U.S. patent application number 10/675660 was filed with the patent office on 2004-08-19 for cartilage repair plug.
This patent application is currently assigned to ChondoSite, LLC. Invention is credited to Aberman, Harold M., Jackson, Douglas W., Simon, Timothy M..
Application Number | 20040162622 10/675660 |
Document ID | / |
Family ID | 24093251 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040162622 |
Kind Code |
A1 |
Simon, Timothy M. ; et
al. |
August 19, 2004 |
Cartilage repair plug
Abstract
A cartilage plug, which is made from a biocompatible, artificial
material, that is used to fill a void in natural cartilage that has
been resected due to traumatic injury or chronic disease is
disclosed. Alternatively, the plug may be relied upon to anchor a
flowable polymer to subchondral bone. The plug is prefabricatable
in any size, shape, and contour and may be utilized either singly
or in a plurality to fill any size void for any application. The
plug may be formed of a laminated structure to match the
physiological requirements of the repair site. Additionally, ridges
may be formed about the periphery of each plug to facilitate its
anchoring to surrounding cartilage, bone and/or adjacent plugs. A
procedure for resecting damaged or diseased cartilage and for
implanting a replacement plug or plugs according to this invention,
as well as a set of instruments for effecting the procedure, and a
self-contained system for orthopaedic surgeons, which includes a
variety of differently sized and shaped plugs, as well as a set of
instruments for the procedure are also disclosed.
Inventors: |
Simon, Timothy M.; (Los
Alamitos, CA) ; Aberman, Harold M.; (Montclair,
NJ) ; Jackson, Douglas W.; (Long Beach, CA) |
Correspondence
Address: |
Gunther Hanke
Fulwider Patton Lee & Utecht, LLP
Suite 1550
200 Oceangate
Long Beach
CA
90801-5615
US
|
Assignee: |
ChondoSite, LLC
|
Family ID: |
24093251 |
Appl. No.: |
10/675660 |
Filed: |
September 30, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10675660 |
Sep 30, 2003 |
|
|
|
09525437 |
Mar 14, 2000 |
|
|
|
6632246 |
|
|
|
|
Current U.S.
Class: |
623/23.5 ;
623/20.32; 623/23.51 |
Current CPC
Class: |
A61F 2002/30153
20130101; A61F 2230/0008 20130101; A61F 2/30767 20130101; A61F
2002/3023 20130101; A61F 2230/0091 20130101; A61F 2002/30759
20130101; A61F 2002/30448 20130101; A61F 2220/0033 20130101; A61B
17/1635 20130101; A61F 2002/30879 20130101; A61F 2240/001 20130101;
A61F 2002/30904 20130101; A61F 2/389 20130101; A61F 2230/0086
20130101; A61F 2002/30169 20130101; A61F 2002/30892 20130101; A61F
2002/3085 20130101; A61F 2230/0017 20130101; A61F 2230/0063
20130101; A61F 2002/30772 20130101; A61F 2002/30583 20130101; A61F
2230/0021 20130101; A61F 2002/30151 20130101; A61F 2002/30154
20130101; A61F 2002/30224 20130101; A61F 2002/30616 20130101; A61F
2002/30451 20130101; A61F 2002/30957 20130101; A61F 2230/0019
20130101; A61B 2090/062 20160201; A61F 2230/0069 20130101; A61F
2002/30143 20130101; A61F 2002/30112 20130101; A61F 2210/0085
20130101; A61F 2220/0025 20130101; A61L 2430/06 20130101; A61F
2002/3028 20130101; A61F 2002/30971 20130101; A61F 2220/0058
20130101; A61F 2250/0023 20130101; A61F 2/30756 20130101; A61F
2002/30016 20130101; A61F 2002/30146 20130101; A61F 2230/0067
20130101; A61F 2002/2839 20130101; A61F 2230/0004 20130101; A61F
2002/30331 20130101; A61F 2002/30795 20130101; A61F 2220/005
20130101; A61F 2002/30011 20130101; A61F 2/3094 20130101; A61F
2002/30113 20130101; A61F 2002/30894 20130101; A61F 2002/30067
20130101; A61F 2/4618 20130101; A61F 2002/30273 20130101; A61F
2002/4627 20130101; A61F 2002/30289 20130101; A61F 2230/0047
20130101; A61F 2002/30125 20130101; A61B 17/1604 20130101; A61F
2002/30276 20130101; A61F 2002/30004 20130101; A61F 2/3859
20130101; A61F 2002/305 20130101; A61F 2002/30205 20130101; A61F
2002/3021 20130101; A61F 2002/30329 20130101; A61B 17/1637
20130101; A61B 2090/036 20160201; A61F 2002/30138 20130101; A61F
2230/0006 20130101; A61F 2250/0019 20130101; A61F 2250/0014
20130101 |
Class at
Publication: |
623/023.5 ;
623/023.51; 623/020.32 |
International
Class: |
A61F 002/28; A61F
002/38 |
Claims
What is claimed is:
1. A cartilage plug for insertion into a void in cartilaginous
tissue in a living mammal, comprising a laminated preformed mass of
artificial biocompatible materials wherein said biocompatible
materials are arranged in layers, each material having different
mechanical and physical properties.
2. The cartilage plug of claim 1, wherein said materials have
different hardnesses.
3. The cartilage plug of claim 2, wherein said plug is configured
so as to be received in said void such that a first end becomes
aligned with the surface of surrounding cartilaginous tissue,
wherein said first end is formed of the least hard of said
materials.
4. The cartilage plug of claim 2, wherein said void extends to
subchondral bone and wherein said plug is configured so as to be
received in such void such that a second end of said plug contacts
said bone, wherein said second end is formed of the hardest of said
materials.
5. The cartilage plug of claim 4, wherein said plug is configured
so as to be received in said void such that a first end becomes
aligned with the surface of surrounding cartilaginous tissue, where
said first-end is formed of the least hard of said materials.
6. The cartilage plug of claim 5, wherein a third layer of material
is interposed between said layers forming said first and said
second end, wherein said third layer is formed of material of
intermediate hardness.
7. The cartilage plug of claim 1, wherein said plug has an exterior
surface with ridges formed therein.
8. The cartilage plug of claim 1, wherein said plug has a bore
formed therein.
9. The cartilage plug of claim 8, wherein said bore has ridges
formed on its internal surface.
10. The cartilage plug of claim 1, wherein said plug has porous
surfaces.
11. The cartilage plug of claim 10, wherein the exposed surfaces of
each of said layers has a different porosity.
12. A cartilage plug for insertion into a void in cartilaginous
tissue in a living being, comprising a preformed mass of an
artificial biocompatible material having a three-dimensional shape
adapted for insertion into said void so as to at least partially
fill said void, said preformed mass having a plurality of ridges
formed about its periphery.
13. The cartilage plug of claim 12, wherein said ridges are
arranged in a parallel orientation relative to one another and
wherein such ridges each define a plane that is substantially
perpendicular to a central axis extending through said plug.
14. The cartilage plug of claim 12, wherein said ridges comprise a
continuous helix that spirals about a central axis extending
through said plug.
15. The cartilage plug of claim 12, wherein said ridges are
discontinuous and are situated at discrete portions of said
plug.
16. The cartilage plug of claim 12, wherein said mass has a
cylindrical shape.
17. The cartilage plug of claim 12, wherein said mass has a
polyhedral shape.
18. The cartilage plug of claim 12, wherein the cross-section of
the distal end of said mass differs from the cross-section of the
proximal end of said mass.
19. The cartilage plug of claim 15, wherein said mass has a
frusto-conical shape.
20. The cartilage plug of claim 12, wherein each such ridge has a
barb shaped cross-section.
21. The cartilage plug of claim 12, wherein each such ridge has a
rib shaped cross-section.
22. The cartilage plug of claim 12, wherein said plug has a bore
formed therein.
23. The cartilage plug of claim 22, wherein bore has ridges formed
on its interior surface.
24. The cartilage plug of claim 12, wherein said plug is formed of
laminated materials, said materials having different
hardnesses.
25. The cartilage plug of claim 12, wherein said plug has porous
surfaces.
26. A cartilage plug for insertion into a void in cartilaginous
tissue in a living mammal, comprising a preformed mass of an
artificial biocompatible material having a three-dimensional shape
adapted for at least partially filling such void, wherein said mass
has an axial bore formed therein.
27. The cartilage plug of claim 26, wherein said bore extends along
the entire axis of said plug.
28. The cartilage plug of claim 26, wherein said bore extends into
but not entirely through said plug.
29. The cartilage plug of claim 26, wherein said bore has ridges
formed on its interior surface.
30. The cartilage plug of claim 29, wherein said ridges are barb
shaped.
31. The cartilage plug of claim 29, wherein said plug has ridges
formed on its exterior surface.
32. The cartilage plug of claim 26, wherein said plug is formed of
laminated layers of materials having different hardnesses.
33. The cartilage plug of claim 32, wherein said plug is configured
to be embedded in subchondral bone at one end and wherein said end
is formed of a layer of the hardest of said materials.
34. The cartilage plug of claim 26, wherein the surfaces of said
plug are porous.
35. A cartilage plug for anchoring a flowable polymer to
subchondral bone, comprising a preformed mass of an artificial
biocompatible material having a three dimensional shape adapted for
insertion into a bore formed in said subchondral bone, said shape
having ridges formed in its exterior surfaces and having a bore
formed therein, said bore being configured for receiving said
flowable polymer therein and further having ridges formed in its
interior surface.
36. The cartilage plug of claim 35, wherein said ridges are
barb-like in cross section and oriented so as to resist pull out of
the plug from a said bore in said subchondral bone and to resist
pull out of polymer from within said bore in said plug.
37. The cartilage plug of claim 35, wherein said plug is formed of
a lamination of materials with different hardnesses.
38. The cartilage plug of claim 37, wherein material to be in
contact with said subchondral bone is harder than material to be in
contact with said polymer.
39. The cartilage plug of claim 35, wherein said plug surfaces have
a preselected pore structure formed therein.
