U.S. patent application number 11/451513 was filed with the patent office on 2006-10-19 for artificial disc and joint replacements with modular cushioning components.
Invention is credited to Bret A. Ferree, David Tompkins.
Application Number | 20060235535 11/451513 |
Document ID | / |
Family ID | 37109576 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060235535 |
Kind Code |
A1 |
Ferree; Bret A. ; et
al. |
October 19, 2006 |
Artificial disc and joint replacements with modular cushioning
components
Abstract
An artificial joint or disc replacement (ADR) broadly includes a
pair of opposing endplate components, each attached to one of the
upper and lower vertebrae, a cushioning component disposed between
the endplate components, and a mechanism for coupling the
cushioning component to one or both of the endplates. In the
preferred embodiment, the cushioning component takes the form of a
tire-like outer structure attached to an inner hub. A filler
material is also preferably contained within the cushioning
component. The filler material may be a gas, liquid, foam, or gel,
including a hydrogel. One or both of the endplate components may
include a modified surface to increase adherence to respective
opposing bone surfaces.
Inventors: |
Ferree; Bret A.;
(Cincinnati, OH) ; Tompkins; David; (Milford,
OH) |
Correspondence
Address: |
John G. Posa;Gifford, Krass, Groh, Sprinkle,
Anderson & Citkowski, P.C.
PO Box 7021
Troy
MI
48007-7021
US
|
Family ID: |
37109576 |
Appl. No.: |
11/451513 |
Filed: |
June 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10892795 |
Jul 16, 2004 |
7060100 |
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11451513 |
Jun 12, 2006 |
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10303385 |
Nov 25, 2002 |
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10892795 |
Jul 16, 2004 |
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|
10191639 |
Jul 9, 2002 |
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10303385 |
Nov 25, 2002 |
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09415382 |
Oct 8, 1999 |
6419704 |
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10191639 |
Jul 9, 2002 |
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09580231 |
May 26, 2000 |
6494883 |
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10191639 |
Jul 9, 2002 |
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Current U.S.
Class: |
623/17.16 ;
623/17.12 |
Current CPC
Class: |
A61B 2017/0256 20130101;
A61F 2/447 20130101; A61F 2002/30584 20130101; A61F 2002/30604
20130101; A61F 2002/30879 20130101; A61F 2002/448 20130101; A61F
2002/2839 20130101; A61F 2002/30578 20130101; A61F 2210/0004
20130101; A61F 2230/0015 20130101; A61F 2002/30507 20130101; A61F
2002/4435 20130101; A61F 2230/0065 20130101; A61F 2002/2835
20130101; A61F 2/30965 20130101; A61F 2002/30774 20130101; A61F
2002/30062 20130101; A61F 2002/30133 20130101; A61F 2002/30546
20130101; A61F 2002/30622 20130101; A61F 2310/00011 20130101; A61F
2002/3085 20130101; A61F 2002/30092 20130101; A61F 2002/30777
20130101; A61F 2002/30329 20130101; A61F 2002/305 20130101; A61F
2002/30828 20130101; A61F 2220/0025 20130101; A61F 2230/0028
20130101; A61L 2430/38 20130101; A61F 2002/30387 20130101; A61F
2250/0018 20130101; A61F 2002/30014 20130101; A61F 2002/30563
20130101; A61F 2/30771 20130101; A61F 2002/30581 20130101; A61F
2002/30075 20130101; A61F 2002/302 20130101; A61F 2210/0014
20130101; A61F 2230/0008 20130101; A61F 2002/30593 20130101; A61F
2220/0033 20130101; A61F 2002/30179 20130101; A61F 2002/30357
20130101; A61F 2002/30785 20130101; A61F 2250/0012 20130101; A61F
2310/00017 20130101; A61F 2002/30113 20130101; A61F 2002/30224
20130101; A61F 2/28 20130101; A61F 2230/0069 20130101; A61F
2310/00023 20130101; A61F 2002/30495 20130101; A61F 2210/0061
20130101; A61F 2/441 20130101; A61F 2002/30405 20130101; A61F
2002/30462 20130101; A61F 2002/30841 20130101; A61F 2/30742
20130101; A61F 2/4465 20130101; A61F 2002/30904 20130101; A61F
2230/0006 20130101; A61F 2/442 20130101; A61F 2/446 20130101; A61F
2002/30125 20130101; A61F 2002/30331 20130101; A61F 2002/30383
20130101; A61F 2002/30428 20130101; A61F 2220/0075 20130101 |
Class at
Publication: |
623/017.16 ;
623/017.12 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. A modular implant configured for placement between opposing bone
surfaces, comprising: at least one endplate component attached to
one of the opposing bone surfaces; a modular cushioning component
removably attached to the endplate component; and a mechanism
allowing the cushioning component to be installed, removed or
replaced with the endplate component attached.
2. The implant of claim 1, wherein the cushioning component
includes a filler material.
3. The implant of claim 2, wherein the filler material is a gas,
liquid, foam, gel or hydrogel.
4. The implant of claim 1, wherein the endplate component includes
a modified surface to increase adherence to the respective bone
surface.
5. The implant of claim 4, wherein the modified surface includes
spikes or other projections.
6. The implant of claim 4, wherein the modified surface is
conducive to bony ingrowth.
