U.S. patent application number 14/473800 was filed with the patent office on 2014-12-18 for intervertebral disc.
This patent application is currently assigned to DEPUY SYNTHES PRODUCTS, LLC. The applicant listed for this patent is DEPUY SYNTHES PRODUCTS, LLC. Invention is credited to Andrew Dooris, Patrick J Fatyol, John Riley Hawkins, Mark Lionetto, Ronald Naughton, Christopher Rogers.
Application Number | 20140371858 14/473800 |
Document ID | / |
Family ID | 29718069 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140371858 |
Kind Code |
A1 |
Rogers; Christopher ; et
al. |
December 18, 2014 |
INTERVERTEBRAL DISC
Abstract
This invention relates to an intervertebral motion disc having
two motion surfaces and. wherein the radius of the upper
articulation surface of the core member is greater than the radius
of the lower articulation surface of the core member, and wherein
the first articulation surface of the core member is spherical and
the second articulation surface of the core member is curved and
non-spherical.
Inventors: |
Rogers; Christopher;
(Mahwah, NJ) ; Dooris; Andrew; (Raynham, MA)
; Fatyol; Patrick J; (Whitman, MA) ; Lionetto;
Mark; (Norton, MA) ; Naughton; Ronald;
(Pleasanton, CA) ; Hawkins; John Riley;
(Cumberland, RI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DEPUY SYNTHES PRODUCTS, LLC |
Raynham |
MA |
US |
|
|
Assignee: |
DEPUY SYNTHES PRODUCTS, LLC
Raynham
MA
|
Family ID: |
29718069 |
Appl. No.: |
14/473800 |
Filed: |
August 29, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12395606 |
Feb 27, 2009 |
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14473800 |
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10465277 |
Jun 19, 2003 |
7517363 |
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12395606 |
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60391845 |
Jun 27, 2002 |
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Current U.S.
Class: |
623/17.15 |
Current CPC
Class: |
A61F 2/08 20130101; A61F
2002/30253 20130101; A61F 2310/00029 20130101; A61F 2002/30245
20130101; A61F 2002/30369 20130101; A61F 2220/0025 20130101; A61F
2310/00017 20130101; A61F 2002/30387 20130101; A61F 2002/30604
20130101; A61F 2310/00203 20130101; A61F 2002/30062 20130101; A61F
2002/30092 20130101; A61F 2002/302 20130101; A61F 2002/30841
20130101; A61F 2230/0076 20130101; A61F 2002/305 20130101; A61F
2002/2817 20130101; A61F 2002/30733 20130101; A61F 2002/30327
20130101; A61F 2230/0069 20130101; A61F 2002/30892 20130101; A61F
2250/0039 20130101; A61F 2/4611 20130101; A61F 2002/30878 20130101;
A61F 2220/0033 20130101; A61F 2002/30528 20130101; A61F 2002/30433
20130101; A61F 2230/0071 20130101; A61F 2002/30649 20130101; A61F
2002/30515 20130101; A61F 2002/30939 20130101; A61F 2002/30838
20130101; A61F 2/4425 20130101; A61F 2002/30224 20130101; A61F
2002/30232 20130101; A61F 2220/0041 20130101; A61F 2002/30563
20130101; A61F 2002/30662 20130101; A61F 2002/3082 20130101; A61F
2002/3008 20130101; A61F 2002/30578 20130101; A61F 2002/30481
20130101; A61F 2/30767 20130101; A61F 2002/30883 20130101; A61F
2230/0065 20130101; A61F 2002/304 20130101; A61F 2/442 20130101;
A61F 2310/00023 20130101; A61F 2002/30565 20130101; A61F 2220/0075
20130101; A61F 2002/30462 20130101; A61F 2310/00796 20130101; A61F
2002/30383 20130101; A61F 2002/30495 20130101; A61F 2210/0004
20130101; A61F 2250/0098 20130101; A61F 2/30724 20130101; A61F
2310/0058 20130101; A61F 2210/0014 20130101; A61F 2002/30843
20130101; A61F 2002/30566 20130101; A61F 2310/00239 20130101; A61F
2002/443 20130101 |
Class at
Publication: |
623/17.15 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, wherein the core has a blind recess extending
into the core from the flat surface, and wherein the recess is
non-articulating.
2. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, and wherein the core has a diameter and a blind
recess extending from diametrically through the core.
3. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, and wherein the lower endplate further comprises
a post, wherein the core comprises a recess, and wherein an upper
face of the post is received in the recess.
4. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, and wherein the core has a recess extending
therein, the lower endplate has a post extending therefrom, and
wherein the post has an inner portion that is fully contained
within the recess.
5. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, and wherein the endplate has a projection
extending therefrom, and wherein the core has a sidewall having a
retaining feature that cooperates with the projection.
6. An intervertebral motion disc comprising: a) an upper prosthetic
vertebral endplate comprising: i) an outer surface adapted to mate
with an upper vertebral body, ii) an inner surface having a first
articulation surface, b) a lower prosthetic vertebral endplate
comprising: i) an outer surface adapted to mate with a lower
vertebral body, and ii) an inner surface having a first
articulation surface, c) a core member comprising: i) an upper
articulation surface adapted for articulation with the first
articulation surface of the upper endplate and having a radius, and
ii) a lower articulation surface adapted for articulation with the
first articulation surface of the lower endplate and having a
radius, wherein the core member is disposed between the endplates
and oriented therein to produce an upper articulation interface
between the first articulation surface of the upper endplate and
the upper articulation surface of the core member, and a lower
articulation interface between the first articulation surface of
the lower endplate and the lower articulation surface of the core
member, and wherein the upper articulation interface forms a
hemispherical interface, and the lower articulation interface forms
a flat interface, and wherein the endplate has a recess depth
(DE.sub.CH) that is greater than a peripheral endplate depth
(DE.sub.P), and the recess depth extends past a plane of the
peripheral outer surface of end plate.
Description
[0001] This application is a continuation application claiming
priority from co-pending U.S. patent application Ser. No.
12/395,606, filed Feb. 27, 2009, (Entitled "Intervertebral Disc"
(Docket No. DEP0719USDIV1), which is a divisional application
claiming priority from U.S. patent application Ser. No. 10/465,277,
filed Jun. 19, 2003, and entitled "Intervertebral Disc Having
Translation" (Docket No. DEP 0719USANP) (now U.S. Pat. No.
7,517,363), which was a nonprovisional application claiming
priority from U.S. Provisional Patent Application No. 60/391,845,
filed Jun. 27, 2002, entitled "Intervertebral Disc Having
Translation". Each of the aforementioned patent application is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The leading cause of lower back pain arises from rupture or
degeneration of lumbar intervertebral discs. Pain in the lower
extremities is caused by the compression of spinal nerve roots by a
bulging disc, while lower back pain is caused by collapse of the
disc and by the adverse effects of articulation weight through a
damaged, unstable vertebral joint. One proposed method of managing
these problems is to remove the problematic disc and replace it
with a prosthetic disc that allows for the natural motion between
the adjacent vertebrae ("a motion disc").
[0003] U.S. Pat. No. 6,368,350 ("Erickson") discloses a three-piece
motion disc providing two articulation surfaces. The disc comprises
a first piece having a curved surface, a second piece having a flat
surface, and an intermediate piece having a corresponding curved
articulation surface and a corresponding flat articulation surface.
In many embodiments, the translation freedom of the intermediate
piece is limited by a raised lip integrally formed around the edge
of a flat surface upon the lower piece. Erickson teaches that the
overall height of the device is varied by increasing or decreasing
the thickness of one or more of the first, second or intermediate
pieces. Erickson teaches that known methods for insertion of
intervertebral prosthetic devices can be used for insertion of its
device. Lastly, Erickson teaches that a variety of materials can be
selected as materials of construction for the components of its
device, including metals, polymers, and ceramics, and specifically
teaches preferred combinations including metal-metal or
metal-plastic combinations.
[0004] In each of Erickson's embodiments having a peripheral raised
lip, the height of the core member appears to exceed the distance
between the peripheral raised lips of the opposing endplates.
Accordingly, the core member can not be inserted between the
prosthetic endplates without overdistracting the disc space.
[0005] Erickson does not teach an open ended channel for inserting
the intermediate piece between the prosthetic endplates, nor an
additional component for retaining the intermediate piece upon the
flat surface. Erickson does not teach piecemeal insertion of the
device into the disc space. Erickson does not teach a metal-ceramic
articulation interface.
[0006] U.S. Pat. No. 5,676,701 ("Yuan") discloses, in one
embodiment, a motion disc having a single articulation surface.
This device includes a first component whose inner surface
comprises a concave inner portion having a 360.degree.
circumference and a convex peripheral portion, and an opposing
second component whose inner surface comprises a conforming convex
inner portion and a convex peripheral portion. The convex/concave
contours of the opposing inner portions forms a ball-and-socket
design that allows unrestricted pivotal motion of the device, while
the opposing convex peripheral contours allow flexion/extension
bending motion in the range of about 20-30.degree..
[0007] In another embodiment, Yuan discloses a device having two
articulation interfaces, wherein one of the above-mentioned
components is made in two pieces having opposing flat surfaces that
form a translation interface to further provide the prosthetic with
a certain amount of translation. See FIG. 9 of Yuan. Yuan discloses
that the translation-producing pieces can be fitted together
mechanically, via shrink-fit, or by welding methods.
[0008] However, Yuan does not disclose an open-ended channel for
fitting the translation producing pieces.
