U.S. patent application number 10/687865 was filed with the patent office on 2005-04-14 for facet joint replacement.
Invention is credited to Chervitz, Alan, Fallin, T. Wade, Goble, E. Marlowe, Hoy, Robert W., Justin, Daniel F., Paganelli, Jude V., Triplott, Dan.
Application Number | 20050080486 10/687865 |
Document ID | / |
Family ID | 34396240 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050080486 |
Kind Code |
A1 |
Fallin, T. Wade ; et
al. |
April 14, 2005 |
Facet joint replacement
Abstract
A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, the
articulating surface being connected to the bone contacting
surface; and a fixation element that attaches the bone contacting
surface to the vertebra, the fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein the prosthesis is configured so that no portion
of the prosthesis contacts the posterior arch of the vertebra.
Inventors: |
Fallin, T. Wade; (Hyde Park,
UT) ; Goble, E. Marlowe; (Alta, WY) ; Hoy,
Robert W.; (Paradise, UT) ; Justin, Daniel F.;
(Logan, UT) ; Chervitz, Alan; (Palm Harbor,
FL) ; Paganelli, Jude V.; (San Diego, CA) ;
Triplott, Dan; (Providence, UT) |
Correspondence
Address: |
MEDICINELODGE INC.
180 SOUTH 600 WEST
LOGAN
UT
84321
US
|
Family ID: |
34396240 |
Appl. No.: |
10/687865 |
Filed: |
October 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10687865 |
Oct 17, 2003 |
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10421078 |
Apr 23, 2003 |
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10421078 |
Apr 23, 2003 |
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09726169 |
Nov 29, 2000 |
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6579319 |
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60505199 |
Sep 23, 2003 |
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Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2002/448 20130101;
A61B 17/7062 20130101; A61B 17/844 20130101; A61F 2/4637 20130101;
A61B 17/7064 20130101; A61F 2/4405 20130101 |
Class at
Publication: |
623/017.11 |
International
Class: |
A61F 002/44 |
Claims
What is claimed is:
1. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said prosthesis is configured so that no portion
of said prosthesis contacts the posterior arch of said
vertebra.
2. A prosthesis according to claim 1 wherein the surface of said
vertebra contacted by said bone contacting surface comprises an
exterior surface of the vertebra.
3. A prosthesis according to claim 1 wherein the surface of the
vertebra contacted by said bone contacting surface comprises a
resected surface of said vertebra.
4. A prosthesis according to claim 1 wherein said fixation element
comprises a post, said bone contacting surface defines an opening
therein, and further wherein said post attaches said bone
contacting surface to the vertebra by extending through said
opening.
5. A prosthesis according to claim 4 wherein said fixation element
comprises an enlarged head attached to said post for capturing said
bone contacting surface against the surface of the vertebra.
6. A prosthesis according to claim 5 wherein said enlarged head is
permanently attached to said post.
7. A prosthesis according to claim 5 wherein said enlarged head is
selectively attachable to said post.
8. A prosthesis according to claim 7 wherein said post is threaded
at its outer end, and further wherein said enlarged head comprises
a nut adapted to be selectively screwed onto said threaded
post.
9. A prosthesis according to claim 4 wherein said post comprises a
non-circular recess on its outer end for turning said post into the
vertebra.
10. A prosthesis according to claim 9 wherein said non-circular
recess comprises a hexagonal cross-section.
11. A prosthesis according to claim 4 wherein said post is
cannulated to facilitate delivery to the vertebra over a
guidewire.
12. A prosthesis according to claim 4 wherein said post is threaded
on its inner end to facilitate attachment to the vertebra.
13. A prosthesis according to claim 4 wherein said post is ribbed
on its inner end to facilitate attachment to the vertebra.
14. A prosthesis according to claim 13 wherein said ribbing extends
parallel to the longitudinal axis of said post.
15. A prosthesis according to claim 13 wherein said ribbing extends
transverse to the longitudinal axis of said post.
16. A prosthesis according to claim 4 wherein said post is barbed
on its inner end to facilitate attachment to the vertebra.
17. A prosthesis according to claim 4 wherein said post has a
circular cross-section along at least a portion of its length.
18. A prosthesis according to claim 4 wherein said post has a
non-circular cross-section along at least a portion of its
length.
19. A prosthesis according to claim 18 wherein said post has an
oval cross-section along at least a portion of its length.
20. A prosthesis according to claim 18 wherein said post has a
polygonal cross-section along at least a portion of its length.
21. A prosthesis according to claim 20 wherein said post has a
rectangular cross-section along at least a portion of its
length.
22. A prosthesis according to claim 20 wherein said post has a
triangular cross-section along at least a portion of its
length.
23. A prosthesis according to claim 4 wherein said post has an
expandable cross-section along at least a portion of its
length.
24. A prosthesis according to claim 23 wherein said post comprises
an inner member and an outer member, said inner member is slidably
received within said outer member, and further wherein said outer
member expands relative to said member according to the
longitudinal position of said inner member relative to said outer
member.
25. A prosthesis according to claim 24 wherein said outer member
comprises a plurality of talons which are cammed outward by said
inner member depending on the longitudinal position of said inner
member relative to said outer member.
26. A prosthesis according to claim 4 wherein said prosthesis
further comprises a supplemental holding element for holding said
fixation element to said vertebra.
27. A prosthesis according to claim 26 wherein said supplemental
holding element comprises a transverse pin, and further wherein
said post comprises a transverse hole for receiving said transverse
pin.
28. A prosthesis according to claim 26 wherein said supplemental
holding element comprises a spiked washer, said fixation element
comprises an enlarged head for capturing said bone contacting
surface against the surface of the vertebra, and further wherein
said spiked washer is captured to said vertebra by said enlarged
head.
29. A prosthesis according to claim 26 wherein said supplemental
holding element comprises a filament extending through a filament
opening formed in said fixation element.
30. A prosthesis according to claim 29 wherein said filament
opening is formed in said post.
31. A prosthesis according to claim 29 wherein said fixation
element comprises an enlarged head for capturing said bone
contacting surface against the surface of the vertebra, and further
wherein said filament opening is formed in said enlarged head.
32. A prosthesis according to claim 1 wherein said prosthesis
comprises a superior facet prosthesis.