40. The cartilage plug of claim 39, wherein pore size of said pore
structure is larger for those surfaces to be contacted by said
polymer than those surfaces to be in contact with said subchondral
bone.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to the field of orthopedic
surgery for the repair and replacement of damaged natural cartilage
in a living mammal particularly human beings. More specifically,
this invention relates to devices, methods, and instruments for the
replacement of defective natural cartilage, where the defects are
caused by traumatic injury which brings about sudden, acute damage
to the cartilage, and/or by disease or the long term effects of
unrepaired cartilage injuries, which over prolonged periods of
time, cause a chronic deterioration of the cartilage. Still more
specifically, the invention relates to an artificial device, made
from a biocompatible material, in the form of a cartilage
replacement plug, which is used individually or in multiples, to
fill void cavities in cartilage created by the resection and
removal of damaged or diseased portions of the natural cartilage or
to anchor material that is used to fill such cavities; to a method
for resecting damaged or diseased. portions of natural cartilage
and replacing the removed portion of natural cartilage with one or
more such artificial cartilage replacement plugs; to a set of
instruments for performing the natural cartilage resection and
removal procedure to create a void cavity in the cartilage and for
performing the artificial cartilage replacement plug implantation
procedure; and to a surgical system for orthopedic surgeons which
includes a selection of cartilage plugs of various sizes and shapes
needed for performing a number of procedures of varying scope and
extent, at various body sites, as well as a set of the surgical
instruments needed to perform both the defective cartilage removal
procedure and the cartilage plug implantation procedure, with all
elements being maintained in a sterile environment in a
self-contained carrier, ready for surgical use.
BACKGROUND OF THE INVENTION
[0002] Human cartilage has very unique properties. It is one of the
few avascular tissues in the body. It serves to prevent bone growth
into the articulating surface of joints, which would otherwise
interfere with the motion of such joints. Cartilage is
semipermeable and receives its nutrients from the synovial fluid
which surrounds cartilaginous tissue in articulating joints and
which diffuses into the cartilage during motion of the joint.
Cartilage itself also possesses viscoelastic and lubricating
properties. Materials which are proposed for use in the repair or
replacement of natural cartilage must possess physical and
mechanical properties which are as close as possible to those of
natural cartilage.
[0003] Younger persons, ranging in age from children to young
adults, often engage extensively in rigorous athletic activities,
such as skiing, surfing, football, basketball, and even roller
blading, which frequently results in accidents which cause
traumatic injury to cartilage, particularly that surrounding the
knees, elbows, and shoulders. In the U.S. alone, there are well
over 300,000 such injuries per year. Most of these injuries are to
the anterior cruciate ligament of the knee, which frequently
becomes torn. Younger persons are also occasionally afflicted with
arthritic diseases, such as juvenile rheumatoid and osteoarthritis,
which cause degeneration of cartilage. Osteoarthritis may also set
in following a traumatic injury to cartilage which is not repaired
or is repaired improperly, leading to a further deterioration of
the previously damaged cartilage. The extent of the cartilage
defect, resulting either from traumatic injury or chronic disease,
can vary considerably from a small area to a larger, more
widespread area, or even involve all of the cartilage of an entire
joint, depending on the extent of the injury or the extent of the
spread of the disease. When the defect is caused by traumatic
injury and is extensive enough in size to involve a large mass of
cartilage, the damage is not capable of self healing. Heretofore it
was not possible to repair extensive cartilage defects. Such
damaged cartilage had to be removed and replaced. Often this
required complete joint replacement surgery. Cartilage which has
become defective through damage caused by traumatic injury from
accident, whether sports related or from other causes, such as an
automobile accident, as well as cartilage which has become
defective as a result of deterioration due to the spread of a
chronic degenerative disease, also typically gives rise to and is
accompanied by severe pain, especially where the sites of the
damage or disease is proximal to or constitutes part of an
articulating joint surface, such as the knee. The damaged or
diseased portion of the cartilage is usually also accompanied by
swelling of the surrounding tissue; and, where an articulating
joint is involved, a disruption in the flow of lubricating synovial
fluid around the joint often occurs, which, in addition to being a
cause of the source of pain, usually leads to further mechanical
abrasion, wear, and deterioration of the cartilage itself, finally
resulting in the onset of osteoarthritis and complete disablement
of the articulating joint, ultimately requiring complete
replacement of the joint.
[0004] Historically the only choices available to patients with
cartilage damage, especially the cartilage of an articulating
joint, such as a knee or elbow, were to initially do nothing if the
extent of the damage was only relatively minor in scope, which
sooner or later usually led to a worsening of the condition and
further damage to the cartilage and to the joint itself, with the
patient feeling discomfort and pain when using the joint, thus
ultimately requiring a complete joint replacement to restore
mobility; or, if the extent of the damage was significant to start
with, to immediately perform a complete joint replacement. In the
case of very young patients, however, complete replacement of a
joint is problematic in that the patient's overall skeletal bone
structure is not yet fully developed and is still growing, so that
the replaced joint may actually be outgrown and no longer be of
appropriate size for the patient when their fully matured adult
size, stature, and skeletal structure is attained. Moreover, in the
past, many replacement knee, elbow joints and shoulder joints have
typically had a maximum active useful life of only about ten years,
due to wear and tear and erosion of the articulating surfaces of
the joint with repetitive use over time, thereby necessitating
periodic invasive surgery to replace the entire joint. For a very
young patient this meant that they would have to face the prospect
for several more such surgeries over their lifetime,
notwithstanding progress and improvements in the wearability of
materials used for joint surfaces that have been made and continue
to be made as new materials are developed.
[0005] In recent years a large number of devices and methods for
the replacement of defective portions of natural cartilage have
been proposed. Some of these have been directed at enabling the
repair of larger portions of defective cartilage without having to
resort to a full joint replacement, when an articulating joint is
involved. Some of the proposed devices are made from natural
cartilage which has been self-harvested or harvested from cadaveric
sources, some devices are based on composite artificial materials,
and some methods involve the growth of new natural cartilage
material. A few of the proposed methods for natural cartilage
replacement utilize artificial cartilage devices in the form of
preformed plugs, which are used to fill-in void cavities created by
the resection and removal of the damaged or diseased portion of
cartilage from the patient.
[0006] The various approaches to the problem of cartilage repair
and replacement can broadly be divided into those offering a
long-term solution, and those offering a short-term solution.
Biological approaches involving the growth of new replacement
cartilage, either within or without the patient, are generally
considered long-term solutions because of the time needed to
regenerate the cartilage; while essentially mechanical approaches
involving the implant of preformed devices or plugs or the in situ
formation of cartilage replacement plugs or devices are considered
short term solutions because they can usually be effected
immediately by surgical procedures which can be completed in a
relatively shorter period of time, and which, therefore, are
capable of alleviating a patient's accompanying pain and of
rehabilitating a patient in a shorter time span. There are,
however, several major problems and disadvantages associated with
all of the various prior art cartilage replacement devices and
methods which have heretofore been proposed.
[0007] The use of naturally derived cartilage plugs presents the
major problems of lack of availability, limitations on the size of
the repair that can be effected, and high potential for infection
and transmission of disease. In some instances it has been
proposed, for minor cartilage replacement procedures which involve
the replacement of relatively small volumes of cartilage, that the
cartilage be harvested from the patient by excising a portion of
cartilage of suitable size from a donor site on the patient's body.
Where the portion of damaged or diseased cartilage that is to be
replaced is more extensive, however, such a self-harvesting
procedure is not feasible because a sufficiently large plug cannot
be extracted from another site without causing damage to or a
weakening of the cartilage and underlying bone at the place of
harvesting, or when being harvested from a site at or near another
articulating joint, without causing damage to the operability of
the articulating joint itself at the point of harvesting. Moreover,
there are a limited number of suitable locations on the body from
which cartilage can be extracted for use elsewhere. Such a
self-harvesting procedure actually involves dual surgical
procedures of first performing the harvesting procedure at one
situs on the patient, followed by the replacement procedure at
another situs on the patient. Depending on the age and overall
health of the patient, as well as on other considerations, it may
not be feasible to perform both procedures at the same time.
Moreover, non-medical considerations must be taken into account.
Such a dual procedure is time consuming and costly, and may be
objected to on cost grounds in some insurance or managed care
contexts. Because the procedures are invasive, there is the
additional risk of infection and pain to the patient occasioned by
the need for two separate surgical procedures, at the cartilage
harvesting site and at the cartilage repair emplacement site.
[0008] As an alternative to such a self-harvesting procedure, some
have proposed that cadaveric cartilage specimens be extracted and
used. This alternative, however, also presents the same problems of
limited sources of availability and potential for infection or
transmission of disease. In cases where it is necessary to reset
larger portions of damaged or diseased cartilage from a patient,
although procedures utilizing natural cartilage replacement plugs
derived from cadaveric sources are not limited by considerations as
to the amount of cartilage that can be excised from a particular
location in order to preclude damage to or a weakening of the
remaining cartilage and/or the joint, at the donor site, as occurs
in a self-harvesting situation, there are still limitations as to
the total amount of suitable cartilage that can be harvested from
cadaveric sources, and the overall reliability of obtaining
acceptable cadaveric cartilage sources at all is not high. In
addition to the threat of infection to the recipient patient from
other external sources, moreover, care must be taken that there is
no chance of transmitting any disease carried by the cadaveric
donor to the recipient.
[0009] One of the long term methods proposed by the prior art
involves the regrowth of replacement natural cartilage material in
the void cavity formed by the resection of damaged or diseased
cartilage. Attempts have been made to isolate and culture
chondrocytes or stem cells in vitro. These cells are then implanted
or injected into the cartilage defects in order to promote healing.
Another such long-term method utilizes morphogenetic growth factors
to inductively stimulate cartilage repair. Some of the obstacles to
this latter method involve the selection of one or more appropriate
growth factors; the selection of appropriate delivery vehicles for
controlled, time-release of the growth factors to ensure that the
proper concentration of growth factor is maintained at the implant
site; and necrosis of immature or newly regenerated tissue under
stress or when subjected to loading conditions.
[0010] An example of one such long-term method, and the
compositions for effecting the method, is disclosed in U.S. Pat.
No. 5,723,331 to Tubo et al. for "Methods and Compositions for the
Repair of Articular Cartilage Defects in Mammals". The method
involves the use of denuded chondrogenic cells which are
proliferated ex vivo as monolayer cultures in order to expand the
pool of available chondrogenic cells. The proliferated cells are
then seeded in a pre-shaped well having a cell contacting adhesive
surface. These cells redifferentiate and begin to excrete
cartilage-specific extracellular matrix.
