U.S. patent application number 11/668577 was filed with the patent office on 2007-07-12 for concentric interior insert ball and dual socket joint.
Invention is credited to Robert L. Diaz, Robert Doubler, John Hammill.
Application Number | 20070162133 11/668577 |
Document ID | / |
Family ID | 39739236 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070162133 |
Kind Code |
A1 |
Doubler; Robert ; et
al. |
July 12, 2007 |
CONCENTRIC INTERIOR INSERT BALL AND DUAL SOCKET JOINT
Abstract
A constrained spinal implant is inserted between adjacent
vertebrae to function as an disk prosthesis. The prosthesis has two
plates fastened to adjacent vertebrae facing each other. The facing
sides of the plates each have a depending skirt formed as
concentric arcs of about 90 degrees. The skirts are either bowed or
tapered in the axial direction. Depressions are centrally located
between the arcs of the plates and a ball is universally movable in
the depressions.
Inventors: |
Doubler; Robert; (Ida,
MI) ; Hammill; John; (Rossford, OH) ; Diaz;
Robert L.; (Palm Beach Gradens, FL) |
Correspondence
Address: |
MCHALE & SLAVIN, P.A.
2855 PGA BLVD
PALM BEACH GARDENS
FL
33410
US
|
Family ID: |
39739236 |
Appl. No.: |
11/668577 |
Filed: |
January 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11207683 |
Aug 18, 2005 |
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11668577 |
Jan 30, 2007 |
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11060206 |
Feb 15, 2005 |
7195644 |
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11207683 |
Aug 18, 2005 |
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11025656 |
Dec 28, 2004 |
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11060206 |
Feb 15, 2005 |
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10793433 |
Mar 3, 2004 |
7083651 |
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11025656 |
Dec 28, 2004 |
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10792399 |
Mar 2, 2004 |
7115144 |
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10793433 |
Mar 3, 2004 |
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Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2220/0058 20130101;
A61F 2002/30563 20130101; A61F 2002/30663 20130101; A61F 2002/30014
20130101; A61F 2310/00029 20130101; A61F 2310/00592 20130101; A61F
2220/0033 20130101; A61F 2002/443 20130101; A61F 2/4425 20130101;
A61F 2220/0025 20130101; A61F 2002/30331 20130101; A61F 2002/30841
20130101; A61F 2310/00317 20130101; A61F 2002/30451 20130101; A61F
2220/0075 20130101; A61F 2310/00395 20130101; A61F 2002/30462
20130101; A61F 2310/00203 20130101; A61F 2002/30649 20130101; A61F
2002/30574 20130101; A61F 2002/30662 20130101; A61F 2002/3097
20130101; A61F 2002/30495 20130101; A61F 2310/00017 20130101; A61F
2002/30242 20130101; A61F 2002/30616 20130101; A61F 2002/30578
20130101; A61F 2250/0018 20130101; A61F 2002/30426 20130101; A61F
2230/0071 20130101; A61F 2/30742 20130101; A61F 2/4611 20130101;
A61F 2002/30904 20130101; A61F 2310/00023 20130101; A61F 2310/00281
20130101 |
Class at
Publication: |
623/017.11 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. A constrained spinal implant for placement between adjacent
vertebrae to replace disk material comprising a first plate and a
second plate adapted to interlock about a central axis, said first
plate having a substantially planar vertebrae engaging side and a
disk side, a first skirt on said disk side extending approximately
normal to said plate, said first skirt formed to include opposing
spherical bearing surfaces on an inner surface thereof, a first
depression along said central axis of said disk side of said plate
centrally located between said opposing spherical bearing surfaces,
said second plate having a second planar vertebrae engaging side
and a second disk side, a second skirt on said second disk side
extending approximately normal to said second plate, said second
skirt formed to include opposing spherical bearing surfaces on an
outer surface thereof, a second depression along said central axis
of said second disk side of said second plate centrally located
between said opposing spherical bearing surfaces and a universally
rotatable ball captured in said depressions; whereby said
substantially planar vertebrae engaging side of said first plate is
adapted to contact a vertebrae and said substantially planar
vertebrae engaging side of said second plate is adapted to contact
an adjacent vertebrae with said depressions each adapted to form a
bearing surface for said ball along said central axis and whereby
said first and second skirts are interlocked forming a universal
joint and shaped to limit lateral, flexion and extension
motion.
2. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said first skirt and said second skirt
are concentric in a plane substantially parallel with said first
and second plates.
3. The constrained spinal implant for placement between adjacent
vertebrae of claim 2 wherein said spherical bearing surfaces on
said first and said second plates are constructed and arranged to
couple said first plate to said second plate for universal movement
therebetween.
4. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said opposed spherical bearing
surfaces of said first skirt are adapted to contact said opposed
spherical bearing surfaces of said second skirt.
5. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said opposed spherical bearing
surfaces of said first skirt and said second skirt each extend
approximately 90 degrees along the perimeter of said first and said
second skirts respectively.
6. The constrained spinal implant for placement between adjacent
vertebrae of claim 2 wherein said first skirt and said second skirt
are concentric in a plane parallel with said first and second
plates, said opposed spherical bearing surfaces of said first
interrupted skirt adapted to contact said opposed spherical bearing
surfaces of said second interrupted skirt to form an interlocked
universally movable outer ball and socket.
7. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said first plate includes a central
bore, a sleeve slidably secured in said bore, said first depression
formed in said sleeve.
8. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said opposed spherical bearing
surfaces of said first interrupted skirt and said opposed spherical
bearing surfaces of said second interrupted skirt are concentric
segments of a sphere whereby said concentric bearing segments of
said first skirt are adapted to contact said concentric segments of
said second skirt to form an interlocked universal joint.
9. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said first plate includes a cavity
between said depression and said vertebrae side, an O-ring spring
secured in said cavity, said ball adapted to flex said O-ring
spring resulting in resilient compression.
10. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein said second plate includes a cavity
between said second depression and said vertebrae side, an O-ring
spring secured in said cavity, said ball adapted to flex said
O-ring spring resulting in resilient compression.
11. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein a plurality of first plates of
different sizes, a plurality of balls of different sizes and a
plurality of second plates of different sizes comprise a kit
whereby a proper sized constrained spinal implant can be selected
from said kit.
12. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein an elastic membrane extends between
said first plate and said second plate about the periphery of said
first plate and said second plate.
13. The constrained spinal implant for placement between adjacent
vertebrae of claim 12 wherein said elastic membrane is continuous
and a viscous polymeric composition is located within said
membrane.
14. The constrained spinal implant for placement between adjacent
vertebrae of claim 1 wherein at least one of said vertebrae
engaging side or said second vertebrae engaging side includes a
plurality of spikes for engaging vertebrae.
15. A drive tool for positioning a constrained spinal implant
between adjacent vertebrae comprising an elongated shaft having a
first end conforming to a superior endplate of a constrained spinal
implant and a second end forming a handle with an impact tip,
whereby said spinal implant is positioned within said first end
with said handle available to align said implant with said impact
tip available for receipt of mallet impact to allow a forced
placement of the implant between the vertebrae.
16. The drive tool for positioning a constrained spinal implant
according to claim 15 wherein said first end is C-shaped having an
upper surface and a lower surface sized to fit between an upper
plate and a lower plate of said spinal implant with said C-shape
engaging said endplate.