7. The implant of claim 1, wherein: the cushioning component
includes an outer, compressible tire-like structure attached to a
central hub; and the central hub includes the mechanism for
interlocking the cushioning component to the endplates.
8. The implant of claim 7, wherein the mechanism for interlocking
the cushioning component to the endplates includes a projection on
the central hub and a corresponding groove on the endplate allowing
the implant to be pushed into position.
9. The implant of claim 8, further including a screw or other
fastener for maintaining the projection in the groove.
10. The implant of claim 8, wherein the compressible tire-like
structure component includes a filler material.
11. The implant of claim 10, wherein the filler material is a gas,
liquid, foam, gel or hydrogel.
12. The implant of claim 1, further including a clip or other
device for compressing the implant until insertion between the
opposing bone surfaces.
13. The implant of claim 1, wherein the component is configured for
adherence to a vertebral endplate.
14. The implant of claim 1, wherein: the endplate is configured for
adherence to the articular portion of a prosthetic tibia
component.
15.-25. (canceled)
26. A method of inserting an artificial disc replacement (ADR) into
an intervertebral disc space, comprising the steps of: inserting a
vertebral endplate into a disc space; affixing the endplate
component to a vertebral body; and inserting a cushioning component
into the disc space after the endplate has been affixed.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/303,385, filed Nov. 25, 2002; which is a
continuation-in-part of U.S. patent application Ser. No.
10/191,639, filed Jul. 9, 2002; which is a continuation-in-part of
U.S. patent application Ser. No. 09/415,382, filed Oct. 8, 1999,
now U.S. Pat. No. 6,419,704, and Ser. No. 09/580,231, filed May 26,
2000, now U.S. Pat. No. 6,494,883. The entire content of each
application and patent is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to surgical techniques and
prosthetic components therefore and, in particular, to
intervertebral disc replacement apparatus and methods of implanting
the same.
BACKGROUND OF THE INVENTION
[0003] Eighty-five percent of the population will experience low
back pain at some point. Fortunately, the majority of people
recover from their back pain with a combination of benign neglect,
rest, exercise, medication, physical therapy, or chiropractic care.
A small percent of the population will suffer chronic low back
pain. The cost of treatment of patients with spinal disorders plus
the patient's lost productivity is estimated at 25 to 100 billion
dollars annually.
[0004] Seven cervical (neck), 12 thoracic, and 5 lumbar (low back)
vertebrae form the normal human spine. Intervertebral discs reside
between adjacent vertebra with two exceptions. First, the
articulation between the first two cervical vertebrae does not
contain a disc. Second, a disc lies between the last lumbar
vertebra and the sacrum (a portion of the pelvis).
[0005] The spine supports the body, and protects the spinal cord
and nerves. The vertebrae of the spine are also supported by
ligaments, tendons, and muscles which allow movement (flexion,
extension, lateral bending, and rotation). Motion between vertebrae
occurs through the disc and two facet joints. The disc lies in the
front or anterior portion of the spine. The facet joints lie
laterally on either side of the posterior portion of the spine.
[0006] The human intervertebral disc is an oval to kidney bean
shaped structure of variable size depending on the location in the
spine. The outer portion of the disc is known as the annulus
fibrosis. The annulus is formed of 10 to 60 fibrous bands. The
fibers in the bands alternate their direction of orientation by 30
degrees between each band. The orientation serves to control
vertebral motion (one half of the bands tighten to check motion
when the vertebra above or below the disc are turned in either
direction).
[0007] The annulus contains the nucleus. The nucleus pulpous serves
to transmit and dampen axial loads. A high water content (70-80
percent) assists the nucleus in this function. The water content
has a diurnal variation. The nucleus imbibes water while a person
lies recumbent. Activity squeezes fluid from the disc. Nuclear
material removed from the body and placed into water will imbibe
water swelling to several times its normal size. The nucleus
comprises roughly 50 percent of the entire disc. The nucleus
contains cells (chondrocytes and fibrocytes) and proteoglycans
(chondroitin sulfate and keratin sulfate). The cell density in the
nucleus is on the order of 4,000 cells per micro liter.
[0008] Interestingly, the adult disc is the largest avascular
structure in the human body. Given the lack of vascularity, the
nucleus is not exposed to the body's immune system. Most cells in
the nucleus obtain their nutrition and fluid exchange through
diffusion from small blood vessels in adjacent vertebra.
[0009] The disc changes with aging. As a person ages the water
content of the disc falls from approximately 85 percent at birth to
70 percent in the elderly. The ratio of chondroitin sulfate to
keratin sulfate decreases with age. The ratio of chondroitin 6
sulfate to chondroitin 4 sulfate increases with age. The
distinction between the annulus and the nucleus decreases with age.
These changes are known as disc degeneration. Generally disc
degeneration is painless.
[0010] Premature or accelerated disc degeneration is known as
degenerative disc disease. A large portion of patients suffering
from chronic low back pain are thought to have this condition. As
the disc degenerates, the nucleus and annulus functions are
compromised. The nucleus becomes thinner and less able to handle
compression loads. The annulus fibers become redundant as the
nucleus shrinks. The redundant annular fibers are less effective in
controlling vertebral motion. The disc pathology can result in: 1)
bulging of the annulus into the spinal cord or nerves; 2) narrowing
of the space between the vertebra where the nerves exit; 3) tears
of the annulus as abnormal loads are transmitted to the annulus and
the annulus is subjected to excessive motion between vertebra; and
4) disc herniation or extrusion of the nucleus through complete
annular tears.