[0009] U.S. Pat. No. 5,507,816 ("Bullivant") discloses a
three-piece motion disc providing two articulation interfaces and
comprises an upper piece having a flat lower surface, a middle
spacer having a flat upper surface and a convex lower surface, and
a lower piece having a concave upper surface. The articulating
convex and concave surfaces form an articulating interface that
allows pivotal motion, while the flat surfaces form a translation
interface that allows translational motion. Bullivant further
teaches that the natural tension of the vertebrae ensures that the
vertebrae are biased together to trap the spacer in place, and that
the 90.degree. extension of the convex and concave surfaces
virtually eliminates any chance of the spacer escaping from between
the plates under normal pivotal movement of the vertebrae.
[0010] The Bullivant device does not possess any channel for
retaining the middle spacer within the device. Accordingly, it is
prone to disengagement.
[0011] In each of the Erickson, Yuan, and Bullivant designs, the
core member has a flat translation surface and a curved
articulation surface.
[0012] There are currently two primary competitive artificial disc
replacement devices on the market that are designed for the lumbar
spine.
[0013] The first device has two articulation interfaces and
comprises three components: an inferior endplate, a superior
endplate, and a core. Both the inferior and superior endplates are
metal and have raised bosses with concave spherical surfaces in the
center. The core is plastic and has convex surfaces on both the top
and bottom which are surrounded by raised rims.
[0014] However, this device does not have an open ended channel for
inserting the core between the endplates. Related devices are
disclosed in U.S. Pat. Nos. 4,759,766; 5,401,269; and
5,556,431.
[0015] In each of the devices disclosed in these three patents, the
core member has either two concave surfaces or two convex
surfaces.
[0016] The second device has a single articulation interface and
comprises three components: an inferior endplate, a superior
endplate, and a plastic insert. The inferior endplate functions as
a baseplate and has a sidewall forming an open ended channel for
reception of the insert. The inner surface of the inferior endplate
provides only stationary support for the insert and does not have a
motion surface. Since the plastic insert is designed to be locked
securely into place within the inferior endplate, the inferior
surface of the insert is not a motion surface. The superior surface
of the insert includes articulation surface for articulation with
the superior endplate. The superior endplate has an inferior
articulation surface that articulates with the superior motion
surface of the plastic insert, and a superior surface designed for
attachment to a vertebral endplate. A related device is disclosed
in U.S. Pat. No. 5,314,477.
[0017] The second device does not have two articulation surfaces.
The second device relies upon downward-extending flexible tabs
disposed upon the insert to keep the insert within the open-ended
channel. These tabs eliminate any ability for the insert to
translate with the adjacent endplate surfaces.
[0018] French Published Patent Application No. 2,730,159
("Germain") discloses a motion disc in which the core member has
one convex and concave surface. Germain further teaches that the
radius of the upper curved surface (3a) of the core member is less
than the radius of the lower curved surface (3b) of the core
member.
[0019] Therefore, there is a need for a motion device having two
articulation interfaces that allows for initial insertion of the
prosthetic endplates into the disc space and then insertion
therebetween of a core member having two articulation surfaces.
SUMMARY OF THE INVENTION
[0020] The present inventors have developed a motion disc having
two articulation interfaces and an open ended channel. The two
articulation interfaces allow the motion disc to more fully restore
the natural motion of the spine than would a single articulation
interface. The open ended channel allows for initial insertion of
the prosthetic endplates into the disc space and then insertion
therebetween of a core member having two articulation surfaces,
thereby lessening the extent of required overdistraction.
[0021] Therefore, in accordance with the present invention, there
is provided a prosthetic vertebral endplate comprising: [0022] i)
an outer surface adapted to mate with a vertebral body, [0023] ii)
an inner surface having a first opening thereon, [0024] iii) a body
portion connecting the inner and outer surfaces and defining a
sidewall comprising a second opening thereon, and [0025] iv) an
articulation surface suitable for supporting articulation
motion,
[0026] wherein the first and second openings communicate to form a
channel having a first open end.
[0027] Also in accordance with the present invention, there is
provided an intervertebral motion disc comprising:
a) a prosthetic vertebral endplate comprising: [0028] i) an outer
surface adapted to mate with a vertebral body, [0029] ii) an inner
surface having a first opening thereon, [0030] iii) a body portion
connecting the inner and outer surfaces and defining a sidewall
comprising a second opening thereon, and [0031] iv) a first
articulation surface suitable for supporting articulation motion.
wherein the first and second openings communicate to form a channel
having a first open end, and b) a core member having a first
articulation surface suitable for supporting articulation motion,
wherein the core member is disposed within the channel and oriented
therein to produce a first articulation interface between the first
articulation surface of the first endplate and the first
articulation surface of the core member.
[0032] The disc of the present invention is superior to that of
Erickson, Yuan and the first commercial device in that the core
member can be inserted through the open ended channel, thereby
allowing for initial insertion of the prosthetic endplates into the
disc space and then insertion therebetween of a core member having
two articulation surfaces through the channel, and lessening the
extent of required overdistraction.
[0033] The disc of the present invention is superior to that of
Bullivant in that the channel helps retain the core member between
the endplates and so need not rely upon natural ligament tension to
retain the core member between the endplates, and prevents
excessive lateral motion of the core.
[0034] The disc of the present invention is superior to that of the
second commercial device in that its two articulation interfaces
allow the motion disc to more fully restore the natural motion of
the spine than would a single articulation interface.
DESCRIPTION OF THE FIGURES
[0035] FIGS. 1a-1c disclose isometric, cross-sectional and front
views of a first embodiment of the present invention.
[0036] FIGS. 2a-2d disclose isometric, cross-sectional, front and
elevated views of the inferior endplate of the first embodiment of
the present invention.
[0037] FIGS. 3a-3c disclose isometric, elevated and front views of
the superior endplate of the first embodiment of the present
invention.
[0038] FIGS. 4-6 disclose embodiments cross-sectioned through the
channel of an endplate.
[0039] FIGS. 7a-7c disclose isometric, cross-sectional and front
views of the core member of the first embodiment of the present
invention.
[0040] FIG. 8 discloses a cross-section of an embodiment of the
present invention in which the core member has a non-articulating
projection.
[0041] FIG. 9 discloses a cross-section of an embodiment of the
present invention in which the core member has two non-articulating
projections.
[0042] FIG. 10 discloses a cross-section of an embodiment of the
present invention in which the core member has an articulating
projection.
[0043] FIG. 11 discloses a cross-section of an embodiment of the
present invention which defines distances.
[0044] FIG. 12 discloses a cross-section of an embodiment of the
present invention in which the translation surface is
hemi-cylindrical.
[0045] FIG. 13 discloses a side view of a core member having a
spring portion.
[0046] FIG. 14 discloses a side view of a core member having a
helical recess therein.
[0047] FIGS. 15a-15b disclose isometric and elevated views of the
locking tab of the first embodiment of the present invention.
[0048] FIG. 16 discloses a locking tab adapted for engagement with
a vertebral body.
[0049] FIG. 17 discloses an elevated view of an endplate, core and
tab, wherein the inner surface of the tab has an elongated
portion.
[0050] FIG. 18 discloses a cross-section of a superior endplate
having a sunken channel.
[0051] FIG. 19 discloses a first endplate having a
horizontally-extending projection and a core member having a recess
for mating with the projection.
[0052] FIGS. 20a-20c disclose isometric, elevated, and
cross-sectional views of an embodiment of the present invention in
which the core member has a significantly convex articulation
surface and a substantially flat articulation surface.
[0053] FIGS. 21a-21b discloses a front and a cross-sectional view
of another embodiment of the present invention having a slightly
curved articulation interface running the anterior-posterior
direction.
[0054] FIGS. 22a-22b discloses a front and a cross-sectional view
of another embodiment of the present invention having a slightly
curved articulation interface running the medial-lateral
direction.
[0055] FIG. 23 discloses an isometric view of a prosthetic
vertebral endplate of the present invention having a channel having
two open ends.
[0056] FIG. 24 discloses an isometric view of the present invention
in which a locking tab comprises first and second arms, and each
arm is shaped to be secured to the endplate in a recess formed in
the lateral wall portions of the endplate.
[0057] FIG. 25 discloses an isometric view of the present invention
in which one endplate is adapted to receive a screw for fixation to
an adjacent vertebra.
[0058] FIGS. 26a and 26b disclose exploded views of an embodiment
of the invention.
[0059] FIG. 27 discloses a notched endplate of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0060] For the purposes of the present invention, "prosthetic
vertebral endplate" broadly describes a component designed to
substantially fit within an interverterbal space and mate with an
opposing surface of one of the adjacent vertebral bodies. The
"prosthetic vertebral endplate" includes all geometric
configurations, including but not limited to substantially thin and
substantially blocky configurations. Types of mating include, but
are not limited to, penetrating the adjacent vertebral body, simply
contacting the adjacent vertebral body, and providing fixation
through a third component such as a fastener (such as a screw) that
is received within or connected to the prosthetic vertebral
endplate. Such fixation may occur upon a non-opposing surface of
the adjacent vertebral body (such as the anterior wall of the
vertebral body). The adjacent vertebral body may be prepared or
unprepared so that the contacting surface thereof may include the
cortical end endplate portion of the vertebral body or the internal
cancellous portion of the vertebral body.
[0061] For the purposes of the present invention, a "substantially
curved articulation interface" produces substantially pivotal
motion during articulation. Examples of such substantially curved
interfaces include but are not limited to hemipsherical interfaces
having a radius of between about 10 mm and about 30 mm.