17. A method of assembling a constrained spinal implant comprising
the steps of: a) providing a first plate, said first plate having a
planar vertebrae engaging side and a disk side, a first shaped
skirt on said disk side extending approximately normal to said
plate, said skirt formed to include opposing spherical bearing
surfaces, a depression in said disk side of said plate centrally
located between said opposing spherical bearing surfaces, b)
providing a second plate having a second planar vertebrae engaging
side and a second disk side, a second shaped skirt on said second
disk side extending approximately normal to said second plate, said
second skirt formed to include opposing separated spherical bearing
surfaces, a second depression in said second disk side of said
second plate centrally located between said opposing arcs, c)
providing a ball and placing said ball in said depression, d)
orienting said first plate and said second plate parallel with each
other and rotated about ninety degrees with respect to said second
plate, e) moving said first plate closer to said second plate to
engage said ball into said depression and said second depression in
axial alignment, and f) rotating said first plate with respect to
said second plate about a central axis until said spherical bearing
surfaces of said first plate interlock with said opposing spherical
bearing surfaces of said second plate to form a universally
moveable connection therebetween.
18. The method of assembling a constrained spinal implant according
to claim 17 wherein said shaped skirt is contoured to provide a
predetermined lateral bending of said first plate with respect to
said second plate.
19. The method of assembling a constrained spinal implant according
to claim 17 wherein said shaped skirt is contoured to provide a
predetermined flexion bending of said first plate with respect to
said second plate.
20. The method of assembling a constrained spinal implant according
to claim 17 wherein said shaped skirt is contoured to provide a
predetermined extension bending of said first plate with respect to
said second plate.
21. A constrained spinal implant for placement between adjacent
vertebrae to replace disk material comprising; a first plate having
a first substantially planar vertebrae engaging side and a disk
side, a first continuous skirt on said disk side extending
approximately normal to said plate, said first skirt formed to
include substantially opposing spherical bearing surfaces on an
inner surface thereof, a spherical depression formed along said
central axis of said disk side of said plate centrally located
between said opposing spherical bearing surfaces; a second plate
having a second substantially planar vertebrae engaging side and a
second disk side, a second skirt on said second disk side extending
approximately normal to said second plate, said second skirt formed
to include opposing spherical bearing surfaces on an outer surface
thereof, a second spherical depression along said central axis of
said second disk side of said second plate centrally located
between said opposing spherical bearing surfaces, and a universally
rotatable ball captured in said depressions, said ball and said
spherical depressions defining an inner universally moveable ball
and socket, said spherical bearing surfaces of said first and said
second skirt interlocking to define a universally movable outer
ball and socket.
22. The constrained spinal implant for placement between adjacent
vertebrae of claim 21 wherein at least one of said first or second
skirts is shaped to limit lateral, flexion and extension
motion.
23. The constrained spinal implant for placement between adjacent
vertebrae of claim 21 wherein said inner ball and socket and said
outer ball and socket both pivot about the same central point.
24. The constrained spinal implant for placement between adjacent
vertebrae of claim 21 wherein said inner ball and socket is
constructed and arranged to be compressible.
25. The constrained spinal implant for placement between adjacent
vertebrae of claim 21 wherein said outer ball and socket is
constructed and arranged to prevent axial separation of said first
and said second plates.
Description
RELATED APPLICATIONS
[0001] This application is continuation in part of U.S patent
application Ser. No. 11/207,683 filed Aug. 18, 2005 which is a
continuation in part of U.S. patent application Ser. No. 11/060,206
filed Feb. 15, 2005 which is a continuation-in-part of a U.S.
patent application Ser. No. 11/025,656, filed Dec. 28, 2004 which
is a continuation-in-part of U.S. application Ser. No. 10/793,433
now 7,083,651 which is a continuation-in-part of U.S. application
Ser. No. 10/792,399 now U.S. Pat. No. 7,115,144; the contents of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to orthopedic surgery and, in
particular, constrained spinal implants for replacement of ruptured
or excised spinal disks.
BACKGROUND OF THE INVENTION
[0003] Several attempts have been made to design a spinal
prosthesis for replacement of missing or excised disk material that
replicates the functions of the missing tissue. U.S. Pat. No.