33. A prosthesis according to claim 32 wherein said articulating
surface comprises a blade.
34. A prosthesis according to claim 4 wherein said articulating
surface comprises a blade, and further wherein said blade is
laterally offset from said opening.
35. A prosthesis according to claim 1 wherein said prosthesis
comprises an inferior facet prosthesis.
36. A prosthesis according to claim 35 wherein said articulating
surface comprises a talon.
37. A prosthesis according to claim 4 wherein said articulating
surface comprises a talon, and further wherein at least a portion
of said talon is laterally offset from said opening.
38. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said bone contacting surface is configured to
engage a resected surface of the vertebra.
39. A prosthesis according to claim 38 wherein the resected surface
of the vertebra is recessed relative to the surrounding portions of
the vertebra, and further wherein said bone contacting surface is
configured to engage the recessed surface.
40. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said bone contacting surface has a smaller
surface area than said articulating surface.
41. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said articulating surface comprises a wing ear
extending upward from said bone contacting surface.
42. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said articulating surface is substantially planar
and extends adjacent to the pedicle.
43. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said articulating surface is substantially planar
and extends substantially parallel to said fixation element.
44. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said fixation element clamps said bone contacting
surface to a resected surface of the vertebra.
45. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating element that articulates with another facet; a bone
contacting element that contacts a surface of the vertebra, said
articulating element being connected to said bone contacting
element; and a fixation element that attaches said bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said prosthesis is configured so that no portion
of said prosthesis contacts the posterior arch of said
vertebra.
46. A prosthesis for the replacement of at least a portion of the
bone of a superior facet located on a mammalian vertebra and for
replacement of at least a portion of the bone of an inferior facet
located on the same mammalian vertebra, comprising: a superior
articulating element that articulates with another facet; a
superior bone contacting element that contacts one of a surface of
the vertebra or another element contacting a surface of the
vertebra, said superior articulating element being connected to
said superior bone contacting element; and an inferior articulating
element that articulates with another facet; an inferior bone
contacting element that contacts one of a surface of the vertebra
or another element contacting a surface of the vertebra, said
inferior articulating element being connected to said inferior bone
contacting element; and a fixation element that attaches said
superior bone contacting element and said inferior bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said prosthesis is configured so that no portion
of said prosthesis contacts the posterior arch of said
vertebra.
47. A prosthesis for the replacement of at least a portion of the
bone of a superior facet located on a first mammalian vertebra and
for replacement of at least a portion of the bone of an inferior
facet located on a second mammalian vertebra, comprising: a
superior articulating element that articulates with another facet;
a superior bone contacting element that contacts one of a surface
of the first vertebra or another element contacting a surface of
the vertebra, said superior articulating element being connected to
said superior bone contacting element; a first fixation element
that attaches said superior bone contacting element to the first
vertebra, said first fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; and an inferior articulating element that articulates
with another facet; an inferior bone contacting element that
contacts one of a surface of the second vertebra or another element
contacting a surface of the vertebra, said inferior articulating
element being connected to said inferior bone contacting element;
and a second fixation element that attaches said inferior bone
contacting element to the second vertebra, said second fixation
element being adapted for implantation into an interior bone space
of a pedicle of the vertebra; and wherein said prosthesis is
configured so that no portion of said prosthesis contacts the
posterior arches of said first and second vertebrae.
48. A method for replacing at least a portion of the bone of a
facet located on a mammalian vertebra, comprising: providing: an
articulating surface that articulates with another facet; a bone
contacting surface that contacts a surface of the vertebra, said
articulating surface being connected to said bone contacting
surface; and a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said prosthesis is configured so that no portion
of said prosthesis contacts the posterior arch of said vertebra;
and positioning said bone contacting surface against a surface of
the vertebra; and attaching said bone contacting surface to the
vertebra using said fixation element.
49. A method according to claim 48 wherein the surface of said
vertebra contacted by said bone contacting surface comprises an
exterior surface of the vertebra.
50. A method according to claim 48 wherein the surface of the
vertebra contacted by said bone contacting surface comprises a
resected surface of said vertebra.
51. A method according to claim 48 wherein said fixation element
comprises a post, said bone contacting surface defines an opening
therein, and further wherein said post attaches said bone
contacting surface to the vertebra by extending through said
opening.
52. A method according to claim 51 wherein said fixation element
comprises an enlarged head attached to said post for capturing said
bone contacting surface against the surface of the vertebra.
53. A method according to claim 52 wherein said enlarged head is
permanently attached to said post.
54. A method according to claim 52 wherein said enlarged head is
selectively attachable to said post.
55. A method according to claim 54 wherein said post is threaded at
its outer end, and further wherein said enlarged head comprises a
nut adapted to be selectively screwed onto said threaded post.
56. A method according to claim 51 wherein said post comprises a
non-circular recess on its outer end for turning said post into the
vertebra.
57. A method according to claim 56 wherein said non-circular recess
comprises a hexagonal cross-section.
58. A method according to claim 51 wherein said post is cannulated
to facilitate delivery to the vertebra over a guidewire.
59. A method according to claim 51 wherein said post is threaded on
its inner end to facilitate attachment to the vertebra.
60. A method according to claim 51 wherein said post is ribbed on
its inner end to facilitate attachment to the vertebra.
61. A method according to claim 60 wherein said ribbing extends
parallel to the longitudinal axis of said post.
62. A method according to claim 60 wherein said ribbing extends
transverse to the longitudinal axis of said post.
63. A method according to claim 51 wherein said post is barbed on
its inner end to facilitate attachment to the vertebra.
64. A method according to claim 51 wherein said post has a circular
cross-section along at least a portion of its length.
65. A method according to claim 51 wherein said post has a
non-circular cross-section along at least a portion of its
length.
66. A method according to claim 65 wherein said post has an oval
cross-section along at least a portion of its length.
67. A method according to claim 65 wherein said post has a
polygonal cross-section along at least a portion of its length.
68. A method according to claim 67 wherein said post has a
rectangular cross-section along at least a portion of its
length.
69. A method according to claim 67 wherein said post has a
triangular cross-section along at least a portion of its
length.