[0011] Current surgical treatments of disc degeneration are
destructive. One group of procedures removes the nucleus or a
portion of the nucleus; lumbar discectomy falls in this category. A
second group of procedures destroy nuclear material; Chymopapin (an
enzyme) injection, laser discectomy, and thermal therapy (heat
treatment to denature proteins) fall in this category. A third
group, spinal fusion procedures either remove the disc or the
disc's function by connecting two or more vertebra together with
bone. These destructive procedures lead to acceleration of disc
degeneration. The first two groups of procedures compromise the
treated disc. Fusion procedures transmit additional stress to the
adjacent discs. The additional stress results in premature disc
degeneration of the adjacent discs.
[0012] Prosthetic disc replacement offers many advantages. The
prosthetic disc attempts to eliminate a patient's pain while
preserving the disc's function. Current prosthetic disc implants,
however, either replace the nucleus or the nucleus and the annulus.
Both types of current procedures remove the degenerated disc
component to allow room for the prosthetic component. Although the
use of resilient materials has been proposed, the need remains for
further improvements in the way in which prosthetic components are
incorporated into the disc space, and in materials to ensure
strength and longevity. Such improvements are necessary, since the
prosthesis may be subjected to 100,000,000 compression cycles over
the life of the implant.
SUMMARY OF THE INVENTION
[0013] This invention resides in an artificial joint or disc
replacement (ADR) configured for placement between upper and lower
vertebrae. The implant broadly includes a pair of opposing endplate
components, each attached to one of the upper and lower vertebrae,
a cushioning component disposed between the endplate components,
and a mechanism for coupling the cushioning component to one or
both of the endplates.
[0014] In the preferred embodiment, the cushioning component takes
the form of a tire-like outer structure attached to an inner hub. A
filler material is also preferably contained within the cushioning
component. The filler material may be a gas, liquid, foam, or gel,
including a hydrogel. If a solid, foam, gel or hydrogel is used,
such material may be used as a single piece or as multiple
pieces.
[0015] One or both of the endplate components may include a
modified surface to increase adherence to the respective vertebral
endplates or opposing bone surfaces in the case of a joint
replacement. Such surface modification may include spikes, barbs or
other projections, and/or pores or roughening conducive to bony
ingrowth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a sagittal cross section of an ADR (artificial
disc replacement) according to the invention;
[0017] FIG. 2 is a view of the anterior aspect of the spine with
the ADR endplates attached to the vertebrae;
[0018] FIG. 3 shows a removable device such as a clip used to hold
the hub-like components to the tire-like components until the
compressible component is inserted into the ADR endplates;
[0019] FIG. 4 is an axial cross section through one embodiment of
the ADR endplate;
[0020] FIG. 5A is a sagittal cross section of a modular ADR during
assembly;
[0021] FIG. 5B is a sagittal cross section of the front of the ADR
of FIG. 5A with a tool positioned over the projection from the
hub;
[0022] FIG. 6 is a sagittal cross section of the front of the ADR
with an alternative mechanism to hold the modular compressible
component between the ADR endplates;
[0023] FIG. 7A is a sagittal cross section of another mechanism to
connect the hubs to the ADR endplates;
[0024] FIG. 7B is a sagittal cross section of the locking mechanism
of FIG. 7A with the cam in the locked position;
[0025] FIG. 8 is a view of the bottom of the top ADR endplate with
a circular cushioning component;
[0026] FIG. 9 is a sagittal cross section of the ADR with
distraction tools;
[0027] FIG. 10 is a sagittal cross section of the ADR with an
alternative distraction mechanism;
[0028] FIG. 11A is the first of a series of drawings showing
insertion of the ADR from the anterior aspect of the spine;
[0029] FIG. 11B shows the next step in the insertion of the ADR
after FIG. 11A. The bottom ADR endplate is shown during insertion
into the inferior vertebra;
[0030] FIG. 11C shows the next step in the insertion of the ADR
after FIG. 11B. Distraction tools are used to increase the space
between the ADR endplates;
[0031] FIG. 11D shows the next step in the insertion of the ADR
after FIG. 11C. The cushioning module is positioned between the ADR
endplates.
[0032] FIG. 11E shows next step in the insertion of the ADR after
FIG. 11D. The distraction tools have been removed;
[0033] FIG. 12A is a sagittal cross section of an embodiment of the
device for cushioning the tibial component of a Total Knee
Replacement (TKR);
[0034] FIG. 12B depicts the front of the tibial component of FIG.
