, and provides
stabilization of the knee joint and proprioceptive feedback.
[0026] U.S. Pat. No. 5,807,303 issued on Sep. 15, 1998, entire
contents of which are incorporated herein by reference, discloses a
device for relieving synovial fluid pressure in a capsule
surrounding a body joint including a valve for placement in the
capsule surrounding the joint for regulating passage of synovial
fluid from the capsule. The valve can include a valve housing
defining a passage between an interior and exterior of the capsule
and a valve member disposed within the valve housing for regulating
synovial fluid pressure within the capsule by permitting synovial
fluid to drain from the capsule when a predetermined synovial fluid
pressure is exceeded. The valve housing can be secured to the
capsule with inlet and outlet flanges disposed at opposite ends of
the housing and, additionally, by use of openings formed in the
outlet flange to allow passage of sutures and to promote integral
tissue fixation over time.
[0027] U.S. Pat. No. 6,005,161 issued on Dec. 21, 1999, entire
contents of which are incorporated herein by reference, discloses a
biodegradable device for facilitating healing of structural voids
in bone, cartilage as well as soft tissue in the most preferred
form including a porous macrostructure made from a biodegradable
polymer and a chemotactic ground substance in the form of an RGD
attachment moiety of fibronectin formed as a porous microstructure.
For repair of articular cartilage, harvested precursor cells are
secured to the biodegradable carrier which is shaped for press
fitting into the articular cartilage lesion. In the most preferred
form, biological modifiers such as transforming growth factor
.beta. and basic fibroblastic growth factor is incorporated in the
biodegradable device to mediate cellular activity and regulate
cellular functions.
[0028] U.S. Pat. No. 6,132,468 issued on Oct. 17, 2000, entire
contents of which are incorporated herein by reference, discloses a
flexible scaffold envelope which can be used to replace damaged
cartilage. Designed for use in arthroscopic surgery, the envelope
is sufficiently flexible to allow it to be rolled up or folded and
inserted into a knee joint via a small skin incision. After the
envelope is inserted into the joint, it is unfolded, positioned
properly, and anchored and cemented to a bone surface. After
anchoring, the envelope is filled via an inlet tube with a
polymeric substance that will set and solidify at body temperature.
During filling and setting, the surgeon can manipulate the exterior
shape of the scaffold envelope, to ensure that the implant will
have a proper final shape after the polymer has cured into fully
solidified form.
[0029] U.S. Pat. No. 6,176,880 issued on Jan. 23, 2001, entire
contents of which are incorporated herein by reference, discloses a
reconstructive structure for a cartilaginous element having a
plurality of superimposed layers of intestinal submucosa tissue
compressed and secured together and shaped to provide a
reconstructive structure having the anatomical shape of the
cartilaginous element to be reconstructed is described. The method
of forming the reconstructive structure includes superimposing the
planar layers of the intestinal submucosa tissue, securing the
layers to form a multi-layered structure and cutting the resulting
multi-layered structure to the desired shape.
[0030] U.S. Pat. No. 6,352,558 issued on Mar. 5, 2002, entire
contents of which are incorporated herein by reference, discloses a
method of promoting regeneration of surface cartilage of a joint
including the steps of forming punctures in a subchondral plate of
an area of the joint to be treated, covering the puncture and the
area to be treated with a chondrocyte-free patch made of a sheet of
collagen membrane material without adding chondrocytes to the area
to be treated, fixing the patch over the area to be treated, and
allowing the area to be treated to regenerate cartilage without
adding chondrocytes to the area to be treated.
[0031] U.S. Pat. No. 6,530,956 issued on Mar. 11, 2003, entire
contents of which are incorporated herein by reference, discloses a
load-sharing resorbable scaffold used to help transplanted
chondrocytes or other cells generate new cartilage in a damaged
joint such as a knee, hip, or shoulder. These scaffolds use two
distinct matrix materials. One is a relatively stiff matrix
material, designed to withstand and resist a compressive
articulating load placed on the joint during the convalescent
period, shortly after surgery. The second material comprises a more
open and porous matrix, designed to promote maximal rapid
generation of new cartilage. The scaffold would support the
membrane with a degree of stiffness and resiliency that allows the
membrane to mimic a healthy cartilage surface.
[0032] U.S. Pat. No. 6,629,997 issued on Oct. 7, 2003, entire
contents of which are incorporated herein by reference, discloses a
device for surgical implantation to replace damaged tissue in a
joint (such as a meniscus in a knee) that is created from a
hydrogel that is reinforced by a three-dimensional flexible fibrous
mesh. In a meniscal implant, the mesh is exposed at one or more
locations around the periphery, to provide anchoring attachments
that can be sutured, pinned, or otherwise securely affixed to
tissue that surrounds the implant. Articulating surfaces which will
rub and slide against cartilage should be coated with a hydrogel
layer that is completely smooth and nonabrasive, and made of a
material that remains constantly wet.
[0033] U.S. Pat. No. 6,800,298 issued on Oct. 5, 2004, entire
contents of which are incorporated herein by reference, discloses
fluid compositions containing a dextran-based hydrogel with lipids
that provides enhanced rheological and tribological properties of
such a fluid. Phospholipids are particularly useful in
dextran-based compositions for synovial fluid. One phospholipid
that can be used advantageously in synovial fluid is dipalmitoyl
phosphatidylcholine.
[0034] U.S. Pat. No. 6,893,463 issued on May 17, 2005, entire
contents of which are incorporated herein by reference, discloses
an implantable knee prosthesis including a two-piece body having a
substantially elliptical shape in plane and including a first piece
and a second piece. The first piece is a tibial piece including a
tibial surface. The second piece is a femoral piece including a
femoral surface. The first piece and the second piece are mutually
slidably engagable and separable.
[0035] U.S. Pat. No. 6,905,514 issued on Jun. 14, 2005, entire
contents of which are incorporated herein by reference, discloses a
replacement device for resurfacing a joint surface of a femur. The
custom replacement device is designed to substantially fit the
trochlear groove surface of an individual femur. Thereby creating a
"customized" replacement device for that individual femur and
maintaining the original kinematics of the joint. The top surface
is designed so as to maintain centrally directed tracking of the
patella perpendicular to the plane established by the distal end of
the femoral condyles and aligned with the center of the femoral
head.
[0036] U.S. Pat. No. 6,960,617 issued on Nov. 1, 2005, entire
contents of which are incorporated herein by reference, discloses
hydrogels having improved elasticity and mechanical strength
properties by subjecting a hydrogel formulation containing a
strengthening agent to chemical or physical crosslinking conditions
subsequent to initial gel formation. Superporous hydrogels having
improved elasticity and mechanical strength properties are
similarly obtained whenever the hydrogel formulation is provided
with a foaming agent. Interpenetrating networks of polymer chains
comprised of primary polymer and strengthening polymer are thereby
formed. The primary polymer affords capillary-based water sorption
properties while the strengthening polymer imparts significantly
enhanced mechanical strength and elasticity to the hydrogel or
superporous hydrogel. Suitable strengthening agents can be natural
or synthetic polymers, polyelectrolytes, or neutral, hydrophilic
polymers.
[0037] U.S. Pat. No. 6,994,730 issued on Feb. 7, 2006, entire
contents of which are incorporated herein by reference, discloses a
method for resurfacing a joint capsule having cartilage and
meniscal surfaces such as a knee joint including resecting a
central portion of the joint cartilage on one joint member such as
the tibia while leaving a meniscal rim attached to the peripheral
joint capsule. A cavity is then formed in the bone underlying the
central portion of the joint surface such as the lateral tibial
surface. A resurfacing implant is then coupled, by cementing for
example, to the cavity. A soft prosthetic meniscal implant is then
coupled to the remaining meniscal ring such as by suturing.
[0038] U.S. Pat. No. 7,008,635 issued on Mar. 7, 2006, entire
contents of which are incorporated herein by reference, discloses
hydrogels intended for orthopedic applications with a hydrogel
formulation which has high strength, toughness, a suitable
mechanical modulus and low equilibrium hydration. It may have
controlled porosity or degradation time. It can be made to
polymerize in situ with high adherence to target tissue or
surfaces. A preferred formulation for forming such gels comprises
40 to 80% by weight of a low-molecular weight polar monomer and 30
to 10% of a hydrophilic macromeric crosslinker.
[0039] U.S. Pat. No. 7,060,074 issued on Jun. 13, 2006, entire
contents of which are incorporated herein by reference, discloses
instrumentation for use in minimally invasive unicompartmental knee
replacement including a tibial cutting guide for establishing a
planar surface along a tibial plateau and a tibial stylus having an
anatomic contour for controlling the depth of the planar surface
along the tibial plateau. The instrumentation further comprises a
posterior resection block for preparing a posterior femoral
resection, with a forward portion of the posterior resection block
having a configuration corresponding to the configuration of a
prosthetic femoral component. Instrumentation comprising a
resection block and a resurfacing guide are provided for surgically
preparing a femoral condyle to receive a prosthetic femoral
component. The instrumentation further includes a resurfacing guide
and a resurfacing instrument for resurfacing a femoral condyle to a
controlled depth.
[0040] U.S. Application publication No. 2001/0043913 published on
Nov. 12, 2001, entire contents of which are incorporated herein by
reference, discloses a meniscal implant biomaterial made of a novel
in situ produced macroporous biomedical polyurethane-amide material
based on chain extended isocyanate terminated polyester prepolymer
units, wherein the chain extension has been done with at least one
dicarboxylic acid or a hydroxy-carboxylic acid.
[0041] U.S. Application publication No. 2002/0022884 published on
Feb. 21, 2002, entire contents of which are incorporated herein by
reference, discloses a device designed for surgical implantation to
replace damaged tissue (such as a meniscus in a knee) having a
hydrogel component reinforced by a three-dimensional mesh. The mesh
component provides strength and structural support for the implant,
which has at least one articulating surface, and at least one
anchoring surface. In one embodiment, the mesh emerges from one or
more selected locations around the peripheral rim of a meniscal
implant, to provide anchoring attachments that can be sutured,
pinned, clipped, or otherwise securely affixed to the fibrous
capsule that surrounds the knee. This composite structure, with
hydrogel layers surrounding an embedded mesh component, provides a
joint-repair implant with improved anchoring, strength, and
performance compared to implants of the prior art.
[0042] U.S. Application publication No. 2002/0127264 published on
Sep. 12, 2002, entire contents of which are incorporated herein by
reference, discloses a method and system for the creation or
modification of the wear surface of orthopedic joints, involving
the preparation and use of one or more partially or fully preformed
and procured components, adapted for insertion and placement into
the body and at the joint site. In a preferred embodiment,
component(s) can be partially cured and generally formed ex vivo
and further formed in vivo at the joint site to enhance conformance
and improve long-term performance. In another embodiment, a
preformed balloon or composite material can be inserted into the
joint site and filled with a flowable biomaterial in situ to
conform to the joint site.
[0043] U.S. Application publication No. 2004/0133275 published on
Jul. 8, 2004, entire contents of which are incorporated herein by
reference, discloses a permanent non-resorbable implant allowing
surgical replacement of cartilage in articulating joints, using a
hydrogel material (such as a synthetic polyacrylonitrile polymer)
reinforced by a flexible fibrous matrix. Articulating hydrogel
surface(s) are chemically treated to provide a negative electrical
charge that emulates the negative charge of natural cartilage, and
also can be treated with halogenating, cross-linking, or other
chemical agents for greater strength.
[0044] U.S. Application publication No. 2004/0195727 published on
Oct. 7, 2004, entire contents of which are incorporated herein by
reference, discloses a method of making a lubricious
polyacrylonitrile knee meniscus implant of a predetermined form and
the resulting product.
[0045] U.S. Application publication No. 2004/0267371 published on
Dec. 30, 2004, entire contents of which are incorporated herein by
reference, discloses a prosthetic tibial component for a prosthetic
total knee joint, that comprises two constructs, one being a metal
base construct that engages the bone and the other being a
polyethylene bearing construct that attaches to the metal base
construct and articulates with a femoral prosthetic component on
the opposing side of the joint. The metal base construct is
composed of two different metals, one of which engages the bone
surface and the other of which engages the polyethylene bearing
construct. The first metal (i.e., the one that engages the bone
surface) is selected so as to provide a superior bone-engaging
face, while the second metal (i.e., the one that engages the
polyethylene bearing construct) is selected so as to provide a
superior polyethylene-engaging face.
[0046] U.S. Application publication No. 2005/0027307 published on
Feb. 3, 2005, entire contents of which are incorporated herein by
reference, discloses unitary surgical devices having a pair of
fixating mechanisms connected to a base with suture, anchors or
pre-formed holes in the base and further including extracellular
matrix material either as part of the base or supported on the
base. The extracellular matrix material serves as tissue
regenerating material. The devices can be used either as an insert
to be placed between and approximated to the inner surfaces of the
tear or as an insert to replace a void in the meniscus left after a
meniscectomy.
[0047] U.S. Application publication No. 2005/0033424 published on
Feb. 10, 2005, entire contents of which are incorporated herein by
reference, discloses a prosthesis for implantation into a knee
joint compartment between a femoral condyle and its corresponding
tibial plateau which reduces any excessive prosthesis motion. The
prosthesis includes a hard body having a generally elliptical shape
in plan and a pair of opposed surfaces including a bottom surface
and an opposed top surface, the top surface having a first portion
which is generally flat.
[0048] U.S. Application publication No. 2005/0043808 published on
Feb. 24, 2005, entire contents of which are incorporated herein by
reference, discloses a method and related composition and apparatus
for repairing a tissue site. The method involves the use of a
curable polyurethane biomaterial composition having a plurality of
parts adapted to be mixed at the time of use in order to provide a
flowable composition and to initiate cure. The flowable composition
can be delivered using minimally invasive means to a tissue site
and there fully cured provide a permanent and biocompatible
prosthesis for repair of the tissue site. Further provided are a
mold apparatus, e.g., in the form of a balloon or tubular cavity,
for receiving a biomaterial composition, and a method for
delivering and filling the mold apparatus with a curable
composition in situ to provide a prosthesis for tissue repair.
[0049] U.S. Application publication No. 2005/0055101 published on
Mar. 10, 2005, entire contents of which are incorporated herein by
reference, discloses an endoprosthesis having improved
self-lubrication mechanisms, the ability to filter the particles
from the debris produced by the moving parts, and a new
viscoelastic behavior under loading which reduce the transmitted
forces. This has been achieved with the use of compressible
materials and mechanisms between the fixed bearing and the tibial
component, allowing the endoprosthesis to have compressibility
under loading, which allows it also to receive or create chambers
with an exit to the surface articulating with the femoral
condyles.
[0050] U.S. Application publication No. 2005/0113840 published on
May 26, 2005, entire contents of which are incorporated herein by
reference, discloses various method and apparatuses used to perform
a resection of a portion of the anatomy for preparation of the
implants of a prosthetic. Various resecting member can be used to
assist in the resection of an anatomy to provide for implantation
of a prosthetic.
[0051] U.S. Application publication No. 2005/0137708 published on
Jun. 23, 2005, entire contents of which are incorporated herein by
reference, discloses a knee joint resurfacing including femoral
implant and tibial implant components. The femoral implant
components may be attached to the femur using screws or other
fixation devices. The femoral implant component may be configured
to share loads between cortical and cancellous bone material. The
tibial implant components are formed in modular portions which may
be assembled within the knee joint and may be free-floating or
fixed to the tibial surface.
[0052] U.S. Application publication No. 2006/0064169 published on
Mar. 23, 2006, entire contents of which are incorporated herein by
reference, discloses numerous joint replacement implant embodiments
including a total knee replacement implant including a femoral
component having a wheel; and a tibial component including a
shock-adsorbing component with a piston assembly and spring. The
implants contain a cushioning or shock-absorbing member to dampen
axial loads and other forces. In many embodiments, fluid is forced
rapidly from the device wherein compression and dampening is
achieved by valves or other pathways that allow for a slower return
of the fluid back into the implant as the pressure is relieved.