70. A method according to claim 51 wherein said post has an
expandable cross-section along at least a portion of its
length.
71. A method according to claim 70 wherein said post comprises an
inner member and an outer member, said inner member is slidably
received within said outer member, and further wherein said outer
member expands relative to said inner member according to the
longitudinal position of said inner member relative to said outer
member.
72. A method according to claim 71 wherein said outer member
comprises a plurality of talons which are cammed outward by said
inner member depending on the longitudinal position of said inner
member relative to said outer member.
73. A method according to claim 51 wherein said prosthesis further
comprises a supplemental holding element for holding said fixation
element to said vertebra.
74. A method according to claim 73 wherein said supplemental
holding element comprises a transverse pin, and further wherein
said post comprises a transverse hole for receiving said transverse
pin.
75. A method according to claim 73 wherein said supplemental
holding element comprises a spiked washer, said fixation element
comprises an enlarged head for capturing said bone contacting
surface against the surface of the vertebra, and further wherein
said spiked washer is captured to said vertebra by said enlarged
head.
76. A method according to claim 73 wherein said supplemental
holding element comprises a filament extending through a filament
opening formed in said fixation element.
77. A method according to claim 76 wherein said filament opening is
formed in said post.
78. A method according to claim 76 wherein said fixation element
comprises an enlarged head for capturing said bone contacting
surface against the surface of the vertebra, and further wherein
said filament opening is formed in said enlarged head.
79. A method according to claim 48 wherein said prosthesis
comprises a superior facet prosthesis.
80. A method according to claim 79 wherein said articulating
surface comprises a blade.
81. A method according to claim 51 wherein said articulating
surface comprises a blade, and further wherein said blade is
laterally offset from said opening.
82. A method according to claim 51 wherein said prosthesis
comprises an inferior facet prosthesis.
83. A method according to claim 82 wherein said articulating
surface comprises a finger.
84. A method according to claim 51 wherein said articulating
surface comprises a finger, and further wherein at least a portion
of said finger is laterally offset from said opening.
85. A prosthesis for the replacement of at least a portion of the
bone of a facet located on a mammalian vertebra, comprising: an
articulating element that articulates with another facet; a bone
contacting element that contacts a surface of the vertebra or
another element contacting a surface of the vertebra, said
articulating element being connected to said bone contacting
element; and a fixation element that attaches said bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra; wherein said prosthesis is configured so that no portion
of said prosthesis contacts the posterior arch of said
vertebra.
86. A prosthesis according to claim 85 wherein said prosthesis
comprises a superior facet prosthesis.
87. A prosthesis according to claim 86 wherein said bone contacting
element is adapted to contact a resected surface of a pedicle or
another element contacting a resected surface of a pedicle.
88. A prosthesis according to claim 85 wherein said articulating
element comprises a blade.
89. A prosthesis according to claim 85 wherein said prosthesis
comprises an inferior facet prosthesis.
90. A prosthesis according to claim 89 wherein said bone contacting
element is adapted to contact a resected surface of a pedicle or
another element contacting a resected surface of a pedicle.
91. A prosthesis according to claim 89 wherein said articulating
element comprises a finger.
92. A prosthesis according to claim 91 wherein said articulating
element is configured to engage a resected surface of an inferior
facet.
93. A prosthesis according to claim 89 wherein at least a portion
of said finger is laterally offset from said bone contacting
element.
94. A method for replacing at least a portion of the bone of a
facet located on a mammalian vertebra, comprising: an articulating
element that articulates with another facet; a bone contacting
element that contacts a surface of the vertebra or another element
contacting a surface of the vertebra, said articulating element
being connected to said bone contacting element; and a fixation
element that attaches said bone contacting element to the vertebra,
said fixation element being adapted for implantation into an
interior bone space of a pedicle of the vertebra; wherein said
prosthesis is configured so that no portion of said prosthesis
contacts the posterior arch of said vertebra; positioning said bone
contacting surface against a surface of the vertebra or another
element contacting a surface of the vertebra; and attaching said
bone contacting surface to the vertebra using said fixation
element.
95. A method according to claim 85 wherein said prosthesis
comprises a superior facet prosthesis.
96. A method according to claim 95 wherein said bone contacting
element is adapted to contact a resected surface of a pedicle or
another element contacting a resected surface of a pedicle.
97. A method according to claim 94 wherein said articulating
element comprises a blade.
98. A method according to claim 94 wherein said prosthesis
comprises an inferior facet prosthesis.
99. A method according to claim 98 wherein said bone contacting
element is adapted to contact a resected surface of a pedicle or
another element contacting a resected surface of a pedicle.
100. A method according to claim 98 wherein said articulating
element comprises a finger.
101. A method according to claim 100 wherein said articulating
element is configured to engage a resected surface of an inferior
facet.
102. A method according to claim 98 wherein at least a portion of
said finger is laterally offset from said bone contacting element.
Description
REFERENCE TO PENDING PRIOR APPLICATIONS
[0001] The present application claims the benefit of:
[0002] (i) pending prior U.S. patent application Ser. No.
10/421,078, filed Apr. 23, 2003 by E. Marlowe Goble et al. for
FACET JOINT REPLACEMENT (Attorney's Docket No. MED-1 CON); and
[0003] (ii) pending prior U.S. Provisional Patent Application Ser.
No. 60/505,199, filed Sep. 23, 2003 by E. Marlowe Goble et al. for
FACET JOINT REPLACEMENT (Attorney's Docket No. MED-1 CIP PROV).
[0004] The two above-identified documents are hereby incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0005] 1. Field Of The Invention
[0006] The present invention relates to surgical devices and
methods to replace a damaged, diseased, or otherwise painful spinal
facet joint.
[0007] 2. Description Of Related Art
[0008] Traumatic, inflammatory, metabolic, and degenerative
disorders of the spine can produce debilitating pain that can have
severe socioeconomic and psychological effects. One of the most
common surgical interventions today is arthrodesis, or spine
fusion, of one or more motion segments, with approximately 300,000
procedures performed annually in the U.S. Clinical success varies
considerably, depending upon technique and indications, and
consideration must be given to the concomitant risks and
complications. For example, Tsantrizos and Nibu have shown that
spine fusion decreases function by limiting the range of motion for
patients in flexion, extension, rotation, and lateral bending.