12A;
[0035] FIG. 12C is an axial cross section of the top tibial tray
including circular pistons;
[0036] FIG. 12D is a view of the top of the bottom tibial tray;
[0037] FIG. 13 is a sagittal cross section of an alternative
embodiment including a metal articulating surface;
[0038] FIG. 14 is a sagittal cross section of an alternative
cushion module;
[0039] FIG. 15 is a sagittal cross section of the anterior portion
of the spine and an alternative embodiment of the ADR wherein the
endplates have been eliminated;
[0040] FIG. 16A is an oblique, lateral view of an embodiment
including projection from the hub which are releaseably attached to
a projection from the ADR endplate;
[0041] FIG. 16B is a view of the front of an alternative embodiment
of the ADR endplate drawn in FIG. 16A;
[0042] FIG. 16C is a view of the front of an alternative embodiment
of the ADR endplate drawn in FIG. 16A;
[0043] FIG. 17 is a sagittal cross section of the ADR with an
alternative plate-hub locking mechanism. Projections from the hubs
fit into holes in the ADR endplates;
[0044] FIG. 18 is a sagittal cross section of another embodiment
wherein a modular cushioning component is attached to a single ADR
endplate;
[0045] FIG. 19 is a sagittal cross section of an alternative
embodiment of the ADR and a vertebra;
[0046] FIG. 20 is a sagittal cross section of another embodiment
including one ADR endplate component tether and a second ADR
endplate without the cushioning component tether;
[0047] FIG. 21A is an axial cross section of the top of the
alternative embodiment of FIG. 16A;
[0048] FIG. 21B is an axial cross section of the ADR drawn in FIG.
21A;
[0049] FIG. 22A is a top view of a circular, tire-like component
and a circular ADR endplate;
[0050] FIG. 22B is a top view of an alternative, elliptically
shaped ADR endplate component;
[0051] FIG. 23 is a top view of the device of FIG. 22C including a
removable member placed around the modular cushion component prior
to insertion;
[0052] FIG. 24A is a top view of a wedge-shaped ADR endplate with
strategically spaced endplate penetration spikes;
[0053] FIG. 24B is a side view of a wedge-shaped ADR endplate with
strategically spaced endplate penetration spikes;
[0054] FIG. 25A is a view of the side of a hoop-mesh skeleton used
in another embodiment of the ADR;
[0055] FIG. 25B is a view of the side of the ADR drawn in FIG. 25A,
after its completion; and
[0056] FIG. 25C is a view of the side of the spine and the ADR
drawn in FIG. 25B.
DETAILED DESCRIPTION OF THE DRAWINGS
[0057] U.S. Pat. No. 6,419,704 discloses artificial replacements
for natural intervertebral discs in humans and animals. Broadly, a
shaped body assumes a final volume sized to consume at least a
portion of the intervertebral disc space, and a material associated
with the shaped body enabling the body to cyclically compress and
expand in a manner similar to the disc material being replaced. The
body may be composed of a compressible material, such as polymeric
urethane or other suitable elastomers, or may include a filling to
impart an appropriate level of compressibility. The superior and
inferior surfaces may be convex, and may further include grooves,
spikes, or other protrusions to maintain the body within the
intervertebral space. The body may further be wedge-shaped to help
restore or maintain lordosis, particularly if the prosthesis is
introduced into the cervical or lumbar regions of the spine.
[0058] To enhance strength or longevity, the body may further
include the use of fiber-reinforced materials on one or more outer
surfaces or wall structures, as the case may be. Similar to
commercial tire construction, such fiber-reinforced materials may
be of a bias-ply, radial-ply or bias-belted construction. According
to one configuration, an artificial disc according to the invention
may further include an outer compressible member peripherally
attached to a central "hub," similar, at least in concept, to the
which a tire is mounted onto a wheel.
[0059] The instant invention extends the teachings of the '704
patent through the addition of metal endplates, bone-ingrowth
surfaces, and/or modular, interlocking components. Although the
invention is described in terms of artificial disc replacement
(ADR), the approach may also be used to dampen other artificial
joints within the body, such as the tibial component of a knee
replacement.
[0060] As noted in the '704 patent, the ADR may be filled with a
gas, liquid, gel (including hydrogels), foam or other compressible
material, and the material may be introduced or otherwise provided
through the use of a valve, port, syringe, or, alternatively, by
way of valveless means. The body in this case is preferably a
sealed unit, and may include self-sealing means in the event of a
leak or rupture.
[0061] If a valve is used to inflate the ADR, it may be configured
so as to be accessible during implantation, enabling the surgeon to
expand the device in situ. A valve may also be provided in the form
of a port enabling subcutaneous post-operative inflation or
re-expansion. If a hydrogel is used as the filler material, it may
introduced within the body in a dehydrated state prior to
implantation, with water being added to expand the material. The
liquid may be added through a valve, port or hypodermic in
conjunction within a sealed structure or, alternatively, at least a
portion of the surface of the body, preferably the superior end or
inferior surfaces, may be at least semi-porous. As a further
alternative to a valveless structure, one or more reactants may be
provided with the body, such that when mixed with one or more other
reactants, a gas or foam is generated to expand and fill the body.
As yet a further alternative, an ampule or cartridge operative to
release a compressed gas or generate a gas, liquid or foam may be
activated by an external source of energy such as ultrasound, heat,
or other stimuli.
[0062] Turning now to the figures, FIG. 1 is a sagittal cross
section of an embodiment of an ADR according to this invention,
including a tire-like component 102, hub-like component 104, and
endplates 106.
[0063] FIG. 2 is a view of the anterior aspect of the spine with
the ADR endplates attached to the vertebrae 110. A sagittal cross
section of the modular compressible member is also illustrated at
120. The ends of the hub have projections 122 that slide into
grooves 124 on the ADR endplates.
[0064] FIG. 3 shows how a removable device such as a clip 302 can
be used to hold the hub-like components to the tire-like components
until the compressible component is inserted into the ADR
endplates. The clip 302 is especially important when the
compressible component contains hydrated hydrogel. In such
embodiments, the hydrogel may be stored in fluid to allow the
component to be inserted with the hydrogel fully hydrated or nearly
fully hydrated. The hydrogel-containing embodiments further include
pores for fluid transport through the ADR endplates, the hub-like
component, and/or the tire-like component.