[0053] U.S. Application publication No. 2006/0155380 published on
Jul. 13, 2006, entire contents of which are incorporated herein by
reference, discloses a femoral component for a total knee joint
replacement having a modular structure including a number of
segments, each of the segments having a femoral fixation surface
for attachment to the distal end of a femur and at least one
assembly surface for joining with an adjacent segment of the
modular femoral component.
[0054] U.S. Application publication No. 2006/0178497 published on
Aug. 10, 2006, entire contents of which are incorporated herein by
reference, discloses implantable devices that include biocompatible
polyurethane materials. In particular, the disclosed polyurethane
materials can maintain desired elastomeric characteristics while
exhibiting thermoset-like behavior and can exhibit improved
characteristics so as to be suitable in load-bearing applications
such as in artificial joints, including total joint replacement
applications.
[0055] Oka and his associates reported that polyvinyl alcohol
hydrogel (PVA-H), `a rubber-like gel`, shows its usefulness as an
artificial articular cartilage (Proc Inst Mech Eng 2000;
214:59-68). As compared to polyethylene (PE), the PVA-H had a
thicker fluid film under higher pressures than polyethylene (PE)
did, and PVA-H had a better damping effect and better wear factor.
The artificial articular cartilage made from PVA-H could be
attached to the underlying bone using a composite osteochondral
device made from titanium fibre mesh. The composite osteochondral
device became rapidly attached to host bone by ingrowth into the
supporting mesh.
[0056] Hyaluronic acid and hyaluronates (HA's), such as Synvisc,
Hyalgan, Supartz, Orthovisc, Neovisc, Euflexxa/Nuflexxz, Durolane,
Fermathron, Suplaysn, are available for injection into joint spaces
to provide additional lubrication and treat pain associated with
osteoarthritis. HA's in solution are very viscous and therefore the
amount of HA per injection (about 2.0 ml) is limited by viscosity.
Although injections appear to be effective, these products require
multiple injections (usually 3-5) and the effectiveness lasts only
for 3-6 months. The present technology is to increase molecular
weight of the HA or to crosslink the HA to retard its degradation
and clearance from the joint space.
[0057] Hence, repairing or replacing a torn meniscus with a
meniscus wafer is suggested as a means to relieve the joint pain
and to treat the knee joint accordingly. The current invention also
discloses devices, methods, formulations, and instruments for
treating a joint of a body.
SUMMARY OF THE INVENTION
[0058] The primary goal for treatment of osteoarthritis using
hyaluronate compositions are to increase the duration of
effectiveness in lubrication and pain reduction, and to reduce the
number of injections required.
[0059] The secondary goal for treatment of osteoarthritis using
hyaluronate compositions are to improve the effectiveness (i.e.
reduce the coefficient of friction) in lubrication and pain
reduction, and to provide a therapy which can have applicability in
joints with relatively healthy (and therefore stiffer) cartilage as
well as older and degenerated (and therefore softer) cartilage.
[0060] These objectives can be attained by increasing the residence
time (half life) of the injected HA in the joint space;
improving/supplementing the lubrication efficacy of HA in the joint
space; and/or increasing the amount of HA per the injection.
[0061] In accordance with preferred embodiments of the present
invention, some aspects of the invention provide a support
structure around the circumference of the meniscus in a patient
configured like a collar around a neck ("meniscal collar"), wherein
the support structure comprises a body with an exterior surface
characterized with enhanced boundary lubrication properties, the
body being durable and abrasiveless that is made of biocompatible
material selected from the group consisting of PVA hydrogel,
elastomers, polypropylene, polyethylene, PEEK, and metals.
[0062] Some aspects of the invention provide meniscal augmentation
using meniscal bulking agent to increase the volume of the meniscus
either by injection or other filling means. The bulking agent may
include biodegradable or non-biodegradable hydrogels, crosslinkable
hydrogels having a higher molecular weight than those of
pre-crosslinked hydrogels, and the solidifiable hydrogels having a
higher viscosity index than those of pre-administered hydrogels.
The bulking agent may also include the scaffold, scaffold material
or scaffoldable biomaterial with cell seeding, ingrowth and
regeneration capabilities. In one aspect, the mesenchymal stem
cells or regenerative cells are included in the product formulation
of the bulking agent. Further, some aspects of the invention
provide cartilage augmentation as a process of increasing the
volume of the cartilage by injection, substitution or grafting. The
above cited method could be applied using imaging guidance or
arthroscopically under direct viewing.
[0063] Some aspects of the invention provide a meniscal wafer, a
generally planar construct, to fit between the tibial
plateau/meniscus and the femoral condyle. In one embodiment, a
meniscal wafer is an implant adapted to encourage tissue healing
and/or mitigate pain. In one embodiment, the meniscal wafer
comprises a surface antistick agent or characterized with boundary
lubrication configured to reduce physical adhesion. In another
embodiment, the meniscal wafer comprises an impregnated/entrapped
chemical marker that is leachable or exposable as a warning after a
predefined thickness of the wafer is worn out.
[0064] Some aspects of the invention provide a composite meniscus
comprising a multiple component or layer structure that serves as a
replacement meniscus. Components may be selected from the group
consisting of metals (stainless steel, NiTi, titanium, porous
titanium, and the like), lubricious polymers (PE, crosslinked PE,
PP, and the like), shape memory material (polymer and metal),
biodegradable polymers (PLA, PVA, PGA, PU and the like), hydrogels
or hydrophilic (PVA hydrogel, polyacrylamide, and the like), and
reinforcing support (porous substrate, woven fibers, filaments, and
the like). Layer configurations may be selected from the group
consisting of sliding layer, transition layer, ingrowth layer,
backing layer, and combinations thereof. The materials and
constructions disclosed herein also apply to the wafer. As
disclosed herein, a meniscal wafer differs from a replacement
meniscus by (1) generally being thinner and (2) attaching to or
abutting the meniscus vs. the tibia or tibial cartilage.
[0065] Some aspects of the invention provide a condyle cap sized
and configured to cover the femoral condoyle, the condyle cap
fitting like a cap (e.g. a form fitting knit hat) over the condylar
cartilage or bone. Further, some aspects of the invention provide
an articular bumper sized and configured as a cap covering the
tibial plateau that either may cover the meniscus or includes a
replacement meniscus.
[0066] Some aspects of the invention provide a method for treating
a joint by assembling the implant in-situ, wherein the implant
comprises two or more components. Further, some aspects of the
invention provide formed-in-place implants. In one embodiment, the
method to achieve a functional low friction joint is to form one or
more components out of a malleable or incompletely cured (e.g.,
polymerized) material in vivo or in vitro. The material is then
placed in the joint space (e.g., the location of the meniscus) and
then the joint cycled under load (full or partial) so the material
forms into a shape appropriate to the motion.
[0067] Some aspects of the invention provide a method for
manufacturing a customized anatomic implant by applying data from
modern imaging modalities such as CAT and MRI to create custom
implants (or tooling to manufacturing implants) with surfaces that
match the anatomy and the retained natural surface.
[0068] Some aspects of the invention provide a synovial lubricant
comprising phospholipids selected from the group consisting of
phosphoglycerides, phosphatidyl choline, phosphatidyl ethanolamine,
phosphatidyl inositol, phosphatidyl serine, diphosphatidyl
glycerol, and the like.
[0069] Some aspects of the invention provide a material or a
surface of the device that preferentially attracts and/or adsorbs
SAPL, the surface comprising a lipid or fatty surface. In one
embodiment of placing a functional phospholipid coating on a
device, one may prepare the surface (e.g. plasma etch or chemically
treat the surface of the device), and then expose the surface to a
reactable phospholipid, such as a phosphorylcholine which contains
an additional acrylic double bond, or a reactable acrylate polymer
with phospholipid side chains. The phospholipid is chemically,
covalently bonded to the surface of the device and to itself.
[0070] One aspect of the invention provides a material for
prosthetic articular surface that has high affinity to adsorb SAPL
or SAPL-like surfactant. Another aspect of this invention provides
for this affinity to absorb SAPL to be incorporated into the
bearing/lubricating surface of any of the devices described
herein.
[0071] Some aspects of the invention provide a
particulate-containing synovial lubricant that is specifically
designed to overcome some of the limitations of fluids such as HA,
wherein the preferred size range is about 50-150 microns with
50-100 microns considered normal desired size. The particles could
be made of any biodegradable polymer, such as PLA or other
hydrogel. The particles could be less than 60 A (shore durometer
scale) hardness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] Additional objects and features of the present invention
will become more apparent and the invention itself will be best
understood from the following Detailed Description of Exemplary
Embodiments, when read with reference to the accompanying
drawings.
[0073] FIG. 1 shows a method of positioning of an inserted meniscal
liner according to the principles of the present invention.
[0074] FIG. 2 shows a method of attachment of a meniscal liner
using sutures.
[0075] FIG. 3 shows insertion of a meniscal liner implant using a
delivery cannula.
[0076] FIG. 4 shows insertion of a meniscal liner without use of an
insertion cannula.
[0077] FIGS. 5A-5D show placement of a meniscal implant.
[0078] FIG. 6 shows a combined meniscal-tibial implant.
[0079] FIGS. 7A-7B shows an exemplary meniscal liner and an
exemplary combined meniscal-tibial liner.
[0080] FIG. 8 shows a prototype of meniscus replacement.
[0081] FIGS. 9A-9C shows meniscus liner variations.
[0082] FIG. 10 shows a condylar cover.
[0083] FIG. 11 shows a flowchart for manufacturing a custom
anatomic implant.
[0084] FIG. 12 shows load transmission in a meniscal collar.
[0085] FIG. 13 shows a meniscal prosthesis with: (A) layer
configuration; and (B) structure configuration.
[0086] FIG. 14 shows a process of repetitive surface coating on an
artificial cartilage.
[0087] FIG. 15 shows an illustration of a composite meniscus.
[0088] FIG. 16 shows one embodiment of a cone/frustum sliding layer
construct.
[0089] FIG. 17 shows a semi-lunar meniscus having a support collar
and an inner collar.
[0090] FIG. 18 shows a meniscus liner having prongs or anchors.
[0091] FIG. 19 shows a meniscus liner having screw or nail like
anchors.
[0092] FIG. 20 shows magnetic unloading mechanism of a joint by
configuring a femur having plural curved magnets which follow the
arc of the femoral condyle.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0093] The preferred embodiments of the present invention described
below relate particularly to medical devices for treating a joint,
for example a knee join. Joints are the place where two bones meet.
All of our bones, except for one (the hyoid bone in our neck), form
a joint with another bone. Joints hold our bones together and allow
our rigid skeleton to move. While the description sets forth
various embodiment specific details, it will be appreciated that
the description is illustrative only and should not be construed in
any way as limiting the invention. Furthermore, various
applications of the invention, and modifications thereto, which may
occur to those who are skilled in the art, are also encompassed by
the general concepts described below.
[0094] To better describe the invention, some terms are defined
herein as follows. "Meniscal collar" in this invention is meant to
refer to a support structure around the circumference of the
meniscus like a collar around a neck. "Meniscal augmentation" (or
"meniscal bulking agent") in this invention is meant to refer to a
process of increasing the volume of the meniscus either by
injection or other means. "Meniscal liner" ("meniscal wafer" or
"joint interface sheet") in this invention is meant to refer to a
generally planar construct that fits between the tibial
plateau/meniscus and the femoral condyle. Meniscal liners are
implants adapted to encourage tissue healing and/or mitigate pain.
The terms meniscal liner, meniscal wafer or joint interface sheet
can refer to devices that (1) cover the meniscus (only), (2) cover
the tibial plateau (only) or (3) cover both. "Composite meniscus"
in this invention is meant to refer to a multiple component or
layer structure that serves as a replacement meniscus. "Condyle
cap" in this invention is meant to refer to a prosthesis covering
the femoral condoyle, fitting like a cap (hat) over the condylar
cartilage or bone. "Cartilage augmentation" in this invention is
meant to refer to a process of increasing the volume of the
cartilage by substitution or grafting. "Articular bumper" is meant
to refer to a cap covering the tibial plateau that may either cover
the meniscus or include a replacement meniscus. Most of our joints
are "synovial joints". They are movable joints containing a
lubricating liquid called synovial fluid. Synovial joints are
predominant in our limbs where mobility is important. Ligaments
help provide their stability and muscles contract to produce
movement.
[0095] The knee includes many components (such as the bones, the
cartilage, the meniscus, and others) with many functions, including
the weight bearing, flexing, and walking. Femoral and tibial
condyles are the hard bones underlying the gliding surfaces of the
joint. Cartilage (articular hyaline) covers the bearing surfaces of
the bone and forms the primary bearing surfaces in a healthy joint.
Meniscus is a secondary bearing surface between the femoral and
tibial cartilages, is a cushioning layer and is a contoured surface
to help guide the joint as it flexes. The bone joint includes
medial and lateral compartments that essentially create two
separate, though not independent, bearing surfaces. Synovial fluid
serves to lubricate, and in some cases, nourish the tissue and
surfaces of the joint.
[0096] A ligament is a short band of tough fibrous connective
tissue composed mainly of long, stringy collagen fibres. Ligaments
connect bones to other bones to form a joint. Capsular ligaments
are part of the articular capsule that surrounds synovial joints.
They act as mechanical reinforcements. Extra-capsular ligaments
join bones together and provide joint stability. Ligaments are
slightly elastic; when under tension, they gradually lengthen. This
is one reason why dislocated joints must be set as quickly as
possible: if the ligaments lengthen too much, then the joint will
be weakened, becoming prone to future dislocations. Athletes,
gymnasts, dancers, and martial artists perform stretching exercises
to lengthen their ligaments, making their joints suppler. Some
ligaments limit the mobility of articulations, or prevent certain
movements altogether.
[0097] New approaches to knee surgery include surgical procedures
as well as apparatus. One current method includes total or partial
replacement of the knee joint using open surgery and arthroscopic
surgery (primarily the work on cartilage, including the meniscus
and ligaments). Current joint replacement surgery uses
standardized, in some cases modular, component inserted through an
incision. Even the procedure called "mini open" uses a 4 to 6
inches incision. Current arthroscopic procedures are performed
through small ports but are limited and not useful in the treatment
of osteoarthritis. These current procedures can be substantially
improved.
[0098] The following outline some methods which could be applied to
treat osteoarthritis and possibly other conditions of the knee.
[0099] (1) Minimally invasive joint replacement with an implant
that can be assembled in-situ: (a) by assembling the implant
in-situ, smaller openings are used to prepare the implant and
install the implant; (b) this requires specialized implants which
can include components traditionally made of one piece now made of
2 or more pieces to allow passage through smaller openings; (c)
assemble components (ideally self aligning when assembled),
particularly when seams occur on bearing surfaces; and (d) this
should have the capability of achieving an identical clinical
result to current procedures with the benefit of decreased
morbidity and the potential cost of a decreased implant life.
[0100] (2) Customized anatomic implants: (a) current total knee
replacement replaces all surfaces of the knee. Historically, and in
some cases presently, replacement of selective bearing surfaces of
the knee with standardized components has or is being attempted;
(b) in a partial replacement where only one of a match pair of
bearing surfaces is replaced and surface mismatch can lead to early
failure; and (c) this method will apply data from modern imaging
modalities such as CAT and MRI to create custom implants (or
tooling to manufacturing implants) with surfaces that match the
anatomy and the retained natural surface; (d) this method can be
applied to implants which replace and/or augment existing anatomic
structures; (e) these implants can be manufactured as used or in
forms that can be assembled or otherwise deployed in-situ. FIG. 11
shows a flowchart for manufacturing a custom anatomic implant. This
method can optionally be enhanced by use of a replaceable or
regeneratable bearing surface. [0101] (3) Formed in place implants.
