U.S. patent application number 10/438294 was filed with the patent office on 2004-11-18 for prostheses, tools and methods for replacement of natural facet joints with artifical facet joint surfaces.
This patent application is currently assigned to Archus Orthopedics Inc.. Invention is credited to Jones, Lawrence R., Reiley, Mark A., Stinson, David, Yuan, Hansen A..
Application Number | 20040230304 10/438294 |
Document ID | / |
Family ID | 33417540 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040230304 |
Kind Code |
A1 |
Yuan, Hansen A. ; et
al. |
November 18, 2004 |
Prostheses, tools and methods for replacement of natural facet
joints with artifical facet joint surfaces
Abstract
Cephalad and caudal vertebral facet joint prostheses and methods
of use are provided. The cephalad prostheses are adapted and
configured to be attached to a lamina portion of a vertebra without
blocking a pedicle portion of the cephalad vertebra.
Inventors: |
Yuan, Hansen A.;
(Fayetteville, NY) ; Stinson, David; (Woodinville,
WA) ; Jones, Lawrence R.; (Conifer, CO) ;
Reiley, Mark A.; (Piedmont, CA) |
Correspondence
Address: |
MAYER, FORTKORT & WILLIAMS, PC
251 NORTH AVENUE WEST
2ND FLOOR
WESTFIELD
NJ
07090
US
|
Assignee: |
Archus Orthopedics Inc.
|
Family ID: |
33417540 |
Appl. No.: |
10/438294 |
Filed: |
May 14, 2003 |
Current U.S.
Class: |
623/17.11 ;
606/96; 623/908 |
Current CPC
Class: |
A61F 2002/4629 20130101;
A61F 2310/00023 20130101; A61F 2002/30332 20130101; A61F 2310/0097
20130101; A61F 2002/30649 20130101; A61F 2002/4628 20130101; A61F
2310/00029 20130101; A61F 2002/30405 20130101; A61F 2/4405
20130101; A61F 2310/00047 20130101; A61F 2310/00017 20130101; A61F
2002/4631 20130101; A61F 2310/00131 20130101; A61F 2220/0025
20130101; A61F 2002/30904 20130101; A61F 2220/0033 20130101; A61F
2310/00796 20130101; A61B 17/1757 20130101; A61F 2002/30841
20130101; A61F 2310/00179 20130101; A61F 2/4611 20130101; A61B
17/86 20130101 |
Class at
Publication: |
623/017.11 ;
623/908; 606/096 |
International
Class: |
A61F 002/44; A61B
017/17; A61F 002/46 |
Claims
What is claimed is:
1. A prosthesis to replace a cephalad portion of a natural facet
joint on a vertebra, the prosthesis comprising: an artificial facet
joint element adapted and configured to replace a cephalad portion
of the natural facet joint; and a fixation element extending from
the artificial facet joint element, the fixation element being
adapted and configured to be inserted through a lamina portion of a
vertebra to affix the artificial facet joint element to the
vertebra.
2. The prosthesis of claim 1 wherein the fixation element is
further adapted and configured to be inserted through the lamina
portion of the vertebra to affix the artificial facet joint element
to the vertebra without blocking access to a pedicle portion of the
vertebra.
3. The prosthesis of claim 1 wherein the lamina portion is a first
lamina portion, the fixation element being further adapted and
configured to be inserted through a second lamina portion of the
vertebra to affix the artificial facet joint element to the
vertebra.
4. The prosthesis of claim 3 wherein first and second lamina
portions are on opposite sides of a midline of the vertebra, the
fixation element being further adapted and configured to traverse
the midline to affix the artificial facet joint element to the
vertebra.
5. The prosthesis of claim 1 wherein the artificial facet joint
element comprises a cephalad bearing surface adapted and configured
to be in an anatomically correct position with respect to the
vertebra when the prosthesis is affixed to the vertebra by the
fixation element.
6. The prosthesis of claim 1 wherein the artificial facet joint
element comprises a cephalad bearing surface adapted and configured
to be in other than an anatomically correct position with respect
to the vertebra when the prosthesis is affixed to the vertebra by
the fixation element.
7. The prosthesis of claim 1 further comprising an attachment
element adapted and configured to attach the artificial facet joint
element to the fixation element.
8. The prosthesis of claim 1 wherein the fixation element comprises
an artificial facet joint element attachment end and an insertion
tool engagement end, the artificial facet joint attachment end
being adapted and configured to lie on one side of the lamina
portion and the artificial facet joint attachment end being adapted
and configured to lie on another side of the lamina portion.
9. The prosthesis of claim 1 wherein the artificial facet joint
element is adapted and configured to be disposed between a caudal
facet joint bearing surface and a portion of the vertebra.
10. The prosthesis of claim 1 wherein the artificial facet joint
element comprises a cephalad bearing surface having a substantially
convex shape.
11. The prosthesis of claim 1 wherein the artificial facet joint
element further comprises an installation fixture attachment
mechanism.
12. A prosthesis to replace a cephalad portion of a natural facet
joint on a vertebra, the prosthesis comprising: an artificial facet
joint element adapted and configured to replace a cephalad portion
of the natural facet joint; and a fixation element adapted and
configured to affix the artificial facet joint element to the
vertebra without blocking access to a pedicle portion of the
vertebra.
13. The prosthesis of claim 12 wherein the artificial facet joint
element comprises a cephalad bearing surface adapted and configured
to be in an anatomically correct position with respect to the
vertebra when the prosthesis is affixed to the vertebra by the
fixation element.
14. The prosthesis of claim 12 wherein the artificial facet joint
element comprises a cephalad bearing surface adapted and configured
to be in other than an anatomically correct position with respect
to the vertebra when the prosthesis is affixed to the vertebra by
the fixation element.
15. The prosthesis of claim 12 further comprising an attachment
element adapted and configured to attach the artificial facet joint
element to the fixation element.
16. The prosthesis of claim 12 wherein the fixation element
comprises an artificial facet joint element attachment end and an
insertion tool engagement end, the artificial facet joint
attachment end being adapted and configured to lie on one side of a
lamina portion of the vertebra and the artificial facet joint
attachment end being adapted and configured to lie on another side
of the lamina portion.
17. The prosthesis of claim 12 wherein the artificial facet joint
element is adapted and configured to be disposed between a caudal
facet joint bearing surface and a portion of the vertebra.
18. The prosthesis of claim 12 wherein the artificial facet joint
element comprises a cephalad bearing surface having a substantially
convex shape.
19. The prosthesis of claim 12 wherein the artificial facet joint
element further comprises an installation fixture attachment
mechanism.
20. A prosthesis to replace a caudal portion of a natural facet
joint on a vertebra, the prosthesis comprising: an artificial facet
joint element comprising a vertebra contacting surface and a caudal
bearing surface, the caudal bearing surface being adapted and
configured to replace a caudal portion of a natural facet joint and
to be substantially entirely posterior of a contact portion of the
vertebra when the vertebra contacting surface contacts the contact
portion; and a fixation element extending from the artificial facet
joint element, the fixation element being adapted and configured to
be inserted into the vertebra to affix the prosthesis to the
vertebra.
