U.S. patent application number 11/841779 was filed with the patent office on 2008-03-13 for artificial spinal disk.
Invention is credited to Neville Alleyne, James R. Gerchow, Makoto Nonaka, Philip James Sluder.
Application Number | 20080065220 11/841779 |
Document ID | / |
Family ID | 33436737 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080065220 |
Kind Code |
A1 |
Alleyne; Neville ; et
al. |
March 13, 2008 |
ARTIFICIAL SPINAL DISK
Abstract
An artificial spinal disk comprises a central capsule that is
configured to slide laterally within the disk space with one or
more of flexion, extension, and lateral bending of the spine so as
to shift an instantaneous center of rotation of the artificial
disk. In one embodiment, the invention comprises an artificial
spinal disk comprising a first plate having an inwardly directed
surface, a second plate having an inwardly directed surface facing
generally toward the inwardly directed surface of the first plate,
and a central capsule with outwardly directed opposed faces that
slidably mate with the inwardly directed surfaces of the first and
second plates.
Inventors: |
Alleyne; Neville; (La Jolla,
CA) ; Gerchow; James R.; (Sturgis, MI) ;
Nonaka; Makoto; (La Jolla, CA) ; Sluder; Philip
James; (El Cajon, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
33436737 |
Appl. No.: |
11/841779 |
Filed: |
August 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10838515 |
May 3, 2004 |
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11841779 |
Aug 20, 2007 |
|
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60467655 |
May 2, 2003 |
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60513238 |
Oct 21, 2003 |
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Current U.S.
Class: |
623/17.16 ;
623/17.15 |
Current CPC
Class: |
A61F 2220/0025 20130101;
A61F 2/4405 20130101; A61F 2002/305 20130101; A61F 2220/0041
20130101; A61F 2310/00017 20130101; A61F 2002/30604 20130101; A61F
2002/30663 20130101; A61F 2002/443 20130101; A61F 2002/30383
20130101; A61F 2002/30579 20130101; A61F 2002/30433 20130101; A61F
2002/30492 20130101; A61F 2002/30517 20130101; A61F 2002/30369
20130101; A61F 2002/30365 20130101; A61F 2002/30662 20130101; A61F
2310/00023 20130101; A61F 2002/30884 20130101; A61F 2002/30133
20130101; A61F 2310/0058 20130101; A61F 2002/30507 20130101; A61F
2/4425 20130101; A61F 2/446 20130101; A61F 2002/30599 20130101;
A61F 2002/2835 20130101; A61F 2002/30685 20130101; A61F 2002/30387
20130101; A61F 2220/0033 20130101; A61F 2250/0063 20130101; A61F
2002/30495 20130101; A61F 2002/30841 20130101; A61F 2230/0015
20130101 |
Class at
Publication: |
623/017.16 ;
623/017.15 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1-6. (canceled)
7. An artificial spinal disk comprising: a first plate defining a
first curved surface; a first retainer disk affixed to said
pedestal having a contour substantially matched to said first
curved surface and held in spaced relation to said first curved
surface; a second plate defining a second curved surface; a second
retainer disk affixed to said second pedestal having a contour
substantially matched to said second curved surface and held in
spaced relation to said second curved surface; a first sliding disk
captured between said first retainer disk and said first curved
surface; a second sliding disk captured between said second
retainer disk and said second curved surface, wherein said second
sliding disk is coupled to said first sliding disk.
8. The artificial disk of claim 7, wherein said first and second
sliding disks are coupled along their respective edges.
9. The artificial disk of claim 8, wherein said first and second
sliding disks are coupled along their respective edges by a
clamp.
10-20. (canceled)
21. The artificial disk of claim 7, wherein said first and second
retainer disks and said first and second sliding disks comprise
surfaces coated with diamond like carbon.
22. The artificial disk of claim 7, wherein said first and second
plates comprise concave surfaces.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
10/838,515. This application claims priority under 35 U.S.C.