Another method to achieve a functional low friction joint is to
form one or more components out of a malleable or incompletely
cured (e.g., polymerized) material. The material is then placed in
the joint space (e.g., the location of the meniscus) and then the
joint cycled under load (full or partial) so the material forms
into a shape appropriate to the motion. As an alternative to motion
under load, a temporary mold of form can be inserted in the joint
or the joint motion can be defined by an external brace or other
mechanism to achieve shaping. Alternately, the material can be
placed in the joint space within completely of partially preshaped
forms. [0102] (4) Internal augmentation. This method
augments/supports/supplements existing structures with internal
support while maintaining and/or supplementing existing bearing
surfaces. Bulky cartilage or filling a bone defect could be
examples of this method. This method could be applied using imaging
guidance or arthroscopically under direct viewing. [0103] (5)
External augmentation. Augmentation differs from other implant
schemes in that it uses rather than replaces existing structures,
particularly bearing surfaces. External augmentation could include
surface treatment (e.g., smoothing, coating, capping or some other
means of enhancing a surface while essentially maintaining its
existing structure and/or shape). This could also include minor
additions/corrections/adjustments of the surfaces. [0104] (6)
Implant preparation. One significant aspect of knee joint
procedures is the criticality of the alignment of the bearing
surfaces as well as the quality of their attachment to underlying
structures. This can be of particular interest with customized
implants manufactured from imaging. Similarly externally
manufactured surface implants must align with the existing
structures they are designed to overlay. Systems to either
artificially create or naturally identify landmarks during both
imaging/design and implantation are necessary, methods and/or
structures for aligning the bones and other anatomic structures may
also be appropriate,
[0105] Osteotomy is an accepted treatment for knee problems. In
this case, a cut is made in a bone (usually the tibia) to allow the
angle of the knee joint (e.g., the tibial plateau) to be adjusted
with appropriate joint alignment. The principle can be applied to
other approaches, for example, the meniscal liner described herein
can have varying thickness (e.g., thicker on the medial side) to
readjust the angle of the joint and its bearing surfaces (see FIG.
9). This could also be applied to a knee prosthesis such as a
uni-knee where the side of the knee which was not replaced may show
wear, thereby providing an opportunity for improved function by (1)
reducing the height of the uni-knee or (2) increasing the height of
the opposite side by the insertion of a spacer (for example a
meniscus liner). In both these cases, aligning the joint to
distribute load over both the lateral and medial side of the joint
will improve joint function/longevity and/or reducing pain.
[0106] FIGS. 9A-9C shows meniscal wafer variations. One aspect of
the invention (FIG. 9A) relates to a meniscal wafer with optional
tibial plateau cover. This example of the meniscal wafer is shown
including a tibial plateau cover. It is shown as having no special
attachment means and is intended for a free-floating application.
However, it could be sutured or adhesively bonded in place.
Exemplary prototypes of this configuration have been assembled
using 2 mm thick hydrogel adhesively bonded to a 0.5 mm thick
relatively rigid polymer backing layer. In this case, the polymer
backing layer was formed using vacuum forming techniques as known
in the art.
[0107] A second aspect of the invention (FIG. 9B) relates to a
meniscal wafer with optional meniscal retaining wing. This example
of the meniscal wafer is shown including tibial plateau cover and a
retention wing to extend the backing layer so it curves over and
around the outer circumference of the meniscus. Though this example
shows the retention wing around the entire circumference of the
meniscus, partial retention wings may be also clinically indicated
in certain situations. Exemplary prototypes of this configuration
have been assembled from vacuum formed polymers of varying
thicknesses and durometers as well as structures as described.
[0108] A third aspect of the invention (FIG. 9C) relates to a
meniscal wafer with optional tibial attachment wing. This example
of the meniscal wafer is shown including tibial plateau cover and a
retention wing to extend the backing layer so it curves over the
meniscus and extends down where it can be attached directly to the
tibia (for reference, U.S. Pat. No. 4,502,161 "Prosthetic meniscus
for the repair of joints" issued to Wall on 03-05-1985). Exemplary
prototypes of this configuration have been assembled as
described.
[0109] One issue relating to meniscus treatment is the
understanding of the process of meniscal degradation and
sensitivity of imaging methodologies for detection of meniscal
degradation.
[0110] In general the peripheral border of each meniscus is thick,
convex, and attached to the inside capsule of the joint. The
opposite border tapers to a thin free edge. The proximal surfaces
of the menisci are concave and in contact with the condyles of the
femur. The distal surfaces are flat and rest on the head of the
tibia.
[0111] The medial meniscus (MM) is somewhat semicircular in form
and is approximately 3.5 cm in length in the anteroposterior
direction and considerably wider posteriorly than it is anteriorly.
The anterior horn of the medial meniscus is attached to the tibial
plateau in the area of the anterior intercondylar fossa in front of
the anterior cruciate ligaments. The posterior fibers of the
anterior horn attachment merge with the transverse ligament, which
connects the anterior horns of the medial and lateral meniscus. The
posterior horn of the medial meniscus is firmly attached to the
posterior intercondylar fossa of the tibia between the attachments
of the lateral meniscus. The periphery of the medial meniscus is
attached to the joint capsule throughout its length. At its
mid-point, the MM is more firmly attached to the femur and tibia
though a condensation in the joint capsule known as the deep medial
collateral ligament (MCL).
[0112] On the other hand, the lateral meniscus (LM) is almost
circular and covers a larger portion of the tibial articular
surface than the MM. It is approximately the same width from front
to back. The anterior horn of the LM is attached to the tibia in
front of the intercondylar eminence and behind the attachment of
the ACL, with which it partially blends. The posterior horn of the
LM is attached behind the intercondylar eminence of the tibia in
front of the posterior end of the MM. There is no attachment of the
LM to the lateral collateral ligament (LCL) but there is a loose
peripheral attachment. The posterior horn of the LM is also
attached to the femur by means of the meniscofemoral ligament.
[0113] The meniscofemoral ligament is an accessory ligament of the
knee. During knee flexion, the meniscofemoral ligament pulls the
posterior horn of the LM anteriorly, increasing the congruity
between the meniscotibial socket and the lateral femoral
condyle.
[0114] It has been demonstrated that for meniscus lesions to heal,
the lesion must communicate with the peripheral blood supply. After
injury within the peripheral vascular zone, a clot forms rich in
inflammatory cells. This is a fibrin scaffold that eventually gets
filled with cellular fibrovascular scar tissue that glues wound
edges together. It becomes continuous with normal meniscus.
[0115] The extracellular matrix of menisci is composed primarily of
the fibrous elements, collagen and elastin, the proteoglycans, the
non-collagenous matrix proteins, and water with dissolved solutes.
The water content of menisci is about 74%. The dry meniscus is
composed of about 75% collagen, 8%-13% non-collagenous proteins and
1% hexosamine. Collagen fibers dominate both the morphology and
composition of the meniscus. Fibers are critical for the
relationship of structure and function of the tissue. The tissue
called fibrocartilage because of the dominance of collagen fibers.
This is apparent both at gross inspection and microscopic
inspection of the tissue. The non-fibrous proteoglycans are also
important for structure and function but also to the metabolism of
the menisci.
[0116] The combination of low compressive stiffness and low
permeability suggests that the menisci, as structures, should
function as highly efficient shock absorbers. Since the combined
mass of the menisci is much greater than that of the articular
cartilage bearing load across the femoromeniscotibial articulation
it is likely that most of the mechanical shocks generated in the
knee joint by the loading is absorbed by the menisci. The
deformation nature of the menisci with this low compressive (and
shear) stiffness and permeability show them to distribute load well
in the knee.
[0117] The strong ligaments, (cruciates and collaterals) menisci
and capsule, and the musculature constitute the primary stabilizers
of the knee. These structures and muscles around the knee
constitute a complete biomechanical system in which the tibia can
move with respect to the femur in many planes, yet also support the
high loads (more than 5 times body weight) commonly found in the
joint during daily activities.
[0118] Congruency is important in load transmission through the
femoromeniscotibial articulation. It has been reported that the
meniscus bears 50-80% of the compressive load of the knee joint. It
was reported that removal of 15-34% of the meniscus increases
contact pressure by more than 350%. The meniscal collar is a
minimally invasive implant device intended to augment the function
of the meniscus. The basic idea is a "collar" or rim placed around
one or both of the menisci. One embodiment is shown in FIG. 12 for
illustration.
[0119] The meniscal collar (MC) can be placed in an open procedure,
arthroscopically using a percutaneous procedure, or a combination
thereof. In a percutaneous approach, a guidewire would be passed
around the meniscus and then the MC could be pulled into position
by the wire or, with an appropriate lumen incorporated into the MC,
pushed over the wire into position. FIG. 1 shows positioning of an
inserted meniscal liner. Though the technique shown in FIG. 1 is
for positioning a meniscal liner, the similar technique can also be
used in positioning a meniscal collar.
[0120] The MC can be constructed from metal such as stainless steel
or tantalum, a lubricious polymer such as polyethylene (PE) or
crosslinked polyethylene or from a lubricating hydrogel such as
polyvinyl alcohol. The MC could optionally have reinforcing mesh or
wire or load transmitting wire or a removable wire that could be
placed in a lumen such as a guidewire lumen. The MC could also be
constructed, wholly, in combination or in part, from a shape memory
and/or biodegradable polymer such as those described in U.S. Pat.
No. 6,720,402 and U.S. Pat. No. 6,160,084, entire contents of both
are incorporated herein by reference.
[0121] The MC could have a variety of cross-section shapes
including round, oblong or custom shapes to mimic the load bearing
surfaces of the meniscus. The MC could be a single continuous shape
or change over the perimeter of the meniscus. The MC could be
smooth, contoured, or notched. Notched construction can facilitate
flexing of the MC if constructed by a more rigid polymer.
[0122] An MC could be constructed in many configurations, such as a
lateral medial construct, a combined heart construct, or a combined
pretzel construct.
[0123] Various shapes can accomplish certain goals such as avoiding
the cruciate ligaments or transmit greater forces (the "pretzel"
shape as shown above can have legs that can be locked and/or
tightened). These means to effect locking and/or tightening can be
optionally reversible and could use structures such as a ratchet
similar to that used in a "zip-tie", a series of balls with one or
more mating sockets or other means well know in the fastener
art.
[0124] The meniscal collar may function directly (by providing a
load bearing surface) or indirectly (by deforming and/or
containing) to supplement the meniscus so it can better support
loads. Or the meniscal collar may function both in combination.
[0125] One issue related to the use of a meniscal collar is the
fact that meniscal innervation and vasculature is on its periphery.
MC design should optionally incorporate means such as cushioning
(e.g., a hydrogel lining) or dimensioning (e.g., sizing to avoid
constant pressure on the meniscus) to avoid pain and/or ischemia.
Reinforcing of the MC can be, for example, NiTi, stainless steel,
other rigid polymers, or shape memory material. Additionally the
capsule of the knee joint surrounds the meniscus (as well as the
rest of the joint). Though in most clinical situations the meniscal
collar would be placed within the joint capsule, if clinically
indicated, certain configurations of a meniscal collar (not the
pretzel) could be placed on the exterior surface of the
capsule.
[0126] The MC design and shapes could be asymmetric in the support
of the knee and could work in extension, flexion or both. The MC
can be "free floating" or attached to the tibial and/or the
meniscus. The MC could be constructed of layered material where
some layers are optimized for their lubricious load bearing (for
example, PE) while other layers could be used for cushioning (e.g.,
a hydrogel or polyurethane). Attachment can be using fasteners or
ingrowth where a portion of the device in contact with the tibial
plateau can be, for example, sintered porous tantalum.
[0127] Meniscal Wafer/Liner
[0128] Some special characteristics of one example of the proposed
meniscal wafer of the present invention are shown below: (1) a PVA
(polyvinyl alcohol) backing plate with appropriate hydrogels (for
example, a PVA hydrogel) such that when wet, the hydrogels are very
slippery and the hydrogels provide good cushioning; (2) the
meniscal wafer might have an attachment wing (in some cases); (3)
the meniscal wafer might have a crescent-shaped NiTi reinforcement
(or reinforced by other material, configuration, or composite
characteristics) around the periphery of the hydrogel; (4) the
thickness of the meniscal wafer could be at least 1 mm, preferably
3 mm or more; (5) the backing plate is material that can be
manufactured as an integral or chemically compatible (for bonding)
to the hydrogel with desired mechanical integrity and properties.
FIG. 8 shows a combined meniscal-tibial implant whereas FIGS. 7A-7B
shows an exemplary meniscal liner and an exemplary combined
meniscal-tibial liner of the present invention. The meniscal-tibial
implant is herein meant to be the same as the replacement meniscus
with combined meniscus-tibia. For illustration, FIGS. 5 and 6 show
the three variations of the meniscal, tibial and combined
liners.
[0129] A meniscal wafer/liner of this construction can be
constructed of materials with flexibility to allow implantation
through a small skin incision. By ways of illustration, FIGS. 5B-5D
and 6B-6D show placement of a meniscal liner, where FIGS. 5A and 6A
show the corresponding anatomy with no implant. Sutures, or a wing
if included in the device, can be grasped from another port or
incision and used to pull the device through the skin and into
position in the knee. FIG. 2 shows attachment of a meniscal liner
using sutures. A meniscus liner can also be inserted with a
delivery catheter (see FIG. 3) or without use of an insertion
cannula (see FIG. 4).
Example No. 1 Meniscal Wafer Manufacturing
[0130] A meniscal wafer (MW) is a medical device implanted via an
arthroscope into the knee joint space (see FIG. 1) to act as a
support and bearing wear surface between the femoral condyle and
the meniscus/tibial plateau. It is for (1) use in partial or total
meniscectomy to supplement or provide meniscus function and
articulating surface (to minimize joint degradation), (2) use in
place of partial or total meniscectomy (to delay joint
degradation), (3) use after arthroscopic clean-up of osteoarthritis
(OA) joint to provide fresh articulating surface and improve
biomechanics (to delay total knee replacement, for example), and/or
(4) to adjust the alignment of the joint though height
supplementation. Meniscal wafers can be used on the medial, lateral
or both sides of one or both joints. Meniscal wafers can (i) cover
the meniscus (only), (ii) cover the tibial plateau (only) or (iii)
cover both. FIG. 5 (B-D) shows placement of a meniscal wafer.
[0131] The manufactured meniscal wafer has one or some of the
following characteristics: [0132] Insertion via an arthroscope and
through a cannula (folded or rolled configuration as shown in FIG.
3) or through a skin incision (as demonstrated in FIG. 4, where
arthroscope and tools are omitted for clarity); [0133] Permanent,
non-biodegradable device with a functional lifetime of 3+ years;
[0134] Non-fixed or floating design, limited in movement by
mechanical/physical means, such as a passive stopper configuration
at a periphery of the meniscal wafer; [0135] Medial, lateral and
dual compartment designs for various indications/presentations;
able to be trimmed (or malleable) by physicians; [0136] Materials
can be polymeric (e.g. crystalline PVA, crosslinked PU, PEEK, UHMW
PE) or a soft metal (e.g. Ti, non-ferrous, alloy). Reinforcing mesh
(e.g. carbon fiber) may be required for tear strength or
combinations of the above; [0137] Lubricious materials (e.g.
hydrogel or surfactant) or coating on device surface by adsorption,
chemical bonding (e.g. phospholipids) or ion implantation
(sputtering); [0138] Sterilization by ETO, H.sub.2O.sub.2, or
radiation (gamma or e-beam); and [0139] Shelf life of about 2 years
or more. [0140] FIG. 7B shows a combined meniscal/tibial liner for
reference.
[0141] The meniscal wafer or liner may need to be well attached,
particularly to resist shear forces. The anatomy might make it
difficult to secure at the perimeter. One approach is to have a
prong or interlocking fiber filled backing, like Velcro that will
stick to tissue when implanted as one approach for anchoring
purposes. An ingrowth encouraging material as described above (e.g.
sintered porous tantalum) may be appropriate. if, in a specific
clinical condition, it is desirable to fix the device to the tibial
plateau. The attachment means can be over all or part of the area
of the meniscal wafer (MW). Alternately, the meniscal wafer may be
sutured to the meniscus (see FIG. 2).
[0142] It is possible that a sheet would fragment, probably
painfully, when it fails. Fiber reinforced sheet may require
replacement before it wears to the reinforcing layer which will be
abrasive. A sheet constructed from metal may fail too and would
probably accelerate cartilage degradation. It may be desirable for
a meniscal wafer to have the property of degradation-on-demand or
other means described herein to facilitate device removal. This may
comprise a step of injecting a medically compatible solvent, for
example DMSO, into the knee that will quickly degrade the implant
(but preserve the surrounding tissue) so it can be removed by
flushing.