[0062] For the purposes of the present invention, both "slightly
curved articulation interfaces" and "substantially flat
articulation interfaces" produce substantially translational motion
during articulation. Examples of such "slightly curved interfaces`
include but are not limited to hemispherical interfaces having a
radius of between about 40 mm and about 100 mm. For the purposes of
the present invention, a "substantially flat articulation
interface" is sufficiently flat so as to allow axial rotation of
either mating component at any point along the interface.
[0063] Now referring to FIG. 1, there is provided a motion disc 1
comprising:
[0064] a) a first prosthetic vertebral endplate 31 comprising:
[0065] i) an outer surface 33 adapted to mate with a first
vertebral body, [0066] ii) an inner surface 35 having a first
opening 34 thereon and a first articulation surface 41, [0067] iii)
a body portion 43 connecting the inner and outer surfaces and
defining a sidewall 45 comprising a second opening 37 thereon,
[0068] b) a second prosthetic vertebral endplate 11 comprising:
[0069] i) an outer surface 13 adapted to mate with a second
vertebral body, and [0070] ii) an inner surface 15 comprising a
first articulation surface 17,
[0071] c) a core member 51 comprising: [0072] i) a first
articulation surface 53 adapted for articulation with the first
articulation surface of the first endplate, and [0073] ii) a second
articulation surface 55 adapted for articulation with the first
articulation surface of the second endplate, wherein the first and
second openings communicate to form a channel 39 having a first
open end 40, and wherein the core member is disposed within the
channel and oriented therein to produce a first articulation
interface between the first articulation surface of the first
endplate and the first articulation surface of the core member, and
a second articulation interface between the first articulation
surface of the second endplate and the second articulation surface
of the core member.
[0074] The motion disc of FIG. 1 further comprises means for
limiting the translation of the core member. In FIG. 1, the means
comprises a locking tab 71 that is adapted to securely lock into
place after the core has been inserted and to help retain the core
within the channel.
[0075] Now referring to FIG. 1, in some embodiments, the device
comprises four main components: an inferior endplate 11, a superior
endplate 31, a core member 51, and a locking tab 71. In one
preferred embodiment, the inferior endplate comprises a
substantially convex surface 17 that is designed to conform to and
mate with a substantially concave surface 55 formed in the core
member. The superior endplate has an open channel 39 within which
substantially flat lower articulation surface 41 is disposed. The
substantially flat lower articulation surface 41 is intended to
mate with the substantially flat upper articulation surface 53 of
the core member. Channel 39 is designed to retain the core and
prevent its lateral expulsion. The core member comprises a
substantially concave bottom articulation surface 55 and a
substantially flat top articulation surface 53, each of which is
designed to mate with the corresponding surfaces on the endplates
to form articulation interfaces. Preferably, the articulation
interfaces are conforming. In addition, the core member is designed
with a retaining feature 57 that mates with a corresponding
undercut formed in the sidewall, thereby promoting its retention
within the superior endplate channel. Lastly, the locking tab 71 is
designed to effectively close the open end of the channel once the
core member has been inserted, thereby promoting retention of the
core.
[0076] In other embodiments, the features on the superior and
inferior endplates can be reversed. For example, the substantially
flat articulation surface of the superior endplate could be
provided upon the inferior endplate, and the substantially curved
surface of the inferior endplate could be provided on the superior
endplate. In addition, the placement of the ball and socket-like
substantially curved surfaces could be reversed so that the core
member has a substantially convex articulation surface and the
corresponding endplate has a matching substantially concave
articulation surface. The substantially flat articulation surfaces
may also be modified to be slightly curved and still provide
substantially translational motion. Lastly, additional components
such as screws for initial fixation of the implant may be added to
the design.
[0077] Each of the four main components of one preferred embodiment
will now be described in more detail:
[0078] Now referring to FIG. 2, in one embodiment, inferior
endplate 11 has an inferior surface 13 designed to mate with a
natural vertebral endplate, a superior surface 15 designed to mate
with both instrumentation and the core member, and a body portion
16 therebetween. The periphery of the inferior endplate comprises
an anterior wall 21, a posterior wall 23, and sidewall portions 25
and 27.
[0079] Preferably, the inferior (outer) surface 13 of this endplate
is either flat, curved or domed to match the natural vertebral
endplate. Alternatively, the geometry of the inferior surface can
be designed so that it will match the shape of the patient's
vertebral endplate after the vertebral endplate has been modified
by an endplate-shaping instrument. In addition, the inferior
surface of this endplate can further comprise features to promote
and secure initial fixation and bony ingrowth including, but not
limited to, spikes, keels, teeth, projections (such as dovetails),
recesses (such as grooves) and porous coatings.
[0080] Superior (inner) surface 15 comprises a peripheral portion 9
and a raised inner portion 7 extending substantially from the
middle of the peripheral portion. This raised inner portion
comprises a raised surface 5, a sloped anterior wall 3, and a pair
of raised sidewalls 2,4.
[0081] Extending from the raised surface of the superior surface of
the inferior endplate is a highly polished substantially convex
articulation surface 17 designed to mate with a corresponding
substantially concave articulation surface (not shown) disposed
upon the core member. Preferably, substantially convex articulation
surface 17 is further designed to conform to the corresponding
concave articulation surface. In the preferred embodiment the
articulation surface 17 is convex. However, the substantially
curved articulation surface can also be concave if desired to mate
with a corresponding substantially convex articulation surface (not
shown) disposed upon the core member. Preferably, the substantially
curved articulation surface 17 has been polished to a surface
roughness Ra of no more than 10 nm.
[0082] Preferably, formed upon each raised sidewall is a slotted
guide rail 60 running substantially along the length of each raised
sidewall. For the purposes of the present invention, a slot is a
longitudinally-extending recess in a first surface having a
continuous opening onto a second lateral surface along at least a
portion of its longitudinal axis. In contrast, a hole is closed
about its periphery along its longitudinal axis and so does not
open onto a second lateral surface. In some embodiments
particularly suited for anterior approaches, the rails run in an
anterior-posterior direction. These two guide rails are designed to
mate with instrumentation used during the surgical procedure, and
optionally with additional implant components (such as a revision
spacer or a locking tab). When used as guide rails, slots formed in
the raised side walls are more advantageous to holes running
through the raised portion because a hole disposed near the edges
of the raised portion would be prone to failure and so additional
material would be required to support the raised sidewall. In
preferred embodiments, the inner surface of the slot is angled.
Without wishing to be tied to a theory, it is believed that angled
slots are often selected over square slots because a square slot
disposed near the edges of the raised portion is prone to failure
and so additional material is required to support the raised
sidewall. Preferably, the guide rails are located within the
footprint of the disc formed by the side wall portions 25 and 27 of
the endplates.
[0083] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising: [0084] a) a
first motion segment comprising: [0085] i) an outer surface adapted
to mate with a first vertebral body, [0086] ii) an inner surface
comprising a first articulation surface, [0087] iii) a front and a
back wall between the inner and outer surfaces, and [0088] iv) a
pair of slots formed in the first motion segment, each slot running
substantially from the front wall and opening onto the front wall,
[0089] b) a second motion segment comprising: [0090] i) an outer
surface adapted to mate with a second vertebral body, [0091] ii) an
inner surface comprising a first articulation surface, and wherein
the articulation surfaces are adapted to produce an articulation
interface.
[0092] In other embodiments particularly suited for translateral
approaches, the rails run at a substantial angle to the
anterior-posterior direction. Typically, this substantial angle is
between about 30 and about 60 degrees from the anterior-posterior
direction.
[0093] Now referring to FIG. 3, superior endplate 31 has a superior
outer surface 33 designed to mate with the vertebral endplate, an
inferior inner surface 35a and 35b that is designed to mate with
both instrumentation and the core member, and a body portion 43
therebetween defining a plurality of sidewalls, including an
anterior wall 45, a posterior wall 46, and lateral wall portions 47
and 48.
[0094] Preferably, the superior outer surface 33 of this endplate
is either flat, curved or domed to match the natural vertebral
endplate. Alternatively, the geometry of the superior surface can
be designed so that it will match the shape of the patient's
vertebral endplate after the vertebral endplate has been modified
by an endplate-shaping instrument. In addition, the superior
surface of this endplate can further comprise features to promote
secure initial fixation and bony ingrowth including, but not
limited to, spikes, keels, teeth, projections (such as dovetails),
recesses (such as grooves) and porous coatings.
[0095] Now referring also to FIG. 1, channel 39 is formed from the
communication of the second opening 37 in the anterior wall with
the first opening 34 formed on inner surface 35a of this endplate.
In this embodiment, the channel has i) a substantially flat
articulation surface 41 that provides linear translation and is
designed to mate with a corresponding substantially flat
articulation surface of the core member and ii) a sidewall 50
surrounding three sides of the substantially flat articulation
surface. Preferably, substantially flat articulation surface 41 is
further designed to conform to a corresponding substantially flat
articulation surface of the core member. In some embodiments, the
substantially flat articulation surface 41 may be replaced with a
slightly curved articulation surface. Preferably, the substantially
flat articulation surface has been polished to a surface roughness
Ra of no more than 10 nm. The channel has a width adapted to
receive and retain the core. Preferably, the channel has a shape
that allows the core to be easily inserted therein and then
retained therein by a means for limiting translation. In the
preferred embodiment, the sidewall 50 of the channel has an angular
undercut 46 formed therein that is designed to retain the core.
[0096] In some embodiments (as in FIG. 1), bottom surface 41 is
substantially flat to provide substantially translational motion
with a corresponding flat superior surface of the core member.