[0065] FIG. 4 is an axial cross section through one embodiment of
an ADR endplate according to the invention including a recess 402
from the side of the endplate configured to trap the projection 122
from the hub-like component.
[0066] FIG. 5A is a sagittal cross section of the ADR during
assembly of the modular components. A tool 502 is used to push the
projections 122 from the hub-like components into the grooves 124
of the ADR endplates, thus forcing the compressible component
between the ADR endplates. FIG. 5B is a sagittal cross section of
the front of the ADR drawn in FIG. 5A with the tool positioned over
the projection from the hub.
[0067] FIG. 6 is a sagittal cross section of the front of the ADR
with an alternative mechanism used to hold the modular compressible
component between the ADR endplates. In this embodiment, screws 602
are threaded into the ADR endplates after insertion of the
compressible component. Hub projections and ADR endplate grooves
similar to those drawn in FIG. 2 can be used with the screws 602.
Mechanisms to prevent screw back-out, such those used in plates
associated with the cervical spine, can be incorporated into the
endplate(s).
[0068] FIG. 7A is a sagittal cross section of yet a different
mechanism used to connect the hubs to the ADR endplates. An
L-shaped projection 702 from the hub 704 slides into a
corresponding groove in the ADR endplate. A cam lock 710 may be
used to hold the components together. In FIG. 7A, the cam is drawn
in the unlocked position. FIG. 7B shows the cam in the locked
position.
[0069] FIG. 8 is a view of the bottom of the top ADR endplate 802
with a circular cushioning component 804. The cushioning component
can also be circular like the ADR endplate (FIG. 22A), or both can
be elliptical (FIG. 22B), or other alternative shape. FIG. 9 is a
sagittal cross section of the ADR with distraction tools 902 fitted
in the area of the eclipse shaped ADR endplates that is not covered
by the circularly shaped cushioning component 804. FIG. 10 is a
sagittal cross section of an ADR with an alternative distraction
mechanism incorporating endplates with holes 1002 for the arms of a
distraction device 1020 placed into the holes on the right side of
the ADR.
[0070] FIG. 11A is the first of a series of drawings showing
insertion of the ADR from the anterior aspect of the spine. In this
Figure, the top ADR endplate is forced into the superior vertebra.
The endplate of the vertebra may be milled to improve the fit
between the ADR endplate and the vertebra. FIG. 11B is a view of
the next step in the insertion of the ADR after FIG. 11A. The
bottom ADR endplate is shown during insertion into the inferior
vertebra. A tool 1102 may be used to align the ADR endplates. The
tool can also be wedge-shaped to help force the ADR endplates into
the vertebrae as the tool is forced between the ADR endplates.
[0071] FIG. 11C is a view of the next step in the insertion of the
ADR after FIG. 11B. Distraction tools 1120 are used to increase the
space between the ADR endplates. The tools can be twisted to cam
open the disc space, as illustrated on the left side of the
drawing. Alternatively, the distraction tools can be wedge-shaped
to force the ADR endplates apart as the wedge shaped tools are
driven between them.
[0072] FIG. 11D is a view of the next step in the insertion of the
ADR after FIG. 11C, with the cushioning module positioned between
the ADR endplates. FIG. 11E is a view of the next step in the
insertion of the ADR after FIG. 11D. The distraction tools have
been removed, and locking screws 1150 have been inserted into the
ADR endplates.
[0073] FIG. 12A is a sagittal cross section of an embodiment of the
device for cushioning the tibial component of a Total Knee
Replacement (TKR). FIG. 12B is the view of the front of the tibial
component drawn in FIG. 12A. Item 1202 represents the polyethylene
tray which is seated in a metal tray 1204 including projections
that piston in and out of a metal tray 1206 in the tibia. The
cushioning elements 1220, 1222 are positioned between the two metal
trays. The polyethylene component can be eliminated in embodiments
of the device that have a metal articular surface. The trays and or
the tire like component are porous to allow fluid movement in
hydrogel-filled embodiments. FIG. 12C is an axial cross section of
the top tibial tray. The circular pistons 1230 are also drawn. FIG.
12D is a view of the top of the bottom tibial tray including
cylinders 1240 for the pistons.
[0074] FIG. 13 is a sagittal cross section of an alternative
embodiment of a TKR device including a metal articulating surface.
A large portion of the cushioning element is positioned within the
intramedullary canal of the tibia. The tibia is represented by the
dotted area of the drawing. The embodiment of the device drawn
eliminates the locking mechanism required with modular cushioning
components. A single piston and cylinder are used in this
embodiment of the device that mentions the option of using shape
memory materials as a mechanism to lock the hub-like component to
the projection from the ADR endplate.
[0075] FIG. 14 is a sagittal cross section of a cushion module
similar to that drawn in FIG. 2, with the exception that the
hydrogel sides of the hub-like components have raised rims 1402
that helps hold the tire like component 1404.
[0076] FIG. 15 is a sagittal cross section of the anterior portion
of the spine and a different alternative embodiment of the ADR with
the endplates eliminated. In this case, a tire-like component 1502
cooperates directly with the hub-like components 1504 and the
vertebral endplates.