21. The prosthesis of claim 20 wherein the caudal bearing surface
is further adapted and configured to be in an anatomically correct
position with respect to the vertebra when the prosthesis is
affixed to the vertebra by the fixation element.
22. The prosthesis of claim 20 wherein the caudal bearing surface
is further adapted and configured to be in an other than
anatomically correct position with respect to the vertebra when the
prosthesis is affixed to the vertebra by the fixation element.
23. The prosthesis of claim 20 further comprising an attachment
element adapted and configured to attach the artificial facet joint
element to the fixation element.
24. The prosthesis of claim 20 wherein the caudal bearing surface
has a substantially concave shape.
25. The prosthesis of claim 20 wherein the artificial facet joint
element further comprises an installation fixture attachment
mechanism.
26. A prosthesis to replace a caudal portion and a cephalad portion
of a natural facet joint of cephalad and caudal vertebrae, the
prosthesis comprising: an artificial cephalad facet joint element
adapted and configured to replace a cephalad portion of the natural
facet joint, the artificial cephalad facet joint element comprising
a cephalad bearing surface; a cephalad fixation element, the
cephalad fixation element being adapted and configured to be
inserted through a lamina portion of the cephalad vertebra to affix
the artificial cephalad facet joint element to the cephalad
vertebra; an artificial caudal facet joint element adapted and
configured to replace a caudal portion of the natural facet joint,
the artificial caudal facet joint element comprising a caudal
bearing surface adapted and configured to mate with the cephalad
bearing surface.
27. The prosthesis of claim 26 wherein the cephalad fixation
element is further adapted and configured to be inserted through
the lamina portion of the vertebra to affix the artificial facet
joint element to the vertebra without blocking access to a pedicle
portion of the vertebra.
28. The prosthesis of claim 26 wherein the lamina portion is a
first lamina portion, the cephalad fixation element being further
adapted and configured to be inserted through a second lamina
portion of the vertebra to affix the artificial facet joint element
to the vertebra.
29. The prosthesis of claim 28 wherein first and second lamina
portions are on opposite sides of a midline of the vertebra, the
cephalad fixation element being further adapted and configured to
traverse the midline to affix the artificial facet joint element to
the vertebra.
30. The prosthesis of claim 26 wherein the artificial cephalad
facet joint element is adapted and configured to be disposed
between the caudal facet joint bearing surface and a portion of the
cephalad vertebra.
31. The prosthesis of claim 26 further comprising a caudal fixation
element extending from the artificial caudal facet joint element,
the caudal fixation element being adapted and configured to be
inserted into the caudal vertebra to affix the artificial caudal
facet joint element to the caudal vertebra.
32. The prosthesis of claim 26 wherein the cephalad bearing surface
and the caudal bearing surface are adapted and configured to be in
anatomically correct positions with respect to the cephalad and
caudal vertebrae when the prosthesis is affixed to the cephalad and
caudal vertebrae, respectively.
33. The prosthesis of claim 26 wherein the cephalad bearing surface
and the caudal bearing surface are adapted and configured to be in
other than anatomically correct positions with respect to the
cephalad and caudal vertebrae when the prosthesis is affixed to the
cephalad and caudal vertebrae, respectively.
34. The prosthesis of claim 26 wherein cephalad bearing surface and
the caudal bearing surface each has a width along its respective
transverse axis, the cephalad bearing surface width being shorter
than the caudal bearing surface width.
35. The prosthesis of claim 26 wherein the cephalad bearing surface
has a substantially convex shape and the caudal bearing surface has
a substantially concave shape.
36. The prosthesis of claim 26 wherein the artificial caudal facet
joint element further comprises a vertebra contacting surface, the
entire caudal bearing surface being adapted and configured to be
posterior of a contact portion of the caudal vertebra when the
vertebra contacting surface contacts the contact portion.
37. A prosthesis to replace a caudal portion and a cephalad portion
of a natural facet joint of cephalad and caudal vertebrae, the
prosthesis comprising: an artificial cephalad facet joint element
adapted and configured to replace a cephalad portion of the natural
facet joint, the artificial cephalad facet joint element comprising
a cephalad bearing surface; a cephalad fixation element adapted and
configured to affix the artificial cephalad facet joint element to
the cephalad vertebra without blocking access to a pedicle portion
of the cephalad vertebra; and an artificial caudal facet joint
element adapted and configured to replace a caudal portion of the
natural facet joint, the artificial caudal facet joint element
comprising a caudal bearing surface adapted and configured to mate
with the cephalad bearing surface.
38. The prosthesis of claim 37 wherein the artificial cephalad
facet joint surface is adapted and configured to be disposed
between the caudal facet joint bearing surface and a portion of the
cephalad vertebra.
39. The prosthesis of claim 37 further comprising a caudal fixation
element extending from the artificial caudal facet joint element,
the caudal fixation element being adapted and configured to be
inserted into the caudal vertebra to affix the artificial caudal
facet joint element to the caudal vertebra.
40. The prosthesis of claim 37 wherein the cephalad bearing surface
and the caudal bearing surface are adapted and configured to be in
anatomically correct positions with respect to the cephalad and
caudal vertebrae when the prosthesis is affixed to the cephalad and
caudal vertebrae, respectively.
41. The prosthesis of claim 37 wherein the cephalad bearing surface
and the caudal bearing surface are adapted and configured to be in
other than anatomically correct positions with respect to the
cephalad and caudal vertebrae when the prosthesis is affixed to the
cephalad and caudal vertebrae, respectively.
42. The prosthesis of claim 37 wherein the cephalad bearing surface
and the caudal bearing surface each has a width along its
respective transverse axis, the cephalad bearing surface width
being shorter than the caudal bearing surface width.
43. The prosthesis of claim 37 wherein the cephalad bearing surface
has a substantially convex shape and the caudal bearing surface has
a substantially concave shape.
44. The prosthesis of claim 37 wherein the artificial caudal facet
joint element further comprises a vertebra contacting surface, the
entire caudal bearing surface being adapted and configured to be
posterior of a contact portion of the caudal vertebra when the
vertebra contacting surface contacts the contact portion.
45. A method for implanting a facet joint prosthesis to replace a
removed cephalad portion of a natural facet joint on a vertebra,
the method comprising the steps of: inserting a fixation element
through a lamina portion of the vertebra; and placing an artificial
cephalad facet joint bearing surface in a position to form a
cephalad portion of a facet joint.
46. The method of claim 45 further comprising attaching an
artificial facet joint element to an end of the fixation element
after the inserting step.
47. The method of claim 45 further comprising attaching an
artificial facet joint element to an end of the fixation element
prior to the inserting step.