However, in other embodiments, this bottom surface is slightly
curved to provide not only substantially translational motion with
a corresponding slightly curved superior surface of the core
member, but also a soft resistance to extreme A-P translation of
the core. Preferably, the slightly curved interface is
hemicylindrical, preferably with the curve of the hemicylinder
running in the anterior-posterior ("A-P") direction. In other
embodiments, the curve of the hemicylinder runs in the
medial-lateral ("M-L") direction, and so allows the use of a
thicker core member.
[0097] The opened end channel of FIGS. 1 and 3 is believed to be
novel in prosthetic intervertebral motion discs having an
intermediate component disposed between a pair of prosthetic
vertebral endplates. The open end of the channel is advantageous in
that it allows the surgeon to insert only the upper and lower
plates into the disc space, and then insert the intermediate piece
through the open end of the channel. Because the combination of the
upper and lower endplates can be inserted with a lower profile than
if the intermediate component were in place, there is a lesser need
to severely overdistract or otherwise harm the opposing natural
vertebral endplates. The substantially translational articulation
capability provided by the first articulation interface allows the
disc to more nearly imitate the natural motion of an intervertebral
disc.
[0098] Therefore, in accordance with the present invention, there
is provided a method of implanting an intervertebral motion disc,
comprising the sequential steps of:
[0099] inserting into a disc space a partial motion disc
comprising: [0100] a) a first prosthetic vertebral endplate
comprising: [0101] i) an outer surface adapted to mate with a first
vertebral body, and [0102] ii) an inner surface comprising a first
motion surface, [0103] b) a second prosthetic vertebral endplate
comprising: [0104] i) an outer surface adapted to mate with a
second vertebral body, [0105] ii) an inner surface comprising an
opening forming a channel comprising opposing side walls, a first
open end and a second motion surface, and
[0106] inserting into the open end of the channel a core member
comprising: [0107] i) a first surface adapted for motion with the
first motion surface, and [0108] ii) a second surface adapted for
motion with the second motion surface, wherein the core member is
disposed within the channel and oriented therein to provide a first
motion with the first motion surface and a second motion with the
second motion surface.
[0109] In some embodiments, now referring to FIG. 4, the channel
comprises a sunken anterior surface 203 and a raised posterior
articulation surface 205. Because these surfaces occupy different
levels, the raised posterior portion can now be more easily
polished. In some embodiments, the transition between these
surfaces defines a ledge 207. This ledge acts as a stop against
overinsertion of the tab, thereby preserving the high polish of the
raised posterior articulation surface, and eases insertion of the
core.
[0110] In some embodiments, now referring to FIG. 5, the anterior
surface 211 is ramped to rise posteriorly. This embodiment also
minimizes the necessary polishing of the articulation surface. As
the tab moves up the ramp, the combined action of the elevation
rise and the elevation limit provided by the undercut dovetail 213
of the sidewall acts as a stop upon the further posterior movement
of the tab.
[0111] When the patient is standing in a supine position, the
natural loads upon the spine are such that the core member is most
preferably positioned in the posterior portion of the motion disc,
as in FIG. 1, and more preferably between about 60-80% towards the
posterior. When the patient first bends forward, the core member
may move anteriorly or posteriorly. If the core moves anteriorly,
when the patient returns to a supine position, the substantially
flat nature of the channel of FIG. 1. does not help the core member
move back to its original posterior position.
[0112] Therefore, in some embodiments, now referring to FIG. 6, at
least a portion of the channel is ramped to slope downward
posteriorly. The channel of FIG. 6 comprises an anterior
articulation surface having a downward sloping ramp 221. If the
core is disposed in an anterior portion of the channel, the
non-parallel nature of the bearing surfaces will urge the core to
move back to its original posterior position when the patient
returns to an erect position.
[0113] Therefore, in accordance with the present invention, there
is provided a prosthetic vertebral endplate, comprising: [0114] i)
an outer surface adapted to mate with a first vertebral body to
define a first attachment plane substantially parallel to the
vertebral body endplate, and [0115] ii) an inner surface comprising
a substantially flat motion surface, wherein the substantially flat
motion surface and the first attachment plane define an angle
.alpha.. In one preferred embodiment, the angle .alpha. of the ramp
is between about 10 and about 30 degrees.
[0116] When the channel of the present invention contains a
substantially flat articulation surface, overdistraction caused by
insertion of the core member is desirably minimized. However, in
other embodiments, the channel may include a slightly curved
surface which rises anteriorly and/or a flat surface having an
anteriorly-disposed lip having a height less than that of
sidewalls. Since the lip or slightly curved surface may desirably
retain the core member within the channel, it is contemplated that
such a lip may obviate the need for another translation-limiting
component such as a tab that prevents expulsion of the core while
still providing a height reduction benefit that lessens the need
for overdistraction. Preferably, this lip has a height that is no
more than 80% of the channel depth, more preferably no more than
50%, more preferably no more than 25%.
[0117] Referring again to FIG. 3, formed in each sidewall 47, 48 is
a recessed guide rail 49. Guide rail 49 begins at the anterior
wall, extends across each sidewall, and ends at the posterior wall.
These two guide rails correspond to the two guide rails 60 of the
inferior plate.
[0118] Now referring to FIG. 7, the core member 51 comprises a body
portion 52 forming a substantially flat superior surface 55 that is
designed to articulate with the bottom surface of the superior
endplate and a substantially curved inferior surface 53 that is
designed to mate with the inferior endplate. In some preferred
embodiments, the body portion has a substantially cylindrical body
portion 52. In some preferred embodiments, the body portion has a
substantially rectangular body portion 52. Preferably, superior
surface 55 is further designed to conform to the bottom surface 41
of the superior endplate. Also preferably, substantially curved
inferior surface 53 is designed to conform with a corresponding
substantially curved upper surface of the inferior endplate. In
some embodiments (as in FIG. 7), superior surface 55 is
substantially flat to provide substantially translational motion
with a corresponding flat bottom surface of the superior endplate.
However, in other embodiments, superior surface 55 is slightly
curved to provide substantially translational motion with a
corresponding curved bottom surface of the superior endplate as
well as soft resistance to extreme translational motion.
[0119] The substantially curved inferior surface can be any shape
designed for pivotal articulation, including hemispherical,
hemicylindrical, hemi-ellipsoidal, and oblong. However, in
preferred embodiments, the curved surface is hemi-spherical. In the
preferred embodiments, the substantially curved inferior
articulation surface of the core is concave. However, the curved
articulation surface can also be convex, if desired, to mate with a
corresponding substantially concave articulation surface disposed
upon an endplate.
[0120] The substantially flat superior surface may be modified to
any slightly curved geometry that allows at least one degree of
substantially translational motion, including a hemi-cylindrical
shape.
[0121] In addition to the two articulation surfaces, the core has a
peripherally disposed retaining feature 57 that is designed to
prevent the core from accidentally dislocating from the implant.
The shape of the retaining feature is adapted to fit a
complementary feature (46 of FIG. 3) in the sidewall of the
retaining channel. In this embodiment, the retaining feature 57
extends from the cylindrical body portion. In a preferred
embodiment, the retaining feature is an angled flare disposed near
the end of the core having the substantially translational surface.
However, in other embodiments, the retaining feature can be a
recess extending into the body portion 52.
[0122] Typically, the core of a conventional motion disc has either
two convex surfaces or two concave surfaces. The Germain motion
disc is the only motion disc known to the present inventors in
which the core comprises one convex motion surface and one concave
motion surface. However, Germain further requires the radius of the
upper surface to be smaller than the radius of the lower motion
surface. Without wishing to be tied to a theory, because of this
requirement, the Germain disc may suffer from a high center of
rotation.
[0123] In an effort to overcome these deficiencies, in some
embodiments of the present invention, the radius of the upper
surface of the core is greater than the radius of the lower motion
surface. Without wishing to be tied to a theory, this embodiment of
the present invention may possess an advantage of a low center of
rotation.
[0124] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0125] a) an upper prosthetic vertebral endplate comprising: [0126]
i) an outer surface adapted to mate with an upper vertebral body,
[0127] ii) an inner surface having a first articulation
surface,
[0128] b) a lower prosthetic vertebral endplate comprising: [0129]
i) an outer surface adapted to mate with a lower vertebral body,
and [0130] ii) an inner surface having a first articulation
surface, and
[0131] c) a core member comprising: [0132] i) an upper articulation
surface adapted for articulation with the first articulation
surface of the upper endplate and having a radius, and [0133] ii) a
lower articulation surface adapted for articulation with the first
articulation surface of the lower endplate and having a radius,
wherein the core member is disposed between the endplates and
oriented therein to produce an upper articulation interface between
the first articulation surface of the upper endplate and the upper
articulation surface of the core member, and a lower articulation
interface between the first articulation surface of the lower
endplate and the lower articulation surface of the core member, and
wherein the radius of the upper articulation surface of the core
member is greater than the radius of the lower articulation surface
of the core member.
[0134] Preferably, the radius of the upper motion surface of the
core is at least three times greater than the radius of the lower
motion surface of the core, more preferably between 3 and 5 times
greater. Preferably, the radius of the upper surface of the core is
between about 40 mm and about 100 mm, and the radius of the lower
motion surface is between about 10 mm and about 30 mm. Preferably,
the radius of the upper surface of the core is between 40 mm and 80
mm. Below 40 mm, the depth of the curve requires adding
significantly more material to the corresponding endplate, thereby
increasing the height of the implant. Above 80 mm, the curve
provides a less significant braking.