4,759,769 to Hedman et al discloses an artificial disk device in
which two plates are attached to the adjacent vertebrae by bone
screws inserted through flanges on the plates. A spring biasing
mechanism is captured between the plates to simulate the actions of
the natural disk material. U.S. Pat. No. 5,246,458 to Graham and
U.S. Pat. No. 6,228,118 to Gordon disclose other intervertebral
implants with spherical flanges used to connect the device to
adjacent vertebra. Graham also teaches a resilient structure.
[0004] The patents to Marnay, U.S. Pat. No. 5,314,477, Buttner-Janz
et al, U.S. Pat. No. 5,401,269, Yuan et al, U.S. Pat. No.
5,676,701, and Shelokov, U.S. Pat. No. 6,039,763, all are directed
to the design of the opposing faces of the adjacent plates of an
implant to provide a limited universal joint to simulate the
natural movement of the spine.
[0005] U.S. Pat. No. 5,683,465 to Shinn et al teaches two plates
with bow shaped skirts which are interlocked.
SUMMARY OF THE PRESENT INVENTION
[0006] The invention is directed to a constrained spinal implant
for insertion between adjacent vertebrae to function as a disk
prosthesis. The prosthesis is formed from two plates fastened to
adjacent vertebrae facing each other. The facing sides of the
plates have an interacting, depending skirt. The skirts are range
limiting wherein the skirt on a superior endplate can be shaped to
limit lateral, flexion and extension motion.
[0007] A depression is centrally located between the arcs of both
plates. A sphere or ball is placed in the central depression of one
of the plates. The plates are oriented to each other at 90 degrees
and the ball is engaged in the depression of the other plate. The
plates are then rotated about 90 degrees and the skirt of one plate
interlocks with an opposed arcs of the other plate to prevent
separation in the axial direction.
[0008] Therefore, it is an objective of this invention to provide a
constrained spinal implant for axial support of the spinal column
which replicates the dimensions and function of an intervertebral
disk.
[0009] It is another objective of this invention to provide a kit
including all the components for assembly and surgical placement of
an artificial spinal disk.
[0010] It is a further objective of this invention to provide a
method of assembly of the components of the kit which results in an
axially interlocked constrained spinal implant. Specifically, one
plate forms a receptacle for a dynamic socket to be inserted and
fixed in place internally.
[0011] It is yet another objective of this invention to provide a
ball and socket joint between two plates attached to adjacent
vertebrae permitting axial rotation, lateral bending, vertical
tilting and axial compression.
[0012] It is a still further objective of this invention to provide
shaped interrupted skirts on two plates which act as stop limits
for tilting and bending.
[0013] It is another objective of this invention is to provide an
axially resilient ball and socket joint, compressive load bearing
poly-axial motion joint.
[0014] It is another objective of this invention is to provide use
of a true roller-ball bearing which reduces radial friction forces
and the entire spherical ball surface area can be utilized for low
wear characteristics.
[0015] Still another objective of this invention is to provide the
use of an endplate that can be shaped to limit lateral, flexion and
extension motion.
[0016] Still another objective of this invention is to provide a
constrained construct implant.
[0017] Still another objective of this invention is to provide an
inserter instrument.
[0018] Other objectives and advantages of this invention will
become apparent from the following description taken in conjunction
with the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include
exemplary embodiments of the present invention and illustrate
various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a perspective view of the concentric spinal disc
of this invention;
[0020] FIG. 2 is a front plane view of the embodiment shown in FIG.