[0143] Active electronic detection could be built in for detection
of incipient failure. One example is to incorporate radiopaque
and/or MRI readable layers so device thickness and/or wear can be
seen at a routine doctor visit (for example, with ferromagnetic
tags) or wear releases something easily (and painlessly)
detectable, for example, methylene blue which turns urine blue.
[0144] In the past, porous material made of an aromatic
polyurethane were successfully used for meniscal reconstruction in
dogs. An aliphatic PU network, synthesized by crosslinking
poly(.epsilon.-caprolactone) and 1,4-trans-cyclohexane diisocyanate
with glycerol, was used (Biomaterial, September 1995). Dislocation
caused by tearing out of the sutures was found to be a problem
because the tear resistance of the material was relatively low.
Meniscal prosthesis turned out to induce fibrocartilage upon
implantation, and degeneration of articular cartilage was less
severe than after meniscectomy.
[0145] In the following embodiment, simple layers are shown with a
porous, woven or filamentous layer for ingrowth (see FIG. 13B).
Sintered porous materials such as tantalum are well known in the
art. They are created by compressing and bonding the particles so
there are a series of connected voids (or open pores) between the
particles. The size of the voids are related to the size and shape
of the particles as well as the processing (sintering)
parameters.
[0146] By ways of illustration, an exemplary meniscal liner and an
exemplary combined meniscal-tibial liner have been shown in FIG. 7A
and FIG. 7B.
[0147] Lubricating Fluid
[0148] The synovium (synovial membrane) generates and contains the
synovial fluid. The inner membrane of synovial joints is called the
synovial membrane, which secrets synovial fluid into the joint
cavity. This fluid forms a thin layer (approximately 50
micrometers) at the surface of cartilage, but also seeps into the
articular cartilage filling any empty space. The fluid within
articular cartilage effectively serves as a synovial fluid reserve.
During normal movement, the synovial fluid held within the
cartilage is squeezed out mechanically (so-called weeping
lubrication) to maintain a layer of fluid on the cartilage surface.
There is about 3.5 ml of synovial fluid bathes the knee joint. Some
lubricant or lubricant component is adsorbed by the articular
cartilage and then released under pressure.
[0149] Lubrication may be categorized as hydrodynamic lubrication,
elasto-hydrodynamic lubrication, transition from hydrodynamic to
elasto-hydrodynamic to boundary lubrication, and boundary
lubrication. Any substance acting as a boundary lubricant must
first be adsorbed or otherwise bound to the surface before it can
impart solid-to-solid boundary lubrication. The stronger the
binding and the more cohesive the adsorbed lining, the better is
the lubrication and resistance to wear under load. Synovial fluid
is believed to act as a vehicle for transporting the boundary
lubricant to its site of adsorption. Hyaluronic acid is often
injected into joints to provide "visco-supplementation", which
would enhance hydrodynamic lubrication in nonload-bearing joints
and other joints when not subjected to load. Basically, it
possesses no load-bearing capability unless surface-active
phospholipid (SAPL) or equivalent is incorporated.
[0150] Some aspects of the invention relate to a meniscal device
comprising a support structure around circumference of a meniscus
in a patient, wherein the support structure comprises a body with
an exterior surface characterized with enhanced boundary
lubrication, the body being made of biocompatible material selected
from the group consisting of PVA hydrogel, elastomers,
polypropylene, polyethylene, PEEK, and metals. In one embodiment,
the device comprises a meniscal collar device, a meniscal wafer
device, a meniscal liner device and the like.
[0151] In one preferred embodiment, the enhanced boundary
lubrication comprises means for attracting or adsorbing a
surface-active phospholipid, for coating a functional phospholipid
on the device, and for coating a reactable acrylate polymer with
phospholipid side chains.
[0152] One group of substances much used in the physical sciences
as boundary lubricants for transforming hydrophilic subphases to
hydrophobic surfaces are surfactants. Moreover, SAPL, known as a
surfactant in the lung, is present in the SF of normal joints in
appreciable quantities. These small molecules bind to amino acid
groups that comprise the protein chains in proteoglycans such as
lubricin. The lipid content of cartilage amounts to 0.3 to 4% and
lipid is composed of three basic components, cholesterol,
triglycerides, and phospholipids. The first two predominate in most
sites in which fat is located in the body. In the normal joint and
in the lung, the major component (about 60%) is phospholipid,
whereas a major sub-fraction of phospholipid is
phosphatidylcholine.
[0153] Phospholipids are a class of lipids formed from four
components: fatty acids, a negatively-charged phosphate group,
nitrogen containing alcohol and a backbone. Phospholipids with a
glycerol backbone are known as glycerophospholipids or
phosphoglycerides. There is only one type of phospholipid with a
sphingosine backbone; sphingomyelin. Phospholipids are a major
component of all biological membranes, along with glycolipids and
cholesterol. In phosphoglycerides, the carboxyl group of each fatty
acid is esterified to the hydroxyl groups on carbon-1 and carbon-2.
The phosphate group is attached to carbon-3 by an ester link. This
molecule, known as aphosphatidate, is present in small quantities
in membranes, but is also a precursor for the other
phosphoglycerides. One aspect of the invention relate to a synovial
lubricant comprising phospholipids selected from the group
consisting of phosphoglycerides, phosphatidyl choline, phosphatidyl
ethanolamine, phosphatidyl inositol, phosphatidyl serine,
diphosphatidyl glycerol, and the like.
[0154] Phosphatidyl choline is the major component of lecithin. It
is also a source for choline in the synthesis of acetylcholine in
cholinergic neurons. Phosphatidyl ethanolamine is the major
component of cephalin. In phosphoglyceride synthesis,
phosphatidates must be activated first. Phospholipids can be formed
from an activated diacylglycerol or an activated alcohol.
Phosphatidyl serine and phosphatidyl inositol are formed from a
phosphoester linkage between the hydroxyl of an alcohol (serine or
inositol) and cytidine diphosphodiacylglycerol
(CDP-diacylglycerol). ##STR1##
[0155] Some aspects of the invention relate to a material or a
surface of the device that preferentially attracts and/or adsorbs
SAPL, comprising a lipid or fatty surface. In one embodiment of
placing a functional phospholipid coating on a device, one must
prepare the surface (e.g. plasma etch or chemically treat the
surface of the device), and then expose the surface to a reactable
phospholipid, such as a phosphorylcholine which contains an
additional acrylic double bond, or a reactable acrylate polymer
with phospholipid side chains. The phosphatidylserine could also be
used. The phospholipid must be chemically, covalently bonded to the
surface of the device and to itself. Without a good covalent
bonding, the coating will rub off. Hydrophilic coatings are applied
in the same manner to the device surface.
[0156] Phospholipids (PL's) are naturally present in blood, plasma,
serum, etc. A mixed protein layer is deposited on a device's
surface within minutes to hours after body contact. PL's will
adsorb on the surface of a device soon after deposition of the
protein layer. Investigators have dip coated PL's from solution
onto an artificial surface and then exposed the device to blood or
plasma to get an even richer PL layer. However, this coating will
not be sturdy enough for a wear surface.
[0157] The capability of SAPL to act as a boundary lubricant was
first recognized in the thoracic cavity, in which frictionless
sliding of the lungs is needed to reduce the work of breathing.
SAPL also acts as a release (antistick) agent. If two normal
articular surfaces are clamped together, they do not stick.
However, if the SAPL lining (the outermost phospholipid zone) of
the articular cartilage is removed by a lipid solvent, then they
would stick. Some aspects of the invention relate to a meniscal
wafer, meniscal liner or a meniscal implant that comprises a
surface antistick agent or characterized with boundary lubrication
configured to reduce physical adhesion. Thus, a nonstick lining of
SAPL-like surfactant would prevent adhesive wear of the device of
the invention.
[0158] One aspect of the invention provides a material for
prosthetic articular surface that has high affinity to adsorb SAPL
like surfactant. Another aspect of this invention provides for this
affinity to absorb SAPL to be incorporated into the
bearing/lubricating surface of any of the devices described
herein.
[0159] It is speculated that changes in synovial fluid properties
accelerate meniscal degradation. The purpose of lubricating the
joint is to relieve pain, not to mask pain. Synovial fluid can be
classified into normal, non-inflammatory, inflammatory, septic and
hemorrhagic fluids. Osteoarthritis and trauma are in the
non-inflammatory class. Rheumatoid arthritis is inflammatory
whereas trauma can also be hemorrhagic.
[0160] To improve lubrication of the joints, it is one embodiment
of the present invention to insert a minimal invasive recirculation
pump. Articular cartilage is elastic, fluid-filled, and backed by a
relatively impervious layer of calcified cartilage and bone. This
means that load-induced compression of cartilage would force
interstitial fluid to flow laterally within the tissue and to
surface through adjacent cartilage. As that area, in turn, becomes
load bearing, it is partially protected by the newly expressed
fluid above it. This is a special form of hydrodynamic lubrication,
so-called because the dynamic motion of the bearing areas produces
an aqueous layer that separates and protects the contact
points.
[0161] Boundary layer lubrication is the second major low-friction
characteristic of normal joints. Some investigators have speculated
that the critical factor is a small glycoprotein called lubricin.
The lubricating properties of this synovium-derived molecule are
highly specific and depend on its ability to bind to articular
cartilage where it retains a protective layer of water molecules.
Lubricin is not effective in artificial systems and thus does not
lubricate artificial joints.
[0162] Joints such as the knee are bathed in lubricating synovial
fluid. If additional synovial fluid could be directed into the
space within the meniscus between the condyle and tibial plateau,
improved lubrication could be achieved. Similarly, if the synovial
fluid can be maintained in and around the surface of the meniscus
and/or between the cartilage of the femoral condyle and tibial
plateau during gait, improved lubrication could be achieved.
Similarly, if the synovial fluid in the meniscus (between the
condyle and the tibial plateau) could be pressurized, force would
be applied to separate and reduce the friction between the condyle
and tibial plateau (as with pressurized "air" bearings). And
thereby, the same effect as improved lubrication can be
achieved.
[0163] Valves have been proposed for use with synovial fluid. U.S.
Pat. No. 5,870,303 proposes a valve to relieve excess pressure in
synovial fluid. U.S. Application publication No. 2006/0064169
proposes a valved cushion where valves control the entrance and/or
exit of fluid into/out of a reservoir and thereby control a
cushioning effect during gait. Some aspects of the invention relate
to a system including valves and a reservoir as described in U.S.
Application publication No. 2006/0064169 with fluid being forced
from the reservoir into the meniscal space between the condyle and
tibial plateau for the purposes of improved lubrication.
[0164] The pumping of synovial fluid for the purposes of
lubrication could be optionally improved by: (1) providing any
piston type means to increase the pressure of the pumped fluid over
the pressure between the meniscus, condyle and tibial plateau by
sizing the piston with an area smaller than the tibial plateau and
meniscus so the weight of walking acts over a smaller area and
generating a higher pressure and (2) using a meniscal collar or
other means to entrap the pressurized fluid within the tibial
plateau and meniscus. An advantage of the use of such piston means
is that controlling the piston areas in a two chamber pump can
allow pressure multiplication to provide high pressure synovial
fluid within the joint. These pumps could be externally powered,
indirectly powered by gait (for example a piezoelectric crystal
could generate energy to power a pump) or directly powered by gait
such as the above referenced U.S. Application publication No.
2006/0064169. Alternately, other pumping and/or entrapment means
such as described below can be used to accomplish improved
lubrication.
[0165] Though higher pressure pumping can be advantageous, pumping
additional synovial fluid into the joint space when unloaded or
open during the gait cycle can also result in improved lubrication.
One such lower pressure embodiment illustrates a non-piston
meniscal pump being placed in meniscus to pump synovial fluid into
meniscus.
[0166] An extension of the meniscal pump disclosed above could be
an entire replacement meniscus designed to be a pump.
[0167] The synovial fluid saturated compressive pumping layer
stores fluid until compression forces the fluid out on to the
tibial plateau. Relief of compressing refills the layer. In one
embodiment, a device surface may contain sponge interstices to
transiently store synovial fluid or made lipophilic to attract SAPL
by treating the surface with reactable chemicals containing lipid
components or by dip-coating lipids onto the surface. The
cartilage-like mechanical properties of the device will reside with
the core material.
[0168] The outflow valve is shown as a thinned portion of the
bearing surface which allows it to move upward and thereby open
under internal pressure when weight is applied. The thinned area
also has room to move because it does not come in contact with the
condyle. The inflow valve deflects inward and would seal under
internal pressure. The inflow flap would incorporate means to
restrict its outward movement and create a seal when internal
pressure is created by compression of the meniscus.
[0169] The lubrication of the knee joints provided by synovial
fluid is necessary for joint function and longevity. It has been
reported that the lubricating ability of synovial fluid can change
due to or in response to, e.g., acute injury or arthritis.
Hyaluronic acid (HA) is used clinically to improve the lubricating
ability of synovial fluid. However, its effectiveness and length of
action (time wise) has been questioned or is not as long as
desired. Burdick et al. in U.S. Application publication No.
2005/0164981 and U.S. Pat. No. 6,800,298 proposed a combination of
a dextran hydrogel and a phospholipid.
[0170] Some aspects of the invention relate to a particulate
synovial lubricant that is specifically designed to overcome some
of the limitations of fluids such as HA which have very limited
half lives when injected into joints. The invention is unique in
that (1) it recognizes that one aspect of creating an artificial
lubricant, can be the criticality of particle size for function and
longevity; (2) it provides for material specifically different
fluid than dextran and phospholipid; and (3) it defines preferred
material parameters. For size consideration, particles should be
greater than 10 microns to avoid macrophage phagocytosis and
greater than 30-40 microns to avoid particles escaping into the
capillaries or other vasculature. As mentioned herein, the typical
SAPL lubricating layer is approximately 50 microns.
[0171] It is suggested that large particle sizes (100 microns) may
keep an artificial lubricant out of the bursae. The bursae are
synovial fluid filled sacs which form a lubricating interface
between soft tissue and bone; e.g. between the patellar tendon and
the underlying bone. Bursae occur at sites of shearing in
subcutaneous tissue or between deeper tissues such as muscle groups
and fascia. Many bursae develop during growth but new or
adventitious bursae can occur at sites of occupational friction.
The preferred size range is 50-150 microns with 50-100 microns
considered normal desired size.
[0172] For materials consideration, though longevity of treatment
is desirable it is expected that any such lubricant would have a
limited life and therefore safe biodegradation to allow
re-treatment is desirable. An example of a possible material is
poly(lactic acid) (PLA) or derivative, a well known material which
is (1) biodegradable (with control over degradation rate by
compounding); (2) available/processible as a solid particle, a
hollow particle or a hydrogel; (3) available in different forces
with controllable hardness; (4) readily accepting other materials
attached/grafted or otherwise incorporated.
[0173] In one embodiment, the configuration is a central (3-D) core
with attached long chain (1-D) hydrophilic molecules.
Alternatively, these attached long chain molecules could be lipids,
e.g. SAPL's, other PL's or hydrophilic molecules. The material
composite core and long chains would have effective particle sizes
in the desired range. This is another advantage of PLA in that it
can be made into particles of various sizes, for example PLA
particles of <0.2 micron have been reported. This combined with
the added long chain hydrophilic or lipophilic molecules would
allow manufacture of particles in the desired size range.
[0174] A lubricant works by reducing friction between bearing
surfaces in the knee. The bearing surfaces of greatest interest are
the femoral condyles and the tibial plateau/meniscus. The lubricant
can function as a thin film (such as when walking) or in a static
squeezed flat mode (such as when initiating motion after standing
still) certain properties of an optimal lubricant will address each
and/or both of these situations. It would not be desirable for any
particles present between bearing surface to be harder than the
bearing surfaces since this could cause the hard particles to dig
into or score the bearing surfaces under load. This would suggest
that the particles should be less than the 60 A (shore durometer
scale) hardness for healthy cartilage. If used with damaged or
degraded cartilage, the material with lower durometers may be
indicated.