Section 119(e) to U.S. Provisional Applications 60/467,655 filed on
May 2, 2003 and 60/513,238 filed Oct. 21, 2003. The disclosures of
all of these applications are hereby incorporated by reference in
their entireties.
BACKGROUND OF THE INVENTION
[0002] A wide variety of artificial spinal disk designs have been
developed over the past several years. Some designs, such as those
described in U.S. Pat. Nos. 6,001,130 and 5,123,926 include
resilient plastic or fluid filled bag type structures that are
placed between adjacent vertebra. These designs provide
flexibility, but present the risk of rupture or breakage, and can
be difficult to contain effectively within the disk space. Other
designs have attempted to use ball-and socket type couplers between
endplates or other retaining devices attached to the vertebral
bodies. Currently, devices which use metal-metal interfaces rather
than resilient bodies are favored for their reliability and
strength. However, these types of couplings do a poor job of
imitating the natural relative movement of vertebral bodies
separated by a natural anatomical disk. Furthermore, this type of
replacement disk typically focuses all the forces from weight and
motion in a single direction and on a very small part of each
vertebral body. This can cause excessive stress on the bone in the
area where the artificial disk connects to the vertebral body.
Improved designs that reduce these problems are needed in the
art.
SUMMARY OF THE INVENTION
[0003] An artificial spinal disk comprises a central capsule that
is configured to slide laterally within the disk space with one or
more of flexion, extension, and lateral bending of the spine so as
to shift an instantaneous center of rotation of the artificial
disk. In one embodiment, the invention comprises an artificial
spinal disk comprising a first plate having an inwardly directed
surface, a second plate having an inwardly directed surface facing
generally toward the inwardly directed surface of the first plate,
and a central capsule with outwardly directed opposed faces that
slidably mate with the inwardly directed surfaces of the first and
second plates.
[0004] In another embodiment, an artificial spinal disk comprises a
plurality of separate pieces, wherein the separate pieces are
configured and sized to be placed in the disk space separate from
one another. The pieces comprise couplers such that the separate
pieces are attached to form a completed artificial disk only after
installation within the disk space. In one such embodiment, the
separate pieces of the artificial disk comprise at least first and
second bone plates and a central capsule.
[0005] Methods of spine surgery are also provided. In one
embodiment, a method of spine surgery comprises placing a first
portion of an artificial disk into a disk space; and
[0006] separately placing one or more additional portions of the
artificial disk into the disk space and mechanically coupling the
additional portions to one or more portions previously placed
inside the disk space so as to assemble a complete artificial disk
within the disk space from artificial disk pieces that are separate
outside of the disk space.
[0007] In another embodiment of the invention, a surgical kit for
spinal surgery comprises a first bone plate configured for
attachment to a first vertebral body;
[0008] a second bone plate configured for attachment to a second
vertebral body; and
[0009] a central capsule configured to couple to the first bone
plate and the second bone plate;
[0010] wherein the first bone plate, the second bone plate, and the
central capsule are uncoupled from one another to allow for
separate installation in a disk space during spine surgery. In some
embodiments, the first bone plate and the second bone plate
comprise a plurality of uncoupled segments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side view of a first embodiment of an artificial
spinal disk with a sliding capsule.
[0012] FIG. 2 is a side view of a second embodiment of an
artificial spinal disk with a sliding capsule.
[0013] FIG. 3 is a cross sectional view of a specific embodiment of
the sliding capsule design of FIG. 1.
[0014] FIG. 4 is an exploded view of the disk of FIG. 3.
[0015] FIG. 5 is a cross sectional view of a specific embodiment of
the sliding capsule design of FIG. 2.
[0016] FIG. 6 is a perspective view of a multi-piece bone plate for
coupling the sliding capsules to upper and lower vertebral
bodies.
[0017] FIGS. 7A and 7B are top and side views of a specific
embodiment of a bottom bone plate.