[0077] FIG. 16A is an oblique, lateral view of a preferred
embodiment of the ADR. The projection 1602 from the hub 1604 is
releaseably attached to a corresponding receptacle in the ADR
endplate 1606. A screw (not shown) is used to lock the seated hub
in place. The threads of the screw preferably deform slightly to
prevent back-out. The ADR endplate 1606 is itself designed to slide
into a previously milled vertebra.
[0078] The modular cushioning component can cooperate with a single
ADR endplate as drawn. Alternatively, the cushioning component can
be placed between ADR endplates placed on the vertebral endplates
on either side of the disc space. The raised circular area in the
central portion of the hub, below the lockable projection, is
smaller than the hole in the tire-like component to highlight the
raised portion of the hub. The raised portion of the hub rests
against the ADR endplate. A recess is created between the widest
portion of the hub, which is inside the tire-like component, and
the ADR endplate. The recess is slightly taller than the thickness
of the tire-like component. The cooperation between the hub and the
ADR endplate protects the portion of the tire-like component, above
the extension of the hub, from axial compression. The smooth
surface of the cushion side of the ADR endplate and the space
between the hub and the ADR endplate facilitate radial expansion of
the tire-like component. The tire-like hoop expands in a radial
direction secondary to the outward force transferred from the
hydrogel within the tire-like hoop. The hydrogel applies outward
force on the tire-like hoop secondary to axial forces on the
spine.
[0079] FIG. 16B is a view of the front of an alternative embodiment
of the ADR endplate drawn in FIG. 16A. Two diverging screws are
placed through holes 1620, 1622 in the ADR endplate. The holes in
the plate may include locking c-rings to prevent screw back-out.
The screws are also recessed into the vertebrae to further decrease
the risk of impingement of the screws on the soft tissues anterior
to the spine.
[0080] FIG. 16C is a view of the front of an alternative embodiment
of the ADR endplate drawn in FIG. 16A. The embodiment of the ADR
endplate drawn in FIG. 16C is press fit into the vertebra from the
disc space. The side walls of the portion of the ADR endplate
tether mechanism are flush with top of the tether mechanism to
allow insertion from the disc space. Spikes 1660 are use to resist
extrusion of the ADR in an anterior or posterior direction. The
tether mechanism prevents lateral movement of the ADR relative to
the vertebrae. The tether and spikes cooperate to limit rotation of
the ADR relative to the vertebrae.
[0081] FIG. 17 is a sagittal cross section of the ADR with an
alternative plate-hub locking mechanism. In this embodiment,
projections 1702 from the hubs fit into holes 1704 in the ADR
endplates. The tire-like component was not drawn. Pressure from the
hydrogel forces the projections from the hubs into the holes in the
ADR endplates. The spikes on the vertebral side of the ADR
endplates were not drawn. The recess between the widest portion of
the hub and the ADR endplate is slightly wider than the thickness
of the tire-like component.
[0082] FIG. 18 is a sagittal cross section of another preferred
embodiment of the ADR, wherein a modular cushioning component is
attached to a single endplate 1802. The opposing side of the
tire-like component cooperates directly with a vertebral endplate.
The locking mechanism, similar to that drawn in FIG. 17, relies on
a hydrogel, elastomer, or other appropriate filler material within
the tire to exert force to the hub. A hole or recess in the center
of the hub fits over a projection 1810 from the ADR endplate. The
space between the hub and the ADR endplate is slightly larger than
the thickness of the tire. FIG. 19 is a sagittal cross section of
the embodiment of FIG. 18 showing the opposing endplate 1804.
[0083] FIG. 20 is a sagittal cross section of yet another ADR
embodiment wherein one endplate 2002 has a cushioning component
tether 2010 and a second ADR endplate 2020 without the cushioning
component tether. FIG. 21A is an axial cross section of the top of
an alternative embodiment of the ADR drawn in FIG. 16A. FIG. 21B is
an axial cross section of the ADR drawn in FIG. 21A. Deployable
protrusions are incorporated into the sides of the ADR component to
hold the projection from the hub. Ridges (horizontal lines 2102)
increase the friction between the ADR endplate and the vertebrae. A
locking screw 2120 deploys the protruding sidewalls of the portion
of the ADR endplate that retains the projection from the hub.
[0084] FIG. 22A is a view of the top of a circular tire-like
component and a circular ADR endplate. FIG. 22B is a view of the
top of an alternative endplate which is elliptical in shape. FIG.
23 is a view of the top of the device drawn in FIG. 22C. A
removable member 2310, such as a ribbon, is placed around the
modular cushion component prior to inserting the modular cushion
component into the disc space. This allows the surgeon to pull on
the ribbon after insertion of the modular cushion component to
assure the hub of the cushion component has seated on the
projection from the ADR endplate. A properly seated cushion
component should be difficult to pull out of the disc space. The
ribbon is removed from behind the ADR by pulling on only one end of
the ribbon.
[0085] FIG. 24A is a top view and FIG. 24B side view of a
wedge-shaped ADR endplate with strategically spaced endplate
penetration spikes.
[0086] The embodiment of the ADR drawn in FIG. 25A-C utilizes the
bead construction of commercial tires. Hoops made of Nitinol,
titanium, Kevlar, or other elastic materials are connected with
perpendicular wires in a basket weave type arrangement. Conversely,
the horizontal hoops could be connected by vertical hoops similar
to the arrangement of the hoops in chain mail. The horizontal hoops
could be somewhat taller anteriorly than posteriorly to fit the
wedge shaped disc space. In any event, the finished hoop-mesh
skeleton is taller anteriorly than posteriorly.