[0175] This lubricant which is composed of (a) particles, (b) long
water or lipid trapping chain, and (c) a carrier fluid, saline or
preferably or an inert water soluble gel with the viscosity and
osmolarity of synovial fluid, will behave as (and in fact is) a
non-Newtonian fluid. This will help to address the needs of static
and dynamic lubrication in that (i) the particle will help to keep
a small separation space between bearing surfaces under static
loading; (ii) long chains will trap water or lipids which, in
combination with the long chains, will create a lubricity layer for
dynamic motion; and (iii) the carrier will assist with injection of
the lubricant, and in the case of inflammation, can help restore
synovial fluid viscosity.
[0176] One aspect of a lubricant is that it functions when in place
between load bearing layers. In other words, this is between the
femoral condyle and the meniscus and tibial plateau. Herein the
improvement of lubrication by pumping lubricant into this portion
of the joint has been discussed. It would alternately and/or
additionally be desirable to attract, and possibly attach,
lubricating molecules/particles to the bearing surfaces of the
joint whether natural and/or artificial. It could be desirable to
have the bearing surface had an inherent attraction to the
particles. This could be accomplished, for example, by having the
surfaces and the lubricating molecules/particles being of opposite
charge. In the case of an artificial bearing surface a magnetic
bearing surface could attract ferrous, or otherwise magnetically
susceptible, lubricating. It is possible that these effects could
be externally controlled by the application of external magnetic
field or be intrinsic properties of the materials. These attractive
effects can be used alone or in combination with chemical bonding,
for example as described herein applying to SAPL or other PL
lubricants.
[0177] Similarly, it would be possible to create particles of
materials which mimic the properties of the bearing layer itself.
This could create a self-healing and/or self lubricating bearing
surface where the combination of the loading and tracking of the
surfaces and the deposition and entrapment of new material could
mimic the living cartilage. Surface coating can be repeated by a
repeat application of artificial cartilage or lubricant particles
circulating in the SF (as shown in FIG. 14).
[0178] Materials for this could include the PLA or PVA hydrogel and
other materials, including the particulate lubricant described
herein. The PVA, or other hydrogel, could optionally be treated as
described herein to create a lipid attracting volume. Particles for
this application could be the same size as the lubricant described
above or could be larger depending upon the clinical situation. The
receptive bearing layer base could be natural cartilage or an
artificial material as described herein. Optionally have an
increased surface roughness or other treatment to increase the
adherence of the particles to the surface. Artificial cartilage
materials could mimic the properties of natural cartilage and have,
for example, durometer of 30 A-60 A; a SF lubricated static
friction of 0.20-0.40 (or 0.10-0.100); and a SF lubricated dynamic
friction of 0.03-0.05 (or 0.01-0.010).
[0179] This method of replenishing and/or replacing the cartilage
could be adjusted to use materials which are liquid when in
synovial fluid but then form a gel or hydrogel in-situ. This is a
variation on the form in place methodology as it can be used to
selectively deposit/create material on a surface from a circulating
biocompatible liquid. For example, Chitosan, a polysaccharide which
is nontoxic, biocompatible and biodegradable can be formulated to
gel at physiologic pH (7.4). Furthermore, Chitosan can be processed
to combine with fatty acyl chlorides to form a hydrogel. Carriers
can be used to attract the Chitosan to the bearing surfaces or a
negatively charges bearing surface base could attract positively
charged Chitosan molecules.
[0180] Composite Meniscus
[0181] The meniscal replacement shown herein is one embodiment of a
composite meniscus. Current replacement menisci are homogenous. The
basic composite meniscus can have 2, 3, 4 or more layer/components
as shown below.
[0182] Materials can be selected or optimized for their specific
function. The bearing layer should be durable (resist shear forces)
and be lubricious. Crosslinked HDPE is one example of a material
candidate for this layer. This layer can be further coated to
improve its lubricity with a hydrophilic or lipophilic coating,
e.g. a SAPL absorbing or adsorptive coating.
[0183] FIG. 8 shows a replacement Meniscus, with optional tibial
plateau cover. This example of the replacement meniscus is shown
including a tibial plateau cover. A soft meniscal portion is molded
from a polymer of appropriate durometer. It can be optionally
reinforced in a uni, bi or triaxial manner to resist flex and/or
prevent tearing or fragmentation. This can be accomplished using
fibers and or metal reinforcing bands or wires. This is then
optionally attached to a backing plate for mounting and interfacing
with the tibial plateau. The replacement meniscus can be attached
to the backing plate along all or a portion of its circumference.
In certain clinical situations, the "horns" of the meniscus are not
bonded to the backing plate to allow flexing during gait. The
backing plate can be attached to the tibial plateau using screw
type fasteners, adhesives or other means know in the art.
[0184] Exemplary prototypes of this configuration have been
assembled using a molded 50 A silicone rubber adhesively bonded to
a 0.25 mm thick metal backing layer. The area of the tibial cover
included a layer of a fiber reinforced lubricious fluoropolymer.
Though not included on these particular prototypes, a hydrogel
coating for the silicone layer was also available.
[0185] The lateral restraint would be to stabilize the knee as it
bends and this component would be expected to have been selected
for controlled resistance to deflection. High density polyethylene
(HDPE) or a fiber reinforced medium density polyethylene (MDPE) are
examples of the types of materials which could be used for this
application. The cushioning layer would be selected for its ability
to deform under load and absorb shocks; a low density polyethylene
(LDPE) or PE/EVA blend could be appropriate for this layer.
[0186] The mounting layer would be selected for rigidity to
facilitate interlocking (e.g., with a dovetail) with the optional
separable tibial base (e.g., SS or Ti) and for its ability to be
bonded to and integrated with the other components (e.g., HDPE).
The mounting layer could also include means such as fiber
reinforcement to facilitate attachment, and resist pull out by
sutures or other means such as darts or anchors The materials
described are all polyethylene, for purposes of illustration. The
materials can be thermally bonded together and the bearing layer is
the material often used in knee prostheses. Alternate materials may
be selected from a variety of sources: biodegradable (e.g., PLA,
PVA, PGA, PU and the like), hydrogels or hydrophilic (e.g., PVA
hydrogel, polyacrylamide, and the like), scaffold for cell growth
(e.g., PU, collagen, and the like) and metals such as porous
Tantalum, SS and NiTi or the like. The material can combine the
above properties and/or components and/or materials to achieve the
desired device useful life and properties.
[0187] A Meniscal liner or cartilage prosthesis, e.g. a meniscal or
condylar prosthesis, consisting of multiple layers (see FIG. 13A)
is illustrated in an exemplary embodiment with three layers as
shown here:
[0188] 1. Backing layer
[0189] a. For mounting to the bone/cartilage surface [0190] i.
(Optionally) to hold the device in place e.g. by ingrowth into a
porous surface as described herein [0191] ii. (Optionally) to allow
motion relative to the bone/cartilage surface [0192] iii.
(Optionally) to incorporate barbs, screws, cement or other means to
hold the backing layer to the bone/cartilage [0193] iv.
(Optionally) to incorporate reinforcement to facilitate attachment
using sutures, darts, anchors et al.
[0194] b. For lateral support (resistance to wrinkling due to
lateral forces)
[0195] c. As a "last line of protection" of the bone/cartilage
surface [0196] i. (Optionally) stronger and/or lower wear than the
other layers [0197] ii. May compromise properties which prevent
damage to mating surface for increased strength [0198] iii.
Ideally, if exposed by wear of the other surfaces, to function and
be lubricious with natural synovial fluid
[0199] 2. Transition layer
[0200] d. To provide a transition between the backing and sliding
layers [0201] i. Optionally (1) to be of intermediate wear and/or
strength; (2) to incorporate a wear indicator; (3) to be formed
from a material with mechanical properties identical to the sliding
layer; (4) to be formed from the same material as the sliding layer
modified/adjusted to have different mechanical properties
[0202] e. To have properties that will induce little or no damage
to its mating surface [0203] i. May compromise properties which
prevent damage to mating surface for increased strength [0204] ii.
When exposed by wear of the sliding surface, to function and be
lubricious with natural synovial fluid
[0205] f. To provide cushioning [0206] i. May resist deformation
more (or less) than the sliding layer
[0207] 3. Sliding interface layer
[0208] g. To provide a low wear low friction sliding surface [0209]
i. In the case of the meniscus to allow the femoral condyle to
slide [0210] ii. To function and compatible with natural synovial
fluid [0211] iii. (Optionally) to incorporate a wear indicator
[0212] h. To have properties that will NOT damage its mating
surface
[0213] i. To provide cushioning
[0214] An exemplary combined meniscal-tibial liner is shown in FIG.
7B which applies some of the above-identified specifications.
[0215] In the following embodiment, simple layers are shown in FIG.
16.
[0216] In the above cone/frustum embodiment the sliding layer can
be radiopaque or MRI opaque. With lucent transition and backing
layers when the device is viewed from above, and when the opaque
layer is worn away, lucent circles become visible or more visible.
The location of the circles will indicate the location of the wear
while the diameter of the circles will indicate the degree of wear.
Wear past the depth of the cones will be visible as a widening
non-opaque area. This can alternately or additionally be
accomplished by using colorants if wear detection by direct
(arthroscopic) vision is desired.
[0217] Double sided devices for placement between cartilage
surfaces (e.g. one embodiment of a meniscus liner) can be created
similarly using, for example, a 5-layer structure: 1. sliding
layer; 2. transition layer; 3. backing layer; transition layer; and
5. sliding layer.
[0218] In the above exemplary embodiment, the materials for the
device could be as follows:
[0219] 1. Backing layer [0220] a. Crystalline Polyvinyl Alcohol
[0221] 2. Transition layer [0222] a. A PVA hydrogel, slightly
stiffer than the PVA-PVP of the sliding layer
[0223] 3. Sliding layer [0224] a. PVA-PVP [0225] i. As described by
Katta et al (Bioengineering Conference, 2004. Proceedings of the
IEEE 30th Annual Northeast, Publication Date: 17-18 Apr. 2004. pp.
142-143) [0226] ii. Including an MRI-opaque ferromagnetic
additive
[0227] An exemplary meniscal liner is shown in FIG. 7A which
applies some or all of the above-identified specifications.
[0228] In another embodiment, the backing layer can be or can mate
with a bone interface layer that allows total or partial relative
motion of the meniscal layers relative to the bone interface
layers. An example of this could be a metal tibial cover with a
multilayer meniscus anchored to the tibial cover at its lateral or
mid portion while the horns of the meniscal layers are allowed to
flex and/or move as the joint extends and flexes. In this case, the
metal layer not covered by the semi-lunar shaped meniscal
prosthesis would be covered with a stationary lubricious low wear
surface (e.g. a phospholipid coating or a multilayer structure as
defined herein). Metal backings can optionally be attached or use
ingrowth for anchoring as previously described herein.
[0229] In these or other embodiments (and other types of meniscal
prostheses or meniscal wafer/liner type devices), as an alternative
or in addition to anchoring as described herein, the flexing and
deformation of the horns or periphery of a device may be controlled
by inclusion of a "C" or "O" shaped collar incorporated in the
periphery of the device. These support collars can also provide
tension on the device to resist lateral forces. These collars can
be metal (e.g. NiTi or SS) or a polymer (e.g. PEEK) or a metal
polymer combination.
[0230] If an inner collar is used (as shown in FIG. 17) it must be
configured not to create high spots or stress concentrations when
impinged by the mating joint surface (if in the area of joint
surface).
[0231] Kobayashi and associates reported that artificial meniscus
replacement using PVA hydrogel can supplement the meniscus function
2 years after implantation (Biomaterials 2005; 26:3243-3248).
Neither wear, dislocation, nor breakage of the PVA hydrogel
meniscus implant (90% water content) was observed. They also
proposed a composite meniscus of PVA hydrogel and the tissue
inducing polymer binding to surrounding peri-meniscus area.
[0232] Meniscus Liner Anchoring
[0233] An implanted ML will be exposed to both normal
(perpendicular to the plane of the ML) and lateral (in the plane of
the ML) forces. While normal forces would tend to compress the ML
between the femoral condyle and the meniscus/tibial plateau,
lateral forces can induce lateral or sliding (or gliding) motion of
the ML relative to the meniscus/tibial plateau. Note that in some
clinical conditions, the ML is intended to remain stationary
relative to the meniscus/tibial plateau while the femoral condyle
slides over the surface of the ML. To prevent lateral motion of the
ML relative to the meniscus/tibial plateau there are a number of
structures which can be employed as follows: [0234] (1)
prongs/anchors--Prongs or anchors extending out of the plane of the
ML where they can (i) extend into the cartilage/meniscus, (ii)
extend through the cartilage into the tibial plateau (TP) as shown
in FIG. 18.
[0235] Optionally the anchors can be angled to improve their
resistance to lateral forces/motion. Forces will be primarily front
to back but they can/will also be side to side. [0236] (2)
Ingrowth--tissue ingrowth is a well known method for establishing
an implant. A porous metal such as sintered Tantalum or a felt type
material or other tissue ingrowth material may be secured to the
meniscal/TP side of the ML or the ML material itself may be
configured to encourage ingrowth, optionally chemical means such as
growth factors or autologous blood clot may be used. Optionally the
meniscus/TP may be prepared to encourage ingrowth by being
pierced/scored or other equivalent means to the point of bleeding
to provide clots (blood cells, endothelial growth factors, platelet
derived growth factors, other growth factors, and fibrin etc.) and
a healing response to encourage ingrowth. [0237] (3)
Screw/Nail/Anchors--In some cases, a 2-stage anchoring process may
be desirable. In this case, the meniscus/TP is prepared by the
placement of one or more primary anchors to which the ML is thus
attached (see FIG. 19). This attachment can be with a peg or socket
or other means known in the art.
[0238] The primary anchor can screw or by other means be secured in
the TP and/or meniscal. Note that forces on the primary anchor
will, for the most part, be lateral and front to back in
particular, and the anchor should be optimized for resistance to
front to back lateral motion. An example of this could be something
similar to an arrowhead with blade surrounding a socket. In this
case, the broad side of the arrowhead would be oriented to resist
front to back motion. Use of individual pegs to resist lateral
motion of a meniscal liner can have additional benefits by allowing
or (by using a concave or concave shape) encouraging separation
between the liner and the underlining tissue. The combination of
this separation and the motion/compression due to gait and joint
flexion and elongation can effectively improve circulation of
synovial fluid by pumping the synovial fluid under the device to
the living cartilage.
[0239] One aspect of an ML type implant is that it would be subject
to wear and may fail mechanically as a result of wear and/or the
stresses imposed by normal and/or athletic activities. Since it is
likely that an ML would have a finite useful life it is desirable
that as the implant nears the end of its life it is not subject to
catastrophic failure in the event, it is not removed prior to the
end of its useful (undamaged) life. For the purposes of this
discussion, we would grade some primary failure modes as follows:
device fragmentation (worst), splitting or tearing (bad), or
thinning/wearing through (most desirable failure mode).
[0240] Cast or extruded polymeric sheets can be prone to
fragmentation as a failure mode. This can be reduced by the
inclusion of fibers as reinforcement. Fiber reinforcement can be
accomplished, for example, by adding chopped fibers, woven strands,
or layered strands. Inclusion of chopped fibers in a polymer matrix
can reduce and/or delay failure but the failure mode of this type
of reinforcement can still be fragmentation. Woven fabric
incorporated into and/or coated by a polymer can be the most
resistant to fragmentation; however, the over and under nature of
the fabric weave can be abrasive once the overlying polymer has
worn away. This can be minimized by selecting fibers which are
softer than the condyle cartilage which will be sliding over the
weave fibers. Layers of parallel fibers will be likely to be weaker
than a woven fabric when used in a polymer composite construction
as an ML. However, if the top layer of fibers is aligned with the
primary motion of the condyle over the TP, exposed fibers will be
less likely to abrade the cartilage.
[0241] In clinical situations, material selection and the ability
to detect the progress of wear of an ML will be factors in
determining the appropriate structure/reinforcing of an ML.