[0018] FIGS. 8A and 8B are top and side views of a specific
embodiment of a top bone plate.
[0019] FIG. 9 is a side view of the capsule of FIG. 3 (in cross
section) coupled to the top and bottom bone plates of FIGS. 7 and
8.
[0020] FIG. 10 illustrates an alternative artificial disk
embodiment.
[0021] FIG. 11 illustrates a three-piece bone plate coupling the
sliding capsules to upper and lower vertebral bodies.
[0022] FIG. 12 is a side cutaway view of the artificial disk
embodiment of FIG. 10.
DETAILED DESCRIPTION
[0023] One embodiment of an artificial disk in accordance with the
invention is shown in FIGS. 1A, 1B and 1C. In this embodiment,
endplates 12, 14 sandwich a sliding central capsule 18. As shown in
these Figures, a first plate 12 defines a first inwardly directed
surface 13 and the second plate 14 defines a second inwardly
directed surface 15. A central capsule 18 defines opposed outwardly
directed surfaces 17, 19 that slidably mate with the inwardly
directed surfaces of the plates. Thus, the central capsule can
slide toward and away from opposed edge portions of the endplates
as the relative endplate orientation changes during flexion,
extension or lateral bending of the motion segment in which the
artificial disk is installed. With this design, the endplates 12,
14 can also rotate with respect to one another as the central
capsule slides between them. In this embodiment, the endplates have
convex spherical contours, and the central capsule 18 is generally
cylindrical with top and bottom surfaces that are concave spherical
contours mating with the convex spherical contours on the
endplates. Thus, the central capsule 18 is generally cylindrical
with a hour-glass shaped cross-section.
[0024] Another embodiment of an artificial disk with a central
sliding capsule is illustrated in FIGS. 2A, 2B, and 2C. In this
embodiment, the inner surfaces 13, 15 of the endplates 12, 14 are
concave rather than convex. The capsule 18 includes mating convex
surfaces 17, 19 that slides along the endplate surfaces in a manner
analogous to that shown in FIGS. 1A, 1B, and 1C.
[0025] There are a variety of important benefits of such a sliding
capsule 18. One is that the instantaneous center of rotation of the
motion segment is allowed to move around inside the disk space with
the capsule during lateral bending, flexion, and extension. Also,
the central capsule spreads mechanical stresses over a larger
portion of the endplates and thus over the adjacent vertebral
bodies as well. This mimics the natural behavior of a spinal disk
much better than existing artificial disk designs. Also, this leads
to a reduced tendency for migration and loosening following
installation, since stresses due to spinal movements are not
continually focused in the same direction or location.
[0026] One mechanical design for implementing the above described
sliding capsule is shown in FIGS. 3 and 4. Referring now to these
figures, retainer disks 22A and 22B are secured to respective end
plates 14 and 12 on pedestals 24A and 24B with screws (designated
26A, B, C, and D in FIG. 4). The retainer disks also have a
spherical contour substantially matching that of the endplates. The
pedestals 24A, 24B may be captured in the end plates in recesses or
they may be integral with the end plates as shown in FIG. 3. Each
retainer disk is secured tightly to the pedestal with the screws
such that it does not move with respect to the endplate. Because of
the pedestal, however, the underside of each retainer disk is
raised up off of the inside spherically contoured surface of the
endplate by the height of the pedestal. In an alternative
embodiment, a single screws can be used, or a single screw can be
made integral with their respective retainer disks 22A, 22B, with
the retainer disks held away from the surfaces of the plates
without the pedestals by screwing the threaded shafts down to a
stop in the plate, for example. If desired, a ring clip or other
device could be used to fix unthreaded shafts for the retainer
disks 22A, 22B, such that the disks themselves are fixed away from
the surfaces of the plates but are allowed to rotate about their
central axes.