[0011] The principal disadvantages of this method are that it is
very complicated and time consuming, requiring up to several months
to fully culture the cartilage cells to the point where they are
available for use in a preformed shape. This method also faces the
obstacles facing all such long-term methods mentioned above.
[0012] In the area of short-term, interim solutions, attempts have
been made to repair or resurface cartilage defects with implantable
medical devices made from biocompatible materials. For example, the
use of collagen sponges has been proposed as an implant to promote
cartilaginous tissue ingrowth, however, this method has not
demonstrated good long-term success. The use of an injectable
liquid polyurethane and poly ethyl methacrylate has also been
proposed. These systems are based on arthroscopic injection of the
reactive liquid composition at the site of the cartilage defect.
The composition then sets in situ. From a practical viewpoint,
these methods are limited to those applications where the
surrounding cartilage forms a natural cartilage capsule that is
capable to acting as a mold to contain and shape the injected
liquid composition until it sets. According to some proposed
methods, the injected material is capable of being arthroscopically
shaped after it has been injected. A major disadvantage of using
reactive polyurethane-based systems is that residue diisocyanate in
the reactant becomes hydrolyzed in the presence of moisture, to
diamine, which is both toxic and carcinogenic.
[0013] One such method based on the injection of a reactive
polyurethane system with arthroscopic shaping of the injected mass
is disclosed in U.S. Pat. No. 4,743,632 to Marinovic for
"Polyurethane Urea Polymers as Space Filling Tissue Adhesives".
According to this method, polyurethane urea polymers are prepared
by mixing purified isocyanate polyurethane prepolymers with an
aqueous solution of an amino, ureido, or hydroxyl substituted amine
or a like-substituted alpha-amino acid. The composition, while
still in liquid form, is injected into a cavity where it
solidifies.
[0014] Another reactive system is disclosed in U.S. Pat. No.
5,556,429 to Felt for "Joint Resurfacing System". The system
involves a method that includes the delivery of a curable
biomaterial, which is a composite of two or more materials,
particularly those comprising two phase systems formed from a
polymeric matrix and a hydrogel filler. The polymeric materials
include polyurethane, polyethylenes, polypropylenes, polyvinyl
chlorides, and others. Matrix materials include silicone polymers
and polyurethane polymers. The hydrogels are water-containing gels.
The composition is introduced in liquid form, by minimally invasive
means, such as by arthroscopic injection, followed by in situ
curing of the material, such as by exposing the liquid polymer to
ultraviolet light, and shaping and contouring of the cured
material, which is also performed arthroscopically.
[0015] One of the prior art artificial cartilage replacement
devices and methods is disclosed in U.S. Pat. No. 5,067,964 to
Richmond et al. for "Articular Surface Repair". The cartilage
repair piece disclosed there is a composite which includes a
backing layer of non-woven, felted fibrous material, which is
conformable to flat and curved surfaces. The front face of the
backing layer is either uncoated or covered by a coating of a tough
pliable material having a front surface which is tough smooth and
slippery in the presence of synovial fluid, so that the device
responds naturally at an interface with other cartilage. A
disadvantage associated with such approach is inherent in the lack
of any physical anchoring to the underlying bone.
[0016] A disadvantage and limitation of this method and this type
of cartilage replacement device is that it requires cell ingrowth
into the felted backing for biologic fixation of the device. This
type of soft tissue fixation is less desirable than fixation
achieved by bone ingrowth or fixation directly with bone without a
fibrous tissue interface. Their device is composed of a layer of
polymer attached to a porous felt like backing which may fatigue
with motion and result in delamination. Moreover, this type of
failure may occur before biologic fixation occurs resulting in
failure of the device. In addition,their device is flexible to
achieve conformation with the cartilage surface and may not allow
adequate weight bearing. In contrast, our device is already
structurally adequate to withstand full weight bearing immediately
without the need to develop biologic fixation.
[0017] Instruments for resecting cartilage, such as for excising a
plug of damaged or diseased cartilage, are known in the art. U.S.
Pat. No. 4,641,651 to Card for "Cartilage Punch and Modified
Prosthesis in Tympanoplasty" discloses a cartilage punch for
removing a cartilage plug of uniform thickness. The instruments
associated with the present invention are customized for effecting
the various steps of the procedure according to the present
invention, and include instruments for resecting the damaged or
diseased cartilage, for shaping the resulting void, and for
implanting the replacement cartilage plug.
[0018] Published World Intellectual Property Organization Patent
Application WO 96/27333 of Hart et al. to Innovasive Devices, Inc.
for "Apparatus and Methods for Articular Cartilage Defect Repair"
discloses a bone plug removal tool that includes a cylindrical
cutting element having a external surface and an internal surface
defining an internal bore extending along a longitudinal axis of
the cutting element from a proximal cutting edge.
[0019] Accordingly, there is a need in the art of orthopedic
replacement surgery, especially for young patients, of a means of
replacing resected portions of damaged or diseased cartilage that
does not involve extensive invasive surgery or removal of extensive
portions of the cartilage beyond the immediately affected portion;
in the case of cartilage that constitutes part of an articulating
joint such as a knee or elbow, that does not require a full joint
replacement when the joint is still substantially viable and motion
of the joint has not been completely compromised; which provides
for a readily available source for the cartilage material in
unlimited quantities; which does not require the harvesting of the
material from the recipient or from cadaveric sources; and which
offers simplicity and speed both in the production of the cartilage
replacement materials itself and in the actual procedure for its
implantation.
OBJECTS OF THE INVENTION
[0020] Accordingly, it is an object of the present invention to
provide a preformed artificial cartilage replacement device, made
from a biocompatible material and fabricated in the shape of a
plug, to repair defects in cartilage.
[0021] It is a further object of the present invention to provide
artificial cartilage replacement devices, which are fabricated as
plugs in a variety of sizes and shapes, and which are used to fill
a void in cartilage, created by the removal of a defective portion
of cartilage of virtually any size and shape, such that the plugs
are capable of being utilized either individually, or in a
plurality as part of a mosaicplasty.
[0022] It is another object of the present invention to provide
artificial cartilage replacement devices having mechanical and
physical properties that closely match the cartilage being
replaced.
[0023] It is a still further object of the present invention to
provide an artificial cartilage plug which has additional means of
anchoring itself to non-defective cartilage and/or bone surrounding
the void cavity into which the plug is implanted.
[0024] It is another object of the present invention to provide
artificial cartilage plugs for anchoring a flowable polymer to the
bony base of a lesion site.
[0025] It is another object of the present invention to provide
artificial cartilage replacement devices that become biologically
fixed in place.
[0026] It is another object of the present invention to provide an
orthopedic surgical procedure for removing a defective portion of
cartilage and refilling the void cavity thereby created with one or
more artificial, biocompatible, preformed cartilage replacement
plugs.
[0027] It is yet another object of the present invention to provide
a set of surgical instruments used to perform the surgical
procedure of removing a portion of defective cartilage and
replacing it with an artificial, biocompatible, preformed cartilage
replacement plug.
[0028] It is still another object of the present invention to
provide a self-contained orthopedic surgical cartilage repair and
replacement system which includes an assortment of preformed,
artificial, biocompatible cartilage replacement plugs of varying
sizes, shapes and configurations, together with a set of surgical
instruments for performing a cartilage removal and replacement
procedure, all maintained under sterile conditions in a portable
container, so as to enable an orthopedic surgeon to have all the
elements for performing one or more cartilage removal and
replacement procedures readily and conveniently available.
[0029] It is an overall objective of the present invention to
provide a device, method, and instruments to enable the repair of
cartilage defects by removing a defective portion of cartilage in a
patient and replacing the removed cartilage and filling the void
created by the removal of the defective cartilage with an
artificial, biocompatible material, such that virtually any size
cartilage defect can be repaired in a safe, simple and fast
procedure that does not involve a long period of time for cartilage
regrowth and does not involve the performance of multiple invasive
surgical procedures on the patient.
SUMMARY OF THE INVENTION
[0030] The present invention includes a preformed, presized, and
preshaped cartilage replacement plug, made from a biocompatible,
artificial material, which is used, either individually or in
combination with other such plugs, depending on the volume of
cartilage to be replaced, to replace a portion of damaged or
diseased cartilage which has been resected, thereby filling the
void left by the resected cartilage. Alternatively, certain
embodiments of such plugs may be employed to serve as anchors for a
flowable polymer that is used to fill the void. The invention also
includes a procedure for removing the portion of damaged or
diseased cartilage and for implanting the replacement artificial
cartilage plug or plugs. The invention still further includes a set
of instruments for effecting the procedure and a complete system
for orthopedic surgeons which includes a selection of artificial
replacement cartilage plugs of varying sizes and shapes suitable
for a variety of applications and specific procedures, together
with a complete set of the instruments used to resect the damaged
or diseased cartilage and for implanting the replacement plug or
plugs, all in a self-contained carrying case.
[0031] Because the material of the cartilage replacement plugs of
the present invention is artificial, there are no limits as to its
availability and because the material is biocompatible and is kept
sterile prior to use, there is no danger of the cartilage plugs of
this invention being rejected when in the body, or of transmitting
any disease or infection. Due to the ready availability of the
cartilage plugs of this invention and the relative simplicity of
the procedure for implanting them, there is no need for any dual
invasive surgical procedures being performed on the recipient,
including any kind of initial harvesting procedure, in addition to
the actual cartilage replacement plug implantation procedure, but
only the implantation procedure itself. The threat of transmission
of disease from a donor source is thereby effectively eliminated,
the overall risk of infection to the patient is greatly reduced and
the overall costs of the procedure are kept to a minimum.
[0032] The cartilage plugs according to the present invention are
fabricated from a biocompatible material which is easy to preform,
presize and preshape. They can be formed and contoured in
essentially any shape and size depending on the particular
application for which they are to be used. Biocompatible polymeric
materials such as biostable polycarbonate polyurethanes are
particularly well suited for use. The cartilage plugs can be
fabricated from a wide variety of synthetic and natural polymeric
materials.
[0033] In preferred embodiments of the present invention, the plugs
are formed of a lamination of a number of various materials each
having different mechanical and physical properties. More
particularly, a material having properties similar to that of
subchondral bone is selected for use in the layer of the plug that
is to be positioned adjacent or within the subchondral bone while
another material, having properties similar to hyaline cartilage is
selected for use in the layer of the plug that is to be positioned
on the surface of the repair. A third material selected for having
properties similar to natural cartilage forms the bulk of the plug
and is positioned between the bone-like and hyaline cartilage-like
materials. Alternatively, one of the three materials may be deleted
or more than three materials may be combined in the
lamnination.