Furthermore, Khoo and Nagata have shown that spine fusion creates
increased stresses and, therefore, accelerated degeneration of
adjacent non-fused motion segments. Additionally, pseudoarthrosis,
as a result of an incomplete or ineffective fusion, may reduce or
even eliminate the desired pain relief for the patient. Finally,
the fusion device, whether artificial or biological, may migrate
out of the fusion site.
[0009] Recently, several attempts have been made to recreate the
natural biomechanics of the spine by use of an artificial disc.
Artificial discs provide for articulation between vertebral bodies
to recreate the full range of motion allowed by the elastic
properties of the natural intervertebral disc that directly
connects two opposed vertebral bodies.
[0010] However, the artificial discs proposed to date do not fully
address the mechanics of motion of the spinal column. In addition
to the intervertebral disc, posterior elements called the facet
joints help to support axial, torsional and shear loads that act on
the spinal column. Furthermore, the facet joints are diarthroidal
joints that provide both sliding articulation and load transmission
features. The effects of their absence as a result of facetectomy
was observed by Goh to produce significant decreases in the
stiffness of the spinal column in all planes of motion: flexion and
extension, lateral bending, and rotation. Furthermore,
contraindications for artificial discs include arthritic facet
joints, absent facet joints, severe facet joint tropism or
otherwise deformed facet joints, as noted by Lemaire.
[0011] U.S. Pat. No. 36,758 to Fitz discloses an artificial facet
joint where the inferior facet, the mating superior facet, or both,
are resurfaced.
[0012] U.S. Pat. No. 6,132,464 to Martin discloses a spinal facet
joint prosthesis that is supported on the posterior arch of the
vertebra. Extending from this support structure are inferior and/or
superior blades that replace the cartilage at the facet joint. Like
the Fitz design, the Martin prosthesis generally preserves existing
bony structures and therefore does not address pathologies that
affect the bone of the facets in addition to affecting the
associated cartilage. Furthermore, the Martin invention requires a
mating condition between the prosthesis and the posterior arch
(also known as the lamina) that is a thin base of curved bone that
carries all four facets and the spinous process. Since the
posterior arch is a very complex and highly variable anatomic
surface, it would be very difficult to design a prosthesis that
provides reproducible positioning to correctly locate the
cartilage-replacing blades for the facet joints.
[0013] Another approach to surgical intervention for spinal facets
is provided in WO9848717A1 to Villaret. While Villaret teaches the
replacement of spine facets, the replacement is interlocked in a
manner to immobilize the joint.
[0014] Facet joint replacement in conjunction with artificial disc
replacements represent a holistic solution to recreating a fully
functional motion segment that is compromised due to disease or
trauma. Together, facet joint and disc replacement can eliminate
all sources of pain, return full function and range of motion, and
completely restore the natural biomechanics of the spinal column.
Additionally, degenerative or traumatized facet joints may be
replaced in the absence of disc replacement when the natural
intervertebral disc is unaffected by the disease or trauma.
[0015] It would therefore be an improvement in the art to provide a
vertebral facet replacement device and method that replaces a bony
portion of the facets so as to remove the source of arthritic,
traumatic, or other disease mediated pain.
SUMMARY OF THE INVENTION
[0016] It is an object of the invention to provide an artificial
vertebral facet that replaces the cartilage and a portion of the
bone of a facet.
[0017] It is a further object of the invention to provide a method
for preparing a vertebra for the installation of an artificial
vertebral facet.
[0018] It is another object to provide a method for replacing a
spinal facet.
[0019] It is yet another object of the invention to provide a total
vertebral facet joint replacement.
[0020] In the preferred embodiment, an inferior facet of a superior
vertebra is resected at the base of the facet where it connects to
the posterior arch. The fin of a prosthetic inferior facet is
pressed into the interior bone space of the posterior arch.
Alternatively, a tool, such as a broach or punch, may be used to
first prepare a space for the fin within the posterior arch.
[0021] Alternatively, or in addition, a superior facet of an
inferior vertebra that articulates with the inferior facet is
resected at the base of the facet where it connects to the pedicle.
The post of a prosthetic superior facet is pressed into the
interior bone space of the pedicle. Alternatively, a tool, such as
a broach or punch, may be used to first prepare a space for the
post within the pedicle.
[0022] The post and the fin may be porous coated to promote bone
ingrowth in order to achieve long term fixation. Long term fixation
is provided by a press fit between the post or fin and the internal
surface of the bone. The porous coating may carry osteoconductive
agents, such as hydroxylapatite, calcium sulfate, or demineralized
bone matrix. Alternatively, the porous coating may carry
osteoinductive agents, such as bone morphogenic proteins, including
rhBMP-2 and rhBMP-7.
[0023] Another embodiment of the present invention provides a
flange extending from the prosthetic facet. The flange is oriented
relative to the body of the prosthesis such that when the flange is
placed against the pedicle and in a manner such that the planar
surface of the flange is perpendicular to the axis of the pedicle
interior bone canal, the articulating surface of the prosthesis
will be properly positioned to match the articulating surface of
the natural facet. The flange includes a hole for the passage of a
fastener to securely attach the prosthesis to the pedicle. The
fastener can be a screw, spike, tack, staple, or the like.
[0024] In one form of the invention, there is provided a prosthesis
for the replacement of at least a portion of the bone of a facet
located on a mammalian vertebra, comprising:
[0025] an articulating surface that articulates with another
facet;
[0026] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0027] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0028] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra.
[0029] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0030] an articulating surface that articulates with another
facet;
[0031] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0032] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0033] wherein said bone contacting surface is configured to engage
a resected surface of the vertebra.
[0034] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0035] an articulating surface that articulates with another
facet;
[0036] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0037] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0038] wherein said bone contacting surface has a smaller surface
area than said articulating surface.
[0039] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0040] an articulating surface that articulates with another
facet;
[0041] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0042] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0043] wherein said articulating surface comprises a wing ear
extending upward from said bone contacting surface.
[0044] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0045] an articulating surface that articulates with another
facet;
[0046] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0047] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0048] wherein said articulating surface is substantially planar
and extends adjacent to the pedicle.