48. The method of claim 45 wherein the inserting step comprises
inserting the fixation element through the lamina portion of the
vertebra without blocking access to a pedicle portion of the
vertebra.
49. The method of claim 45 wherein the lamina portion is a first
lamina portion, the inserting step comprising inserting the
fixation element through a second lamina portion.
50. The method of claim 49 wherein the first lamina portion and the
second lamina portion are on opposite sides of a midline of the
vertebra, the inserting step comprising traversing the midline with
the fixation element.
51. The method of claim 45 wherein the placing step comprises
disposing the artificial facet joint bearing surface between a
caudal facet joint bearing surface and a portion of the
vertebra.
52. The method of claim 45 wherein the placing step comprises
placing the artificial facet joint bearing surface in an
anatomically correct position with respect to the vertebra.
53. The method of claim 45 wherein the placing step comprises
placing the artificial facet joint bearing surface in an other than
anatomically correct position with respect to the vertebra.
54. The method of claim 45 further comprising the step of aligning
the artificial cephalad facet joint bearing surface with a
corresponding caudal bearing surface.
55. The method of claim 45 further comprising the step of defining
an insertion path through the lamina prior to the inserting
step.
56. The method of claim 55 further comprising forming a passage
through the lamina corresponding to the insertion path.
57. The method of claim 55 wherein the defining step comprises
aligning a guide with the artificial facet joint element to direct
the location and orientation of the insertion path.
58. The method of claim 57 further comprising forming a passage
through the lamina corresponding to the insertion path.
59. The method of claim 45 wherein the inserting step comprises
inserting the fixation element through the lamina portion of the
vertebra to affix the fixation element to the vertebra without
using cement.
60. A method for implanting a cephalad facet joint prosthesis to
replace a removed cephalad portion of a natural facet joint on a
vertebra, the method comprising the steps of: aligning the cephalad
facet joint prosthesis with a caudal facet joint bearing surface;
and attaching the cephalad facet joint prosthesis to the vertebra
without blocking a pedicle portion of the vertebra.
61. The method of claim 60 wherein the attaching step comprises
inserting a fixation element through a lamina portion of the
vertebra.
62. The method of claim 60 wherein the attaching step comprises
disposing the cephalad facet joint prosthesis between the caudal
facet joint bearing surface and a portion of the vertebra.
63. The method of claim 60 wherein the attaching step comprises
placing the cephalad facet joint prosthesis in an anatomically
correct position with respect to the vertebra.
64. The method of claim 60 wherein the attaching step comprises
placing the cephalad facet joint prosthesis in an other than
anatomically correct position with respect to the vertebra.
65. The method of claim 60 wherein the attaching step comprises
inserting a fixation element into a portion of the vertebra.
66. The method of claim 65 further comprising the step of defining
an insertion path in the vertebra prior to the inserting step.
67. The method of claim 66 further comprising forming a passage in
the vertebra corresponding to the insertion path.
68. The method of claim 66 wherein the defining step comprises
aligning a guide with the artificial facet joint element to direct
the location and orientation of the insertion path.
69. The method of claim 68 further comprising forming a passage in
the vertebra corresponding to the insertion path.
70. A method for implanting a facet joint prosthesis to replace
removed cephalad and caudal portions of a natural facet joint of
cephalad and caudal vertebrae, the method comprising the steps of:
affixing an artificial caudal facet joint element to the caudal
vertebra; inserting a cephalad fixation element through a lamina
portion of the cephalad vertebra; and placing an artificial
cephalad facet joint bearing surface in a position to form a
cephalad portion of a facet joint.
71. The method of claim 70 further comprising attaching an
artificial cephalad facet joint element to an end of the fixation
element after the inserting step, the artificial cephalad facet
joint element comprising the artificial cephalad facet joint
bearing surface.
72. The method of claim 70 further comprising attaching an
artificial cephalad facet joint element to an end of the fixation
element prior to the inserting step, the artificial cephalad facet
joint element comprising the artificial cephalad facet joint
bearing surface.
73. The method of claim 70 wherein the affixing step comprises
affixing the artificial caudal facet joint element at or near to a
pedicle of the caudal vertebra.
74. The method of claim 70 wherein the affixing step comprises
placing the artificial caudal facet joint element in an
anatomically correct position with respect to the caudal
vertebra.
75. The method of claim 70 wherein the affixing step comprises
placing the artificial caudal facet joint element in an other than
anatomically correct position with respect to the caudal
vertebra.
76. The method of claim 70 wherein the inserting step comprises
inserting the fixation element through the lamina portion of the
cephalad vertebra without blocking access to a pedicle portion of
the cephalad vertebra.
77. The method of claim 70 wherein the lamina portion is a first
lamina portion, the inserting step comprising inserting the
fixation element through a second lamina portion of the cephalad
vertebra.
78. The method of claim 77 wherein the first lamina portion and the
second lamina portion are on opposite sides of a midline of the
cephalad vertebra, the inserting step comprising traversing the
midline with the fixation element.
79. The method of claim 70 wherein the placing step comprises
disposing the artificial cephalad facet joint bearing surface
between the artificial caudal facet joint element and a portion of
the cephalad vertebra.
80. The method of claim 70 wherein the placing step comprises
placing the artificial cephalad facet joint bearing surface in an
anatomically correct position with respect to the cephalad
vertebra.
81. The method of claim 70 wherein the placing step comprises
placing the artificial cephalad facet joint bearing surface in an
other than anatomically correct position with respect to the
cephalad vertebra.
82. The method of claim 70 further comprising aligning the
artificial cephalad facet joint bearing surface with a
corresponding caudal bearing surface of the artificial caudal facet
joint element.
83. The method of claim 82 wherein the aligning step comprises
mounting an artificial cephalad facet joint element and the
artificial caudal facet joint element in an installation fixture,
the artificial cephalad facet joint element comprising the
artificial cephalad facet joint bearing surface.
84. The method of claim 70 further comprising the step of defining
an insertion path through the lamina prior to the inserting
step.
85. The method of claim 84 further comprising forming a passage
corresponding to the insertion path.
86. The method of claim 84 wherein the defining step comprises
aligning a guide with the artificial cephalad facet joint element
to direct the location and orientation of the insertion path.
87. The method of claim 86 further comprising forming a passage
corresponding to the insertion path.
88. The method of claim 86 wherein the aligning step comprises
orienting the guide with an installation fixture to which the
artificial cephalad facet joint element has been attached.
89. A method for implanting a facet joint prosthesis to replace
removed cephalad and caudal portions of a natural facet joint of
cephalad and caudal vertebrae, the method comprising the steps of:
affixing an artificial caudal facet joint element to the caudal
vertebra; and affixing an artificial cephalad facet joint element
to the cephalad vertebra in alignment with the artificial caudal
facet joint element and without blocking access to a pedicle
portion of the cephalad vertebra.
90. The method of claim 89 wherein the first affixing step
comprises affixing the artificial caudal facet joint element to at
or near to a pedicle of the caudal vertebra.