[0034] In additionally preferred embodiments, ridges are formed
about the periphery of the plugs to facilitate a mechanical
interlocking with the surrounding natural cartilage, with bone
and/or with one another. Such ridges may define parallel planes,
each perpendicular to the central axis of the plug. Alternatively,
the ridges may comprise a single helix extending about the plug's
central axis. The ridges may be continuous or may be segmented,
confined to certain areas of the plug's exterior. The cross-section
of each such ridge may be symmetrical or may define a barb-like
protuberance that eases insertion but resists retraction.
[0035] Additionally preferred embodiments of the present invention
include plugs that have a hollow interior. A void formed in the
interior of the plug may extend partially into the interior of the
plug to varying degrees or may extend completely therethrough.
Additionally, ridges may optionally be formed on the interior
surface of such voids in various configurations. Such plugs are
preferably employed as anchors in conjunction with a flowable
polymer. The voids serve to more positively fix the polymer to the
plug once the polymer has cured.
[0036] Preferred embodiments of the plugs of the present invention
may be formed with roughened and/or porous surfaces. Asperity and
pores within a certain size range facilitate cell ingrowth that
results in biologic fixation. Larger pores are useful when the plug
is used as an anchor in conjunction with a flowable polymer wherein
an influx of the polymer into the pores facilitates a mechanical
fixation thereto upon curing.
[0037] Finally, the plugs of the present invention may be formed in
any of a large number of different geometric shapes ranging from
cylindrical to polyhedral. The plug may be of constant or of
variable diameter as for example a truncated cone.
[0038] These and other features and advantages of the present
invention will become apparent from the following detailed
description of preferred embodiments which, taken in conjunction
with the accompanying drawings, illustrate by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a greatly enlarged perspective view of a preferred
embodiment of the present invention;
[0040] FIG. 2 is a greatly enlarged perspective view of an
alternative preferred embodiment of the present invention;
[0041] FIG. 3 is a greatly enlarged perspective view of another
alternative preferred embodiment of the present invention;
[0042] FIG. 4 is a greatly enlarged perspective view of another
alternative preferred embodiment of the present invention;
[0043] FIG. 5 is a partial cross-sectional view taken along lines
5-5 of FIG. 4;
[0044] FIG. 6 is a partial cross-sectional view similar to FIG. 5
of an alternative embodiment of the present invention;
[0045] FIG. 7 is a greatly enlarged perspective view of another
alternative preferred embodiment of the present invention;
[0046] FIGS. 8a-c are greatly enlarged cross-sectional views of
alternative preferred embodiments of the present invention;
[0047] FIGS. 9a-g show instruments for effecting a defective
cartilage resection and replacement cartilage plug implantation
procedure according to the present invention;
[0048] FIGS. 10a-d illustrate anchor plugs of the present invention
in place within a repair site; and
[0049] FIGS. 11a and b schematically illustrate a surgical site in
which anchor plugs of the present invention are employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] Definitions
[0051] As used herein, the following words and terms shall have the
meanings ascribed below:
[0052] "distal" refers to the end of a cartilage replacement plug
which is inserted into the void and is nearest to the subchondral
layer of bone;
[0053] "proximal" refers to the end of a cartilage replacement plug
which is nearest to the surface of the surrounding cartilage;
[0054] "equilateral" means having a plurality of linear sides or
edges, all of which are equally identical in length.
[0055] "congruent" means, with respect to three-dimensional figures
that any two such three dimensional figures are completely
superposable throughout, about all three dimensional axes, that is,
both figures have identical corresponding three dimensional angles
and equilateral sides or edges, i.e., the two figures are both
equiangular and equilateral; and, with respect to two-dimensional,
planar figures, that any two such two-dimensional, planar figures
are completely superposable throughout, about both planar axes,
that is, both figures have identical corresponding internal angles
and equilateral sides or edges, i.e., the two figures are both
equiangular and equilateral.
[0056] "similar" means, with respect to three-dimensional figures,
that any two such three-dimensional figures have identical shapes,
but are not superposable in that they have different sizes, that
is, both figures have identical corresponding three-dimensional
angles, but corresponding sides or edges of proportionately
different lengths, i.e., the two figures are equiangular but not
equilateral; and with respect to two-dimensional, planar figures,
that any two such two-dimensional, planar figures have identical
shapes, but are not superposable in that they have different sizes,
that is, both figures have identical corresponding internal angles,
but corresponding sides or edges of proportionately different
lengths, i.e., the two figures are equiangular but not
equilateral.
[0057] "curviplanar" means a planar surface existing in
three-dimensional space, and which may be a plane which is arcuate
or curved, undulating (i.e., has a sinusoidal wave shape), or which
is closed on itself and continuous about an axis. The side surface
of a circular cylinder, between the two circular faces of the
cylinder, is an example of a curviplanar surface which is closed on
itself and continuous about an axis which is the circumference of
the surface.
[0058] "polyhedron" means a three-dimensional geometrical shape
formed by the intersection of a plurality of flat planar surfaces
or a three-dimensional geometrical shape formed by the intersection
of one or more flat planar surfaces and at least one curviplanar
surface that is closed on itself so as to be continuous.
[0059] "regular" means, with respect to a three-dimensional
geometrical figure, composed of a plurality of flat planar
two-dimensional surfaces, each such flat planar two-dimensional
surface having a defined shape, a situation wherein all of the
component flat planar two-dimensional surfaces of the
three-dimensional geometrical figure have the same shape and are
both congruent and identical, that is, all component flat planar
two-dimensional surfaces are both equiangular and equilateral; and,
with respect to a plurality of flat planar two-dimensional
geometrical surfaces having the same shape, which constitute parts
of the same three-dimensional geometrical figure, together with one
or more other flat planar two-dimensional surfaces or at least one
curviplanar surface that is closed on itself so as to be
continuous, having a different shape or shapes from the plurality
of flat planar two-dimensional geometrical surfaces having the same
shape, a situation wherein all such flat planar two-dimensional
geometrical surfaces having the same shape, are both congruent and
identical, that is, all such flat planar two dimensional
geometrical surfaces having the same shape are both equiangular and
equilateral.
[0060] "irregular" means, with respect to a three-dimensional
geometrical figure, composed of a plurality of flat planar
two-dimensional geometrical surfaces or a combination of a
plurality of flat planar two-dimensional geometrical surfaces and
at least one curviplanar geometrical surface that is closed on
itself so as to be continuous, a situation where at least two of
said flat planar two-dimensional geometrical surfaces have the same
shape and are both congruent and identical, that is, said at least
two flat planar two-dimensional geometrical surfaces are both
equiangular and equilateral; and, with respect to a plurality of
flat planar two-dimensional geometrical surfaces, which constitute
parts of the same three-dimensional geometrical figure, a situation
where at least two of said flat planar two-dimensional geometrical
surfaces have the same shape and are both congruent and identical,
that is, said at least two flat planar two-dimensional geometrical
surfaces are both equiangular and equilateral.
[0061] "completely irregular" means, with respect to a
three-dimensional geometrical figure, composed of a plurality of
flat planar two-dimensional geometrical surfaces or a combination
of a plurality of flat planar two-dimensional geometrical surfaces
and at least one curviplanar geometrical surface that is closed on
itself so as to be continuous, a situation where no two of said
flat planar two-dimensional geometrical surfaces have the same
shape, or, if they are similar and have the same shape, are not
also both congruent and identical, that is, if two or more flat
planar two-dimensional geometrical surfaces are similar and have
the same shape, they are not also equilateral; and, with respect to
a plurality of flat planar two-dimensional geometrical surfaces,
which constitute parts of the same three-dimensional geometrical
figure, a situation where no two of said flat planar
two-dimensional geometrical surfaces have the same shape, or, if
they are similar and have the same shape, are not also both
congruent and identical, that is, if two or more flat planar
two-dimensional geometrical surfaces are similar and have the same
shape, they are not also equilateral.
[0062] "symmetrical" means, with respect to a three-dimensional
figure, one in which a plane bisecting the figure along any axis
creates two half figures which are mirror images of one another;
and, with respect to a two-dimensional figure, one in which a plane
bisecting the figure along any axis creates two half, planar,
two-dimensional figures which are mirror images of one another.
[0063] "asymmetrical" means, with respect to a three-dimensional
figure, one in which a plane bisecting the figure along at least
one axis creates two half figures which are not mirror images of
one another; and, with respect to a two-dimensional figure, one in
which a plane bisecting the figure along any axis creates two half,
planar, two-dimensional figures which are not mirror images of one
another.
[0064] "polygon" means a two-dimensional flat planar surface
forming a defined, closed shape bounded by a plurality of sides or
edges of the polygon.
[0065] "chord" means, with respect to a regularly shaped closed
curvilinear planar surface figure, the longest straight line
between any two points on the circumference of the closed
curvilinear planar surface figure which also passes through the
geometric center of the figure.
[0066] "right" means, with respect to a cone or a pyramid,
respectively, a conical or a pyramidal shape wherein a straight
line between the apex of the cone or pyramid and the geometric
center of the base is perpendicular to the plane of the base, and
forms a pair of right angles at the intersection therewith; and,
with respect to a cylinder or a frustum of a cone or pyramid,
respectively, a cylinder of or a frustum wherein the a straight
line between the geometric centers of the first and second faces of
the cylinder or frustum is perpendicular to the plane of each face,
and forms a pair of right angles at the intersection with each
plane.
[0067] "oblique" means, with respect to a cone or a pyramid,
respectively, a conical or pyramidal shape wherein a straight line
between the apex of the cone or pyramid and the geometric center of
the base is not perpendicular to the plane of the base and forms a
pair of non-right angles at the intersection therewith, including
one acute angle and a complementary obtuse angle, which together
form a straight angle; and, with respect to a cylinder or a frustum
of a cone or pyramid, respectively, a cylinder or a frustum wherein
a straight line between the respective geometric centers of the
first and second faces of the frustum is not perpendicular to the
plane of either face, and forms a pair of non-right angles at the
intersection with each plane, each pair including one acute angle
and a complementary obtuse angle, which together form a straight
angle.