Further, detection of the wear progression or wear on an implant
before failure or before wear becomes detrimental to the patient
can be desirable. The defining parameter of an ML is its height or
thickness. The thickness of an ML defines the height (or
separation) of the knee joints. As the ML wears, it would be
expected that the thickness and height would be reduced. Though
significant height change can be detected using known imaging
techniques (e.g., MRI), greater precision could be desirable. For
example, in the case of a fabric reinforced ML, it would be
desirable to know when a certain thickness of polymer remained
above the fabric. This could be accomplished by creating a layered
polymer above the fabric where for example radiopaque and
radiolucent layers of 0.5 mm could be alternated. Similarly,
ferromagnetic particles could be used to create such a structure
that could be visualized using an MRI.
[0242] Another alternative would be to have a radiopaque or
Ferro-opaque layer 0.5 mm above the fabric in which case the
distance between the opaque layer and the bone vs. the known
preoperative distance corresponding to the articular cartilage
would indicate the wear limit had been reached. Please note that
the strategies can be used in many scenarios, in addition to the
fabric reinforced polymers. Another approach would be to have a
layer or defined zone of the material subject to wear been
impregnated with a chemical marker. This chemical marker would be
compatible and inert in that it could have no effect on the body
means of detection and could be by a routine blood test or other
diagnostic means.
[0243] One embodiment of this type of detector could be a material
such as methylene blue, a well known medical dye. This material has
been known to turn urine blue when ingested. If impregnation and
wear does not release sufficient material to be detected, then
marker material can be deposited in a small pocket or reservoir in
the implant which will be released by wear.
[0244] One other aspect of an implant relating to wear is the issue
of replacement. Removal of an implant can be a problemic part of
the replacement procedure. The idea of degrade-on-demand (DOD) is
that, when a naturally wearing or degrading implant should be
removed, the materials would allow quick and easy replacement by
accelerating the wear/degradation by causing the device to rapidly
degrade to allow reabsorbance and/or removal (for example, by
flushing).
[0245] For example, an ML may be constructed of a polymer which is
soluble in DMSO at body temperature. When wear is detected, the
knee joint may be flushed with DMSO until the ML degrades and is
flushed out of the knee joint by the flush fluid (DMSO). This can
then allow immediate replacement of the ML. Similarly, anchors used
to retain the ML in place may be soluble in DMSO or some other
biocompatible solvent. This would facilitate release of the ML from
its attachment to speed up or ease removal. Another aspect of
degradation on demand could be automatic degradation. This could be
an embodiment of a multilayer construction as described herein. In
this case, for example, an inner layer made of gelatin or some
other rapidly dissolving material would be surrounded and sealed by
a water impervious layer which could then be combined with a
primary outer layer composed of a hydrogel. The inner layers could
provide bulk and/or support to the softer outer layer which will be
of low friction and the primary load bearing interface layer. Wear
of the device through the water impervious layer would allow water
to attack the gelatin layer and a rapid decrease in the size and
stiffness of the device. Though this may be a painful means of
informing the patient that it is time to remove/replace the device,
its removal will be simplified by the dissolution of the inner
layer.
[0246] Magnetic Unloading and/or Alignment
[0247] The knee joints bear the weight of the body and have
transient loading more than double the body static weight. The
weight translates to normal forces on the bearing surfaces of the
joint. Reducing these normal forces can reduce the load, and
therefore the wear of the joint. It is suggested herein that
opposing magnets placed in or on the femoral condyle and tibial
plateau could be used to reduce these normal forces. Since it is
desirable for this force reduction to occur during gait and not
only when standing, it is preferable that this magnetic opposition
occurs while the joint flexes or extends.
[0248] The following options include both means to preserve and/or
replace the bearing surfaces of the joint. In the case of
replacement of the bearing surfaces (e.g., in a total knee
replacement) all or part of the femoral and tibial components which
are anchored to the bone are typically metal and could include
and/or be constructed from or include magnetic materials. For
example, rare earth magnets could be used with both components
having like poles (e.g., negative) facing each other. If it is
desired to unload the joint while preserving the bearing surfaces
of the knee, the mechanism as shown in FIG. 20 can be applied.
[0249] In this case, the femur has two or more curved magnets which
follow the arc of motion of the femoral condyle as it slides along
the tibial plateau.
[0250] Opposing bones in the tibia, shown here as opposing pairs,
can be straight or curved depending upon clinical requirements.
Though the opposing magnets are intended to provide a reduction in
the upward normal forces, geometric relationships can be selected
to include lateral force vectors to help stabilize the joint.
[0251] It is understood that lateral forces can be used to
stabilize a joint. These forces can, by their orientation, help to
align the path of the elongation and flexion of the knee. Thought
the rods should be parallel to each other for proper tracking they
can be angled to the left or right from the natural axis of the
relative (e.g. femoral vs. tibial) bending of the joint. In certain
clinical situations, it may be desirable to change this relative
angle. The gentle magnetic bias imposed by these off axis magnets
can result in a reorientation of the relative bending angle.
[0252] In other clinical situations, it may be desirable to adjust
the left-right (inside-outside) angle of the joint. Use of magnets
on one (not both) sides of the knee would result in biasing forces
which could result in realignment of the side to side tracking of
the knee.
[0253] Meniscal Allografting
[0254] One aspect of the partial meniscectomy, particularly in the
case of an acute injury to a young patient, is that the tissue
removed is basically healthy. During the partial meniscectomy
procedure, the tissue can be collected, prepared and then
reimplanted into the meniscus as an allograft. Collection could be
performed using an arthroscopic shaver (which will result in
relatively small chunks) or other methods can be used to remove the
tissue block.
[0255] Tissue allograft preparation could consist of one or more of
the following: (a) slicing, dicing, grinding, (b) and optionally
mixing with other components such as blood/clot, growth factors
and/or other agents, (c) preparation for implantation could be as
simple as loading in a syringe alternately the tissue could be
loaded into a miniature sausage casing (optionally biodegradable).
Sausage casing implies porosity with porosity optimized for
nutrients and possibly blood cells.
[0256] Re-implantation could be as simple as injecting the tissue
back into the remaining meniscus as a bulking agent or if loaded in
a sausage casing could be all or partially implanted.
[0257] Though it is not necessary that the autograft sausage
traverse the meniscus from outside-in (or inside-out), this has
advantages in that at least a portion of the autograft is exposed
to the vascularized meniscal rim. Therefore, the autograft itself
may serve as a conduit for nutrients et al. from the outer rim to
the inside portions of the meniscus.
[0258] The exposed portion of the autograft may be protected by an
ML as an option. Similarly, multiple autografts may be used to form
a replacement for the tissue removed. Also additional autogeneous
material may be added to the meniscal tissue to enable use of a
larger number of autograft plugs.
[0259] Other Aspect-Custom Condyle Caps
[0260] The custom condyle cap (CCC) is based upon the concept of
covering the existing surface(s) at the femoral condyle with a
custom made form fitting prosthesis. One example is a half red
blood cell shape that covers the condyle to relieve pain. For
simplicity, the following examples would model the condyle as a
hemisphere. The CCC is a customized anatomic implant. The CCC may
be made of a metal, such as NiTi as follows: (a) image the condyle
or condyles; (b) create male & female tools; (c) stamp and
clamp a sheet of metal between the tools; (d) trim the sheet as
appropriate (this step may precede step c above); (e) if integral
retainer tabs are included with design, position tabs in their
final intended position; (f) heat the metal sheet and tools above
the transition temperature (about 1000.degree. F.) to the
austenitic phase; (g) after an appropriate time at the desired
temperature, remove CCC from tools and cool below the metal
austenitic/martinesetic transition temperature of about 90.degree.
F. (Note: the metal NiTi is selected to achieve this
austenitic/martinestic transition temperature); (h) reform the CCC
to be optimal for the desired surgical procedure for
implantation/attachment; (i) maintain CCC below the transition
temperature until implantation; and (j) implant and allow CCC to
achieve its final shape on the face of the femoral condyle. Note
that with shape memory CCC's, it is critical that the CCC be
maintained at temperature until positioned for attachment to the
condyle and maintained in position until shape change is complete.
At any stage, generally after (e) or (h), the metal can be coated
on one or both sides with an appropriate polymer (e.g. a PE or
Fluoropolyment or a hydrogel) or other coating. If applied after
(f) or (g) and before (j) it must have sufficient flexibility
deformability to accommodate the shape change at step (j). If
applied before step (f), the coating must withstand the processing
temperature and have the flexibility/deformability previously
mentioned. If applied in-situ using attraction deposition as
mentioned herein, the metal should be made receptive/attractive to
the coating.
[0261] FIG. 10 shows a condylar cap with a lubricious bearing
surface and surfaces on the side to hold the cap in place. Though
this example of the condylar cap is intended to represent a custom
anatomically designed specifically fit on this individual patient's
anatomy, it could be also a standard implant placed on a prepared
surface. In this example, a 3-layer structure is employed with a
flexible middle land a top sliding layers limited to the load
bearing regions of the device. The backing layer has additional
material which extends around the femoral condyle to retain the
device in place. Optionally additional fastenings and/or adhesives
can be used to hold the device in place.
[0262] Use of a shape change material for a CCC is exemplary.
Stainless steel, titanium or other materials (alloy with suitable
fabrication techniques) can be used. Materials used for CCC's may
have an impact on surgical procedures. Flexible or shape changing
implants may allow implantation through a smaller incision or even
arthroscopically. NiTi can be used to make a superelastic CCC also.
The concept of a custom cap of this invention may apply to other
implant caps beyond the standardized shaped and sized condylar
caps.
[0263] One aspect of the CCC is that it is ideally of a relatively
thin thickness or cross-section. Another aspect is that it requires
little or no removal of bone. Cartilage overlying the condyle is
optionally or non-optionally removed. The CCC designs can include
coating and/or layer(s) which would simulate or substitute for the
cartilage. This artificial cartilage may be designed to be
replaceable. It can be PE, crosslinked PE, hydrogel or other
suitable material. This artificial cartilage layer can also
optionally include self-healing capability as described above.
[0264] In an extremely superelastic CCC, the CCC may be formed and
then rolled into a cylinder which can be passed through an
arthroscopic portal into the knee. The CCC then would unroll and be
positioned accordingly. The procedure/method as outlined should
include the step of preparing the condyle or condyles for receiving
the CCC implant. CCC design may also include spikes or pegs to
attach them to the femur and prevent shifting or slipping. Cement
or other adhesives can also be used.
[0265] Tibial/meniscal cover devices (for medial or lateral
compartment menisci) may be constructed as an artificial cartilage
covered metal plate over the tibia/meniscus with wings for
attachment. In one embodiment, the backing should be directly over
the tibia and include a total meniscus replacement. In another
embodiment, the above-identified plate is without wings. If needed,
the mounting of the cover device is on or very close to the tibial
face, possibly under the meniscus replacement. Similarly, a condyle
cover may be consisted of a tin backing plate with wings for
attachment to an artificial cartilage sliding surface.
[0266] Other Solutions-Localization or Relocalization
[0267] One aspect of implants which are custom constructed for
existing anatomy is the desire or need to match and/or duplicate
the geometry of the joint from which the implant was designed with
the geometry of the joint into which the implant is placed. This
can be an issue when minimally sized incisions or portals are used
to place an implant. Current technology for open total knee
replacement and especially mini open procedures makes use of
cutting guides to correctly position components of the implant.
This is also the practice with partial knee replacements such as
uni-component (or uni-knee) prosthesis.
[0268] One of the advantages that may be achieved with a custom
constructed implant is the minimization or elimination of cutting
notches in the bone to position the implant. Absent notches cut in
the bone or in a situation where an implant is designed and/or
constructed using an anatomy dependent notch which may be defined
(but not formed) at a procedure other than the procedure in which
the implant is placed, other methods and apparatus are needed.
[0269] Some aspects of the invention relate to a method and
apparatus involving: (1) using an external frame to position
markers on the femur and tibia prior to performing an imaging
study; (2) at a later date replacing the frame at the same location
on the femur and tibia to match the localization of the initial
imaging with the implant procedure. Apparatus of the marking would
be matched to the imaging modality, e.g., radiopaque for CAT scan
marking must be sufficient to define the location in
space--specifically a minimum of 3 points on each bone or 2 lines
on each bone.
[0270] Marker should be designed so as to facilitate relocation,
that is, precise relocation of the frame at the follow up
procedure.
[0271] Markers would prefer to be biodegradable or removable. This
can be accomplished by having an opening in the bottom of the
marker into which a hydrogel or barbed removal tool can be placed.
In one embodiment, the removal tool is part of the frame used for
the second procedure (not the first) so removal at the frame
removes the marker.
[0272] Three markers can have the advantage of surrounding the
limb.
[0273] Two line type markers can accept and restrain elongated
pines that can allow the use of a guide frame that does not need to
surround the limbs. The above shows the most basic frame where it
is used only to accurately localize and relocalize the limbs.
Additional arms or beams attached to the frame can be used to guide
placement of an implant or cutting a notch in a base.
[0274] The meniscus bears a great deal of the load which is borne
by the knee. Replacement menisci have had mixed result while
arthroscopic procedures on the meniscus are effective. In an effort
to preserve and supplement the performance of the meniscus, the
idea of injecting materials into tissue to augment the appearance
or function of tissue is well known. U.S. Pat. No. 6,390,096 is an
example of where a needle is used to implant a solid prosthesis
into the palate to alter the mechanical response of the palate to
air flow. The idea of meniscal augmentation or bulking would
involve using a needle system, similar to U.S. Pat. No. 6,390,096
to inject a hydrogel or other polymer into the meniscus.
[0275] Based upon the clinical situation, it can be beneficial to
use a system with a non-coring type needle as is well known in the
art. Similarly, use of a needle with a little or no cutting (like a
taper style surgical needle) can be beneficial in some cases. The
implant which is placed in the cavity formed by the needle
penetrating into the meniscus. Then serves to build up, i.e.,
expand the volume of the meniscus and thereby provide additional
support to the joint. Multiple implants can be inserted and repeat
procedures can be performed. Implant material can be optionally
biodegradable or bioresorbable.
[0276] Implant material can be relatively rigid or soft and springy
as would be a hydrogel which will cyclically absorb and expel fluid
due to changes in external stress. This would duplicate the
performance of natural cartilage. Elastomers such as silicone or
polyurethane may also be useful in this application. One advantage
of this type of implant is that it maintains the meniscus tissue as
the bearing material in contact with cartilage and bone.
Optionally, the bulking implant can be a growth encouraging
scaffold which would facilitate growth and regeneration of meniscal
cells. Optionally, the building implant can be biodegradable.
[0277] Fixed or variably curved implantation needles may
enable/facilitate implantation around the circumference of a
crescent shaped meniscus. For the mechanic, one approach to
extending the life of a worn bearing is to replace or resurface the
worn bearing surface. This can be accomplished through the use of a
replaceable liner or added sleeve placed within an existing liner.
In the case of the knee, some have considered the meniscus as a
replaceable bearing liner and have contemplated replacing the
meniscus (for example, U.S. Pat. No. 6,893,463, entire contents of
which are incorporated herein by reference).
[0278] The idea of the meniscal liner (ML, also referred to herein
as meniscal wafer MW) is more akin to the concept of placing a
sleeve within an existing bearing liner. A sleeve type liner placed
over the existing meniscus and/or tibial plateau could achieve
multiple objectives: (1) It can isolate the meniscus from tear
inducing shear stresses; (2) It can provide a fresh smooth
lubricious bearing surface; (3) It can optionally add height to the
joint by adjusting the thickness at the liner; and (4) It can
optionally adjust or modify the shape/configuration of the bearing
surface of the joint.
[0279] The ML can be constructed in a number of manners. One
example would be to make a positive mold of the meniscus from CAT
or MRI data. This mold could then be used with standard vacuum form
equipment. After forming, the liner could be trimmed and optionally
modified, coated and/or otherwise prepared for implantation before
sterilization. The liner could be made from many materials (some of
the following can be thermoformed: PE, PP, acrylic, PU et al.,
biodegradable materials such as PLA, PGA etc). The ML can also be
used as an adjunct to a meniscal tissue engineering procedure. In
this case, the ML is used to provide a bearing surface for the
joint while a paste graft, collagen (or other) scaffold or other
collagen regenerating procedure is performed. In some cases, an ML
made from a biodegradable material would be used for this
application. In some cases, an ML made from or coated with a
hydrogel material would be used for this application.