[0049] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0050] an articulating surface that articulates with another
facet;
[0051] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0052] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0053] wherein said articulating surface is substantially planar
and extends substantially parallel to said fixation element.
[0054] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0055] an articulating surface that articulates with another
facet;
[0056] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0057] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0058] wherein said fixation element clamps said bone contacting
surface to a resected surface of the vertebra.
[0059] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0060] an articulating element that articulates with another
facet;
[0061] a bone contacting element that contacts a surface of the
vertebra, said articulating element being connected to said bone
contacting element; and
[0062] a fixation element that attaches said bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0063] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra.
[0064] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a superior facet located on a mammalian vertebra and for
replacement of at least a portion of the bone of an inferior facet
located on the same mammalian vertebra, comprising:
[0065] a superior articulating element that articulates with
another facet;
[0066] a superior bone contacting element that contacts one of a
surface of the vertebra or another element contacting a surface of
the vertebra, said superior articulating element being connected to
said superior bone contacting element; and
[0067] an inferior articulating element that articulates with
another facet;
[0068] an inferior bone contacting element that contacts one of a
surface of the vertebra or another element contacting a surface of
the vertebra, said inferior articulating element being connected to
said inferior bone contacting element; and
[0069] a fixation element that attaches said superior bone
contacting element and said inferior bone contacting element to the
vertebra, said fixation element being adapted for implantation into
an interior bone space of a pedicle of the vertebra;
[0070] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra.
[0071] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a superior facet located on a first mammalian vertebra and for
replacement of at least a portion of the bone of an inferior facet
located on a second mammalian vertebra, comprising:
[0072] a superior articulating element that articulates with
another facet;
[0073] a superior bone contacting element that contacts one of a
surface of the first vertebra or another element contacting a
surface of the vertebra, said superior articulating element being
connected to said superior bone contacting element;
[0074] a first fixation element that attaches said superior bone
contacting element to the first vertebra, said first fixation
element being adapted for implantation into an interior bone space
of a pedicle of the vertebra; and
[0075] an inferior articulating element that articulates with
another facet;
[0076] an inferior bone contacting element that contacts one of a
surface of the second vertebra or another element contacting a
surface of the vertebra, said inferior articulating element being
connected to said inferior bone contacting element; and
[0077] a second fixation element that attaches said inferior bone
contacting element to the second vertebra, said second fixation
element being adapted for implantation into an interior bone space
of a pedicle of the vertebra; and
[0078] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arches of said first and
second vertebrae.
[0079] In another form of the present invention, there is provided
a method for replacing at least a portion of the bone of a facet
located on a mammalian vertebra, comprising:
[0080] providing:
[0081] an articulating surface that articulates with another
facet;
[0082] a bone contacting surface that contacts a surface of the
vertebra, said articulating surface being connected to said bone
contacting surface; and
[0083] a fixation element that attaches said bone contacting
surface to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0084] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra;
and
[0085] positioning said bone contacting surface against a surface
of the vertebra; and
[0086] attaching said bone contacting surface to the vertebra using
said fixation element.
[0087] In another form of the present invention, there is provided
a prosthesis for the replacement of at least a portion of the bone
of a facet located on a mammalian vertebra, comprising:
[0088] an articulating element that articulates with another
facet;
[0089] a bone contacting element that contacts a surface of the
vertebra or another element contacting a surface of the vertebra,
said articulating element being connected to said bone contacting
element; and
[0090] a fixation element that attaches said bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0091] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra.
[0092] In another form of the present invention, there is provided
a method for replacing at least a portion of the bone of a facet
located on a mammalian vertebra, comprising:
[0093] an articulating element that articulates with another
facet;
[0094] a bone contacting element that contacts a surface of the
vertebra or another element contacting a surface of the vertebra,
said articulating element being connected to said bone contacting
element; and
[0095] a fixation element that attaches said bone contacting
element to the vertebra, said fixation element being adapted for
implantation into an interior bone space of a pedicle of the
vertebra;
[0096] wherein said prosthesis is configured so that no portion of
said prosthesis contacts the posterior arch of said vertebra;
[0097] positioning said bone contacting surface against a surface
of the vertebra or another element contacting a surface of the
vertebra; and
[0098] attaching said bone contacting surface to the vertebra using
said fixation element.
[0099] Because the present invention allows for the individual
replacements of facets, only comprised facets need be replaced. For
example, if only one facet is affected by disease or trauma, it can
be resected and replaced with a facet prosthesis that articulates
with an opposing natural facet.
[0100] The present invention has numerous advantages over the prior
art. One advantage is that the quality of attachment of the
prosthesis is improved. The present invention provides a precise
press fit into bones, as opposed to relying on prosthetic surfaces
mating with highly complex and variable external surfaces of the
vertebra, such as the posterior arch or facet. Another advantage is
that the optional porous coating is placed into interior bone
spaces where porous coatings have proven to achieve bone ingrowth
for excellent long term fixation strength. This ability to achieve
bone ingrowth is uncertain for the prior art devices that engage
the external bone surfaces of the vertebra. Yet another advantage
lies in the removal of the facet bone structure; where the facet
bone is involved in the disease pathology or the trauma that
compromised the articular or cartilaginous surface of the facet,
resection provides a means for ensuring that all pain associated
with the disease or trauma is removed.
[0101] The above, and other objects, features and advantages of the
present invention, will become apparent from the following
description which is to be read in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0102] FIG. 1 is a perspective view of a portion of the spine;
[0103] FIG. 1A is a dorsal view of the portion of the spine shown
in FIG. 1;
[0104] FIG. 2 is a lateral view of a facet joint reconstructed in
accordance with the present invention;
[0105] FIG. 3 is a dorsal view of the facet joint shown in FIG.