[0027] Captured underneath each endplate, between the surface of
the endplate and the underside of each retainer disk, are sliding
inner disks 30A and 30B, which are also spherically contoured to
match the contour of the endplate inner surfaces. The thickness of
these sliding disks 30A, 30B is selected with respect to the height
of the pedestals 24A, 24B such that each disk 30A and 30B are
slidably captured between the inner surface of the endplate and the
underside of the respective retainer disk. The two separate
endplates, with attached sliding and retainer disks, are held in
facing relation by a sliding inner disk clamp, which in this
embodiment comprises two parts, designated 40A and 40B in these
Figures, and which are held to each other with screws. The clamp
pieces 40A and 40B engage the edges of the sliding disks 30A and
30B in a tongue and groove arrangement. In the pictured embodiment,
the edge of each sliding inner disk 30A and 30B is provided with a
groove 42A and 42B, and the inner surface of the clamp is provided
with a pair of extending flanges 44A and 44B. When the flanges on
the clamp engage the grooves of the sliding disks 30A and 30B, a
cylindrical sliding assembly with an hourglass shaped cross section
is created comprising the clamp 40A, 40B and the sliding disks 30A,
30B. This sliding assembly couples the endplates via the position
of the sliding disks under the retainer disks and is slidable with
respect thereto between the endplates and the retainer disks 22A
and 22B.
[0028] The amount of lateral motion and rotation that the sliding
assembly is allowed is governed by the shape and size of central
openings in the sliding disks with respect to the shape and size of
the pedestals 24A and 24B fixed to the center of the endplates. The
sliding disks will be able to slide away from the center and rotate
until the edges of the openings in the sliding disks contact the
sides of the pedestals. In one embodiment, it has been found
advantageous for the relative dimensions of these features to allow
for a few millimeters of lateral movement. For round pedestals and
openings, rotation around the central axis of the device is
unlimited throughout 360 degrees. It has been found advantageous,
however, to use the oblong shapes shown in FIG. 4, which limit
rotation to about 30-60 degrees.
[0029] An alternative embodiment is illustrated in cross section in
FIG. 5. This embodiment corresponds to the capsule design
illustrated in general in FIG. 2. In this design, the retainer
disks 22A and 22B and the inner sliding disks 30A and 30B are
curved in the opposite contour from the embodiment of FIGS. 1 and
3-4. Thus, in the embodiment of FIG. 5, the concave sides of the
retainer disks and sliding disks face each other, and the convex
sides face corresponding concave surfaces of the endplates 12, 14.
Operation of this embodiment is analogous to that described above,
with the inner sliding disks 30A and 30B sliding along the endplate
inner surfaces and between the retainer disks and the endplate
surfaces during flexion, extension, and lateral bending of the
spinal column.
[0030] One advantage of the design of FIG. 5 is that the clamp 40A,
40B of FIGS. 3 and 4 can be eliminated. This can be accomplished by
including mating press-fit flanges 46A, 46B around the outer edges
of the two sliding disks 30A, 30B. To assemble the device, each
half is constructed comprising an endplate, a retainer disk, and a
sliding inner disk. Then, the two halves are coupled with a snap
fit that engages the flanges 46A, 46B and holds the two halves
together.
[0031] All components of the device may be made of biocompatible
metals and metal alloys such as stainless steel or titanium. In one
embodiment, the sliding coefficient of friction between the disks
and the endplate surfaces is reduced by coating the sliding
surfaces with a low friction coating. One example of such a useful
coating is known as Casidiam.TM. diamond-like carbon coating. This
coating typically includes carbon, hydrogen, and possibly some
additional dopant materials and is a mixture of tertagonal diamond
type carbon crystal structure and trigonal graphitic carbon crystal
structure. It is a commercially available coating and is used in a
variety of industrial and medical applications requiring hardness,
chemical inertness, biocompatibility, and low friction.