91. The method of claim 89 wherein the first affixing step
comprises placing the artificial caudal facet joint element in an
anatomically correct position with respect to the caudal
vertebra.
92. The method of claim 89 wherein the first affixing step
comprises placing the artificial caudal facet joint element in an
other than anatomically correct position with respect to the caudal
vertebra.
93. The method of claim 89 wherein the second affixing step
comprises disposing the artificial cephalad facet joint element
between the artificial caudal facet joint element and a portion of
the cephalad vertebra.
94. The method of claim 89 wherein the second affixing step
comprises placing the artificial cephalad facet joint element in an
anatomically correct position with respect to the cephalad
vertebra.
95. The method of claim 89 wherein the second affixing step
comprises placing the artificial cephalad facet joint element in an
other than anatomically correct position with respect to the
cephalad vertebra.
96. The method of claim 89 further comprising aligning a cephalad
bearing surface of the artificial cephalad facet joint element with
a corresponding caudal bearing surface of the caudal facet joint
element.
97. The method of claim 96 wherein the aligning step comprises
mounting the cephalad facet joint element and the caudal facet
joint element in an installation fixture.
98. The method of claim 89 further comprising the step of defining
an insertion path in the cephalad vertebra prior to the second
affixing step.
99. The method of claim 98 further comprising forming a passage in
the cephalad vertebra corresponding to the insertion path.
100. The method of claim 98 wherein the defining step comprises
aligning a guide with the artificial cephalad facet joint element
to direct the location and orientation of the insertion path.
101. The method of claim 100 further comprising forming a passage
in the cephalad vertebra corresponding to the insertion path.
102. The method of claim 100 wherein the aligning step comprises
orienting the guide with an installation fixture to which the
artificial cephalad facet joint element has been attached.
Description
FIELD OF THE INVENTION
[0001] This invention relates to prostheses for treating various
types of spinal pathologies, as well as to methods of treating
spinal pathologies.
BACKGROUND OF THE INVENTION
[0002] I. Vertebral Anatomy
[0003] As FIG. 1 shows, the human spinal column 10 is comprised of
a series of thirty-three stacked vertebrae 12 divided into five
regions. The cervical region includes seven vertebrae 12, known as
C1-C7. The thoracic region includes twelve vertebrae 12, known as
T1-T12. The lumbar region contains five vertebrae 12, known as
L1-L5. The sacral region is comprised of five vertebrae 12, known
as S1-S5. The coccygeal region contains four vertebrae 12, known as
Co1-Co4.
[0004] FIG. 2 shows a normal human lumbar vertebra 12. Although the
lumbar vertebrae 12 vary somewhat according to location, they share
many features common to most vertebrae 12. Each vertebra 12
includes a vertebral body 14 and posterior elements as follows:
[0005] Two short bones, the pedicles 16, extend backward from each
side of the vertebral body 14 to form a vertebral arch 18. At the
posterior end of each pedicle 16 the vertebral arch 18 flares out
into broad plates of bone known as the laminae 20. The laminae 20
fuse with each other to form a spinous process 22. The spinous
process 22 serves for muscle and ligamentous attachment. A smooth
transition from the pedicles 16 into the laminae 20 is interrupted
by the formation of a series of processes.
[0006] Two transverse processes 24 thrust out laterally on each
side from the junction of the pedicle 16 with the lamina 20. The
transverse processes 24 serve as levers for the attachment of
muscles to the vertebrae 12. Four articular processes, two superior
26 and two inferior 28, also rise from the junctions of the
pedicles 16 and the laminae 20. The superior articular processes 26
are sharp oval plates of bone rising upward on each side from the
union of the pedicle 16 with the lamina 20. The inferior processes
28 are oval plates of bone that extend in an inferior direction on
each side.
[0007] The superior and inferior articular processes 26 and 28 each
have a natural bony structure known as a facet. The superior
articular facet 30 faces upward or superiorly, while the inferior
articular facet 31 faces downward. As FIG. 3 shows, when adjacent
(i.e., cephalad and caudal) vertebrae 12 are aligned, the facets 30
and '31, capped with a smooth articular cartilage, interlock to
form a facet joint 32, also known as a zygapophysial joint.
[0008] The facet joint 32 is composed of a superior half and an
inferior half. The superior half is formed by the vertebral level
below the joint 32, and the inferior half is formed by the
vertebral level above the joint 32. For example, in the L4-L5 facet
joint, the superior portion of the joint is formed by bony
structure on the L-5 vertebra (e.g., a superior articular surface
and supporting bone on the L-5 vertebra), and the inferior portion
of the joint is formed by bony structure on the L-4 vertebra (e.g.,
an inferior articular surface and supporting bone on the L-4
vertebra).
[0009] As also shown in FIG. 3, an intervertebral disc 34 between
each pair of vertebrae 12 permits relative movement between
vertebrae 12. Thus, the structure and alignment of the vertebrae 12
permit a range of movement of the vertebrae 12 relative to each
other.
[0010] II. Facet Joint Dysfunction
[0011] Back pain, particularly in the "small of the back", or
lumbosacral (L4-S1) region, is a common ailment. In many cases, the
pain severely limits a person's functional ability and quality of
life. Such pain can result from a variety of spinal
pathologies.
[0012] Through disease or injury, the laminae, spinous process,
articular processes, or facets of one or more vertebrae can become
damaged, such that the vertebrae no longer articulate or properly
align with each other. This can result in an undesired anatomy,
pain or discomfort, and loss of mobility.
[0013] For example, the vertebral facet joints can be damaged by
either traumatic injury or by various disease processes. These
disease processes include osteoarthritis, ankylosing spondylolysis,
and degenerative spondylolisthesis. The damage to the facet joints
often results in pressure on nerves, also called a "pinched" nerve,
or nerve compression or impingement. The result is pain, misaligned
anatomy, and a corresponding loss of mobility. Pressure on nerves
can also occur without facet joint pathology, e.g., a herniated
disc.
[0014] One type of conventional treatment of facet joint pathology
is spinal stabilization, also known as intervertebral
stabilization. Intervertebral stabilization prevents relative
motion between the vertebrae. By preventing movement, pain can be
reduced. Stabilization can be accomplished by various methods.
[0015] One method of stabilization is posterior spinal fusion.
Another method of stabilization is anterior spinal fusion, fixation
of any number of vertebrae to stabilize and prevent movement of the
vertebrae.
[0016] Another type of conventional treatment is decompressive
laminectomy. This procedure involves excision of the laminae to
relieve compression of nerves.
[0017] These traditional treatments are subject to a variety of
limitations and varying success rates. Furthermore, none of the
described treatments puts the spine in proper alignment or return
the spine to a desired anatomy. In addition, stabilization
techniques, by holding the vertebrae in a fixed position,
permanently limit the relative motion of the vertebrae, altering
spine biomechanics.