[0280] The ML can be a totally separate component or can be
integrated with the graft/scaffold/collagen. In certain clinical
situations, a key of the use of the ML can be that it protects a
regenerating meniscus. It should be noted that though described as
being specific to the knee, the devices and methods might apply to
other joints, such as hip and shoulder.
[0281] The meniscal liner can optionally include a liner that
covers the tibial plateau in addition to the meniscus. Optionally
the ML can be porous to allow passage of synovial fluids.
Optionally the ML can be made from a hydrogel and/or lipophilic
material where the trapped/absorbed water or lipids could improve
the lubricity of the ML surface. A mock up meniscal liner was
prepared using 0.5 mm PP and a dental thermoforming machine. The ML
was trimmed and removed from a meniscus mold. A plastic knee model
was then reassembled with the ML in place. Prototypes were also
constructed using hydrogel layers of varying thicknesses on the PP
backing layer. In bench-top experiments, the knee articulated
appropriately with the polypropylene and PP/Hydrogel ML mock-up
sheets in place. The bearing surfaces at the knee include the
condyles (their articular cartilage lining), the meniscus and the
tibial plateau.
[0282] The surfaces can be improved in a number of manners using a
number of technologies/techniques that differ from improvement of
their lubricating synovial fluid. The surfaces could be improved
by: (1) making them smoother and harder (to reduce friction and
resist wear and damage); (2) making them more lubricious (to reduce
friction); (3) making them softer to avoid damage to the natural
surfaces; and (4) making them tougher (to resist tears and other
damage). The surface improvement could be accomplished by: (1)
attaching a material or lubricant directly to the cartilage using a
chemical bond; (2) attaching the material or lubricant directly to
the cartilage using a photo activated bond; (3) attaching the
material or lubricant to the cartilage using a carrier material;
(4) attaching an intermediate material to the cartilage which will
scavenge and bond active particles, moieties or ingredient
circulating in the synovial fluid; and (5) placing an active
particles, moiety/molecule in the synovial fluid where it is
absorbed by the cartilage.
[0283] Long chain hydrophilic or 3-D hydrogel materials may be
other candidates for a lubricious coating material. Coating of
interpenetrating and/or crosslinking long chains may serve to
protect the area and isolate the meniscus from tear-inducing shear
stresses while similar coatings may be optimized for hardness
and/or load distribution. In many situations, it would be desirable
for these coatings to be porous to some degree to allow nutrients
and other active agents from the synovial fluid to penetrate to the
cartilage underlying the coating.
[0284] One method for surface coating the joints could include
steps: removing the synovial fluid (SF), replacing the SF with
another fluid, drying the interior of the joint, applying a first
agent, applying a second agent, applying activity energy (e.g.
light, UV light, RF energy), applying a third agent, rinsing the
joint and replacing the SF. One aspect of the invention relates to
activated coating active components of the synovial fluid, such as
SAPL and the like, onto a joint or onto implantable devices (such
as a meniscal liner, meniscal wafer, meniscal collar, composite
meniscus, condyle cap, cartilage cap, articular bumper, meniscal
bulking agent, and the like). The following prior art is
incorporated herein by reference: U.S. Pat. No. 4,722,906 issued on
Feb. 2, 1988, U.S. Pat. No. 5,512,320 issued on Apr. 30, 1996, and
U.S. Pat. No. 6,077,698 issued on Jun. 20, 2000.
[0285] Meniscus augmentation is a subset of the idea of cartilage
augmentation (CA). Augmenting or bulking (these terms are used
interchangeably) agents can be: (a) rigid, elastomeric, porous; (b)
biostable or biodegradable (used interchangeably with the term
bioresorbable); (c) coated, impregnated or seeded with cells or
bioactive agents; (d) biological materials such as cells (e.g.,
cartilage cells) from the patient or other sources; or (e)
combinations thereof.
[0286] The bulking agent can be biocompatible and/or serves as a
scaffold for the growth and regeneration of cells/tissue. To
scaffold, a material must have a combination of surfaces and voids.
The voids should communicate as in an open cell form or a matrix of
round pellets. The scaffold could be a combination e.g., particles
of open cell foam. Scaffold material should be compatible with the
cells which are desired to colonize the scaffold and regenerate the
desired tissue. Hydrogels can be used as scaffolds and can act in a
manner similar to an open cell foam. In addition to compatibility,
it can be desirable in some situations to encourage this
colonization and regeneration.
[0287] Some aspects of the invention relate to a method of meniscal
augmentation comprising administering a meniscal bulking agent to
increase a volume of the meniscus, wherein the meniscal bulking
agent is preferably administered by injection. In one embodiment,
the injection step is applied using imaging guidance or
arthroscopically under direct viewing. In one embodiment, the
meniscal bulking agent comprises a biodegradable hydrogel. In
another embodiment, the meniscal bulking agent comprises a
crosslinkable hydrogel with a first molecular weight, the
crosslinked hydrogel having a second molecular weight higher than
the first molecular weight. In still another embodiment, the
meniscal bulking agent is a liquid with a first viscosity index
before an administering step, the meniscal bulking agent having a
second viscosity index after the administering step, wherein the
second viscosity index is higher than the first viscosity index. In
a further embodiment, the bulking agent has a first volume before
an administering step and expands to a second volume after the
administering step. In a preferred embodiment, the bulking agent
further comprises a scaffold seeded with autologous cells,
mesenchymal stem cells or regenerative cells.
[0288] This can be done with coatings, impregnation and/or
preseeding the material with cells of the desired type.
Alternately, some materials (e.g., collagen and PU) inherently or
through additives as other types of surface treatment encourage
colonization and cell growth. One exemplary CA agent could be a
biodegradable foam that would act as a scaffold. This material
could be injected into the cartilage as a liquid and form the foam
in-situ as described in U.S. Application publication No.
2001/0043913 A1. Alternately, small pieces of foam material can be
passed through a cannula to the implant site. Examples of this
could be foams formed from PU, PLA, PGA or other materials commonly
used to make biodegradable structures. Foam particles could also be
made from a hydrogel. An example of material to be added to or
incorporated into a CA agent to encourage cell growth and
regeneration could be growth factors or allograft cells such as
described in Arthroscopy 2006; 22(3):291-299.
[0289] The combination of the foam scaffold which has been designed
and/or selected to provide mechanical support of the cartilage
before it degrades and while the cells infiltrate the scaffold and
regeneration.
[0290] Cartilage Augmentation Methods: One of the aspects of tissue
augmentation is matching the augmenting material to the
tissue/anatomy being augmented. Specifically soft tissues are
augmented by relatively soft materials and hard tissues. Different
tissues also require different methods for implantation. Soft
tissues allow material to be injected directly into tissue where
the injection pressure creates space in the tissue. In the case of
hard tissue, means to create space in the tissue must be developed.
In one embodiment, a balloon was used to create space in bone to
allow implantation of cement in the space created within a
vertebrate.
[0291] Cartilage, articular and meniscal, are intermediate tissues
softer than bone but harder than soft tissue such as muscle.
Furthermore, both the meniscus and most articular cartilage (e.g.,
that overlying the femoral condyle) are attached on one side to
bone. In the knee and other joints, one or more of the non-attached
surfaces are lubricated bearing surfaces. These cartilaginous
tissues also are compressible and serve to cushion loads
transmitted within and through the joint. Furthermore, some
cartilage, in particular the meniscus, is known to be prone to
tearing and other mechanical failure.
[0292] These aspects of the function and properties of cartilage
suggest that any material/method for CA address one or more of the
following issues: (1) do not result in the cartilage detaching from
the surface of the bone; (2) do not split or tear the collagen or
create stress concentrations; (3) do not adversely impact the
surface smoothness or lubricious nature of the bearing surface of
the cartilage; (4) do have properties that match the cushioning of
the natural materials--mechanical augmentation; (5) do have the
ability to be implanted in a manner to increase the size/volume of
the cartilage--volume augmentation; (6) optionally provide a
surface or surfaces to allow cell growth and regeneration--biologic
augmentation; (7) optionally accelerate/facilitate biological
augmentation by drugs, cell seeding et al.; and (8) do
encourage/enable healing and ultimate fusing and re-attachment of
the augmented tissue.
[0293] The following is an example of a detailed CA procedure. Some
optimal steps and alternatives are included to provide a better
understanding of some of the issues involved in CA: [0294] (1)
advance a needle into the cartilage along the margin between the
cartilage and its underlying bone; [0295] (2) (alternately) slide a
trocar cannula over the needle, or optionally remove the cannula
after it has dilated the cartilage; [0296] (3a) (alternately) slide
a trephine over the needle and spin the trephine to cut into the
cartilage and/or the bone; (3b) remove the trephine and optionally
collect any cartilage and bone tissue from the trephine; (3c)
optionally suction and/or flush around the needle to collect
additional tissue; (3d) optionally set aside the collected tissue
and optionally remove any excess liquid and optionally mercerize
the tissue into a paste; [0297] (4) optionally pass a balloon over
the needle and inflate to deflect the cartilage and create space
between the cartilage and bone; [0298] (5) select a material for
placement in the created space (in this case, we may select
particles of open cell foam of PU, PVA et al.); [0299] (6)
optionally mix the foam with the previously collected cells; [0300]
(7) optionally add growth factors; [0301] (8) insert a thin cannula
over the needle; [0302] (9) remove the needle; [0303] (10) insert
the foam cell mixture through the cannula into the space created by
the balloon; and [0304] (11) insert a plug through the cannula or
suture, close the defect in the cartilage.
[0305] Certain aspects of this procedure are optimized for cell
regeneration as outlined below: (1) The use of the trephine in step
3 in the above paragraph is to collect tissue for this purpose; (2)
Sliding the trephine over the needle along the bone/cartilage
border (step 3) allows collection of both cartilage and bone cells.
Furthermore, this can optionally cut deep into the bone to cause
bleeding; (3) The use of a porous foam; (4) In step 4, the foam
provides mechanical support to the cartilage and would also flex to
cushion loads in addition to facilitate/accelerate the cell growth
and regeneration; and (5) The use of a plug or suture to close the
defect at the implant site is to prevent escape of the material
from the implant site. As the materials are expected to be
pressurized as the cartilage deflects, this step improves the
augmentation by providing escape of the cells or the augmenting
foam.
[0306] Biomaterials for Meniscal Liner
[0307] Biomaterials for implantable knee devices, wafer, liner,
meniscal/tibial cover, condylar cover may include:
[0308] (1) Core material:
[0309] (a) High Modulus (>300,000 psi) [0310]
Metals--ferrous/non-ferrous metals, metal alloys (stainless steels,
cobalt steels, cobalt chromium alloys, Nitinol) [0311]
Ceramics--zirconium [0312] Polymers--polysulfones, polycarbonates,
polyesters, epoxies, PEEK, polyimides
[0313] (b) Moderate Modulus (50,000-300,000 psi) [0314]
Polymers--nylons, polyurethanes, polypropylenes, polyethylenes,
polyesters, polyureas, polyacrylates, polyvinyl alcohol, polymer
blends, natural polymers (collagen) [0315] (2) Optional
Reinforcement: (woven or non-woven) [0316] Polyester fibers [0317]
Carbon fibers [0318] (3) Optional Lubricious Surface Coating:
[0319] Hydrogels--polyacrylates, PVP, PEO [0320]
Lipids--phospholipids (phosphatidyl choline) [0321]
Protein--tribonectins, glycoproteins
[0322] There are many biocompatible polymers, such as PVA,
polyurethanes, polyolefins, that can meet requirements for the core
of the device, (e.g. shore hardness of 70 A to 60 D, or a
compressive modulus about 400 kPa). It is noted that the materials
challenge is in the wear/friction surface against the natural
tissues. Without causing tissue degradation, the device must stand
up to the repeated frictional forces in the knee joint, and give
acceptable wear with minimal particulate generation. A tough, wear
resistant, lubricious surface is needed.
[0323] HA Microparticles
[0324] The goals for treatment of osteoarthritis using hyaluronate
compositions, hyaluronic acid and hyaluronates (collectively herein
called as "HA"), can be met by injection of a suspension of HA
microparticles into the joint space. The particles will act as
depots for supply of soluble HA's in the joint space--a slow or
time release of HA's. Suspensions have viscosities similar to that
of the carrier fluid, such as saline, therefore injection of large
loading doses of HA's are possible. Injection needle can be e.g.
18-22 ga.
[0325] Microparticles can be made by known techniques such as spray
evaporation, precipitation, emulsification and filtration, or
grinding. Particle size needs to be >10.mu., preferably
>25.mu. to minimize inflammation and diffusive leaching. A
preferred range is 50-1000.mu.. In some clinical situations, this
preferred range could be 100-200 .mu.l. High molecular weight of
the HA is preferred and MW should be at least 500,000. In some
clinical situations MW>1,000,000 or even >10,000,000 may be
indicated. Bacterial sourced HA may be preferred to minimize
pathogenic contamination and allergic reactions. Since the HA
particle is soluble, it will initially become hydrated and soft,
thereby further acting as a cushioning agent within the joint
space.
[0326] HA particles can form in-situ from a liquid injection.
Methods for self agglutination of this type have been described by
Bell et al. Alternately, HA can be bound or otherwise attached to a
molecule which will aggregate into particles in situ.
[0327] Water soluble radiopaque agents (RO) such as metrizamide may
be added to the composition to allow visualization upon injection
to insure the target joint space is successfully treated. RO
ingredient could alternately be biodegradable and/or MRI visible.
MRI visible agents can be, for example ferromagnetic. RO
ingredients, such as gadolinium complexes, could alternately
enhance MRI visibility. RO agents can be optionally incorporated in
particles and/or bound to HA molecules. RO agents can optionally be
excretable through the kidneys such as diatrizoate meglumine
[0328] Dissolution rates can be adjusted. Rates can be decreased
with larger particle sizes or incorporation of additives to retard
dissolution, such as lactic and/or glycolic acid polymers, PEG,
collagen, gelatin, etc. Use of the free HA acid or the partial salt
of HA (sodium, calcium, ferric) or cross-linking may also decrease
dissolution times. Other methods e.g. cross-linking can also be
used to control the dissolution of HA. Cross-linking is an example
of a method that is known to effect the hardness (durometer) and
durability of materials. Cross-linking can be induced, for example,
chemically or by radiation.
[0329] HA can be formed into particles of various durometer
hardnesses. In most clinical situations it will be desirable that
the HA particles be softer (with lower durometer numbers) than the
cartilage to avoid damaging the cartilage. Bae et al. have
published data indicating the durometer of young healthy cartilage
can be on the order of 60 Shore A while the durometer of older or
unhealthy cartilage can be on the order of 30 Shore A. The
preferred durometer of the HA particles would range from 10 Shore A
to 50 Shore A depending upon the clinical situation. This invention
also includes a method by which the durometer of the cartilage will
be measured, and a HA particle durometer selected based upon the
durometer of the cartilage.
[0330] Therapeutic medications, such as steroids, growth factors,
etc., can also be incorporated into the HA particle. Lubrication
enhancers, such as proteins, e.g. lubricin or phospholipids, e.g.
dipalmitoyl phosphatidylcholine may also be incorporated in the
formulation. For example, Pasquali-Ranchetti et al. have described
methods by which HA and PL's can be combined.
Alternate Embodiments
[0331] Another approach is to inject and form a large depot of HA
within a space in the joint capsule (bursa), similar to slow
release (3 to 6 month) drug delivery depots such as Depot Provera
and Lupron Depot. The HA would be formulated with a slow dissolving
agent, such as a PEG or a copolymer of lactic and glycolic acids,
and injected into a joint cavity to form an in situ depot for
HA.
[0332] An approach to provide for a greater concentration of HA per
injection is to employ a biocompatible co-solvent in the normally
aqueous (saline) HA solution for injection. The co-solvent, such as
DMSO, ethanol, ethyl lactate, is a "poor" solvent for the HA.