1;
[0021] FIG. 3 is a front plane view illustrating a 10 degree
lateral movement;
[0022] FIG. 4 is a side view illustrating a 10 degree flexion;
[0023] FIG. 5 is a side view illustrating a 15 degree
extension;
[0024] FIG. 5A is a side view illustrating a 75% component
lateral/extension position with 5 degrees of axial rotation;
[0025] FIG. 6 is a partial exploded view depicting the superior
endplate separated from the inferior endplate;
[0026] FIG. 7 is a fully exploded view depicting the superior
endplate separated from the inferior endplate and a ball seat and
retainer ring separated from the endplates;
[0027] FIG. 8 is a cross sectional side view of the concentric
spinal disc;
[0028] FIG. 9A is a perspective view of the inner surface of the
superior endplate;
[0029] FIG. 9B is a perspective view of the inner surface of the
inferior endplate;
[0030] FIG. 9C is a top view illustrating the inferior endplate and
superior endplate in a pre-coupled orientation;
[0031] FIG. 9D is a front plant view illustrating the endplates
coupled together;
[0032] FIG. 10 is a perspective view of the inner surface of the
superior endplate depicting the range limiting surface;
[0033] FIG. 11 is a cross sectional side view of the concentric
spinal disc having an embodiment with a axial compression
o-rings;
[0034] FIG. 12 is a side view having an embodiment with tapered
endplates;
[0035] FIG. 13 is a perspective view of the inserter
instrument;
[0036] FIG. 14 is an enlarged view of the tip of the inserter
instrument depicted in FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Referring to the Figures, the constrained spinal implant 10,
shown in FIG. 1, has an upper plate 11, a lower plate 12 pivotable
on a universally rotatable sphere or ball 50. The upper plate 11
and the lower plate 12 form a cage when assembled with the ball 50
captured for universal movement within the interior of the cage to
define an inner ball and socket 86. Of course, the position of the
plates can be reversed, in use. Both upper plate 11 and lower plate
12 have a plan form substantially the size and shape of the end
wall of the vertebra between which the implant will be placed to
produce the maximum area of contact between the implant and the
vertebra for stability and support. Obviously, different sized
plates are necessary because of the difference in size of vertebra
within regions of the spinal column and the different sizes or ages
of patients. The concentric spinal disc can be sized as a cervical
disc, a thoracic disc, or a lumbar disc.
[0038] The upper plate 11 has a planar surface 14 for contact with
the end wall of a vertebra and an opposite disk surface 15.
Depending from the disk surface is a continuous skirt 16 with
opposed internal spherical bearing surfaces 17 and 18. The
spherical bearing surfaces are approximately 180 degrees apart at
their centers and extend about 90 degrees around the continuous
skirt. However, it should be noted that smaller or larger spherical
bearing surfaces spaced to provide axial guidance and load bearing
may be utilized without departing from the scope of the invention.
In the preferred embodiment, the diameter of the arcs is less than
the periphery of the plate 11 leaving a horizontal flange 19.
Centrally located within the spherical bearing surfaces formed
within the continuous skirt is a receptacle 13. A sleeve 51 is
inserted in the receptacle 13 and telescopes in the plate 11. The
sleeve 51 has a spherical depression 52.
[0039] The lower plate 12 has a planar surface 20 for contact with
the end wall of a vertebra and an opposite disk surface 21.
Upstanding from the disk surface is an continuous skirt 22 with
opposed external spherical bearing surfaces 23 and 24. The
spherical bearing surfaces are approximately 180 degrees apart at
their centers and extend about 90 degrees around the skirt.
However, it should be noted that smaller or larger spherical
bearing surfaces spaced to provide axial guidance and load bearing
may be utilized without departing from the scope of the invention.
The diameter of the arcs is less than the periphery of the plate 12
leaving a horizontal flange 25. Centrally located within the
semi-circular arcs is a receptacle 26. A sleeve 53 is inserted in
the receptacle and reciprocates in the plate 12. The sleeve 53 has
a depression 54 that is rounded and shaped to closely mirror the
contours of the depression 52. The depressions 52 and 54, as well
as the diameter of the ball 50, are of such dimensions construction
to provide bearing surfaces suitable to support the weight of the
spinal column.