SUMMARY OF THE INVENTION
[0018] There is a need for prostheses, installation tools, and
methods that overcome the problems and disadvantages associated
with current strategies and designs in various treatments for spine
pathologies.
[0019] The invention provides prostheses, installation tools, and
methods designed to replace natural facet joints at virtually all
spinal levels including L1-L2, L2-L3, L3-L4, L4-L5, L5-S1,
T-11-T12, and T12-L1. The prostheses, installation tools, and
methods can restore a desired anatomy to a spine and give back to
an individual a desired range of relative vertebral motion. The
prostheses, installation tools, and methods also can lessen or
alleviate spinal pain by relieving the source of nerve compression
or impingement.
[0020] For the sake of description, the prostheses that embody
features of the invention will be called either "cephalad" or
"caudal" with relation to the portion of a given natural facet
joint they replace. As previously described, a given natural facet
joint has a superior half and an inferior half. In anatomical
terms, the superior half of the joint is formed by the vertebral
level below the joint (which can thus be called the caudal portion
of the facet joint, i.e., because it is near the feet). The
inferior half of the joint is formed by the vertebral level above
the joint (which can thus be called the cephalad portion of the
facet joint, i.e., because it is near the head). Thus, a prosthesis
that, in use, replaces the caudal portion of a facet joint (i.e.,
the superior half) will be called a "caudal" prosthesis. Likewise,
a prosthesis that, in use, replaces the cephalad portion of a facet
joint (i.e., the inferior half) will be called a "cephalad"
prosthesis.
[0021] One aspect of the invention provides a cephalad facet joint
prosthesis to replace a cephalad portion of a natural facet joint
(e.g., an inferior articular surface and its supporting bone
structure on the posterior elements of the vertebra) in the
posterior elements of a vertebra. According to this aspect of the
invention, the prosthesis includes an artificial facet joint
element adapted and configured to replace a cephalad portion of the
natural facet joint and a fixation element extending from the
artificial facet joint element, the fixation element being adapted
and configured to be inserted through a lamina portion of a
vertebra to affix the artificial facet joint element to the
vertebra, preferably without blocking access to a pedicle portion
of the vertebra. The fixation element may also extend through a
second lamina portion of the vertebra, such as by traversing the
midline of the vertebra through or adjacent to the spinous process.
In one embodiment, after installation the cephalad bearing element
is disposed between a caudal facet joint bearing surface and a
portion of the vertebra, such as a lamina portion.
[0022] This aspect of the invention also provides a method of
implanting an artificial cephalad facet joint prosthesis on a
vertebra and/or the posterior elements of a vertebra. According to
this method, a fixation element is inserted through a lamina
portion of the vertebra, and a cephalad facet joint bearing surface
is placed in a position to form a cephalad portion of a facet
joint. An artificial facet joint element is attached to a distal
end of the fixation element either after or prior to insertion of
the fixation element. The fixation element preferably does not
block access to a pedicle portion of the vertebra. The fixation
element may also extend through a second lamina portion of the
vertebra, such as by traversing the midline of the vertebra through
or adjacent to the spinous process. In one embodiment, the placing
step includes disposing the artificial facet joint bearing surface
between a caudal facet joint bearing surface and a portion of the
vertebra, such as a lamina portion. The method may also include the
steps of using a guide to define an insertion path for the fixation
element and forming a passage through the lamina corresponding to
the insertion path.
[0023] Another aspect of the invention provides a prosthesis to
replace a cephalad portion of a natural facet joint on a vertebra.
In this aspect of the invention the prosthesis includes an
artificial facet joint element adapted and configured to replace a
cephalad portion of the natural facet joint; and a fixation element
adapted and configured to affix the artificial facet joint element
to the vertebra without blocking access to a pedicle portion of the
vertebra. In one embodiment, after installation the cephalad
bearing element is disposed between a caudal facet joint bearing
surface and a portion of the vertebra, such as a lamina
portion.
[0024] This aspect of the invention also provides a method for
implanting a cephalad facet joint prosthesis to replace a removed
cephalad portion of a natural facet joint on a vertebra. The method
includes the steps of aligning the cephalad facet joint prosthesis
with a caudal facet joint bearing surface; and attaching the
cephalad facet joint prosthesis to the vertebra without blocking a
pedicle portion of the vertebra. The attaching step of the method
may also include disposing the cephalad facet joint prosthesis
between the caudal facet joint bearing surface and a portion of the
vertebra. The attaching step may also include the step of inserting
a fixation element through a portion of the vertebra, such as the
lamina. In this case, the method may include the steps of defining
an insertion path in the vertebra prior to the inserting step and
forming a passage in the vertebra corresponding to the insertion
path. A guide may be used to direct the location and orientation of
the insertion path.
[0025] Another aspect of the invention provides a facet joint
prosthesis to replace, on a vertebra, a caudal portion of a natural
facet joint (e.g., a superior articular surface and supporting bone
structure on the vertebra). The prosthesis includes an artificial
facet joint element with a vertebra contacting surface and a caudal
bearing surface, the caudal bearing surface being adapted and
configured to replace a caudal portion of a natural facet joint and
to be substantially entirely posterior of a contact portion of the
vertebra when the vertebra contacting surface contacts the contact
portion. The prosthesis also includes a fixation element extending
from the artificial facet joint element, the fixation element being
adapted and configured to be inserted into the vertebra to affix
the prosthesis to the vertebra.
[0026] Another aspect of the invention provides a prosthesis for
replacing a caudal portion and a cephalad portion of a natural
facet joint of cephalad and caudal vertebrae of a spine motion
segment. The prosthesis includes an artificial cephalad facet joint
element adapted and configured to replace a cephalad portion of the
natural facet joint, the artificial cephalad facet joint element
having a cephalad bearing surface; a cephalad fixation element, the
cephalad fixation element being adapted and configured to be
inserted through a lamina portion of a vertebra to affix the
artificial cephalad facet joint element to the cephalad vertebra;
and an artificial caudal facet-joint element adapted and configured
to replace a caudal portion of the natural facet joint, the
artificial caudal facet joint element including a caudal bearing
surface adapted and configured to mate with the cephalad bearing
surface.
[0027] Yet another aspect of the invention provides a method for
implanting a facet joint prosthesis to replace removed cephalad and
caudal portions of a natural facet joint of cephalad and caudal
vertebrae. The method includes the steps of: affixing an artificial
caudal facet joint element to the caudal vertebra; inserting a
cephalad fixation element through a lamina portion of the cephalad
vertebra; and placing an artificial cephalad facet joint bearing
surface in a position to form a cephalad portion of a facet joint.