[0135] Typically, the core of a conventional motion disc has either
one flat surface and one curved surface (as in Erickson, Yuan and
Bullivant), two cylindrical surfaces (as in Charite '766), or two
hemispherical surfaces (as in Germain). However, a substantially
flat surface in a motion disc does not resist extreme movement of
the core. Motion discs having two hemicylindrical surfaces can not
provide the desired pivotal movement over 360 degrees. Motion discs
having two hemispherical surfaces do not allow for the easy
correction of misaligned endplates.
[0136] In an effort to overcome these deficiencies, in some
embodiments of the present invention, the core of the present
invention has one hemispherical surface and one non-hemispherical
curved surface. Preferably, the non-hemispherical curved surface is
hemicylindrical. In this condition, the hemispherical surface
provides the pivotal rotation freedom found in the natural disc,
while the linear dimension of the hemicylindrical surface (when
provided in the medial-lateral direction, as in FIGS. 12 and 22a)
provides substantially translational movement in a first direction
(thereby providing easy correction of misaligned endplates), and
curved dimension of the hemicylindrical surface provides some
resistance against extreme movement in a second direction.
[0137] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0138] a) a first prosthetic vertebral endplate comprising: [0139]
i) an outer surface adapted to mate with a first vertebral body,
[0140] ii) an inner surface having a first articulation
surface,
[0141] b) a second prosthetic vertebral endplate comprising: [0142]
i) an outer surface adapted to mate with a second vertebral body,
and [0143] ii) an inner surface having a first articulation
surface, and
[0144] c) a core member comprising: [0145] i) a first articulation
surface adapted for articulation with the first articulation
surface of the first endplate, and [0146] ii) a second articulation
surface adapted for articulation with the first articulation
surface of the second endplate, wherein the core member is disposed
between the endplates and oriented therein to produce a first
articulation interface between the first articulation surface of
the first endplate and the first articulation surface of the core
member, and a second articulation interface between the first
articulation surface of the second endplate and the second
articulation surface of the core member, and wherein the first
articulation surface of the core member is spherical and the second
articulation surface of the core member is curved and
non-spherical.
[0147] Also in accordance with the present invention, there is
provided a core member for articulation between first and second
prosthetic vertebral endplates, comprising: [0148] i) a first
articulation surface adapted for articulation with a first
articulation surface of the first prosthetic vertebral endplate,
and [0149] ii) a second articulation surface adapted for
articulation with the first articulation surface of the second
prosthetic vertebral endplate, wherein the first articulation
surface is a portion of a sphere and the second articulation
surface is a portion of a curved, non-spherical shape.
[0150] Preferably, the non-spherical curved surface is a
hemicylindrical surface, as such a surface that can articulate with
a similar opposing hemicylindrical surface and provide conforming
articulation. Also preferably, the curved dimension of the
hemicylindrical surface is provided in the A-P direction (to
provide a soft braking) while the linear dimension is provided in
the medial-lateral direction. However, in other embodiments, the
curved dimension of the hemicylindrical surface is provided in the
medial-lateral direction, while the linear dimension is provided in
the anterior-posterior direction.
[0151] Also preferably, the hemispherical surface is substantially
curved and the curved, non-hemispherical surface is slightly
curved.
[0152] In the embodiment of FIG. 3, because the translational
articulation surface 41 that mates with the core member is disposed
within the channel, both the core retention function and
translation surface function of this endplate are provided by the
same surface within the channel. However, in other embodiments, the
core retention function and translation surface function can be
provided by separate surfaces. For example, now referring to FIG.
8, there is provided a motion disc wherein the core member has a
projection 501 that extends only partially into channel 503. The
channel and projection elements of this device function merely to
limit the lateral translational freedom of the core member. In this
embodiment, the bottom of the channel does not have to be adapted
to support articulation motion. Rather, substantially flat
articulation surface 505 provided on the inner surface of the
endplate forms an articulation interface with the substantially
flat articulation surface 507 of the core member.
[0153] Similarly, in FIG. 9, there is provided a prosthetic
vertebral endplate 551 having two channels with an articulation
surface therebetween. In particular, endplate 551 comprises an
inner surface 552 having first 553 and second 555 channels formed
therein, and an articulation surface 567 formed between the
channels. The channels begin at the anterior wall 557 of the
endplate and terminate prior to opening onto the posterior wall
(not shown) of the endplate. Core member 561 comprises first 563
and second 565 projections and an articulation surface 569
therebetween, each projection having a shape that mates with its
corresponding channel to limit the medial-lateral translation of
the core member. Anterior-posterior translation is accomplished by
the mating of articulation surface 569 of the core and articulation
surface 567 of the endplate to produce an articulation interface.
Expulsion of the core member of this embodiment can be prevented by
any number of means. For example, after the core member is slid
into the channels, locking tabs can be inserted into the anterior
end of each channel. Alternatively, the intermediate portion 567 of
the inner surface can comprise at least one flexible tab that
allows the passage of the core member towards the posterior portion
of the endplate, but prevents its passage back out.
[0154] In other embodiments, the core member and superior endplate
can be adapted to provide more than one articulation interface. Now
referring to FIG. 10, the bottom surface 511 of the projection is
polished and extends sufficiently into the channel to bear upon the
bottom surface 513 of the channel to form a first articulation
interface, while an articulation surface 515 is also provided on
the inner surface of the endplate to form a second articulation
interface with a second articulation surface 517 of the core
member.
[0155] Likewise, in FIG. 9, projections 563,565 may optionally mate
with the bottom surfaces of the channels to form additional
articulation interfaces.
[0156] In preferred embodiments, the core member is adapted to
provide pivotal motion with a first endplate. Preferably, the
pivotal motion is provided by the corresponding substantially
curved surfaces of the core member and a first endplate. More
preferably, the curved surfaces are conforming. More preferably,
the conforming curved surfaces are selected from the group
consisting of hemispherical and hemicylindrical surfaces. Still
more preferably, the conforming curved surfaces are hemispherical
surfaces.
[0157] In preferred embodiments, the core member is adapted to
provide at least one degree of translation motion with a second
endplate. Preferably, the at least one degree of translation motion
is provided by corresponding substantially flat planar surfaces of
the core member and a second endplate. Now referring to FIG. 11, in
some embodiments, exactly one degree of translation motion is
achieved by sizing the core member so that its diameter D.sub.C
equals the width W of the channel in which it is disposed. In this
case, the one degree of freedom is translation in the A-P
direction. Now referring to FIG. 10, in other embodiments, one
degree of translation motion is realized by sizing a projection
upon the core member so that the diameter of the projection D.sub.P
equals the width W of the channel in which it is disposed.
Preferably, the motion provided by the one-degree-of-freedom
embodiment is in the anterior-posterior direction. In other
embodiments, more than one degree of freedom may be realized by
sizing the core member so that its diameter (or the diameter of its
projection that bears upon the articulation surface) is smaller
than the width W of the channel, thereby allowing the core to move
laterally as well.
[0158] In other embodiments, as in FIG. 12, one degree of
translation motion is realized by providing a channel having a
hemicylindrical surface 701 and a core member having a
corresponding hemicylindrical surface 703 to produce a
hemicylindrical interface. In this particular embodiment, the core
has a slightly convex hemicylindrical surface adapted to provide
translational motion in the A-P direction with the slightly concave
hemicylindrical bottom surface of the channel.
[0159] The flat surfaces that provide translation movement in
Erickson are either circular or elongated. However, in the circular
embodiments, since there is very little medial-lateral movement in
natural spinal movement, the circular designs of Erickson do not
readily mimic the natural spinal movements. In the elongated
embodiments, Erickson teaches that the elongated embodiment
provides movement along only one axis. Accordingly, if an elongated
(uniaxial) design of Erickson is selected, any misalignment of the
components in the M-L axis can not be easily corrected by simple
translation of this motion surface.
[0160] Therefore, in some embodiments, the core member and its
slightly curved or substantially flat translation surface are
adapted to provide a translation surface that provides for
substantial movement in the A-P axis and lesser movement in the M-L
axis. When this embodiment is selected, the device provides not
only the degree of A-P movement that substantially mimics the A-P
motion of the natural intervertebral disc but also a limited amount
of M-L motion that allows the surgeon to use this interface to
compensate for any surgical misalignment of the prosthetic
vertebral endplates.
[0161] Therefore, in accordance with the present invention, there
is provided intervertebral motion disc comprising:
[0162] a) a first prosthetic vertebral endplate comprising: [0163]
i) an outer surface adapted to be attached to a first vertebral
body, and [0164] ii) an inner surface comprising a first
articulation surface,
[0165] b) a core member comprising: [0166] i) a first articulation
surface, and wherein the first articulation surface of the core
member and the first articulation surface of the first endplate are
adapted to form a first articulation interface having a range of
anterior-posterior A-P motion and a range of medial-lateral M-L
motion, wherein the range of A-P motion is between 1.5 and 50 times
greater than the range of M-L motion.
[0167] Preferably, the maximum range of A-P motion is between 1.5
and 50 times greater than the maximum range of M-L motion, more
preferably between 1.5 and 8 times, more preferably between 4 and 8
times, more preferably between 5 and 7 times, and still more
preferably between 5.5 and 6.5 times.
[0168] In some embodiments designed for use in the lumbar spine,
the maximum range of A-P motion is between 2 and 5 mm, preferably
between 3 and 4 mm, and the maximum range of M-L motion is between
0.25 mm and 2 mm, preferably between 0.25 mm and 1 mm.
[0169] Now referring to FIG. 11, in preferred embodiments, the
channel is defined by a length L.sub.CH and a width W.sub.CH, the
articulation surface portion of the channel is defined by a length
L.sub.MS and a width W.sub.MS, and the core member is defined by a
diameter D.sub.CO. As shown in FIG. 11, the length of the
articulation surface does not include the space occupied by a tab
T.