[0040] As shown, though the relationship could be reversed, the
opposed spherical bearing surfaces 17 and 18 of the depending skirt
16 are concentric with the opposed spherical bearing surfaces 23
and 24 of the upstanding skirt and of larger diameter allowing
rotation of the plates relative to each other with surface contact
between the outer spherical bearing surface(s) of the upstanding
skirt and the inner bearing surface(s) 29 of the depending skirt to
define an outer ball and socket 85.
[0041] The constrained spinal implant provides support and range of
motion similar to the natural joint in that the plates 11 and 12
may rotate axially limited by natural anatomical structures, such
as tendons, ligaments and muscles. To simulate the compression of
the natural disk during normal activities, such as walking, an
alternative embodiment as shown in FIG. 11 may include a spring
mechanism o-ring 60, 61 placed in the vertical axis of the plates
11 and 12. The springs are resiliently compressible.
[0042] In the manufacturing step, the o-ring 61 is inserted and
covered by the sleeve 53. A retainer ring 58 is placed between the
upper circumference of the sleeve 53 and is preferably laser welded
to the plate. Other suitable permanent attachment methods well
known in the art may also be used without departing from the scope
of the invention. Similarly, an o-ring 60 may be used in the upper
plate 11 with the sleeve 51 inserted and held in position by a
retainer ring 55, the retainer ring can then be laser welded to the
plate or other permanent attachment methods may be used. By
absorbing some of the longitudinal loads, the prosthesis lessens
the stresses on the adjacent natural disks. Further, during
placement of the prosthesis, the springs may be compressed to
lessen the overall height of the prosthesis.
[0043] The spine may bend laterally and tilt medially in
flexion/extension in a range comparable to the normal range of
motion. The implant of the instant invention provides limitation of
these movements through interaction of the depending skirt and the
upstanding skirt. As shown in FIGS. 9a-9d, the components of the
implant are connected together by orienting the spherical bearing
surfaces 17-18 and 23-24 at about 90 degrees relative to each
other. This action allows the skirts to be vertically overlapped.
In a pre-couple orientation, the ball 50 is placed in the inferior
endplate 12 and the superior endplate 11 is placed over the ball
and then the plates 11 & 12 are rotated through 90 degrees
relative to each other. This rotation aligns the depending opposed
spherical bearing surface(s) with the upstanding opposed spherical
bearing surface(s) and interlocks the plates in a movable joint
that cannot be separated axially. The inner surface 28 of the
continuous skirt 16 slidably contacts the outer surface 29 of the
skirt 22. The contacting bearing surfaces are spherical or bowed,
from the plate at least to the height of the diameter of the ball
50, forming another ball and socket joint with the bottom edge of
the depending arc 23 of a larger diameter than the top edge of the
upstanding arc 17 by which the plates are interlocked. Of course,
the remainder of the inner and outer surfaces of the skirts may be
straight or tapered and spaced apart to allow for bending and
tilting. As shown in FIG. 2 the inferior endplate 12 and the
superior endplate 11 are interlocked and FIG. 3 depicting the
lateral movement of the superior endplate 11 in a range of
.+-.10.degree.. FIG. 4 depicts the inferior endplate in a flexion
of about 10.degree. and FIG. 5 depicts the inferior endplate in an
extension position of about 15.degree.. These ranges are only to be
considered as illustrative, the skirts can be ground to a
particular geometry to meet a particular patient needs. FIG. 10
illustrates the range limiting surface 17 that can be contoured to
limit the lateral, flexion and extension motion for the superior
endplate 11.
[0044] In the preferred embodiment, fastening to the vertebra can
be enhanced by the use of spikes 34 attached or formed on flanges
19 and 25 which are to be driven into the end walls of the adjacent
vertebra.