[0087] The hoop-mesh skeleton is covered with vulcanized elastomer
much like the wire hoops within the bead of commercial tires are
covered with vulcanized elastomer. Molds, liquid elastomers, and
heat as used in the commercial tire industry could be used to
surround the hoop-mesh skeleton with elastomers. Bias ply fibers
could be incorporated into the elastomer.
[0088] The elastic horizontal hoops and vertical skeleton members
resist radial expansion of the tire. The elastic horizontal hoops
and vertical members expand and contract in reaction to forces
applied by a hydrogel, gas, liquid, or other polymer within the
center of the ADR.
[0089] The elastomer surrounding the hoop-mesh skeleton provides a
smooth surface to cooperate with the hydrogel or other polymer
center of the ARD. The elastomer also serves to prevent the
extrusion of the hydrogel or other polymer from spaces between the
hoops. Lastly, the elastomer assists the hoops in resisting radial
expansion.
[0090] The completed carcass is flexible in a superior to inferior
direction. The carcass may be more flexible anteriorly than
posteriorly or at the sides of the carcass.
[0091] In the preferred embodiment, the carcass cooperates with an
ADR endplate (EP) on its, superior and inferior surfaces, to
contain a hydrogel core. The carcass is connected to the perimeter
of the ADR EPs. Wire rings could connect the carcass to holes in
the ADR EPs. The wire rings could be laser welded after connecting
the two components. Alternatively, the carcass could be stretched
over the perimeter of the ADR EPs much like a tire stretches over
the hub of a wheel. A band could be tightened over the portion of
the tire that lies over the ADR EPs.
[0092] Fluid could move into the hydrogel through holes in the ADR
EPs, the elastomer, or the space between the tire and the ADR
EPs.
[0093] The ADR could be compressed prior to its insertion in the
disc space. The arms of the tool that compress the ADR would also
help make the spikes from the ADR EP less prominent, thus reducing
the risk of soft tissue injury during the insertion process. The
partially hydrated hydrogel imbibes additional fluid after
insertion of the ADR to further improve the ADR press fit.
[0094] FIG. 25A is a view of the side of a hoop-mesh skeleton used
in another embodiment of the ADR. Horizontal hoops made of an
elastic material, are connected by vertical members. The open rings
at the top and bottom of the skeleton are used to connect the
elastic skeleton to the ADR endplates.
[0095] FIG. 25B is a view of the side of the ADR drawn in FIG. 25A,
after its completion. The skeleton has been embedded in an
elastomeric material. Rings connect the elastomerized skeleton to
two ADR endplates. The rings connecting the two components have
been closed and laser welded.
[0096] FIG. 25C is a view of the side of the spine and the ADR
drawn in FIG. 25B. A clamp like tool is used to compress the ADR.
The tool is removed after inserting the compressed ADR into the
disc space.
[0097] This invention offers numerous advantages over existing
designs. As opposed to all metal or metal/polyethylene designs, the
cushioning components disclosed herein behave more like a natural
disc while protecting adjacent discs (transfers less force to the
adjacent discs). The modular cushion components and other design
elements allow replacement of the cushion component without
revising well fixed ADR EPs. The modular designs also reduce
implant inventory and allow insertion of ADR EP or EPs first.
Inserting the ADR EPs separately allows longer spikes or
projections that are press fit into the vertebrae EP.
[0098] Indeed, certain embodiments allow replacement of the
cushioning component without removing one or both of the ADR
endplates. The use of polyethylene provides minimal cushioning,
since the components are shaped to articulate with metal components
to permit spinal motion. The modular cushion components disclosed
herein permit spinal motion through compression of the modular
cushion component rather than articulation as seen in the above
mentioned patents.
[0099] The use of a hybrid design (ADR EP attached to superior
vertebra and tire-like component) acts directly on the superior EP
of the inferior vertebra. The ADR EP fits over a milled or shaped
surface of the superior vertebra. The inferior EPs of vertebrae are
generally less flat than the superior EPs of vertebrae. The shapes
of the inferior EPs are also more variable than the shapes of the
superior EPs. Extensive experience with Total Knee Replacement over
the last few decades suggest it is better to prepare a reproducible
flat surface on the tibia than to manufacture a wide variety of
tibia component shapes to fit the various shapes of the tibia
articular surface. Similar to TKRs, the hybrid ADR attaches a flat
ADR EP onto the cut surface of the superior vertebrae.
[0100] Disc space is limited in size, and experience with TKRs
suggests thin polyethylene components leads to early failure. By
eliminating one of the ADR endplates, the modular cushioning
component of the disclosed hybrid ADR can be thicker. The modular
cushion components disclosed herein can conform to the EP of the
inferior vertebra. Furthermore, the durability of tire-like
components give the cushion component excellent wear
characteristics, even with direct placement of the cushion
component onto the EP of the vertebra. The smooth surface of our
tire like component should minimize wear on the vertebra EP.
Certain design are unique in that they use a single ADR EP. It is
also the only ADR design that attaches a cushion component to a
single ADR endplate.