2;
[0106] FIG. 4 is a perspective view of the implanted left inferior
facet prosthesis shown in FIGS. 2 and 3;
[0107] FIG. 5 is a perspective view of the left inferior facet
prosthesis shown in FIGS. 2 and 3;
[0108] FIG. 6 is a cranial view of the implanted left superior
facet prosthesis shown in FIGS. 2 and 3;
[0109] FIG. 7 is a perspective view of the left superior facet
prosthesis shown in FIGS. 2 and 3;
[0110] FIG. 8 is a perspective view of an alternate implanted left
inferior facet prosthesis;
[0111] FIG. 9 is a perspective view of an alternate left inferior
facet prosthesis;
[0112] FIG. 10 is a lateral view of an alternative reconstructed
facet joint;
[0113] FIG. 11 is a dorsal view of an alternative reconstructed
facet joint;
[0114] FIG. 12 is a perspective view of the implanted left inferior
facet prosthesis shown in FIGS. 10 and 11;
[0115] FIG. 13 is a perspective view of the alternative left
inferior facet prosthesis shown in FIGS. 10 and
[0116] FIG. 14 is a cranial view of the alternative implanted left
superior facet prosthesis shown in FIGS. 10 and 11;
[0117] FIG. 15 is a perspective view of the alternative left
superior facet prosthesis shown in FIGS. 10 and 11;
[0118] FIG. 16 is a perspective view of an alternate bearing
surface for the superior facet prosthesis shown in FIG. 15;
[0119] FIG. 17 is a dorsal view of a single intact vertebra;
[0120] FIG. 18 is a lateral view of the same intact vertebra shown
in FIG. 17;
[0121] FIG. 19 is a dorsal view of the same vertebra of FIG. 17 and
FIG. 18, with a portion of the superior facet resected and a
portion of the inferior facet resected;
[0122] FIG. 20 is a lateral view of the resected vertebra shown in
FIG. 19;
[0123] FIG. 21 is a dorsal view of the same resected vertebra shown
in FIG. 18 and FIG. 19 with a fixation element placed through the
first superior resection surface and into the pedicle bone;
[0124] FIG. 22 is a dorsal view showing the resected vertebra, the
fixation element, and a superior facet prosthesis;
[0125] FIG. 23 is a dorsal view of the vertebra and the implant of
FIG. 23 and also showing the addition of an inferior facet
prosthesis;
[0126] FIG. 24 is a dorsal view of the implant and vertebra of FIG.
23 and also showing the addition of an enlarged head that has the
shape of a locking nut;
[0127] FIG. 25 is an isometric posteriolateral view of a vertebra
with an assembled implant comprising a fixation element, superior
facet prosthesis, and a locking nut;
[0128] FIG. 26 is a cross-sectional view of the same vertebra and
implant of FIG. 25 showing the result of a cross-sectional view cut
aligned with the axis of the fixation element;
[0129] FIG. 27 is a view of the same cross-section described in
FIG. 26, aligned to face the viewer;
[0130] FIG. 28 is a side view of embodiments A, B, C, D, E, and F
of the fixation element, and a cross-sectional view of the same
embodiments, and a side view of the enlarged head in the shape of a
locking nut;
[0131] FIG. 28A is a side view of embodiments G, H, I, J, K, and L
of the fixation element with attached enlarged heads, and a
cross-sectional view of the same embodiments;
[0132] FIG. 29 is an isometric view of a radially expanding
fixation element in its unexpanded state;
[0133] FIG. 30 is a side view and a bottom view of (i) an expanded
radially expanding fixation element and (ii) an unexpanded radially
expanding fixation element;
[0134] FIG. 31 is an isometric cross-sectional view of a vertebra
and a facet implant showing a cross-pin torsionally and axially
securing the fixation element;
[0135] FIG. 32 is a dorsal view of a spinal section showing a top,
middle, and bottom vertebra with unilateral facet replacements on
the right side of the spine section, both between the top and
middle vertebra, and between the middle and bottom vertebra;
[0136] FIG. 33 is a dorsal view of a spine section showing a
superior hemiplasty facet replacement between the top and the
middle vertebra and unilateral replacement between the middle and
the bottom vertebra;
[0137] FIG. 34 is a dorsal view of a spinal section showing an
inferior facet hemiplasty replacement between the top and the
middle vertebra and a unilateral replacement on the right side
between the middle and the bottom vertebra;
[0138] FIG. 35 is a dorsal view of a spinal section showing a
unilateral replacement between the top and the middle vertebra on
the right side, and an inferior facet hemiplasty replacement
between the middle and the bottom vertebra on the same side;
[0139] FIG. 36 is a dorsal view of a spinal section showing a
unilateral replacement between the top and the middle vertebra on
the right side and a superior facet hemiplasty replacement on the
right side between the middle and the bottom vertebra on the same
side;
[0140] FIG. 37 is a spinal section of two vertebra showing the
inferior facet of the top vertebra and the superior facet of the
joining bottom vertebra replaced by an articulating facet
implant;
[0141] FIG. 38 is an isometric view of a curved superior facet
prosthesis;
[0142] FIG. 39 is an isometric view of the bone ingrowth surface on
a superior facet prosthesis;
[0143] FIG. 40 is an isometric view of an inferior facet
prosthesis;
[0144] FIG. 41 is an isometric view of an inferior facet prosthesis
with a bone ingrowth surface;
[0145] FIG. 42 shows the addition of a locking washer to the
construction of the implant shown in FIG. 25;
[0146] FIG. 43 shows the assembly of the construct shown in FIG.
42;
[0147] FIG. 44 shows an isometric view of the locking washer shown
in FIG. 42;
[0148] FIG. 45 shows superior and inferior facet prostheses held to
a vertebra by flexible fixation elements; and
[0149] FIG. 46 is a dorsal view of a bilateral inferior
implant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0150] Referring now to FIGS. 1 and 1A, there is shown a superior
vertebra 1 and an inferior vertebra 3, with an intervertebral disc
2 located in between. Vertebra 1 has superior facets 43, inferior
facets 6, posterior arch (or lamina) 35 and spinous process 46.
Vertebra 3 has superior facets 7, inferior facets 44, posterior
arch (or lamina) 36 and spinous process 45.
[0151] Referring now to FIG. 2, the left inferior facet 6 of
vertebra 1 shown in FIG. 1 and FIG. 1A has been resected and
inferior facet prosthesis 4 has been attached to vertebra 1.
Similarly, the left superior facet 7 of vertebra 3 has been
resected and a superior facet prosthesis 5 has been attached to
vertebra 3.