[0032] The device may be installed in a variety of ways. The device
may, for example, be installed in an anterior surgical procedure
using installation and securement methods currently used for
artificial disks of conventional design. For example, the endplates
12, 14 could include vertically extending central fins to engage
the vertebral bodies on either side of the disk. This installation
technique, however, has serious drawbacks. First, anterior
installation is inherently risky due to the presence of the large
blood vessels that run down the anterior of the spinal column.
These vessels are especially vulnerable in the event the artificial
disk needs to be removed, as revision surgeries must contend with
scar tissue and adhesions that form in the surgical field and
attach to these vessels. It is therefore desirable to provide an
artificial disk design that is installed via a posterior or
posterior-lateral approach. Although beneficial from a surgical
point of view, the spinal cord, facets, lamina, and other bony
structures in the posterior of the spine limit the available
insertion space. This difficulty has limited the availability of
posterior inserted artificial disks. To resolve this difficulty,
and to increase the use of minimally invasive procedures, an
especially advantageous embodiment has been designed in which the
artificial disk is placed inside the disk space in several separate
individual smaller pieces and is assembled within the disk
space.
[0033] In one such embodiment a pair of bone plates, each of which
comes in two pieces, are installed and fixed to the upper and lower
vertebral bodies. The bone plates include aligned channels into
which a cassette comprising the central capsule 18 plus the two
endplates 12, 14 is inserted. The artificial disk thus comes in a
five-piece assembly that is inserted into the disk space one piece
at a time, allowing for a smaller incision and surgical field and
making posterior installation of an artificial disk a practical
surgical alternative.
[0034] Bone plates which may be used in one such embodiment are
illustrated in FIGS. 6 through 8. FIG. 6 is a general conceptual
3-D view from above an upper bone plate. FIGS. 7A-B and 8A-B show
plan views and side views of upper and lower bone plates according
to one embodiment of the invention.
[0035] In this embodiment, each bone plate includes a larger
section 54 and a smaller section 52. The two sections are coupled
together by a tongue and groove mating region 58. In the embodiment
of FIG. 6, the larger section 54 includes a dovetail groove on a
straight interior edge, and the smaller section includes a mating
dovetail flange on an adjacent straight interior edge. The two
pieces 52, 54 are further held together with a screw 60 (FIGS. 7
and 8) that is installed into a countersunk hole in the smaller
section 52 and which terminates in a threaded hole in the larger
section 54. When installed, this screw holds the two parts 52, 54
firmly together such that relative motion along the grooved mating
region 58 is prevented after the pieces are installed.
[0036] The bone plates may also incorporate captured pins 72 that
are deployed into the vertebral body after installation. A variety
of pin deployment methods are known and could be used, including
those described in U.S. Pat. Nos. 5,800,547; 5,123,926; and
5,102,950, all three of which are hereby incorporated by reference
in their entireties.
[0037] When mated as shown in FIGS. 7A and 8A, the two sections 52
and 54 create a dovetail channel 70 that extends diagonally on the
surface of each bone plate. As described briefly above, the
channels 70 accept mating dovetail flanges which extend from the
outer surfaces of the endplates 12, 14 of FIGS. 1 to 3. In this
way, the cassette comprising the end-plates and sliding capsule can
itself be slid into position between the bone plates after
installation of the bone plates.
[0038] In one embodiment, disk installation proceeds as follows. A
lateral posterior hemilaminotomy incision is made and the natural
disk is resected in a conventional manner. For the bone plate
design shown in FIGS. 6-8, this incision would be on the left of
the spine. After removal of the natural disk, the larger of the two
bone plate sections 52 for either the top or bottom vertebral body
is inserted through the incision. This section of the bone plate is
then pushed laterally over to the right side of the disk space into
alignment with the right side of the vertebral body and such that
the groove on its flat interior edge runs substantially straight
from back to front. The captured pins 72 are now deployed. The most
convenient method is typically the insertion of an expandable
device that presses the pins into place in the facing bone tissue.