[0068] "parallel" means, with respect to a frustum of a cone or a
pyramid, a frustum of a cone or a pyramid wherein the first and
second planar faces of the frustum lie in parallel planes.
[0069] "non-parallel" means, with respect to a frustum of a cone or
a pyramid, wherein the first and second planar faces of the frustum
do not lie in parallel planes, but lie in intersecting planes.
[0070] "flowable polymer" means a polymer that, when initially
placed int the application site or mold at the time of use, has
reactive components in the prepolymerized or early polymerization
state and is physically fluid or flowable but is capable of curing
(polymerizing) to a solid state relatively quickly after
application.
[0071] "natural polymer" means any of a variety of long chain
molecules that have repeating structural units that are derived
from biologic (cellular) synthesis. Examples include collagens,
gelatins (denatured collagen), fibrin, alginates, etc.
[0072] "synthetic polymer" means any of a variety of long chain
molecules that consist of a number of repeating structural unit
that are derived in laboratory chemical synthesis.
[0073] In its most basic form, the cartilage replacement plug
device according to the present invention is fabricated by molding
biostable polycarbonate polyurethane material into preformed
shapes. A single such material may be used to form a plug or anchor
plug or, alternatively, a number of different such materials may be
combined as a lamination.
[0074] The cartilage plug of the present invention has a polygonal
or circular cross-section, with a height-to-diameter ratio of from
about less than one to one to about 20:1. The plugs may be molded
in a wide range of sizes and having various height-to-diameter
ratios in order to accommodate a wide range of cartilage
replacement situations. Thus, the generally round devices have
shapes ranging from flat disks to cylinders. A variety of factors
must be taken into consideration for each particular application,
such as the location where the cartilage replacement plug or plugs
are to be implanted, the size of the cartilage defect that is to be
repaired, and the size and shape of the void cavity, either as
initially formed by resection of the defect, or by any subsequent
surgical contouring of the cavity, into which the cartilage
replacement plug is to be implanted. Cartilage replacement plug
devices having a flattened, disk shape are most suitable for more
extensive but shallow defects, while devices having a large
height-to-diameter ratio are suitable for defects having a smaller
surface area, but which extend deeper into the cartilage and/or the
subchondral bone layer.
[0075] The generally cylindrically-shaped family of basic cartilage
replacement plugs according to the present invention are
characterized in that they have uniformly sized and shaped circular
end surfaces which are connected by a single continuous cylindrical
side surface between the end surfaces. In these embodiments, the
side surface is perpendicular to both of the end surfaces, with the
side and end surfaces forming right angles with one another.
Cartilage replacement plugs according to the present invention are
generally fabricated as solid elements, but may alternatively be
fabricated as hollow elements as long as they retain overall
mechanical properties, such as strength and load bearing ability,
similar to those of the natural cartilage which they are
replacing.
[0076] The plugs of the present invention may optionally be
configured to serve as anchors for a flowable polymer that is
subsequently introduced into the cavity. Such anchors are
positioned so as to be partially embedded within the subchondral
bone while a portion of the plug remains protruding above the
surface of the bone. The protruding portion serves as a fixed
element to which the curing polymer can bond and which provides a
mechanical interconnection between the bone and the polymer. In
order to enhance the anchoring ability of the plug, the exterior of
the plug may be formed with ridges, the plug may have a hollow
interior to receive the polymer and such hollow interior surfaces
may have ridges formed thereon.
[0077] The surfaces of the cartilage plugs of the present invention
may be treated so as to expose a porous or roughened surface. By
treating the surface of the plug such that it is roughened or
textured, cell attachment is enhanced and allows for cell migration
and overgrowth of a tissue layer. With appropriate surface
asperity, the resultant cells adhere via ongrowth and ingrowth into
the surface of the plug enhancing fixation. Such cell ingrowth may
be ultimately transformed into a bony interface with the plug and
is considered a desirable characteristic. Important in this
transformation is how load is transferred from the device to the
surrounding tissue. A large mismatch in deformation between the
plug and surrounding tissue can lead to a fibrous tissue layer
around the plug that, although flexible, does not provide the
desired fixation. Porosity, like asperity, can be important and
beneficial when considering biologic fixation. A porosity that is
too small, i.e. equal to or smaller than 10 micrometers, can
inhibit cell ingrowth and results in no biologic fixation. A
porosity that is too large, i.e., equal to or greater than 1-2 mm,
results in less cell filling of the porous voids and poorer
biologic fixation. However, a large porosity may be beneficial if
used in an anchoring application for synthetic or natural polymer.
Sufficiently large pores allow the influx of the polymer while in
its flowable state and facilitates a mechanical fixation upon
curing.
[0078] FIG. 1 shows a cartilage plug 12 according to the present
invention which has a circular cross-section and end surfaces 14
and 16, with the side 18 and end surfaces being perpendicular to
one another while FIG. 2 illustrates a tapered embodiment 20 of
circular cross-section. Other embodiments 22 of cartilage plugs
with circular cross-sections include oblique shapes wherein the
side 24 and end surfaces 26, 28 are not perpendicular to one
another but intersect at an angle other than a right angle as is
shown in FIG. 3.
[0079] Cartilage replacement plugs according to the present
invention having such an oblique configuration are suitable for
replacing defects, most often those resulting from a chronic
disease condition in which the defect has penetrated into the
cartilage in a pattern which does not extend down into the
cartilage at a right angle to the outer end surface of the defect,
but which may extend obliquely into the cartilage from the surface.
Rather than having to resect a portion of cartilage that is greater
in surface area at the outer surface than is necessary in order to
get to the off-centered base of the defect, it is less invasive to
remove a defect core which is not at a right angle to the outer
surface, and which extends obliquely into the cartilage. These
oblique void cavities are easily filled by uniquely shaped
cartilage replacement plugs.
[0080] A basic cartilage plug according to the present invention is
not, however, limited to having a cylindrical shape with circular
end surfaces. Other configurations for the basic cartilage
replacement plugs of the present invention include shapes having
oval, ovoid, elliptical, and irregular closed curvilinear (i.e.,
curviplanar) shaped end surfaces, with a correspondingly shaped
continuous closed side surface. Cartilage plugs with non-circular
curviplanar end surfaces may also be fabricated as straight sided
or obliquely sided elements.
[0081] Still other basic cartilage plugs according to the present
invention include polyhedra having polygonal cross-sections and end
surfaces with from three to twenty or more edges and rectangular
sides, instead of circular ends and a single continuous, curved,
cylindrical side surface. Irregular polygonal shapes may also be
used for the end surfaces of such plugs instead of those having a
set number of equal side edges. Typically, the polygonal end
surfaces for the cartilage replacement plugs range from three-sided
triangles to twelve-sided dodecahedrons. Although polygons having a
greater number of sides than twelve may be fabricated within the
scope of the invention, the difficulty of molding such embodiments
and the related cost of making them exceed any advantage of being
able to more closely fit a void cavity in the cartilage. It is
generally easier to recontour the shape of the void cavity to
accommodate one of a standard set of plug shapes, than to produce a
plug having a custom shape. For cartilage plugs having polygonal
shaped end surfaces, it is particularly preferred to fabricate them
having either four-sided square or rectangular ends, the six-sided
hexagonal ends 30, 32 shown in FIG. 4 or eight-sided octahedral
ends.
[0082] According to another preferred embodiment, a cartilage plug
of the present invention may also be shaped with a taper towards
its distal end as is shown in FIG. 2. In this embodiment, the
distal end surface 34 is congruent to the proximal end surface 36,
but is proportionally smaller, so that the side walls 38 of the
plug taper inward toward the distal end of the plug. It has been
found that such tapered plugs remain in place in the cavity into
which they have been implanted better than straight-sided plugs
wherein both the proximal and distal end surfaces are the same size
and the side walls of the plug are all parallel and form right
angles with both end surfaces. The taper can range from 0 to 15
degrees. The cartilage plugs may also be fully tapered at one end
to a point, so that, in the case of a cartilage plug with a
circular end surface, the plug has a conical configuration, and in
the case of a plug having a polygonal end surface, the plug has a
polygonal pyramid configuration.
[0083] According to still other embodiments, the cartilage plugs
according to the present invention may have tapered sides and still
retain congruent end surfaces of different sizes so that the plug
has the shape of a frustum of a cone in the case of a plug with
circular or other rounded end surfaces, and the shape of a frustum
of a polygonal pyramid having polygonal end surfaces.
[0084] It has been found that, in general, disk-shaped and
cylindrical cartilage replacement plugs are the easiest to mold and
have been found to be best suited for use in the repair of small to
medium sized defects which are effectively repaired using a single
plug. It has additionally been found that plugs with tapered sides
or obliquely configured plugs have the best adhesion to the walls
of the surrounding void cavity into which the plugs are implanted.
Generally, the deeper the plug and the higher the
height-to-diameter ratio, the better the plug remains in place in
the void cavity. Flatter, shallower, disk-shaped plugs have a
greater chance of becoming loose in the cavity.
[0085] In order to improve the anchorability of plugs and prevent
them from coming loose, the cartilage replacement plugs of the
present invention may also have additional features to help anchor
them to adjacent cartilage and/or adjacent plugs so as to hold them
in place within the void cavity into which they are implanted.
These additional features include ridges that are formed on the
side surfaces of the plugs. The ridges may be discretely situated
at various points on the sides of the plugs, or they may form a
continuous band spirally wound around the side surface of the plug,
or forming a series of separate, discrete, parallel bands around
the side of the plug. FIG. 4 illustrates a plug 34 having a series
of parallel ridges extending about its hexagonal periphery. The
cross-sectional view (FIG. 5) shows that the ridges 36 have a
barbed configuration wherein the distal side 38 of each ridge is
gently sloped while the proximal side 40 has a steeper angle, which
in this embodiment is substantially perpendicular to the side 42 of
the plug. FIG. 6 illustrates the cross-section of another
embodiment wherein the ridges 44 comprise ribs that have similarly
sloped distal 46 and proximal 48 sides. FIG. 7 illustrates yet
another alternative embodiment 50, wherein the ridges 52 comprise a
single helix that spirals about the periphery of the plug. Ridges
maybe formed on any of the plug configurations of the present
invention, including configurations having circular or polygonal
cross-sections or with tapered side surfaces or oblique end
surfaces.