[0170] Preferably, the length of the articulation surface L.sub.MS
is between about 10% to about 50% greater than the diameter
D.sub.CO of the core. When this range is achieved in typical
geometries, the core member can move between about 1 mm and about 5
mm in the anterior-posterior direction. Within this range, the core
member has translation capability that mimics typical anatomical
anterior-posterior motion.
[0171] Preferably, the width of the channel W.sub.CH is between
about 5% and about 20% greater than the diameter D.sub.CO of the
core. When this range is achieved in typical geometries, the core
can move between about 0.5 mm and about 2 mm in the medial-lateral
direction. This 0.5-2 mm of freedom may correct for misplacement of
the pivotal articulation surface elements.
[0172] Preferably, when the channel has a closed end, the length of
the channel L.sub.CH extends to between about 60% to 80% the
distance from the anterior wall to the posterior wall of the
endplate. When this range is achieved, the core can reside
substantially near the anatomically typical vertical axis of
rotation.
[0173] In preferred embodiments, each of the inferior endplate,
superior endplate and core member is manufactured from a material
that possesses the strength and high wear resistance desired for
use as a motion disc component.
[0174] These components of the present invention may be made from
any non-resorbable material appropriate for human surgical
implantation, including but not limited to, surgically appropriate
metals, and non-metallic materials, such as carbon fiber
composites, polymers and ceramics.
[0175] If a metal is chosen as the material of construction for a
component, then the metal is preferably selected from the group
consisting of titanium, titanium alloys (such as Ti-6Al-4V), chrome
alloys (such as CrCo or Cr--Co--Mo) and stainless steel. If an
articulation interface is formed from first and second metal
articulation surfaces, then the components are preferably
manufactured so that the grains of the first metal articulation
surface are disposed substantially perpendicular to the grains of
the second metal articulation surface grains of the first metal
articulation surface.
[0176] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0177] a) a first prosthetic vertebral endplate comprising: [0178]
i) an outer surface adapted to be attached to a first vertebral
body, and [0179] ii) an inner surface comprising a first
articulation surface comprising a first metal having grains
oriented in a first direction, and
[0180] b) a core member comprising: [0181] i) a first articulation
surface comprising a metal having grains oriented in a second
direction, wherein the first articulation surface of the core
member and the first articulation surface of the first endplate are
adapted to form a first articulation interface, and wherein the
first and second directions of grain orientation are not
parallel.
[0182] If a polymer is chosen as a material of construction for a
component, then the polymer is preferably selected from the group
consisting of polyesters, (particularly aromatic esters such as
polyalkylene terephthalates, polyamides; polyalkenes; poly(vinyl
fluoride); PTFE; polyarylethyl ketone PAEK; and mixtures
thereof.
[0183] If a ceramic is chosen as the material of construction for a
component, then the ceramic is preferably selected from the group
consisting of alumina, zirconia and mixtures thereof. It is
preferred to select an alumina-zirconia ceramic, such as BIOLOX
Delta.TM., available from CeramTec of Plochingen, Germany.
Depending on the material chosen, a smooth surface coating may be
provided thereon to improve performance and reduce particulate wear
debris.
[0184] The present inventors believe that metal-ceramic interfaces
will provide the best resistance to wear. Accordingly, in
particularly preferred embodiments, there is provided an
intervertebral motion disc comprising:
[0185] a) a first prosthetic vertebral endplate comprising: [0186]
i) an outer surface adapted to mate with a first vertebral body,
and [0187] ii) an inner surface comprising a first articulation
surface comprising a non-ceramic material
[0188] b) a core member comprising: [0189] i) a first articulation
surface comprising a ceramic, and wherein the first articulation
surface of the core member and the first articulation surface of
the first endplate are adapted to form a first articulation
interface.
[0190] More preferably, the second articulation interface will also
have a corresponding ceramic-metal interface.
[0191] In some preferred embodiments, the entire core member
consists essentially of a ceramic, preferably a sintered
polycrystalline ceramic. Preferably, the sintered polycrystalline
ceramic comprises at least 50 wt % of a material selected from the
group consisting of alumina, zirconia, and alumina-zirconia
mixtures. In some alumina-zirconia mixture embodiments, the ceramic
comprises 10-30 wt % alumina.
[0192] In some alumina-zirconia mixture embodiments, the ceramic
comprises 70-90 wt % alumina. In some embodiments, the ceramic
comprises alumina having a median grain size of no more than 5
micron, preferably less than 3 microns, more preferably less than 2
microns, more preferably less than one micron. In some embodiments,
the ceramic comprises tetragonal zirconia having a median grain
size of no more 2 microns, more preferably less than one micron. In
some embodiments, the ceramic comprises alumina made from a seeded
gel process.
[0193] In some embodiments, the core member is polyethylene.
[0194] In some preferred embodiments, the first endplate consists
essentially of a metallic material, preferably a titanium alloy or
a chrome-cobalt alloy. In some preferred embodiments, the second
endplate consists essentially of the same metallic material as the
first plate.
[0195] In some embodiments, the articulation surfaces of the
endplates may be coated with a wear-resistant coating, such as
diamond film, in order to reduce wear.
[0196] In some embodiments, the endplates are made of a stainless
steel alloy, preferably BioDur.RTM. CCM Plus.RTM. Alloy available
from Carpenter Specialty Alloys, Carpenter Technology Corporation
of Wyomissing, Pa.; and the core member is made of polyethylene,
preferably Marathon.TM., available from DePuy Orthopaedics of
Warsaw, Ind. In some embodiments, the endplate articulation
surfaces are coated with a sintered beadcoating, preferably
Porocoat.TM., available from DePuy Orthopaedics of Warsaw, Ind.
[0197] In some embodiments, the endplates are made from a composite
comprising carbon fiber. Composites comprising carbon fiber are
advantageous in that they typically have a strength and stiffness
that is superior to neat polymer materials such as a polyarylethyl
ketone PAEK.
[0198] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0199] a) a first prosthetic vertebral endplate comprising: [0200]
i) an outer surface adapted to be attached to a first vertebral
body, and [0201] ii) an inner surface comprising a first
articulation surface comprising a composite comprising carbon
fiber, and
[0202] b) a core member comprising: [0203] i) a first articulation
surface comprising a metal, wherein the first articulation surface
of the core member and the first articulation surface of the first
endplate are adapted to form a first articulation interface.
[0204] Also in accordance with the present invention, there is
provided an intervertebral motion disc comprising:
[0205] a) a first prosthetic vertebral endplate comprising: [0206]
i) an outer surface adapted to be attached to a first vertebral
body, [0207] ii) an inner surface comprising a first articulation
surface, and [0208] iii) a body portion therebetween comprising
carbon fiber, and
[0209] b) a core member comprising: [0210] i) a first articulation
surface, wherein the first articulation surface of the core member
and the first articulation surface of the first endplate are
adapted to form a first articulation interface.
[0211] Preferably, the composite comprising carbon fiber further
comprises a polymer. Preferably, the polymer is a polyarylethyl
ketone PAEK. More preferably, the PAEK is selected from the group
consisting of polyetherether ketone PEEK, polyether ketone ketone
PEKK and polyether ketone PEK. In preferred embodiments, the PAEK
is PEEK.
[0212] In some embodiments, the carbon fiber comprises between 1
vol % and 60 vol % (more preferably, between 10 vol % and 50 vol %)
of the composite. In some embodiments, the polymer and carbon
fibers are homogeneously mixed. In others, the material is a
laminate. In some embodiments, the carbon fiber is present as
chopped state. Preferably, the chopped carbon fibers have a median
length of between 1 mm and 12 mm, more preferably between 4.5 mm
and 7.5 mm. In some embodiments, the carbon fiber is present as
continuous strands.
[0213] In especially preferred embodiments, the composite
comprises:
[0214] a) 40-99% (more preferably, 60-80 vol %) polyarylethyl
ketone PAEK, and
[0215] b) 1-60% (more preferably, 20-40 vol %) carbon fiber,
wherein the polyarylethyl ketone PAEK is selected from the group
consisting of polyetherether ketone PEEK, polyether ketone ketone
PEKK and polyether ketone PEK.
[0216] In some embodiments, the composite consists essentially of
PAEK and carbon fiber. More preferably, the composite comprises
60-80 wt % PAEK and 20-40 wt % carbon fiber. Still more preferably
the composite comprises 65-75 wt % PAEK and 25-35 wt % carbon
fiber.
[0217] If both the core and endplates are made of materials having
a significantly high stiffness, then the device may not fully mimic
the shock absorbing function of the natural intervertebral
disc.
[0218] Therefore, in order to augment the shock absorbing function
of the core member, in some embodiments, the core member comprises
a shock-absorbing component characterized by a specified range of a
spring constant.
[0219] Therefore, in accordance with the present invention, there
is provided intervertebral motion disc comprising:
[0220] a) a first prosthetic vertebral endplate comprising: [0221]
i) an outer surface adapted to be attached to a first vertebral
body, and [0222] ii) an inner surface comprising a first
articulation surface, and
[0223] b) a core member comprising a stiff component and a shock
absorbing component having a spring constant of between 500 N/mm
and 1000 N/mm, and comprising: [0224] i) a first articulation
surface, wherein the first articulation surface of the core member
and the first articulation surface of the first endplate are
adapted to form a first articulation interface.
[0225] In some embodiments, the core member comprises a stiff
component and a shock-absorbing component, and the shock-absorbing
component has a spring constant of between about 500 N/mm and 1000
N/mm and a thickness of between 1 mm and 5 mm. When the
shock-absorbing component is so designed, it can absorb between
about 1000N and 2000 N of load.