The method may also include attaching an artificial cephalad facet
joint element comprising the cephalad facet joint bearing surface
to an end of the fixation element either prior to or after the
inserting step. In one embodiment, the fixation element does not
block access to a pedicle portion of the cephalad vertebra. The
cephalad fixation element may also extend through a second lamina
portion of the cephalad vertebra, such as by traversing the midline
of the cephalad vertebra through or adjacent to the spinous
process. The placing step may also include the step of disposing
the artificial cephalad facet joint bearing surface between the
artificial caudal facet joint element and a portion of the cephalad
vertebra. An installation fixture may be used to align the caudal
and cephalad elements, although the prosthesis may also be
installed without using an installation fixture. The method may
also include the step of using a guide to define an insertion path
for the cephalad fixation element, although the prosthesis may also
be installed without using a guide.
[0028] Another aspect of the invention provides a prosthesis to
replace a caudal portion and a cephalad portion of a natural facet
joint of cephalad and caudal vertebrae. The prosthesis may include
an artificial cephalad facet joint element adapted and configured
to replace a cephalad portion of the natural facet joint, with the
artificial cephalad facet joint element including a cephalad
bearing surface; a cephalad fixation element adapted and configured
to affix the artificial cephalad facet joint element to the
cephalad vertebra without blocking access to a pedicle portion of
the cephalad vertebra; and an artificial caudal facet joint element
adapted and configured to replace a caudal portion of the natural
facet joint, the artificial caudal facet joint element including a
caudal bearing surface adapted and configured to mate with the
cephalad bearing surface. In one embodiment, after installation the
cephalad facet joint bearing surface is disposed between a caudal
facet joint bearing surface and a portion of the vertebra, such as
a lamina portion. In one embodiment, the cephalad bearing surface
and the caudal bearing surface each has a width along its
respective transverse axis, with the cephalad bearing surface width
being shorter than the caudal bearing surface width. The artificial
caudal facet joint element may also include a vertebra contacting
surface, with the entire caudal bearing surface being adapted and
configured to be posterior of a contact portion of the caudal
vertebra when the vertebra contacting surface contacts the contact
portion.
[0029] This aspect of the invention also includes a method for
implanting a facet joint prosthesis to replace removed cephalad and
caudal portions of a natural facet joint of cephalad and caudal
vertebrae. The method includes the steps of affixing an artificial
caudal facet joint element to the caudal vertebra; and affixing an
artificial cephalad facet joint element to the cephalad vertebra in
alignment with the artificial caudal facet joint element and
without blocking access to a pedicle portion of the cephalad
vertebra. The second affixing step may also include the step of
disposing the artificial cephalad facet joint element between the
artificial caudal facet joint element and a portion of the cephalad
vertebra. An installation fixture may be used to align the caudal
and cephalad element, although the prosthesis may also be installed
without using an installation fixture. The method may also include
the step of using a guide to define an insertion path for the
cephalad fixation element, although the prosthesis may also be
installed without using a guide.
[0030] Other features and advantages of the inventions are set
forth in the following Description and Drawings, as well as in the
appended Claims.
DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a lateral elevation view of a normal human spinal
column;
[0032] FIG. 2 is a superior view of a normal human lumbar
vertebra;
[0033] FIG. 3 is a lateral elevation view of a vertebral lumbar
facet joint;
[0034] FIG. 4 is a posterior view of an artificial facet joint
prosthesis installed in a patient according to one embodiment of
this invention;
[0035] FIG. 5 is a left side view of the embodiment of FIG. 4, as
installed in a patient;
[0036] FIG. 6 is yet another view of the embodiment of FIG. 4, as
installed in a patient;
[0037] FIG. 7A is a cross-sectional view of a cephalad bearing
element and fixation element according to the embodiment of FIG.
4;
[0038] FIG. 7B is a posterior view of a pair of artificial cephalad
and caudal facet joint prostheses according to one embodiment of
this invention;
[0039] FIG. 7C is a top view of a pair of artificial cephalad and
caudal facet joint prostheses in the embodiment of FIG. 7A;
[0040] FIG. 7D is a left view of a pair of artificial cephalad and
caudal facet joint prostheses in the embodiment of FIG. 7A;
[0041] FIG. 7E is a bottom view of a pair of artificial cephalad
and caudal facet joint prostheses in the embodiment of FIG. 7A;
[0042] FIG. 7F is an anterior view of a pair of artificial cephalad
and caudal facet joint prostheses in the embodiment of FIG. 7A;
[0043] FIG. 8A is a perspective view of an installation fixture
according to one embodiment of this invention;
[0044] FIG. 8B is a top view of the installation fixture of FIG.
8A;
[0045] FIG. 8C is a side view of the installation fixture of FIG.
8A;
[0046] FIG. 8D is a back view of the installation fixture of FIG.
8A;
[0047] FIG. 9 is an exploded view of the installation fixture of
FIG. 8 along with a pair of caudal facet bearing elements and a
pair of cephalad facet bearing elements according to one embodiment
of the invention;
[0048] FIGS. 10A-D are views of a guide tool according to one
embodiment of the invention;
[0049] FIG. 11 is a posterior view of the installation fixture of
FIGS. 8 and 9 to which a pair of caudal facet bearing elements and
a pair of cephalad bearing elements have been attached and with the
caudal bearing elements attached to the patient;
[0050] FIG. 12 is a left side view of the installation fixture and
bearing elements of FIG. 11 with the caudal bearing elements
attached to the patient;
[0051] FIG. 13 is a perspective view of the installation fixture
and bearing elements of FIGS. 11 and 12 showing a guide tool
according to one embodiment of this invention;
[0052] FIG. 14 is a perspective view of the installation fixture
and bearing elements of FIGS. 11 and 12 showing the use of a drill
bit with the guide tool according to one embodiment of this
invention.
[0053] The invention may be embodied in several forms without
departing from its spirit or essential characteristics. The scope
of the invention is defined in the appended claims, rather than in
the specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DETAILED DESCRIPTION
[0054] Although the disclosure hereof is detailed and exact to
enable those skilled in the art to practice the invention, the
physical embodiments herein disclosed merely exemplify the
invention that may be embodied in other specific structure. While
the preferred embodiment has been described, the details may be
changed without departing from the invention, which is defined by
the claims.
[0055] FIGS. 4-7 show artificial cephalad and caudal facet joint
prostheses 36 and 50 for replacing a natural facet joint according
to one aspect of this invention. Cephalad prosthesis 36 has a
bearing element 38 with a bearing surface 40. In this embodiment,
bearing surface 40 has a convex shape. Bearing element 38 may be
formed from biocompatible metals (such as cobalt chromium steel,
surgical steels, titanium, titanium alloys, tantalum, tantalum
alloys, aluminum, etc.), ceramics, polyethylene, biocompatible
polymers, and other materials known in the prosthetic arts, and
bearing surface 40 may be formed from biocompatible metals (such as
cobalt chromium steel, surgical steels, titanium, titanium alloys,
tantalum, tantalum alloys, aluminum, etc.), ceramics, polyethylene,
biocompatible polymers, and other materials known in the prosthetic
arts.