[0086] The barbs and ribs, either as a plurality of individual such
elements, or as a single continuous, spiral band or a series of
parallel rings or bands of barbed or ribbed elements, may be
fabricated as an intrinsic part of the plug during the original
injection molding process, or alternatively, they may be added to a
basic, smooth-sided cylindrical plug, such as by machining, gluing
or otherwise fusing them to the side surface of the plug, after the
basic plug has been formed. It is preferable, however, that the
barbs or ribs be formed as an intrinsic part of the overall plug
when it is molded to ensure that the elements afford the maximum
anchoring contact between the plug and the surrounding cartilage,
and that the elements do not themselves come loose from the main
side body of the plug over time as might eventually occur if they
are simply glued to the plug.
[0087] It is also possible to anchor the cartilage replacement plug
to the base of the cavity into which it is being implanted through
use of a fastening element which penetrates into the underlying
cartilage or subchondral bone layer, depending on the depth to
which the plug is implanted. Such fastening or anchoring element
may be in the form of a nail or screw which holds the plug to the
base of the cavity.
[0088] Although there is no limit to the size of single plugs which
may be made according to the present invention, and even large
defects can be filled using plugs fabricated to have a sufficient
size and volume capable of filling large voids, it has been found
that it is easier to fill large voids in cartilage created by the
removal of defective cartilage with a plurality of cartilage
replacement plugs, each made of a smaller size and standard
shape.
[0089] A plurality of cartilage plugs are used to fill larger void
in what is known as a mosaicplasty. In such a procedure, a
plurality of from two to twenty individual cartilage plugs are used
to fill substantial voids. Although a mosaicplasty procedure may be
carried out using individual cartilage plugs of any shape,
including the disk or cylindrical shapes frequently used for single
plug replacement procedures, and although a variety of different
shaped and sized plugs may be used in such a mosaicplasty
procedure, such a procedure works best when plugs having polygonal
shaped end surfaces are utilized so that the side surfaces of
adjacent plugs in the mosaic can fit tightly up against one
another. When round end surface plugs such as disks or cylinders
are used in a mosaicplasty, interstitial void spaces between
adjacent plugs remain. Although various types of fillers, such as
bone cement or polyurethane, may be used to fill-in these
interstitial voids, that step further complicates the procedure.
Alternatively, such interstitial voids may be left open for natural
ingrowth, however, that takes a considerable period of time and may
not occur uniformly, particularly near the inner sections of the
mosaic of plugs. Natural subchondral bone and cartilage regrowth
around the outer edges of the mosaic, that are in contact with the
adjacent natural cartilage and bone may occur relatively faster,
but nevertheless would be at a slow pace. If such interstitial
voids are allowed to remain due to lack of infilling, or due to
awaiting natural ingrowth, the integrity of the mosaicplasty of
plugs may become compromised over time due to the plugs loosening
in place. One alternative way of overcoming this is to have the
side surfaces of the plugs fitted with an interlocking "tongue and
groove" mechanism or the like which holds adjacent plugs tight with
respect to one another.
[0090] According to yet another preferred embodiment of the
invention, a cartilage replacement plug may be fabricated as a
multi-layer composite structure formed from several layers 54, 56,
58 of different materials. One embodiment of such a plug 12 (FIG.
1) is made with three layers of different materials which are fused
or bonded together. A first layer 54, at the distal end of the
device, which upon implantation is closest to the subchondral bone
layer, is made from biostable polycarbonate polyurethane 75-D, a
material having an elastic modulus similar to subchondral bone. An
intermediate 56, central layer of the device is made from
polycarbonate polyurethane 55-D, which has properties similar to
natural cartilage. A third layer 58, at the proximal end of the
device, which is closest to the surface of the cartilage
surrounding the implanted plug, is made from polycarbonate
polyurethane 80-A or a thermoplastic hydrogel coating, which has
properties similar to those of hyaline cartilage, which is the type
of cartilage which occurs nearest to the outer surface of an
articulating joint, and is lubricated by the synovial fluid. Other
combinations of materials may be employed to more accurately
duplicate the stiffness characteristics of the native cartilage.
Materials of construction for such a multi-layer cartilage
replacement plug may further include polyurethane adhesives that
contain non-leachable isocyanate groups that are used to bond the
multiple layers together, and injectable polyglyceryl methacrylate
hydrogels with viscoelastic and lubricious properties. Intermediate
layers may be relied upon to provide a desirable load transfer
between upper and lower layers of different hardnesses. A layer may
also be developed through solvent polymer-hydrogel treatment of the
exposed articulating surface of the plug device thereby imparting a
hydogel coating with good lubricity. FIGS. 2 and 3 illustrate an
alternative embodiment wherein only two different materials 60, 62
and 64, 66 are combined in a lamination.
[0091] The dimensional proportions of polymer layers for
construction of a plug in accordance with the present invention may
vary widely to accommodate various applications. In an embodiment
wherein the 50% of the plug is to be embedded in the bone, the base
layer with the hardest material would comprise about 50% of the
length of the plug while the softest superficial layer which will
interface with opposing articular cartilage surface may comprise
about 33% of the total length of the plug. The intermediate layer,
of intermediate softness, may therefore comprise about 17% of the
total length of the plug.
[0092] The advantages to the multi-layer construction include a
more physiologic load transfer to the underlying subchondral bone.
This is achieved through the plug having zones of differing
mechanical and physical properties. The result enhances the
stability of the implant and the cartilage surrounding it.
[0093] FIGS. 8a-c illustrate alternative preferred embodiments of
the present invention wherein a bore is formed in a cartilage plug.
FIG. 8a illustrates an embodiment wherein an axial bore 70 extends
completely through the plug 72, while FIGS. 8b and 8c show plugs
74, 76 that have bores 78, 80 formed therein that extend well into
the interior of the respective plug but do not extend all the way
therethrough. The particular plug that are shown employ two layer
laminates 82, 84 and while the bore 78 of plug 74 shown in FIG. 8b
extends through the top layer and partially into the second layer,
bore 80 of plug 76 shown in FIG. 8c extends exclusively into only
the top layer. The bores of these particular embodiments
additionally have ridges 86 formed therein. The ridges have a
barbed configuration wherein the upwardly facing slope 88 of the
ridge is gentle while the downwardly facing slope 90 is
substantially perpendicular to the wall of the bore. The ridges
formed in the interior of the bores may optionally be symmetrical
to define ribs and the ridges may further optionally have a helical
configuration winding along the interior of the bore. As a further
alternative, the interior wall of the bore may be smooth.
[0094] The following described methods are examples of how a
laminated plug of the present invention may be manufactured.
[0095] Method 1
[0096] Extruded rods of biocompatible medical grade polyurethane
polymer are available from a variety of commercial vendors
specializing in this polymer. Furthermore, such rods are available
in different hardnesses and elastomeric properties, e.g. 55 Shore
D. Two rods of two different hardnesses, referred to as rod
hardness 1 (RH1) and rod hardness 2 (RH2) are selected. In a
preferred embodiment, the RH1 rod has a hardness H1 that closely
matches mechanical properties of native articular cartilage while
the RH2 rod has hardness H2 that closely matches mechanical
properties of trabecular bone. For machining purposes, and because
said rods of hardness H1 and H2 can be soft and pliable and may not
cut when subjected to standard lathe machine turning techniques,
the rods may be deep frozen to stiffen them for lathe turning and
machining. Once the RH1 rod is frozen, it is placed in a lathe
chuck and the exposed end that is perpendicular to the long axis of
the rod is radius faced to match any of a variety of predetermined
curved surfaces that match the curve surface of the target
articular cartilage that is being replaced. The radius-faced
surface is identified as surface SA. A cylinder blank is then
formed by cutting off the end portion of the said rod RH1 at a
predetermined length using a cutoff tool forming a flat bottom
surface of the cylinder identified as surface SB.
[0097] The H2 rod is deep frozen and similarly chucked for turning
but its surface parallel to the long axis is surface machined to
form the desired ridges in the form of ribs or barbs, after which
the exposed end surface that is perpendicular to the long axis of
the rod is faced off with a flat surface identified as SC. The
exposed end that is perpendicular to the long axis of the rod is
faced forming a surface that is perpendicular to the long axis of
the RH2 rod and forming a flat surface identified as SC. A cylinder
blank is then formed by cutting off the end portion of the RH2 rod
at a predetermined length using a cutoff tool forming a flat bottom
surface of the cylinder identified as surface SD.
[0098] The surface SB of the RH1 rod is to be mated and permanently
joined with surface SC of the RH2 rod. The joining process can be
accomplished in a variety of ways. A preferred iteration involves
placing said cylinder blank with hardness H1 and cylinder blank
with hardness H2 each in a holding collet. The surface SC and SB
that are to be joined are treated with a suitable adhesive glue
that will bond the two cylinders together. Such adhesive glues may
include but are not limited to cyanoacrylates, methylacrylates,
octylacrylates, polyurethane solvents, visible or UV light
activated adhesives that are commercially available. Glues may be
spread thinly and evenly over the surface SC and SB or placed in a
suitable pattern of glue dots that results in an evenly spread
distribution without glue flashing. The rod cylinders are placed in
an alignment guide clamp assembly and the surface SC and SB brought
together for glue bonding. After bonding the laminate structure is
ultrasonically cleaned and rinsed and prepared for packaging and
sterilization.
[0099] An alternative method to bond the said two cylinder
interface surfaces SB of RH1 and SC of RH2 together include the
generation of heat at the SC and SB interface causing the interface
to fuse the two surfaces together. The method to generate heat may
include but is not limited to the use of focused ultrasonic waves
energy at the said interface surface forming a fusion weld. After
bonding the laminate structure is ultrasonically cleaned and rinsed
and prepared for packaging and sterilization.
[0100] Another method involves treatment of said surface SC and SB
with a dark pigment such that laser light energy may be absorbed
creating an intense heat and shock wave thereby fusing the
interface together. After bonding the laminate structure is
ultrasonically cleaned and rinsed and prepared for packaging and
sterilization.
[0101] Yet another method involved the treatment of said surface SC
and SB with a powdered metal or fine wire paste that can react with
microwaves energy with said metallic elements absorbing the energy
creating sufficient heat such that a fusion of the interface
occurs. After bonding the laminate structure is ultrasonically
cleaned and rinsed and prepared for packaging and
sterilization.