[0226] In some embodiments, the shock absorbing function of the
core is provided by a spring within the core member. Therefore, in
accordance with the present invention, there is provided a core
member for articulation between first and second prosthetic
vertebral endplates, comprising: [0227] i) a first portion having a
first articulation surface adapted for articulation with a first
articulation surface of the first prosthetic vertebral endplate,
[0228] ii) a second portion having a second articulation surface
adapted for articulation with a first articulation surface of the
second prosthetic vertebral endplate, and [0229] iii) a spring
portion disposed between the first and second portions.
[0230] Now referring to FIG. 13, in some embodiments, the spring
may be provided by simply manufacturing upper and lower halves of a
core member, and then attaching the opposite ends of a compression
spring to the opposite ends of the core halves. For example, in
FIG. 18, upper core half 721 comprises a first articulation surface
723 and a lower attachment surface 725, while lower core half 731
comprises a second articulation surface 733 and an upper attachment
surface 735. Compression spring 741 comprises upper end 743 and
lower end 745, wherein the upper end 743 is attached to the lower
attachment surface 725 of the upper core half, and the lower end
745 is attached to the upper attachment surface 735 of the lower
core half.
[0231] Now referring to FIG. 14, in other embodiments, the spring
action is provided by first providing an integral core member
having opposing articulation surfaces 751,753 and then shaping the
surface of the intermediate portion of the core member with a
cutting tool to provide at least one recess 755 therein that
provides the spring effect. In some embodiments, the intermediate
surface comprises multiple recesses spaced to provide the spring
effect. In other embodiments, a helical recess is provided, as in
FIG. 14. In other embodiments, the helical recess is made by using
a wire and a spinning fixture to produce a deep helical slit in the
core member.
[0232] Now referring to FIG. 15, the locking tab 71 is adapted to
securely lock in the channel after the core member has been
inserted and to retain the core member within the channel. In one
preferred embodiment, the locking tab comprises a body portion 82
having deformable arms 78 extending therefrom and oriented
substantially parallel to each other to fit within the channel of
the superior endplate. Each arm 78 further comprises a laterally
extending wing 79. Because the wingspan defined by the wings is
greater than the width of the channel, the arms are deflected
inwards as the tab is slid into the retaining channel. These wings
are further designed to fit within sockets 32 (of FIG. 3) laterally
disposed within the channel so that the deflected arms can move
back to their original parallel orientation when the wings are
accepted by the channel sockets, thereby locking tab securely in
place.
[0233] The locking tab should be manufactured from a material with
the requisite elasticity such as stainless steel, plastic, or
nitinol. However, in some embodiments, the elasticity of the
locking tab may be relatively low, thereby making it difficult to
provide the snap-in function. Accordingly, in some embodiments, the
locking means is fastened to the prosthetic vertebral endplate by a
fastener such as a screw or anchor.
[0234] In preferred embodiments, the locking tab is sized so as to
allow the core member to move in the A-P direction. However, in
other embodiments, the locking tab may be sized so as to
substantially prevent any A-P movement of the core member.
[0235] Now referring to FIG. 16, in some embodiments, the locking
tab further comprises an attachment portion 1001 extending from the
body of the tab and adapted to attach to a patient's vertebral
body. The attachment portion provides an opportunity for short term
fixation of the motion disc within the disc space.
[0236] In other embodiments, the means for limiting translation
comprises: [0237] a) a pin and slot arrangement (preferably spring
loaded) wherein the slot runs in the direction of the channel,
[0238] b) a sliding door disposed near the first opening, and
[0239] c) a hinged door disposed near the first opening.
[0240] In some embodiments, the means for limiting translation
comprises a third component shaped to be inserted into the channel
from the direction of the inner surface of the endplate.
[0241] Now referring to FIG. 15, in some embodiments, the tab is
provided with an inner surface 81 adapted to mate with the outer
surface of the core member. In preferred embodiments, the inner
surface of the tab is concave and substantially hemispherical.
[0242] In some embodiments, the inner surface of the tab can be
further shaped so as to provide substantial translational motion.
Now referring to FIG. 17, the tab 601 comprises an inner surface
having an elongated portion 603 and a hemispherical portion 605,
wherein the elongated portion allows for substantial translation of
the core 607 therein. In this case, the channel 609 formed within
the inner surface of the endplate 611 can be relatively short. In
other embodiments, the channel formed within the inner surface of
the endplate can be simply a back wall. The tab of this embodiment
can be affixed to the endplate by any conventional means.
[0243] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0244] a) a first prosthetic vertebral endplate comprising: [0245]
i) an outer surface adapted to be attached to a first vertebral
body, and [0246] ii) an inner surface comprising: [0247] a first
articulation surface, and [0248] a raised portion extending from
the inner surface substantially adjacent the first articulation
surface and having first and second ends, and
[0249] b) a removable tab having first and second ends,
wherein the tab is attached to the endplate and oriented so that
the first end of the raised portion is substantially adjacent the
first end of the tab, and the second end of the raised portion is
substantially adjacent the second end of the tab to form an
enclosure which substantially encloses the first articulation
surface.
[0250] Now referring to FIG. 18, in some embodiments, the
translation surface of the retaining channel is disposed below the
level of peripheral surface 115 of the prosthetic vertebral
endplate. In this case, the interior portion of the outer surface
of the endplate forms a keel to promote the initial and long-term
stability of the device, and the translation surface 123 of the
retaining channel is contained within the keel. In addition, this
embodiment allows the translation surface of the core member to
contact the translation surface 123 of the endplate at a much lower
location. Therefore, either the overall height of the device could
be reduced (thereby allowing for easier insertion of the core
member) or the height of the core member could be increased (to
provide increased strength). In addition, the large surface area of
the keel could be porous coated to promote bony ingrowth.
[0251] Therefore, in accordance with the present invention, there
is provided a prosthetic vertebral endplate 111 comprising: [0252]
i) an outer surface 113 having a peripheral portion 115 and an
interior portion 117, each portion being adapted to be attached to
a vertebral body, and [0253] ii) an inner surface 119 comprising an
opening 120 forming a channel 121 defining a channel depth
DE.sub.CH, wherein the peripheral portions of the inner and outer
surfaces define a peripheral depth DE.sub.P, and wherein the
channel depth is at least 80% of (and preferably is at least as
great as) the peripheral depth.
[0254] Also in accordance with the present invention, there is
provided prosthetic vertebral endplate comprising: [0255] i) an
outer surface having: [0256] a) a peripheral portion adapted to
mate with a vertebral body, and [0257] b) and an interior portion
forming a keel having a width, [0258] ii) an inner surface
comprising an opening forming a channel having a width, wherein the
keel width is greater than the channel width.
[0259] In this condition, the keel is wide enough to accommodate at
least a portion of the channel and therefore at least a portion of
the core member. When the keel can accommodate the core member, the
overall height of the device may be advantageously decreased.
[0260] Whereas the embodiments of the present invention disclosed
thus far each possess an open-ended channel having a pair of side
walls for limiting the medial-lateral translation motion of the
core member, other embodiments of the present invention possess
other means for limiting the medial-lateral translation motion of
the core member while allowing easy A-P insertion of the core
member.
[0261] Now referring to FIG. 19, there is provided an endplate 1201
having an inner surface 1203 and a projection 1205 extending
therefrom. The projection runs from the anterior wall 1207 to the
posterior wall 1209 of the endplate. Core member 1211 has a recess
1213 having a shape that mates with the projection 1205. Sidewalls
1215 and 1217 of the projection limit the lateral translation of
the core member. The articulation surface of the endplate may be
either the inner surface 1203 or the upper surface 1217 of the
projection.
[0262] Expulsion of the core member of this embodiment can be
prevented by any number of means. For example, after the core
member is slid upon the projection locking clips can be put in
place at either end of the projection. Alternatively, the upper
surface of the projection can comprise at least one flexible tab
that allows passage of the recess of the core member towards the
inner portion of the endplate, but prevents its passage back
out.
[0263] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0264] a) a first prosthetic vertebral endplate comprising: [0265]
i) an outer surface adapted to be attached to a first vertebral
body, and [0266] ii) an inner surface comprising a first
articulation surface, and [0267] iii) an elongated rail extending
from the inner surface,
[0268] b) a core member comprising: [0269] i) a first articulation
surface, and [0270] ii) an elongated slot for receiving the rail,
wherein the first articulation surface of the core member and the
first articulation surface of the first endplate are adapted to
form a first articulation interface, and the elongated rail is
received in the elongated slot.
[0271] Although the primary function of the guide rails on the
superior and inferior prosthetic endplates is to mate with
instrumentation during the surgical procedure, they are also
designed to accommodate the addition of optional device components.
For example, if the surgeon sought to render the device completely
immobile for the first few weeks immediately following
implantation, the surgeon could add a stabilizing component to the
device. For example, one possible geometry for such a stabilization
component would be a "U" shape that could be slid into place along
the guide rails. In the preferred embodiment, the stabilization
component could be made of a bioresorbable material that would
provide support for a few weeks after implantation and then resorb
and allow the device to restore motion to the spinal segment.
[0272] In other embodiments, the additional stabilization component
can transform the motion disc into a permanent spacer that prevents
motion. In this case, the component would likely be used by a
surgeon in a revision case. If the patient continued to experience
pain or other problems after the implantation of the artificial
disc replacement device, then the surgeon may feel that it would be
best to reoperate and substantially eliminate motion from the
spinal segment. Since the removal of implants is often problematic,
the stabilization component would provide a much-desired
alternative. Rather than removing the artificial disc replacement
device, the surgeon could simply slide the stabilization member
into place and essentially convert the motion disc into a
spacer.