After the larger section 54 is installed, the smaller section 52 is
installed by sliding it straight into the left side of the disk
space such that its dovetail flange is engaged with the dovetail
groove in the first section 54 and such that the channel 70 is
aligned across the entire bone plate. The pins of the second
installed section 52 are then deployed in the same manner as the
first. This same procedure is repeated to attach a bone plate to
the other vertebral body. To ensure that the channels 70 in both
bone plates are appropriately aligned along their length and with
each other, it is possible to use a tool that can slide into both
channels to test that they do not diverge in position or direction
from back left to front right along the bone plate surfaces.
[0039] After the bone plates of FIGS. 7 and 8 are installed, the
cassette comprising the endplates 12, 14, and central sliding
capsule 18 is inserted by mating a dovetail flange on the outer
surfaces of the endplates 12/14 (not shown in FIGS. 3 and 4) to the
dovetail grooves 70 and sliding the cassette into position between
the bone plates and approximately the center of the disk space. The
cassette can be held in place with a set screw 80. A conceptual
side view of an assembly is pictured in FIG. 9.
[0040] An embodiment having a central capsule similar to that
described above with reference to FIGS. 2 and 5 is illustrated in
FIGS. 10-12. As with the embodiment of FIG. 5, sliding disks 30A,
30B slide between the endplate inner surfaces and the bottom
surfaces of inner retaining disks 22A, 22B. The retaining disks, in
this embodiment, comprise threaded shafts that are screwed into
threaded through holes 82A, 82B in the end plates 12, 14. After
they are threaded down to the appropriate clearance, the bottom of
the shafts are orbited in place to lock them tightly and prevent
any rotation or movement out of position. In this embodiment, the
endplates 12, 14 are captured in between the bone plates through
central orifices 92, 94. Grooved posts 96A, 96B extend from each
endplate 14, 12 respectively. Captured in each grooved post is a
snap ring. When the posts are engaged in the bone plates, ears on
each snap ring engage an internal groove 102 in the orifice of each
bone plate.
[0041] As shown in FIG. 11, the endplates may come in three parts
instead of two as shown in FIGS. 6-8. The rightmost portion 104 may
be installed first, followed by the central portion 106, and then
the left-most portion 108. The portions are engaged by a series of
mating dovetail tongue and groove segments. In the embodiment of
FIG. 11, the central portion 106 has groove segments on the left,
and tongue segments on the right. With this design, a tongue and
groove mating along about half of the length of the bone plates can
be made during installation with a sliding motion of only the
length of a single dovetail segment. If desired, lips above and/or
below the segments can be provided to discourage bone growth
between the segments after installation.
[0042] FIG. 12 illustrates the embodiment of FIG. 10 after complete
assembly. With this embodiment, the centerline of the device moves
in accordance with the human body in relationship to the
centerline, mimicking the response of a natural disk.
[0043] To install the device in the spinal column, the bone plates
are installed as shown in FIG. 11. The bone plates may include
deployable spikes or pins as described above, or they may have
integral pre-deployed pins on their outer surfaces that are pressed
into the vertebral bodies during installation.
[0044] The vertebra are then distracted to allow the central
cassette comprising endplates 12, 14, central sliding capsule to be
inserted between them. The vertebra are distracted to allow
clearance for the posts 96A, 96B before they are set in the
orifices 92, 94 in the bone plates. Once the posts are aligned with
the orifices, the distraction is removed, and the posts drop into
the orifices, engaging each snap ring 98A, 98B in its respective
groove in the bone plate. The snap rings may be dimensioned to
deform slightly during installation and snap into place, or a tool
can be used to compress the rings slightly and allow the posts to
engage the orifices. Toll access holes 106, 108 can be provided for
this purpose, and to compress the rings for cassette removal,
should removal be necessary.