[0102] Similar methods may be employed to form laminates having
three or more layers. Alternatively, an 80-A material may be the
sole polymer used, may be used in conjunction with the 55-D
material and/or a hydrogel material may be applied thereto to form
an additional layer.
[0103] Method 2
[0104] A metal casting block is prepared as a mold that has the
desired .dimensions of the final plug geometry. It is envisioned
that said mold has a base plate and at least two components that
form the walls of said plug. For orientation, said base plate forms
the surface on the plug representing the surface of the target
articular cartilage that is being replaced. Such mold also has
machine cuts for all fixation barbs or ribs that are part of the
polyurethane plug. In this iteration, the base plate of the mold is
designed to have a curved sulcus which corresponds to the surface
curve of the articular cartilage at the target implantation site.
This approach requires multiple molds that provide curves that
match the potential implantation site. Alternatively, the base
plate may be flat and the resultant cast plug is machined in a
secondary procedure to attain the desired surface curvature.
[0105] In practice, biocompatible polyurethane polymer beads of
appropriate hardness are obtained from a commercial source that
specializes in this product. The polymer beads are obtained in two
hardnesses H1 and H2. The polymer beads H1 (for example 55 Shore D)
is harder than H2 polymer beads (for example 80 Shore A). An
appropriate mass of H1 polymer beads are placed at base of mold for
the first layer (L1) of said plug. An appropriate mass of H2
polymer beads are placed in the mold on top of the H1 polymer beads
to from the second layer (L2). The mold is then transferred to the
vacuum oven. Vacuum and heat are applied to accomplish the melting
and fusion of said beads thereby forming the desired laminate
structured plug. After the molding process is complete, the mold is
removed from the oven and the mold disassembled to release said
plug. The plug is then ultrasonically cleaned and rinsed and
prepared for packaging and sterilization.
[0106] In an alternative method, a metal casting block is prepared
as a mold that has the desired dimensions of the final plug
geometry as set forth above. In this iteration, the mold has
sufficient structural dimensions to make it compatible with
compression molding standards and can be assembled to standard
compression molding equipment. It is envisioned that the mold
connects to the polymer ram piston assembly that delivers the
compression and heat energy for the molding cycle. The compression
cycle on the polymer should be matched so that heat from
compression is sufficient to fuse the polymer bead raw
material.
[0107] In practice, biocompatible polyurethane polymer beads of
appropriate hardness are obtained from a commercial source that
specializes in this product. Such polymer beads are obtained in two
hardnesses H1 and H2. The H1 polymer beads (for example 55 Shore D)
are harder than H2 polymer beads (for example 80 Shore A). An
appropriate mass of H1 polymer beads followed by an appropriate
mass of H2 polymer beads are loaded in the supply hopper of the ram
piston such that said ram piston forces both H1 and H2 polymer
beads simultaneously and in a serial manner into the mold cavity.
In the preferred iteration, the speed and force of said ram piston
generates sufficient heat to cause fusion of the polymer beads. The
mold is then cooled and the completed plug is then removed from the
mold assembly. Said plug is ultrasonically cleaned and rinsed and
prepared for packaging and sterilization.
[0108] Alternatively, a metal injection molding block is prepared
having multiple interconnected plug mold voids each having the
desired dimensions for producing the final plug geometry including
all fixation barbs or ribs. Such mold has a capability for at least
dual polymer injection. The injection mold may be so designed that
the two inflow pathways for the two polymers are at opposite ends
of the plug mold and the outflow pathway at the desired interface
level. Alternatively, the injection mold may be designed with a
single inflow pathway at the base of the plug mold for both
polymers that will be serially injected and a single outflow
pathway at the opposite end of the plug mold. In these iterations,
the articular cartilage end of said plug may be molded with a flat
or a near flat curve that can be secondarily machined to achieve
the final curvature that corresponds to the surface curve of the
articular cartilage at the target implantation site.
[0109] In practice, biocompatible polyurethane polymer beads of
appropriate hardness are obtained from a commercial source that
specializes in this product. The polymer beads are obtained in two
hardnesses H1 and H2. The H1 polymer beads (for example 55 Shore D)
is harder than H2 polymer beads (for example 80 Shore A). An
appropriate mass of H1 polymer beads is placed in the injection
mold reservoir for the first polymer H1. An appropriate mass of H2
polymer beads is placed in the injection mold reservoir for the
second polymer H2. The polymers are heated to appropriate injection
temperature.
[0110] Using appropriate gate valves and pressure the polymers are
injected into the mold. In one mold configuration the H2 polymer
enters on the side that will be the articular cartilage surface and
said H1 polymer enters on the side that will be the bone side of
the plug. The two polymers meet and exit at the outflow port
located at the desired level of the interface between the two
polymers. A precise volume of said H1 polymer enters the plug mold
from the bone side of the plug. During this injection, the gate
control valve is activated to allow injection of a precise amount
of said H2 polymer such that displacement of the H1 polymer by said
H2 polymer forms an interface at the desired level on the plug.
After injection molding is complete, the plugs are removed and
flashing removed. The plugs are ultrasonically cleaned and rinsed
and prepared for packaging and sterilization.
[0111] Similar methods may be employed to form laminates having
three or more layers.
[0112] Method 3
[0113] In this method cylinders of two different polymer hardnesses
H1 and H2 are obtained as described in method 1 and at least the H2
cylinder is complete with fixation barbs or ribs. The cylinders are
placed in an alignment jig that hold said cylinders in collets that
also align said cylinders in axial alignment. The collets are
mounted on linear rails that allow them to move the cylinder ends
for joining. In practice the faces of cylinders H1 and H2 that are
to be joined are slightly separated to allow the introduction of a
nichrome or other appropriate heating wire element between the said
cylinder faces. A voltage is applied to said heating wire allowing
these surfaces to heat. At a critical fusion temperature, said
heating element is removed and said collets are brought together
allowing surfaces of said cylinders to fuse forming a laminate
structure. The plug is allowed to cool and then removed from the
collet assembly. Said plugs are ultrasonically cleaned and rinsed
and prepared for packaging and sterilization.
[0114] Similar methods may be employed to form laminates having
three or more layers.
[0115] Method 4
[0116] Extruded rods of biocompatible medical grade polyurethane
polymer are available from a variety of commercial vendors
specializing in this polymer as described in Method 1. Two rods of
two different hardnesses, referred to as rod hardness 1 (H1) and
rod hardness 2 (H2). For machining purposes, and because said rods
of hardness H1 and H2 can be soft and pliable and may not cut when
subjected to standard lathe machine turning techniques, the rods
may be deep frozen to stiffen them for lathe turning and machining.
Once the H1 rod is frozen, it is placed in a lathe chuck and the
exposed end that is perpendicular to the long axis of the rod is
faced and the diameter of the rod reduced to 1/2 the original
diameter and threaded forming a threaded end (TEH1). A cylinder
blank is then formed by cutting off the end portion of the said rod
H1 at a predetermined length using a cutoff tool that allows
secondary machining to obtain matching curves to the articular
cartilage implantation target site.
[0117] The H2 rod is deep frozen and similarly chucked for turning
but its surface parallel to the long axis is surface machined to
form the desired ribs or barbs, after which the exposed end surface
that is perpendicular to the long axis of the rod is faced off and
center drilled. The end is then bored out and threaded to match the
threaded end TEH1 of said H1 cylinder. A cylinder blank is then
formed by cutting off the end portion of the said rod H2 at a
predetermined length using a cutoff tool forming a flat bottom
surface of the cylinder identified as surface SD.
[0118] The cylinders H1 and H2 are then cleaned and rinsed of any
machining debris. The cylinders are then assembled by threading the
end TEH1 of said cylinder H1 into the threaded hole located in the
end of said cylinder H2. After inspection of the fit, the cylinders
are disassembled and an appropriate aliquot of suitable glue is
applied the base of the threaded hole and the cylinders quickly
reassemble so that the glue may bond the threaded surfaces together
forming a laminate structure. After the glue is cured, the finished
plug is then ultrasonically cleaned and rinsed and prepared for
packaging and sterilization.
[0119] Similar methods may be employed to form laminates having
three or more layers.
[0120] A pore structure or surface asperity may imparted to a plug
of the present invention using any of a number of techniques. For
example, crystals or powders of suitable dimensions of non-toxic
soluble compounds, for example, but not limited to sucrose, salt,
calcium carbonate, sodium bicarbonate, etc. may be added to the
mold process whereby they become imbedded in selected portions of
the polymer. Since these compounds are water soluble, they may be
removed from the polymer by dissolving them in a water bath.
Residual crystals not removed by the waterbath may eventually be
naturally dissolved with no untoward effects as they are non-toxic.
Different size crystals may be used in different portions of the
plug and/or in different polymers to be combined to form the plug
in order to provided differently sized pores in selected portions
of the plug. For example, in a plug anchor application, it may be
desirable to have smaller sized pores in that region of the plug
that will be in direct contact with the subchondral bone in order
to promote biologic fixation therewith, while the surfaces to be
exposed to a flowable polymer will benefit from larger sized pores
in order to facilitate the influx of the polymer and promote
mechanical fixation therewith. Regardless of whether the plug has
pores formed therein, it is desirable for all surfaces to be
treated in a manner to provide conditions for cell attachment and
biologic fixation. Such surface treatment may be accomplished by
exposure to energetic plasmas, e.g. hydrogen peroxide plasma or
argon plasma. An added benefit to such treatment is that the
exposure aids in removal of minor contamination and also renders
the surface sterile. Surface treatments may range from conservative
techniques imparting subtle changes in asperity to the surface to
aggressive techniques resulting in larger porosities.
[0121] The present invention also includes a process or procedure
for resecting a portion of defective cartilage and filling the void
cavity thereby created by implanting therein one or more cartilage
replacement plugs according to the present invention. The present
invention still further includes a set of operating instruments
utilized in the procedure. Both the procedure and the instruments
utilized in performing it will now be described.
[0122] According to the process, an orthopaedic surgeon first
ascertains the extent, shape and dimensions of the cartilage
defect, resulting either from traumatic injury or chronic disease,
by means of radiographic analysis or other standard diagnostic
methods.
[0123] Referring to FIG. 9a, the general situs of the cartilage
defect is surgically opened and an approximate center of the
cartilage defect is marked and scored using cartilage scoring and
pointer instrument 500. This instrument has a solid sharpened
pointed tip 501 at a distal end 502 thereof for scoring the
cartilage or just the outer layer of the cartilage at the location
where the defect is to be removed. The instrument also has a handle
503 at a proximal end 504 of the instrument. The instrument may
additionally include a hatched cutting surface with an outer
core.