[0056] Depending on the patient's disease state, the condition of
the patient's natural facet joint-including the facet joint's
strength, location and orientation-may not be acceptable. As shown
in FIGS. 4-7, therefore, the natural cephalad and caudal facet
joint surfaces have been removed to enable the installation of a
prosthetic facet joint without limitations presented by remaining
portions of the natural facet joint.
[0057] In one embodiment of the invention, fixation element 42
attaches cephalad prosthesis 36 to a vertebra 60 in an orientation
and position that places bearing surface 40 in approximately the
same location as the natural facet joint surface the prosthesis
replaces. The prosthesis may also be placed in a location other
than the natural facet joint location without departing from the
invention, such as by orienting the fixation element along a
different angle, by moving the joint cephalad or caudad, or by
moving the joint medially or laterally.
[0058] In the embodiment shown in FIGS. 4-7, fixation element 42 is
a screw. Other possible fixation elements include headless screws,
stems, corkscrews, wire, staples, adhesives, bone cements, and
other materials known in the prosthetic arts.
[0059] In this embodiment of the invention, the cephalad facet
joint prosthesis attaches to a posterior element of the vertebra,
such as one or portions of the lamina and/or the spinous process.
For example, as shown in FIGS. 4-6, fixation element 42 may extend
through a lamina portion 62 of vertebra 60 at the base of spinous
process 64, traversing the vertebra midline as defined by the
spinous process 64 and through another lamina portion 66. This
orientation of the fixation element is similar to that used in
translaminar facet joint screw fixation, as known in the art. Other
orientations of fixation element 42 are possible, of course,
depending on the dictates of the specific vertebral anatomy and the
desires of the clinician. For example, fixation element 42 may
extend through only one lamina portion, only through the spinous
process, etc.
[0060] Unlike other facet joint prostheses that attach to the
pedicle, this embodiment's use of one or more posterior elements of
the vertebra to attach the cephalad facet joint prosthesis of this
invention does not block access to the pedicle area, leaving this
area free to be used to attach other prostheses or devices. Other
embodiments of the invention may block the pedicle area, of course,
without departing from the scope or spirit of the invention. In
addition, because of the inherent strength of the lamina, the
cephalad facet joint prosthesis may be affixed without the use of
bone cement, especially when using a bone ingrowth surface or
trabecular metal.
[0061] In the orientation shown in FIGS. 4-6 as well as in some
alternative embodiments, after insertion the fixation element's
proximal end 43 (preferably formed to mate with a suitable
insertion tool) and distal end 44 lie on opposite sides of the
lamina. Bearing element 38 attaches to the distal end 44 of
fixation element 42 to be disposed between a caudal facet joint
bearing surface (either natural or artificial, such as the
artificial caudal facet joint prosthesis described below) and a
portion of the vertebra, such as the lamina portion shown in FIGS.
4-6. To attach bearing element 38 to fixation element 42 in the
embodiment shown in FIG. 4, a hole 46 in bearing element 38 is
formed with a Morse taper that mates with the distal end 44 of
fixation element 42. Other means of attaching bearing element 38 to
fixation element 42 may be used, of course, such as other Morse or
other taper connections, machine screw threads, NPT screw threads
or other known mechanical fastening means. Fixation element 42 may
be coated with antimicrobial, antithrombotic, hydroxyapatite, or
osteoinductive materials to promote bone ingrowth and fixation.
Bearing element 38 may be attached to fixation element 42 before or
after implantation in the patient, depending on the manner of
implantation and the requirements of the situation.
[0062] Prosthesis 36 may be used to form the cephalad portion of a
facet joint with either a natural caudal facet joint portion or an
artificial caudal facet joint prosthesis.
[0063] FIGS. 4-7 also show an artificial caudal joint prosthesis 50
for replacing the superior half of a natural facet joint according
to one aspect of this invention. Caudal prosthesis 50 has a bearing
element 52 with a bearing surface 54. In this embodiment, bearing
surface 54 is concave. Bearing element 52 may be formed from
biocompatible metals (such as cobalt chromium steel, surgical
steels, titanium, titanium alloys, tantalum, tantalum alloys,
aluminum, etc.), ceramics, polyethylene, biocompatible polymers,
and other materials known in the prosthetic arts, and bearing
surface 54 may be formed from biocompatible metals (such as cobalt
chromium steel, surgical steels, titanium, titanium alloys,
tantalum, tantalum alloys, aluminum, etc.), ceramics, polyethylene,
biocompatible polymers, and other materials known in the prosthetic
arts.
[0064] In one embodiment, the natural caudal facet surface has been
removed, and fixation element 56 attaches prosthesis 50 to a
vertebra 70 via a pedicle in an orientation and position that
places bearing surface 54 in approximately the same location as the
natural facet joint surface the prosthesis replaces. In an
alternative embodiment, the bearing surface 54 may be placed in a
location different than the natural facet joint surface, either
more medial or more lateral, more cephalad or more caudad, and/or
rotated from the natural anatomical orientation and orientation. In
addition, in other embodiments the caudal component can be attached
to the vertebral body in addition to the pedicle or to the
vertebral body alone.
[0065] As shown in the embodiment of FIGS. 4-7, fixation element 56
is a screw attached to bearing element 54 via a hole 58 formed in
bearing element 52 and is inserted into a pedicle portion 72 of
vertebra 70. Other possible fixation elements include stems,
corkscrews, wire, staples, adhesives, bone cements, and other
materials known in the prosthetic arts. Fixation element 56 can
also be inserted into the vertebral body in addition to or in place
of the pedicle.
[0066] In this embodiment, bearing element 52 has a serrated
fixation surface 57 adapted to contact a contact portion 74 of
vertebra 70. This optional fixation surface 57 helps prevent
rotation of the bearing element 52. In addition, fixation surface
57 may be coated with bone ingrowth material, and any optional
serrations increase the surface area for bone ingrowth. As shown in
FIG. 5, in this embodiment the entire bearing surface 54 is
posterior to surface 57 and contact portion 74.
[0067] Prosthesis 50 may be used to form the caudal portion of a
facet joint with either a natural cephalad facet joint portion or
an artificial cephalad facet joint prosthesis.
[0068] FIGS. 7A-F show the artificial facet joint prosthesis
according to one embodiment of this invention apart from the
vertebrae. As shown, cephalad bearing surface 40 and caudal bearing
surface 54 meet to form an artificial facet joint. As seen best in
FIG. 7B, the width of caudal bearing surface 54 along its
transverse axis is greater than the width of cephalad bearing
surface 40 along its transverse axis. This feature helps align the
cephalad and caudal joints during implant. In addition, this
feature permits the point of contact between the two bearing
surface to change with flexion, extension, left and right rotation
and lateral bending of the patient's spine.
[0069] The prostheses of FIGS. 4-7 may be implanted without special
tools. One embodiment of the invention, however, includes an
installation fixture to assist with the implantation procedure.