[0152] FIG. 3 illustrates a dorsal view of the elements shown in
FIG. 2. It can be appreciated that inferior facet prosthesis 4
replicates the natural anatomy when compared to the contralateral
inferior facet 6 of vertebra 1. Similarly, it can be appreciated
that superior facet prosthesis 5 replicates the natural anatomy
when compared to the contralateral superior facet 7 of vertebra 3.
Neither inferior facet prosthesis 4 nor superior facet prosthesis 5
rests on the lamina.
[0153] Turning now to FIG. 4, a perspective view of vertebra 1 with
implanted inferior facet prosthesis 4 is provided. A bone resection
on the left side of the vertebra 1, shown as resection 31, has
removed the natural inferior facet 6 at the bony junction between
the inferior facet 6 and the posterior arch (or lamina) 35. In this
manner, any bone pain associated with a disease, such as
osteoarthritis, or trauma of the left inferior facet 6 will be
eliminated as the involved bony tissue has been osteotomized.
[0154] FIG. 5 illustrates a perspective view of inferior facet
prosthesis 4. Surface 8 replicates the natural articular surface of
the replaced inferior facet 6. Post 9 provides a means to affix
inferior facet prosthesis 4 to vertebra 1. Post 9 is implanted into
the interior bone space of the left pedicle on vertebra 1 and may
or may not extend into the vertebral body of vertebra 1 to provide
additional stability.
[0155] FIG. 6 illustrates a cranial view of vertebra 3 with
implanted superior facet prosthesis 5. Resection surface 32
represents the bony junction between the natural superior facet 7
and the posterior arch 35.
[0156] FIG. 7 illustrates a perspective view of superior facet
prosthesis 5. Surface 36 replicates the natural articular surface
of the replaced superior facet 7. Post 37 provides a means for
affixing superior facet prosthesis 5 to vertebra 3. Post 37 is
implanted into the interior bone space of the left pedicle P (FIG.
6) on vertebra 3 and may or may not extend into the vertebral body
of vertebra 3 to provide additional stability.
[0157] When the total facet joint is replaced, as shown in FIGS. 2
and 3, then surface 8 (FIG. 5) articulates with surface 36 (FIG. 7)
to recreate the natural biomechanics of the spine motion segment
made up of vertebra 1, vertebra 3, and intervertebral disc 2.
Neither inferior facet prosthesis 4 nor superior facet prosthesis 5
rests on the lamina.
[0158] FIG. 8 illustrates an alternative inferior facet prosthesis
10 which is implanted into the interior bone space of posterior
arch (or lamina) 35. The interior bone space is accessed from the
resection 31.
[0159] FIG. 9 shows details of alternative inferior facet
prosthesis 10, including the fin 13 that extends into the interior
bone space of posterior arch 35. Surface 12 replicates the natural
articular surface of the replaced facet.
[0160] The surfaces of post 9 (FIG. 5), post 37 (FIG. 7) and fin 13
(FIG. 9) may or may not include porous coatings to facilitate bone
ingrowth to enhance the long term fixation of the implant.
Furthermore, such porous coatings may or may not include
osteoinductive or osteoconductive substances to further enhance the
bone remodeling into the porous coating.
[0161] Referring now to FIG. 10, there is shown a lateral view of a
superior vertebra 14 and an inferior vertebra 16, with an
intervertebral disc 15 located in between. The left inferior facet
of vertebra 14 has been resected and an inferior facet prosthesis
18 has been attached to vertebra 14 by means of a screw fastener
17. Similarly, the left superior facet of vertebra 16 has been
resected and a superior facet prosthesis 19 has been attached to
vertebra 16 by means of a screw fastener 17.
[0162] FIG. 11 illustrates a dorsal view of the elements of FIG.
10. It can be appreciated that inferior facet prosthesis 18
replicates the natural anatomy when compared to the contralateral
inferior facet 22 of vertebra 14. Similarly, it can be appreciated
that superior facet prosthesis 19 replicates the natural anatomy
when compared to the contralateral superior facet 21 of vertebra
16. Neither inferior facet prosthesis 18 nor superior facet
prosthesis 19 rests on the lamina.
[0163] Turning now to FIG. 12, there is provided a perspective view
of vertebra 14 with implanted inferior facet prosthesis 18.
Resection 34 has removed the natural inferior facet at the bony
junction between the inferior facet and the posterior arch 37. In
this manner, any bone pain associated with a disease, such as
osteoarthritis, or trauma of the natural inferior facet 22 will be
eliminated inasmuch as the involved bony tissue has been
osteotomized.
[0164] FIG. 13 illustrates a perspective view of inferior facet
prosthesis 18. Surface 23 replicates the natural articular surface
of the replaced facet. Flange 25 contacts the pedicle P (FIG. 12)
and hole 24 receives a screw fastener 17 to attach inferior facet
prosthesis 18 to vertebra 14.
[0165] FIG. 14 illustrates a cranial view of vertebra 16 with
implanted superior facet prosthesis 19. Resection surface 35A
represents the bony junction between the natural superior facet 21
(FIG. 11) and the posterior arch 38.
[0166] FIG. 15 illustrates a perspective view of superior facet
prosthesis 19. Surface 27 replicates the natural articular surface
of the replaced facet. Flange 39 contacts the pedicle P (FIG. 14)
and hole 26 receives a screw fastener 17 to attach superior facet
prosthesis 19 to vertebra 16.
[0167] FIG. 16 illustrates an alternative superior facet prosthesis
40 with a bearing surface 41 that mounts to substrate 42. The
bearing surface 41 is a biocompatible polymeric material, such as
ultra high molecular weight polyethylene. Alternately, the bearing
surface can be ceramic, such as zirconia or alumina. The substrate
is a biocompatible metal alloy, such as an alloy of titanium,
cobalt, or iron.
[0168] Referring to FIG. 17 and FIG. 18, a single intact vertebra
100 is shown. FIG. 17 is a dorsal view of the vertebra 100. FIG. 18
is a lateral view of the same vertebra 100. Similar to the two
vertebra shown in the portion of the spine illustrated in FIGS. 1
through 3, the vertebra 100 has posterior anatomy comprising left
and right superior facets 43 on the superior, or top side in this
view of the dorsal vertebra 100, left and right inferior facets 6
on the inferior or bottom side of the posterior vertebra 100, left
and right transverse processes 105 extending laterally from the
posterior portion of vertebra 100, and left and right pedicles P.