[0124] Referring to FIG. 9b, after marking the center of the defect
that is to be resected, cartilage punch 510 is centrally positioned
over the scored marking point on the outer surface of the cartilage
and is used to punch an outline of the end view of the shape that
is to be removed into the cartilage at the site of the defect. This
in effect sets the perimeter of the defect that is to be removed.
Cartilage punch 510 may have an adjustable punch diameter or width
511 whereby the diameter or width of the cartilage defect "core"
which is to be resected can be set, or alternatively, a set of
punches of fixed diameter or width can be utilized with a punch of
appropriate size being selected for any given procedure. Cartilage
punch 510 has a hollow tubular distal end section 512 with a
sharpened edge or attached cartilage cutting blade 513 around the
periphery of the tubular distal end section, such that the
sharpened edge or blade is directed outwardly from the instrument
and a proximal handle section 514. The hollow tubular distal end
section 512 of cartilage punch 510 and the cartilage cutting blade
513 both have the same cross sectional shape and area. Generally,
the cartilage punch 510 has a cross sectional shape corresponding
to the shape of the cartilage replacement plug that is to be
implanted. Typically, this will be a circular cross section,
although any shape cross section may be utilized, including
non-circular curvilinear shapes such as ovals, ellipses, and
irregular closed curvilinear shapes, and polygonal shapes.
[0125] Referring to FIG. 9c, an alternative tip design for
cartilage punch 510 shown in FIG. 9b allows for a disposable
tubular punch section 517 to be used in scoring the articular
cartilage repair site. Said disposable punch section 517 has a
shoulder flange 518 that seats against the distal end 515 of punch
510 and is secured with a locking nut 516.
[0126] Referring to FIG. 9d, actual resection of the cartilage
defect is next commenced using first drill instrument 520 to drill
into the defective cartilage inside the previously designated
perimeter. The action of the drill pulverizes the defective
cartilage which is thereby removed leaving a void space for
implantation of the cartilage replacement plug or plugs. First
drill instrument 520 has a flat bottomed bit 521 at distal end 522
thereof which produces a drilled cavity in the cartilage having a
generally cylindrical shape. First drill instrument has a handle
523 at a proximal end of the instrument.
[0127] Referring to FIG. 9e, second drill instrument 530, having a
tapered bit 531 at a distal end 532 thereof, is then used to
produce a tapered distal end in the drilled cavity. Second drill
instrument also has a handle 533 at a proximal end of the
instrument.
[0128] Referring to FIG. 9d, depth gauge 540 may be utilized to
control the depth of the cavity which is drilled by either the
first drill instrument 520 or the second drill instrument 530.
Depth gauge 540 is alternatively attachable to the first drill
instrument 520 and the said second drill instrument 530 as they are
used in sequence as described above to measure the depth of
penetration into the cartilage of each of the first and second
drill instruments, respectively.
[0129] Referring to FIG. 9e, drill stop 550, which is also is
alternatively attachable to the first drill instrument 520 and the
said second drill instrument 530, and which cooperates with the
depth gauge 540, may be used to cause penetration of each of said
first and second drill instruments into the cartilage to stop at a
predetermined depth.
[0130] Referring to FIG. 9f, after the void cavity has been
completely cleaned and prepared, cartilage plug insertion
instrument 560 is then used to insert a preselected cartilage
replacement plug, or, a series of plugs, sequentially, into the
void cavity in the cartilage.
[0131] Referring to FIG. 9g, an alternate cartilage plug insertion
instrument 570 with central drive 571 may be used to seat a plug
into the void cavity in the cartilage.
EXAMPLE 1
[0132] A pilot study utilizing preformed polyurethane cartilage
replacement plugs according to the present invention, fabricated in
both hard and soft versions, and having both ribbed and barbed
fixation elements, was undertaken for the repair of full thickness
medial femoral condylar damage in the goat with the objectives of:
determining the effectiveness of repairing a full thickness
cartilage defect with a polyurethane plug; determining the ease
with which such plugs can be fixed into a defect; determining the
necessity of having a hard or a soft layer in contact with the
opposing joint surface; determining the criticality of matching the
surrounding surface contour; determining the extent to which the
implanted cartilage replacement plug prevents further damage to
surrounding cartilage; determining an appropriate tribological
environment within a repaired joint by observing the hydrodynamic
lubrication of compliant polyurethane bearing surfaces; and
determining how well the implanted cartilage replacement plugs
remained in place following function of the joint.
[0133] Under strict asepsis, a subchondral defect (40% by area) was
created in the right medial femoral condyle of 4 adult, skeletally
mature, disease-free, female Spanish goats. The cartilage defects
created were 6 mm in diameter and 6 mm in depth, passing well into
the subchondral bone. The defects were made 15 mm distal to the
condyle groove junction and were aligned with the medial crest of
the trochlear groove. The cartilage core cutter instrument
according to the present invention was used first to slice through
the cartilage layer to prevent tearing of the cartilage during
drilling. With the core cutter in place, the centering awl
instrument according to the present invention was introduced to
locate the center of the core and allow for the point of the 6 mm
drill bit to be located properly. A 6 mm collared drill bit was
used under power to drill to a fixed depth of 6 mm, maintaining a
drill plane perpendicular to the tangent of the condyle after which
the drill bit was carefully removed. The appropriate cartilage plug
implant was manually inserted and tapped into place with the
insertion device instrument of the present invention. The joint was
routinely closed. The opposite leg served as an unoperated
control.
[0134] In all, two groups of two goats each were fitted with
artificial cartilage plugs according to the present invention, made
from hard and soft materials and using ribbed and barbed fixation
means, as follows:
1 Fixation Animal Plug Material Means 1 Hard Ribbed 2 Hard Barbed 3
Soft Ribbed 4 Soft Barbed
[0135] Six weeks after the cartilage plug implantation surgery, all
subject animals were humanely euthanized according to guidelines
set forth by the AVMA Panel on Euthanasia. The operated and control
joints were opened, grossly evaluated according to established
criteria. The femora were cut approximately 10 cm above the joint
line and split sagittally along the intercondylar notch. The
control and implanted medial femoral condyles were fixed for
histologic processing and analysis.
[0136] The results of the gross and histologic evaluation showed
that fixation could successfully be achieved into the subchondral
space with either barbs or ribs and that replacement of the defect
with an artificial cartilage plug prevented further damage to the
surrounding articular cartilage.
EXAMPLE 2
[0137] The cartilage plugs of the present invention may
alternatively be used to anchor a flowable polymer to the
subchondral bone. An implantation hole for the plug is drilled into
the prepared bony base of the articular cartilage defect.
Preparation of the bony base of the defect in this context entails
the removal of loose tissue debris and exposure and/or surface
modification of part or ll of the subchondral bone in the defect
area by the surgeon. Using an inserter instrument that holds and
drives the plug for implantantion, the base unit is inserted into
the bone to a depth of approximately 50-60% of the plug height. The
cylindrical devices-are seated such that approximately half of the
barbs or ridges on the outer surface of the plug engage the bony
walls of the tunnel and the remaining half of the plug's external
ridges remain exposed. The inserter tool is removed and rearmed
with another anchor plug as necessary and the process is repeated.
Multiple anchor plugs may be placed in a variety of patterns at the
base of the lesion site as desired by the surgeon.
[0138] Once the anchor plugs are in place, a flowable polymer is
introduced into the defect site. The flowable polymer will flow
into the lesion site, including in and around the implanted plugs
as well as into any bores that may be formed in such plugs. At an
appropriate fill level, the flowable polymer will cover the anchor
plugs with an overlay of polymer approximately 3 mm above the top
the plugs or to an overlay determined to be appropriate from
surgeon experience. The flowable polymer is allowed to polymerize
and cure. The action of the curing process of the flowable polymer
to the interior and exterior surfaces of the plug will provide for
a mechanical fixing of the flowable polymer to the subchondral
bone. Any ridges in the form of ribs or barbs in parallel or
helical arrangements, on the exterior and interior surfaces will
further enhance the mechanical fixation. Any adhesive qualities of
the flowable polymer will also help to augment the desired fixation
to the anchor plug. In addition, such polymerization will result in
a multi-laminate structure in conjunction with the plug device.
Transmission of load to subchondral bone will be through the
flowable polymer and polymer plug anchor device interface. Load
transmission is believed to be beneficial to biologic fixation of
the anchor device and in turn the fixation of the flowable polymer
in the correct anatomic location.
[0139] FIGS. 10a-d illustrate four different plug configurations
implanted in subchondral bone. Each anchor plug 100, 102, 104, 106
is formed of two different polymers 108, 110 wherein the harder
polymer comprises that portion of the plug in contact with the
subchondral bone 112 while the softer polymer comprises that
portion of the plug that extends above the surface of the bone. All
of the plug embodiments that are illustrated have barbs formed on
their external surfaces. Plug 100 has a bore 114 formed therein
that extends through its entire length, while plugs 102 and 104
have bores 116, 118 formed therein that only extend partially into
the plug. All of the plugs with bores have barbs formed in the
their interior surfaces. The barbs formed on the exterior of the
plugs are oriented so as to resist pull-out of the plug from the
bone while the barbs formed on the interior are oriented to resist
the pull-out of cured polymer 120 from therewithin. After the
implantation of the plugs into the subchondral bone, a flowable
polymer is poured thereover which completely encapsulates the
plugs, intrudes into the bores and covers the plugs to a
predetermined depth. The polymer adheres to the plugs and the
subcondral bone and additionally becomes mechanically fixed to the
plugs to form an additional layer in the laminate structure.
[0140] FIG. 11 schematically illustrates an example of a surgical
site wherein four artificial cartilage plugs 122 serve to anchor a
flowable polymer 124 in place. The knee repaired in such manner
will have the cured polymer mechanically and adhesively fixed in
place. The plug anchors are in turn mechanically fixed in the bone
and will eventually additionally become biologically fixed
thereto.
[0141] While particular forms of the invention have been
illustrated and described, it will also he apparent to those
skilled in the art that various modifications can be made without
departing from the spirit and scope of the invention. Accordingly,
it is not intended for the invention to be limited except by the
appended claims.
* * * * *