[0273] Therefore, in accordance with the present invention, there
is provided intervertebral spacer, comprising: [0274] a) a first
motion segment comprising: [0275] i) an outer surface adapted to
mate with a first vertebral body, [0276] ii) an inner surface
comprising a motion surface, and [0277] iii) a body portion
therebetween having an anterior portion and a posterior portion,
[0278] and [0279] b) a second motion segment comprising: [0280] i)
an outer surface adapted to mate with a second vertebral body,
[0281] ii) an inner surface comprising a motion surface, and [0282]
iii) a body portion therebetween having an anterior portion and a
posterior portion, and [0283] c) a spacing component having a first
surface and an opposing second surface, wherein the motion surfaces
are adapted to form a motion interface, and wherein the spacing
component is disposed between the inner surfaces of the motion
segments to substantially prevent motion at the motion
interface.
[0284] In some embodiments, the spacing component is substantially
U-shaped. Preferably, the substantially U-shaped spacing component
has first and second end portions disposed substantially parallel
to each other. In some embodiments, the first end of the spacing
component is oriented substantially in the anterior-posterior
direction, while in others, the first end of the spacing component
is oriented at a substantial angle from the anterior-posterior
direction. Preferably, this spacing component is adapted to be
inserted from the anterior direction.
[0285] In some embodiments adapted to be inserted from the
posterior direction, the spacing component comprises first and
second independent bodies.
[0286] In some embodiments, the spacing component comprises a
biologic enhancement selected from the group consisting of
osteoinductive materials, osteoconductive materials, and osteogenic
materials.
[0287] In some embodiments, the spacing component comprises stem
cells.
[0288] The present invention is designed such that the implantation
of the device can be accomplished in a straightforward manner with
a minimum of distraction. The guides are designed such that the
superior and inferior prosthetic vertebral endplates can be placed
on an instrument that will hold them very close together without
allowing the articulation surfaces to touch. The prosthetic
vertebral endplates can then be inserted into the disc space in
this position. This allows the surgeon to insert these components
without having to significantly overdistract the disc space. The
instrument can then separate the prosthetic vertebral endplates and
securely force them against their respective natural vertebral
endplates. At this point, a sizing tool can be used to determine
the ideal height of the disc space and the appropriately sized core
member can be selected. The core member is then slid into place
within the retaining channel and the instrument is removed. The
surgeon can then perform a final check of the placement and sizing
of the device. If the surgeon is satisfied, the locking tab is
secured in place.
[0289] In preferred embodiments, the disc can be inserted modularly
into the disc space, wherein the endplates are first inserted
(either at the same time or consecutively) and then the core member
is inserted. Because the distance separating the endplates at the
periphery of the disc exceeds the height of a concave core member,
the core member may be inserted between the prosthetic endplates
without excessive overdistraction of the disc space.
[0290] Therefore, in accordance with the present invention, there
is provided a intervertebral motion disc comprising:
[0291] a) a first prosthetic vertebral endplate comprising: [0292]
i) an outer surface adapted to be attached to a first vertebral
body, [0293] ii) an inner surface comprising an inner portion and a
peripheral portion, [0294] wherein at least one of the portions
comprises a first articulation surface, and
[0295] b) a second prosthetic vertebral endplate comprising: [0296]
i) an outer surface adapted to be attached to a second vertebral
body, [0297] ii) an inner surface comprising an inner portion and a
peripheral portion, [0298] wherein at least one of the portions
comprises a first articulation surface,
[0299] c) a core member comprising: [0300] i) a first articulation
surface adapted for articulation with the first articulation
surface of the first endplate, and [0301] ii) a second articulation
surface adapted for articulation with the first articulation
surface of the second endplate, and
[0302] d) means for limiting the translation motion of the core
member,
wherein the core member is disposed between the endplates and
oriented therein to produce a first articulation interface between
the first articulation surface of the first endplate and the first
articulation surface of the core member, and a second articulation
interface between the first articulation surface of the second
endplate and the second articulation surface of the core member,
and a distance between the peripheral portions of the first and
second endplates, and wherein the distance between the peripheral
portions is greater than the height of the core member.
[0303] Because the motion disc of the present invention will
substantially mimic the motion of the natural interverterbal disc,
there may be times in which the spine hyperextends to create an
extreme lordotic posture. In these situations, the distance between
the anterior portions of the prosthetic vertebral endplates may
become unacceptably large. In order to limit the extent of lordotic
hyperextension, in some embodiments, a ligament is attached between
the anterior portions of the endplates.
[0304] Therefore, in accordance with the present invention, there
is provided an intervertebral motion disc comprising:
[0305] a) a first motion segment comprising: [0306] i) an outer
surface adapted to mate with a first vertebral body, [0307] ii) an
inner surface comprising a motion surface, and [0308] iii) a body
portion therebetween having an anterior portion and a posterior
portion,
[0309] b) a second motion segment comprising: [0310] i) an outer
surface adapted to mate with a second vertebral body, [0311] ii) an
inner surface comprising a motion surface, and [0312] iii) a body
portion therebetween having an anterior portion and a posterior
portion, and
[0313] c) a ligament having a first end and a second end,
wherein the motion surfaces are adapted to form a motion interface,
and wherein the first end of the ligament is connected to the
anterior portion of the first motion segment and the second end of
the ligament is connected to the anterior portion of the second
motion segment.
[0314] Preferably, the ligament comprises a biocompatible flexible
material. More preferably, the biocompatible flexible material is
selected from the group consisting of: [0315] i) a polyester fiber
weave, [0316] ii) an elastic material (such as silicon,
polyurethane, and natural rubber), [0317] iii) a polyvinyl
material, and [0318] iv) a biological material capable of forming a
scaffold for natural regeneration of a resected ligament, such as
small intestinal submucosa SIS.
[0319] Although the present invention has been described with
reference to its preferred embodiments, those skillful in the art
will recognize changes that may be made in form and structure which
do not depart from the spirit of the invention.
[0320] For example, any of the devices disclosed in the FIGS. may
be rotated 180 degrees such that the inferior and superior
endplates swap places. In addition, the articulation surfaces of
the core member could be made either concave or convex. For
example, FIG. 20 provides one such alternative embodiment wherein
the core member has a convex articulation surface. Moreover,
additional components could be added to the device to enhance the
design such as screws through the endplates to provide for improved
fixation as shown in FIG. 25.
[0321] Now referring to FIGS. 21a and 21b, there is provided an
alternative embodiment of the present invention. The intervertebral
motion disc of FIG. 21 is substantially similar to the motion disc
of FIG. 1, with the following modifications:
[0322] First, the relative size of the core member in FIGS. 21a and
21b is substantially larger than that of the core member in FIG. 1
and is preferably made of a polymeric material such as
polyethylene.
[0323] Second, the second articulation interface formed by the core
member and the upper endplate is slightly curved and
hemicylindrical. The slight curve of the hemicylinder is oriented
in the A-P direction (as shown in FIG. 21b), while the linear
dimension thereof is oriented in the M-L direction (as shown in
FIG. 21a). The articulation interfaces are oriented in the same
direction.
[0324] Now referring to FIGS. 22a and 22b, there is provided a
motion disc substantially similar to that shown in FIGS. 21a and
21b, except that the slight curve of the hemicylinder is oriented
in the M-L direction (as shown in FIG. 22a), while the linear
dimension thereof is oriented in the A-P direction (as shown in
FIG. 22b).
[0325] Now referring to FIG. 23, there is provided an endplate for
a motion disc wherein the sidewall of the endplate comprises a
third opening 301 in communication with the first opening in the
sidewall and the second opening in the inner surface, so that the
channel formed thereby is substantially open at each of its ends. A
small lip 305 rises from the bottom surface of the posterior end of
the channel and functions to keep the core from sliding out the
posterior end of the channel.
[0326] Now referring to FIG. 24, there is provided another
embodiment of the present invention in which the means comprises a
locking tab comprising first and second arms, the endplate further
comprises first and second lateral wall portions comprising first
and second respective recesses, wherein the first arm is shaped to
be secured to the endplate in the first recess, and the second arm
is shaped to be secured to the endplate in the second recess. In
this FIG., the tab is secured in place.
[0327] Now referring to FIG. 25, there is provided another
embodiment of the present invention in which one endplate is
adapted to receive a screw for fixation to an adjacent vertebra. In
this FIG., the screw is received within the through-hole.
[0328] Now referring to FIGS. 26a and 26b, there is provided an
alternative embodiment of the present invention. The intervertebral
motion disc of FIGS. 26a and b is substantially similar to the
motion discs described above, with the following modifications:
First, the endplate fins are now located more laterally on the
outer surfaces of the prosthetic endplates in order to better
resist lateral migration. Second, a more substantial radius has
been provided on the posterior edges of the outer surfaces of the
prosthetic endplates in order to provide a better anatomical fit
with the natural endplate. Third, the core material is made of a
standard, non-cross-linked ultrahigh molecular weight polyethylene.
In addition, the core component may include tantalum markers for
x-ray visualization. Fourth, the prosthetic endplates are made of a
standard CoCr material. Fifth, the central portions of the outer
surfaces of the prosthetic endplates each have a recessed portion
for providing a better fixation. In other embodiments, the central
recessed portion is removed and the entire outer surfaces of the
endplates are coated with an HA-based coating.
[0329] FIG. 27 discloses an isometric view of a superior endplate
of the present invention having a pair of notches on its inner
surface for mating with an insertion instrument.
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