Therefore, the solution viscosity with the co-solvent will be
substantially reduced from that of an aqueous solution. This will
permit a significantly greater concentration of HA for a given
viscosity.
[0333] A two part product may be manufactured, which consists of
the HA/polymer microparticles in a vial (part A) and a second vial
containing the liquid vehicle (part B). The liquid from vial A
would be injected into the powder in vial B to produce the
suspension, and then the suspension injected into the patient. The
product could be a dual chamber syringe, with the dry or
lyophilized HA/polymer microparticle in one chamber and the liquid
vehicle, such as phosphate buffered saline, in the second chamber.
The two chambers are mixed to create the suspension immediately
before injection. Alternately, the lyophilized HA can reconstitute
in situ after being injected as a powder or injected after being
pelletized (e.g. compressed) into particles.
[0334] Some aspects of the invention relate a method for treatment
of osteoarthritis of a patient, the method comprising injecting a
suspension of HA microparticles into a joint space of the patient,
wherein the microparticles have a hardness number less than the
hardness number of a cartilage within the joint space. In one
embodiment, the HA nanoparticles are suspended in aqueous solution.
In another embodiment, the HA nanoparticles are suspended in a
co-solvent that is a poor solvent for the nanoparticles so that the
HA component inside nanoparticles are controllably released from
the nanoparticles after being injected. In an alternate embodiment,
the microparticles comprise lyophilized HA, the lyophilized HA
reconstitutes in situ after being injected into the joint
space.
[0335] An alternate approach would be to use the tissue within the
joint as the depot for slow release of the HA. It is known that the
cartilage can absorb HA. It is also known that absorption is an
equilibrium phenomenon. Typically, 1% HA is injected into joints
while 3% HA has been injected in toxicity studies. For example,
injecting HA at 3% and maintaining this high concentration of HA
until equilibrium is achieved would turn the cartilage into a depot
containing 3% HA that could then leach out over time.
[0336] Dosages for Slow Release Microparticle Hyaluronates (HA)
[0337] Available HA viscosupplementation products (10 to 15 mg
HA/ml) provide 20 to 30 mg of HA (sodium salt) per injection, using
2.0 to 2.5 ml per injection. A total of 3 to 5 injections are given
once per week. Present average dosage of four commercially
available HA products over a course of treatment is 101 mg HA over
4.25 weeks.
[0338] Synovial fluid volume in a typical knee joint is 3.0 to 3.5
ml. HA concentration in normal joint synovial fluid is 3 to 4 mg
HA/ml. The half-life of HA in the joint space is reported to be
about 20 hours with "complete" elimination from the joint by about
4 days.
[0339] For an equivalent dosage of a single injection of
microparticles, inject 100 mg of HA in the form of slow release
microparticles in a suitable carrier, i.e. saline or phosphate
buffered saline. The HA should completely dissolve by the end of
week four.
[0340] For extended therapy, proportionately more HA can be
injected that possess longer dissolution times, e.g. 300 mg HA that
dissolves within twelve weeks.
[0341] Alternatively, more aggressive therapy can be administered
by increasing the amount of HA that is injected within a fixed
dissolution time, e.g. 300 mg HA that dissolves within four
weeks.
[0342] Note that dosage regimens with current soluble HA injections
are restricted, due to high solution viscosity limitations, and
synovial fluid concentration spikes upon each new injection. These
disadvantages are overcome with the use of slow release
microparticles. In one embodiment, the various microparticles may
have distinct biodegradation rates over a duration of
biodegradation to 3 months or longer. In another embodiment, the
HA-containing microparticles comprise at least two distinct
subgroups of microparticles, the first subgroup has its average
biodegradation rate that is different from that of the second
subgroup. TABLE-US-00001 TABLE 1 Volumes and Weights for a Single
Injection of HA Microparticles The ingredients are: A B C HA
(sodium salt) 100 100 100 mg Polymer (control release) 0 100 200 mg
Particles weight 100 200 300 mg Saline (phosphate buffer) to 2.0 to
2.0 to 2.0 ml Particles volume 0.125 0.174 0.236 ml Number
particles 240,000 333,000 452,000
[0343] Assuming a density of about 0.8 g/ml for the HA and about
1.5 g/ml for the polymer (poly(lactic-glycolic acid)), the
densities for the solid microparticles would be 0.8 for composition
A, 1.15 for composition B and 1.27 for composition C. (Density may
be decreased somewhat due to the production method for the
microparticle.)
[0344] Since density is equal to g/ml, the volume that the
microparticles occupy would be 0.125 ml for composition A, 0.174 ml
for composition B, and 0.236 ml for composition C. Particle size
has no significant effect on total volume of the suspension. By
calculation, each 100 .mu.m microparticle sphere occupies
0.522.times.10.sup.-6 cc.
[0345] The amount (if any) of the polymer for control release
depends on solubility of the HA (sodium salt or free acid), HA
particle size, and how it was made, as well as the selection of the
control release polymer. For example, polyglycolic acid dissolves
in vivo over a period of weeks; polylactic acid dissolves over
several months.
[0346] There is a limit on how much solids can be injected in 2.0
ml of fluid, probably about 400 mg. An injection volume of 2.5 ml
could hold up to 500 mg.
[0347] Hydrated particle hardness will also depend on selection of
the HA and polymeric ingredients.
[0348] Joint toxicity due to the presence of microparticles may be
addressed by injection of the microparticle depot into a "safe"
joint space, such as bursa.
[0349] Subcutaneous Depot
[0350] Implant HA in a manner similar to a subcutaneous bleb or
where the injected agent (liquid and/or solid) is injected directly
into tissue where it creates space rather than into an existing
space or potential space as a slow release subcutaneous depot to
increase concentrations.
[0351] Use of the suprapatellar fat pads as a location for an
injected intracutaneous depot. Just above the patella and right
behind the quadriceps tendon is the anterior suprapatellar fat pad.
Just anterior to the femur is the prefemoral fat pad. Unlike the
anterior suprapatellar fat pad, which is relatively constant in
shape and size, this fat pad is quite variable in size, and may
appear either fairly flat or quite plump. Extending up between
these two fat pads is the suprapatellar bursa, an extension of the
knee joint space.
[0352] The Suprapatellar Bursa as a Depot
[0353] These two fat pads can usually be seen on a lateral plain
film. Usually the suprapatellar bursa is only a potential space,
and contains very little fluid. In this case, the two fat pads are
separated by less than 5 mm. If a suprapatellar effusion is
present, the two fat pads are pushed apart by the effusion. If the
distance separating them is 5 mm or greater, we consider this
sufficient evidence to diagnose a knee effusion on plain film
[0354] The bursa could be the location of an injectable depot. With
a 5-10 mm depth, a length of 30-40 mm and a width of 20-30 mm the
volume of such a depot could be 3-12 cc.
[0355] Refillable Reservoir or Depot
[0356] As known in the art, both reservoir and contents
distribution and distribution rate control the HA release.
Optionally with a port that is local (e.g. on reservoir) or remote
(e.g. with a fill tube connecting to the reservoir). Optionally,
the reservoir can be expandable and be delivered through a
relatively small diameter cannula (e.g. a silicone structure
similar to the balloon described in U.S. Pat. No. 4,213,461 which
can inflate to many times (e.g. 8-10.times.) their formed
diameter.
[0357] Injectable Depot Formula
[0358] As an alternative to microparticle injection for depot
viscosupplementation, a biocompatible, liquid polymer solution
containing the viscosupplementation agent can be injected. Upon
injection, the solution immediately solidifies in situ to form a
solid mass depot, which dissipates over an extended period of time
to deliver the viscosupplementation agent. The biocompatible mass
would be about 2 cc, porous and spongy; deliver about 100-300 mg of
HA by dissolution/degradation in about 4-12 weeks.
[0359] Compositions: [0360] 1. Agent--HA: sodium salt, partial salt
or other cation, 1 MM+ molecular weight [0361] 2.
Solvent--biocompatible, water soluble: DMSO, ethyl lactate,
EtOH/water, acetone/water [0362] 3. Polymeric Encapsulant--soluble
in solvent, insoluble in water/tissues to form suitable
precipitate; biocompatible itself and its degradation products;
dissolves/degrades within 4-12 weeks: PLGA, PLA, PGA, PEG, PCL,
copolymers, terpolymers and mixtures of the preceding, PHB, PHBV,
zein. Optimum concentrations of the ingredients, mole ratios and
molecular weights (2-10 k-Daltons) of the polymer to be
determined.
[0363] PLGA is soluble in DMSO and will form a precipitate depot
for proteins (J. Control. Release, (1995) Vol. 33, no. 1, p
189-195). A composition consisting of PLGA with HA in DMSO may work
as an injectable depot for HA viscosupplementation.
[0364] Viscosupplementation with HA Microparticles Supplemental
Information
[0365] 1. Slow or controlled release of substances, such as drugs,
from soluble/degradable microparticle depots has been known and
developed since the late 1970's. There exists a well developed
technological and patent base. Medical products include: Pharmacia
& Upjohn's Depo-Provera (progesterone with PEG, IM injection),
TAP's Lupron Depot (leuprolide in PLA microspheres, IM injection),
Chiron's Depocyt (cytarabine in liposomes, CSF injection).
[0366] 2. Results from intra-articular injection of microparticles
have been published within the last seven years. These have dealt
with site specific release of drugs, such as paclitaxel,
hydrocortisone and NTHE's, to treat osteoarthritis. Results have
been generally favorable, with claims of biocompatibility of the
microparticles within the joint cavity.
[0367] Note that small molecule (drug) release is diffusion
controlled through the microcapsules, which disappear after the
drug is released. We are dealing with a different mechanism in
microparticle viscosupplementation, which is particle dissolution
or degradation controlled, since we have a macromolecule (HA) to
release.
[0368] 3. The most favored encapsulants are poly(alpha esters),
such as PLA, PGA and PLGA copolymers; poly(hydroxyalkanoates), such
as PHB and PHBV copolymers; polylactones, such as PCL; and various
poly(ethylene glycols). HA has been reported as an encapsulant
also.
[0369] 4. The following patent applications were particularly
valuable: U.S. Application publication 2006/0148755 from Genzyme is
of special interest--a single 6 ml (vs. 2 ml) injection of HA, good
for 6 months; U.S. Application publication 2005/0123593 from
J&J describes intra-articular delivery of HA in liposomes
(phosphatidylcholine) for extended release of HA; U.S. Application
publication 2005/0227911 from SoluBest discloses nanoparticles of
starch with HA, forming an inclusion complex, for delivery of HA;
U.S. Application publication 2006/0140988 claims compositions and
methods for an injectable depot using an emulsion of biodegradable
(PLGA) particles for sustained delivery of HA for
viscosupplementation, a solvent and surfactant are required.
[0370] Exemplary Viscosupplementation Depots e.g. Polymer/Solvent
and Compositions of Hyaluronic Acid
[0371] Polymer/Solvent Compositions: To obtain a composition that
models an injectable liquid, which solidifies upon contact with an
aqueous environment, it is suggested a process of solidification by
precipitation with 8 grams ethylene vinyl alcohol copolymer
(Aldrich #414107-100) and 110 grams dimethyl sulfoxide (Aldrich
#154938-500); (110 g=100 ml).
[0372] The polymer dissolves at room temperature (or
.about.50.degree. C.) with stirring within a few hours. Store all
items in sealed containers, in a dry, cool place.
[0373] If a denser precipitate solid is required, use 12 g of
copolymer; for a less dense precipitate solid, use 6 g of
copolymer. If radio-opacity is needed, add 40 g of tantalum powder
(Aldrich #262846-100) to the polymer solution and vigorously shake
to disperse the powder.
[0374] Hyaluronic Acid Compositions: To obtain a depot for
feasibility that will slowly dissolve in vivo and yield hyaluronic
acid (HA), it is suggested as follows. This is equivalent to the
current treatment, a total of 4 weekly injections--100 mg of HA.
[0375] 0.1 g HA sodium salt (Sigma or other choice; rooster or
bacterial source). [0376] 0.3 g poly(ethylene glycol) or PEG
(Aldrich #202436-250 rapid dissolution, or #202452-250 slower
dissolution in vivo)
[0377] One can increase or decrease the amounts of each ingredient
during preparation, but keep the ratio of 1:3. Next, try a ratio of
1:10. Mixing can be accomplished by (1) melting the PEG
(50-65.degree. C.) and rapidly stirring in the HA, then cool, or
(2) mechanically working the two ingredients with a spatula,
(addition of few drops of H.sub.2O may help). Remember, HA degrades
when exposed to heat and O.sub.2. Store all items in sealed
containers, in a dry, cool place. Another polymer to try later is
poly(lactide-co-glycolide). This will dissolve very, very
slowly--weeks to months.
[0378] One method of HA administration is to inject a suspension of
microparticles. If one wishes, the HA-PEG composition can be cooled
(<0.degree. C.) and pulverized, or as a liquid sprayed through
an orifice to generate the particles.
[0379] Optionally layered particles can be formed (with e.g.
increasingly higher concentration HA incorporated into concentric
inner layers) thereby maintaining a constant HA dissemination
rate.
[0380] Long Term Depots
[0381] For 2 years at 3.3 mg/day (equivalent to 101 mg over 4.25
weeks)=2.times.365.times.3.3=2,409 mg or 2.4 gm
[0382] 2.4 grams of HA mixed .about.50/50 with PGA (or PLA or other
appropriate drug carrier) would lead to .about.5.0 ml of
material+solvent carrier (e.g. DMSO). With an approximate constant
dissolution rate, 3.3 mg carrier/day would dissolve releasing 3.3
mg/day HA. Other carrier/HA ratios and proportional dissolution
rates can also be used.
[0383] Coaxial depot injection could be used to provide multiple
layers such that the outer layers (which will have greater surface
area than inner layers) disseminate HA at a slower rate than the
internal layers thereby releasing HA at a near constant rate. This
could be accomplished e.g. with a constant concentration of HA and
a faster dissolving/degrading carrier on the inner layer or an
inner layer with a higher HA concentration. Some aspects of the
invention relate to a method for treatment of osteoarthritis of a
patient, the method comprising injecting a suspension of HA
microparticles into a joint space of the patient, wherein the
microparticles have a hardness number less than the hardness number
of a cartilage within the joint space, wherein the microparticles
have plural concentric layers and plural concentric compartments
separated by the layers, each compartment being filled with the HA,
wherein an outer layer of the concentric layers is configured with
a higher degradation rate than a second degradation rate of an
inner layer.
[0384] Composite Depot
[0385] One concern about injectable solvent carrier depots could be
related to depot migration as depot size decreases over time.
Various means can be combined with an injectable depot to
physically contain and/or stabilize the depot over its life as it
dissolves/degrades, such as [0386] Inject into open cell foam where
the depot invades and fills the open cells and the struts reinforce
the injected material. [0387] Coaxial injection over a suture or
other filament [0388] Injection into a membrane or other potential
space enclosing bladder (porous to fluids and HA or with ports to
allow fluid exchange). For example, a thin permeable silicone
balloon inflated as the depot material is injected
[0389] All of the above support materials could be optionally
degradable with similar or longer degradation times relative to the
depot material.
[0390] Depot Anchors
[0391] One concern about depots could be related to the potential
for depot migration. Depots could be anchors using well known means
such as t-tags, sutures, clips or the like. The coaxially injected
over suture depot, as well as other depots, could be anchored by
barbed sutures. The barbed suture can be especially useful with the
injectable depot as a single needle stick can easily anchor and
deploy the depot. This can also be accomplished with a t-tag or
other type of barbed anchor et al.
[0392] From the foregoing, it should now be appreciated that a
meniscal implant and other medical devices for treating knee joint
has been disclosed. Furthermore, hyaluronate compositions lubricant
and methods for treatment of osteoarthritis were also disclosed.
While the invention has been described with reference to a specific
embodiment, the description is illustrative of the invention and is
not to be construed as limiting the invention. Various
modifications and applications may occur to those skilled in the
art without departing from the true spirit and scope of the
invention as described by the appended claims.
* * * * *