[0045] Alternatively, or in conjunction with spikes, each of
flanges 19 and 25 of the constrained spinal implant may include a
vertical extension, not shown, which cooperate with bone screws to
mount the constrained spinal implant on the vertebra. The vertical
extension is illustrated in the inventors prior application(s)
which are incorporated by reference. The vertical extensions can be
on opposite lateral sides of the flanges 19 and 25 permitting
fastening of each plate on the opposite side of adjacent vertebrae.
The fasteners may be used together, e.g., the spikes may be on one
plate and the vertical extensions on the other plate of the same
constrained spinal implant.
[0046] The components are made from materials that are suitable for
implantation in the living body and have the requisite strength to
perform the described functions without deformation, e.g., the
opposed bearing surfaces of the depressions and ball may be made of
metal or ceramic or a suitable combination thereof, respectively,
the ceramic material is implant grade alumina ceramic or a silicon
nitride or carbide and the metal may be a nitrogen alloyed chromium
stainless steel or cobalt chrome alloy, or titanium, and alloys of
each, coated metals, ceramics, ceramic coatings, and polymer
coatings.
[0047] The plates may be made entirely of cobalt chrome alloy or
only the inserts. In the high wear areas, such as the depressions,
coatings or inserts may be used to prevent galling and permit
repair. In this modular concept, the end plates may be titanium,
titanium alloy, or stainless steel among other materials as
discussed above.
[0048] The prosthetic ball 50 is preferably made from an implant
grade alumina ceramic or a silicon nitride or silicon carbide
material. The ball 50 may be formed entirely of the ceramic
material or a ceramic coating on another matrix. The alumina
ceramic or silicon nitride or silicon carbide material can be
manufactured by isostatic pressing or any other suitable method
well known in the art. The ball 50 is then machined to shape and
the surface polished to a mirror-like finish. The ceramic ball is
completely corrosion resistant and is non-abrasive. The solid
matrix eliminates the wear particles, such as those liberated from
metal, other coated metals and polyethylene implants. The ball 50
has excellent thermal conductivity thereby reducing patient
discomfort associated with exposure to cold weather. Further, the
alumina ceramic or silicon nitride implant will react well with
x-ray and MRI (magnetic resonance imaging) diagnostic
procedures.
[0049] The kit contains plates with protrusions and skirts of
varying lengths to allow selection of components for an implant
with the axial dimension substantially the same as the thickness of
the disk the implant will replace. The kit may also contain upper
and lower plate components of varying sizes. FIG. 12 illustrates
the implant 10 having tapered endplates 11 and 12 that can be used
for ease of insertion. Further, the implant can be assembled by a
surgeon in the operating room allowing for modular endplate
selection to make-up for custom disc construct. Modular endplates
would allow control over disc-space height and enable a better
match of the kyphotic/lordotic endplate angles.
[0050] Referring now to FIG. 13, the use of the instant implant
provides for a constrained construct when the plates are coupled
together. In addition to coupling the plates together, the outer
ball and socket construction prevents migration of the plates in
relation to each other. The face of each endplate may include a
radial surface positioned in relation to the ball bearing
centerline. Insertion of the instant invention may be aided by a
drive tool 80 having a handle 82 and a implant holder 84 formed
from a rigid shank. The implant holder 84 allows for impacting
forces to be on the endplate faces 19 and 25, thereby eliminating
an impact on the outer skirt 16. In this manner, both endplates are
manipulated as a single unit. In use, the implant holder 84 is
positioned along the first end and conforms to the superior
endplate of a constrained spinal implant by use of a C-shaped end
with an upper surface 21 and a lower surface 23 sized to fit
between the upper plate and lower plate of the spinal implant. The
second end forming a handle 82 with an impact tip 83. The spinal
implant is positioned within the first end 84 with the handle
available to align the spinal implant. The impact tip available for
receipt of mallet impact to allow a forced placement of the implant
between the vertebrae.
[0051] A number of embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, it is to be understood that
the invention is not to be limited by the specific illustrated
embodiment but only by the scope of the appended claims.
* * * * *