[0045] The facets can also be addressed at the same time the
artificial disk is being placed, and attention to the spinous
process abutment can also be addressed at the time of surgery. In
some surgical procedures, the posterior elements will also have an
implant applied to the facets to improve on range of motion in
flexion and extension without pain. These facet implants or
articulations will facilitate the gliding mechanism that is well
documented on scinradiography when the spine is taken through a
range of motion in flexion, extension, lateral bend and torque. If
the facet joint is not addressed, which is a significant
stabilization unit of the motion segment, there may continue to be
problems with back pain. At the time of our artificial disk
implantation, the capsule of the facet joint may be removed, and a
metal on metal artificial facet may be inserted to minimize pain
and to preserve movement.
[0046] The facet arthroplasty will be an articulation with the
inferolateral facet and superomedial facet. This arthroplasty will
have a mechanism that will allow flexion, extension and lateral
translation to occur. This arthroplasty may be accomplished by
opening the facet joint and placing the implants on the articular
cartilage (as illustrated in FIG. 2 for example). In may cases
there may hypertrophy or arthrosis to these complexes, which may
require a partial resection with a high speed burr or osteotome.
Once the opening in the facet joint is achieved the arthroplasty
can then be undertaken, and the implants are then attached to the
inferior aspect of the ventral surface of the vertebra above and to
the dorsal articulating surface of the vertebra below. With this
facet arthroplasty done bilaterally, which can be achieved through
minimally invasive technology, and the artificial disk in place, we
have now addressed the three articulations, anterior, middle column
and posterior.
[0047] The spinous processes can be partially resected to give
space if there is abutment noted. A space may be created between
the spinous processes to allow a placement of a shield with a metal
on metal articulation at the spinal laminar junction of the
vertebra above and below. This metal on metal articulation will
give some partial support and also prevent the abutment of spinous
processes which would restrict range of motion and could result in
pain. This will not only give a partial ligamentous stability, but
will also keep the spinous processes from abutting. As you can see,
our artificial disk complex comprises both a posterior placement or
lateral placement of the disk with supplementing the facet and
possibly the spinous processes. Therefore, the entire complex
anterior, middle and posterior column can be addressed to preserve
circumferential stability to the motion segment. The artificial
disk embodiments described herein do not preclude the device from
being placed anteriorly, but it may often be preferable to perform
one incision that can address both the posterior elements, as well
as the interbody disk level with that one incision.
[0048] This modular design has a variety of advantages. One
advantage already mentioned is that the design makes a posterior
surgical approach practical. The bone plates for the vertebral
bodies are inserted in multiple pieces. As shown in FIG. 9, the
cassette itself can be made smaller than the bone plates, allowing
insertion through the same small posterior lateral hemilaminotomy
incision following the two-piece bone plates.
[0049] Another advantage to this design is that it allows the
artificial disk to be easily replaced with a fusion cage if this
becomes necessary. In such a revision surgery, the artificial disk
cassette can be pulled out, and replaced with another cassette
comprising a fusion cage filled with harvested bone. In some
embodiments, the cassette could include an attachment point for a
slap-hammer so that the cassette could be removed more easily. This
process is much simpler and less traumatic than current artificial
disk removal procedures. With conventional anterior installations,
implant removal to perform a fusion often involves significant bone
removal from the vertebral bodies to get the implant out.
[0050] The modular design described above can even be useful as a
replacement for a removed disk as well. Because the bone plates are
separate from the central cassette, the bone plates can be made in
varying thicknesses, or two or more can be stacked, so that if bone
removal from the vertebral bodies has significantly extended the
height of the disk space, this can be compensated for by extended
bone plate thickness. Thus, during revision surgeries, the bone
plates can be exchanged for different versions having alternative
thicknesses and sizes.
[0051] To further produce an easy and successful transition from
artificial disk to fusion, the bone plates can be made fenestrated.
In some embodiments it might be desirable to replace solid plates
with fenestrated ones during the revision surgery to convert from
an artificial disk to a fusion. As another alternative, fenestrated
bone plates could be removably attached to solid covers that are
left in place when used with an artificial disk installation but
which are removed during a revision to a fusion.
* * * * *