FIGS. 8-14 show installation tools used to implant two artificial
facet joints, i.e., two cephalad facet joint prostheses and two
corresponding caudal facet joint prostheses. The invention also
includes installation tools for implanting a single facet joint
prosthesis, two caudal facet joint prostheses, two cephalad facet
joint prostheses, a caudal and cephalad joint prosthesis, or any
other combination of facet joint prostheses.
[0070] As shown in FIGS. 8 and 9, installation fixture 80 has
alignment elements 82 to align the cephalad bearing elements 38 and
caudal bearing elements 52. In this embodiment, the alignment
elements are two dowels for each bearing element. Alignment
elements 82 mate with corresponding alignment elements in the
bearing elements, such as holes 84 (shown, e.g., in FIG. 7B) formed
in cephalad bearing elements 38 and caudal bearing elements 52.
Other alignment elements may be used, of course, such as pins,
grooves, indentations, etc. Attachment elements such as screws 86
attach the bearing elements 38 and 52 to the installation fixture
via screw holes 88 (shown, e.g., in FIG. 7B) formed in the bearing
elements and in installation fixture 80.
[0071] When attached to installation fixture 80, cephalad and
caudal bearing surfaces 40 and 54 are in contact and in proper
alignment with respect to each other, as shown in FIG. 8. In one
embodiment, the cephalad and caudal bearing surfaces 40 and 54 are
preloaded to be in compression when attached to installation
fixture 80. To bring the pairs of bearing surfaces in proper
alignment with respect to the patient's vertebrae, the spacing
between the pairs of bearing surfaces might need to be adjusted. In
the embodiment of FIGS. 8, 9 and 11-14, installation fixture 80 has
two bearing support components 90 and 92 that move in a controlled
manner with respect to each other. Specifically, in this embodiment
a threaded shaft 94 extends between support components 90 and 92.
Shaft 94 engages bores formed in support components 90 and 92; one
or both of the bores are threaded so that rotation of shaft 94
causes support components 90 and 92 to move towards or away from
each other. Shaft 94 may be provided with a thumbwheel 96 or other
actuator for ease of use. One or more guide rods 98 may be provided
to maintain the alignment of support components 90 and 92. Other
means of moving the cephalad/caudal bearing elements pairs with
respect to each other may be used, such as a guided or unguided
sliding connection between installation fixture elements.
[0072] In use, after preparing the implant site by removal of all
or a portion of existing natural cephalad and caudal facet joint
portions of the cephalad and caudal vertebrae 60 and 70,
respectively, of the spine motion segment, bearing elements 38 and
52 are attached to installation fixture 80 as described above. The
spacing between the bearing element pairs is then adjusted using
thumbwheel 96 to align the fixation holes 58 of caudal bearing
elements 52 with the proper fixation screw insertion sites in the
pedicle portions of the caudal vertebra (or other suitable
location), thus placing the artificial facet joints in positions
corresponding to the position of natural facet joints or in any
other position desired by the physician, including positions that
do not correspond to the position of natural facet joints. Passages
aligning with holes 58 are formed and in the pedicle- or into
another part of the caudal vertebra near or adjacent to the
pedicle-using a drill, awl, pedicle probe, or other tool known in
the surgical arts. Fixation screws 56 are then inserted through
holes 58 into the pedicle or other portion of the caudal vertebra
to attach the caudal bearing elements as well as the entire
prosthesis and installation fixture to the caudal vertebra 70, as
shown in FIGS. 11 and 12. Alternatively, self-tapping screws or
other caudal fixation elements may be used, thereby eliminating the
need to pre-form the passages.
[0073] Thereafter, the cephalad bearing elements are attached to
the cephalad vertebra 60. In one embodiment, an insertion path is
first determined for each fixation element, then a passage is
formed along the insertion path corresponding to cephalad bearing
element holes 46 (e.g., in the lamina at the base of the spinous
process and through the lamina on the other side, through only one
lamina portion, through the spinous process, etc.). Fixation screws
42 can then be inserted through the holes 46 into the passages.
Alternatively, self-tapping screws or other caudal fixation
elements may be used, thereby eliminating the need to pre-form the
passages.
[0074] After all four bearing elements have been affixed, the
installation fixture 80 may be detached and removed. Installation
fixture 80 may be used to implant fewer than four bearing elements,
of course.
[0075] FIGS. 10, 13 and 14 show a tool that may be used to define
the insertion path (location, orientation, etc.) for the fixation
element of the left cephalad bearing element. For example, the tool
may be used to guide the formation of a cephalad bearing element
attachment passage for the left bearing element. A corresponding
mirror image tool may be used for the right cephalad bearing
element. In alternative embodiments, a single tool may be used for
defining the insertion path for both left and right cephalad
bearing elements.
[0076] As shown, tool 100 has a handle 102 and an alignment
interface (such as dowels 104 in tool 100 and holes 106 in fixture
80) to align the tool in the proper orientation with respect to
installation fixture 80 and a cephalad facet joint bearing element.
With the caudal and cephalad bearing elements still attached to
installation fixture 80 and preferably with caudal bearing elements
already affixed to the caudal vertebra 70, tool 100 engages
installation fixture through the alignment interface as shown in
FIGS. 13 and 14. In this position, tool 100 may be used to define
an insertion path for the cephalad fixation elements.
[0077] In the embodiment shown in FIGS. 10, 13 and 14, the
insertion path guide is a drill guide 108 supported by arms 110 and
112 and is aligned with hole 46 in cephalad bearing element 38 by
the alignment interface between installation fixture 80 and guide
tool 100. In this embodiment, drill guide 108 is a tube, but other
guide elements may be used, such as a guide groove or surface. A
drill bit 114 may be inserted through drill guide 108 to form an
insertion passage, such as a passage through a lamina portion of
the cephalad vertebra. A fixation screw may then be inserted
through the passage in the cephalad vertebra and into the Morse
taper connection of hole 46 (or other type connection, as discussed
above) of cephalad bearing element 38. As discussed above, the
fixation screw may be coated with a bone ingrowth material.
Alternatively, a self-tapping screw may be used, thereby removing
the need to pre-form a passage.
[0078] A mirror image tool may then be used to define an insertion
path or to form a hole for the right cephalad bearing element,
which is then affixed to the vertebral body in the same way. The
installation fixture is then removed, such as by unscrewing screws
86.
[0079] As mentioned above, in alternative embodiments the guide
tool may be used to define a path for a self-tapping screw or other
fixation element that does not require the use of a drill. In those
embodiments, element 108 may be used to define a path for the
self-tapping screw or other fixation element. The fixation element
path may be through only a single lamina portion, through the
spinous process alone, or any other suitable path.
[0080] In some embodiments, the entire prosthesis other than the
bearing surface may be coated with bone ingrowth material.
[0081] The above described embodiments of this invention are merely
descriptive of its principles and are not to be limited. The scope
of this invention instead shall be determined from the scope of the
following claims, including their equivalents.
* * * * *