[0101] The coupling mechanisms between the ADR EP and the modular
cushion component prevent the cushion component from extruding from
the disc space. The coupling mechanism also keeps the cushion
component centered in the disc space. Eccentric placement of free
compressible components or NR ADRs increases the probability of
extrusion of the component or ADR. The coupling mechanisms also
enable the insertion of a component between the ADR EPs that is
wedge shaped and thickest in the front of the component. The disc
in the cervical and lumbar spines are naturally thickest at their
anterior most portion.
[0102] The Hybrid design is the only known ADR to couple the
components using a reversibly deformable cushion component that
cooperates with a metal projection from the ADR EP. The Hybrid
design, as well as a few of the other embodiments, do not require
precise alignment between ADR EPs placed over both vertebral EPs.
Other modular ADRs place polyethylene between two metal ADR EPs.
The ADR EPs must align perfectly for the polyethylene insert to
articulate properly with the ADR EPs.
[0103] The various materials prescribed herein are biocompatible
and approved for use in humans. These include hydrogels,
elastomers, and metals such as titanium. The hydrogels are able to
change their fluid content, and thus size, as pressure on the
hydrogel is applied. The migration of fluid to and from the disc
space may improve the nutrition of the living cells within the
disc. The hydrogel embodiments are also capable of increasing in
size by imbibing fluid after they are inserted. Thus, hydrogels can
grow to "custom fit" the available disc space. Dehydrated hydrogels
can be inserted through smaller openings in the ADR or disc space.
Hydrated hydrogels grow to fit the available space after
insertion.
[0104] In certain embodiments, hydrogel is contained within an
elastomeric hoop called a tire. The preferred hydrogel has high
water content to function like the NP of the natural disc. In
particular, axial loads on the hydrogel are converted into radial
forces on the tire. The tire expands in a radial direction due to
the loads transferred by the hydrogel, and resists the loads via
hoop stresses. The "tire" also limits the amount of hydrogel shape
change (the hydrogel wants to decrease in height and increase in
width and length with axial load).
[0105] The preferred high water content hydrogel is mucous like in
consistency, acting similar to hydraulic fluid which transfers load
to the tire. In contrast, the hydrogels of prior-art devices are
firmer, to act as the primary load bearing member In our device,
axial compression of the disk space is transformed into radial
distension of the tire and enlargement of the cross sectional area.
Because area grows as the square of the radius, an increment of
axial deflection produces a smaller increment of radial
deflection.
[0106] The tire designs also act as a spring to restore the disk
space as the load is decreased. The tire dampens most of the forces
on the spine. The hydrogel, for the most part, transfers forces to
the hoop. These devices rely on the hydrogel and the tire to share
the dampening forces, with the tire doing bulk of the dampening.
The tire may contain cloth-like material and elastomers.
[0107] A preferred embodiment is elliptical in shape to maximize
the amount of cushioning material in the disc space. Circular
shaped ADRs may leave precious disc space unoccupied. According to
this invention, a single ADR device is inserted, since paired ADRs
may risk extrusion. If one of the paired ADR maintains the disc
height, the lack of axial load and thus friction on the other
paired ADR can lead to extrusion of the unloaded ADR.
[0108] The use of a "hub" has several important features. For one,
the hub cooperates with the ADR EP to create a space for the top of
the tire that is slightly wider than the thickness of the hub. The
space protects the portion of the tire between the hub and the ADR
EP from axial compression. Sparing the tire from axial compression
facilitates radial expansion of the hub during axial compression of
the ADR. The smooth surface of the hub and the ADR EP further
promotes expansion of the tire with axial compression. Protecting a
portion of the tire from axial compression may prolong the life of
the tire.
[0109] The tire also stretches to allow hub insertion through a
hole in the hoop that is smaller than the hub. The tire returns to
its original shape after the hub is inserted. Inelastic bags would
not have the elastic properties of our tire.
[0110] One embodiment of the tire has a hole in the top; another
has holes in the top and bottom of the tire. The hub cooperates
with the tire to trap the hydrogel in the tire. The overlap between
hub and the tire permit the hole in the tire to enlarge (with
radial expansion) yet hold the hydrogel in place.
[0111] The use of a variable center of rotation, as opposed to a
fixed center of rotation, also function more like natural disc by
restoring normal disc kinematics. This allows all normal disc
motions (direction and magnitude) including flexion, extension,
lateral bending, translocation, and rotation. The various ADR
designs maintain distraction to decrease the pressure on compressed
nerves and to decrease the pressure on the facet joints.
[0112] ADR endplates with holes for insertion of a distraction
instrument is believed to be unique. Among other advantages, this
allows distraction instruments to hold the disc space in a
distracted position while the modular cushion component is
inserted. The use of a `ribbon` to test proper-coupling of the
modular components, and the resistance to extrusion of the ADR, is
also thought to be unique.
[0113] Other novel disclosures include the use of screws recessed
into the body of the vertebra. Recessed screws minimize the risk of
the screws backing out into the aorta. The ADR plates may also
include a mechanism, similar to those used in plates for the
cervical spine, to prevent screw back-out. The use of a keel with
an enlargement in the portion above the endplate of the vertebra is
also believed to be unique. The enlargement in the keyhole-like
slot resists forces trying to pull the ADR EP from the vertebra.
Another unique feature is the use of deployable projections into
the vertebrae to resist extrusion of ADRs, as is the use of
perpendicular projections from the surface of the ADR EP.
* * * * *