The posterior portion of vertebra 100 also has a posterior arch (or
lamina) 35, and a spinous process 46 that protrudes from the
posterior arch 35 posteriorly, out of the page in FIG. 17 and to
the left in FIG. 18. In FIG. 17, the bony structure of the superior
facets 43 and the inferior facets 6 are intact, as it would be
presented in a vertebra without significant tissue degeneration or
remodeling resulting from facet joint disease. Although the
vertebra 100 is shown in FIG. 17 as a generally structurally
healthy and intact vertebra, if the vertebra 100 were a diseased
vertebra, the vertebra could exhibit signs of facet joint
disease.
[0169] Consequently, structural pathology related to facet joint
disease would likely be visible. For example, the left superior
facet 43 and the right superior facet 43 of the vertebra 100 are
symmetrical in FIG. 17 and FIG. 18. But in the case of a vertebra
100 with only one diseased joint, the facet on the diseased side
would likely be showing pathological signs of disease such as
tissue degeneration or inflammation resulting in an asymmetrical
structural comparison between the two facets. Also, in more extreme
cases the facet disease could progress to a state in which the
articular process of the facet is eroded or inflamed resulting in
anatomic morphology that is unique to the pathology of a particular
facet joint of an individual patient. This could present unusual
facet morphology that could be different from what is shown in
FIGS. 17 and 18. Furthermore, the facet disease could eventually
disable the biomechanics of a patient such that the facet joint is
essentially non-articulating and immobile. In this case, one
superior facet of a first vertebra could essentially be fused to
one inferior facet of a second vertebra.
[0170] Since the structural pathology of the diseased facet is
variable, a surgeon may determine that the best bone apposition
surface or foundation for securing a facet implant is a resected
bone surface. Referring to FIG. 19 and FIG. 20 which are dorsal and
lateral views of the same vertebra shown in FIG. 17 and FIG. 18
after a portion of the right superior facet 43 and a portion of the
right inferior facet 6 have been resected. The removal of a portion
of the superior facet 43 by resection results in a superior facet
resection 111. In the resection shown in FIG. 19 and FIG. 20, the
superior resection 111 has two resulting faces, a first resection
surface 112 and a second resection surface 113. Likewise, the
inferior facet resection results in an inferior facet resection
surface 121.
[0171] Tissue removal tools (not shown) such as a bone burr, rasp,
reamer, mill, saw, rounger, osteotome or similar tools designed to
cut and remove bone tissue can be used to create these resection
surfaces. The surgeon uses anatomic landmarks such as the pedicle P
or transverse process 105 to align the tissue removal tools in such
a way as to remove the portion of the facet necessary to provide a
superior resection 111 that serves as a bone apposition surface or
foundation to eventually support the superior facet prosthesis 300,
as shown in FIG. 22. The left superior facet 43 is shown intact in
both FIG. 19 and FIG. 20, but a portion of the right superior facet
43 is resected resulting in the first resection surface 112 and the
adjacent second resection surface 113 (FIG. 19). The shape of
superior resection 111 will vary in accordance with the structure
of the tissue removal tool. In this embodiment shown in FIG. 19 and
FIG. 20, the first resection surface 112 and the second resection
surface 113 are on approximately perpendicular planes. However, the
geometry of the resections surfaces are a function of the patient
anatomy, the pathology of the diseased tissue, the technique of the
surgeon, and other factors such as the type of tissue removal tools
used to prepare the resection. In general, the first resection
surface 112 will be formed in such a way that it will serve as a
foundation to support the superior facet prosthesis 300 (FIG. 22).
The second resection surface 113 or other additional resection
surfaces may or may not be present.
[0172] FIG. 19 and FIG. 20 also show that a portion of the inferior
facet 6 is resected by tissue removal instruments resulting in an
inferior resection surface 121. Such resection is preferably
effected so that resection is confined to the tissue of inferior
facet 6 and does not extend into the tissue of posterior arch (or
lamina) 35. In FIGS. 19 and 20, the left inferior facet 6 is
intact, while a portion of the right inferior facet 6 is resected
resulting in an inferior resection surface 121 on the right side.
The bone surrounding the inferior resection surface 121 is formed
by tissue removal tools in a shape designed to cradle and support
the inferior facet prosthesis 400 (FIG. 23) on the medial side such
that when the inferior facet prosthesis 400 is loaded on the
lateral side it compresses against and is supported by the inferior
resection surface 121.
[0173] Alternatively, inferior facet 6 can be resected, and
inferior facet prosthesis 400 sized and shaped, so that inferior
facet prosthesis 400 does not engage inferior resection surface
121.
[0174] FIG. 21 shows the vertebra 100 with a fixation element 200
portion of the facet implant placed through the superior resection
111 and into the bone of the pedicle P. The fixation element 200 is
aligned and placed into the pedicle, similar to how other pedicle
screws for posterior stabilization involved with vertebrae fusion
are placed in the pedicle. In one method, a long guide wire (not
shown), with a diameter sized to fit freely into a cannulation 211
(as shown in FIG. 26 and FIG. 27) in the fixation element 200, is
placed through the first resection surface 112 and into the pedicle
bone P. The alignment of the long guide wire can be confirmed by
x-ray. The fixation element 200 is then guided over the guide wire
and driven into the vertebra by a driver (not shown) engaged with
the drive feature 212 (FIG. 21) on the proximal post 230 of the
fixation element 200. The fixation element 200 is driven into the
vertebra until a connection feature 213 (e.g., a screw thread) is
just above the first resection surface 112. This connection feature
213 is eventually used to secure the superior facet prosthesis 300
to the vertebra 100.
[0175] In a second method for guiding the fixation element 200 in
the pedicle P, a long guide wire (not shown), with a diameter sized
to fit freely into a cannulation in a bone preparation instrument
(not shown) such as a tap, drill, broach or reamer, is placed
through the first resection surface 112 and into the pedicle bone
P. The alignment of the long guide wire can be confirmed by x-ray.
The bone preparation instrument is then guided over the guide wire
and driven into the pedicle P bone to prepare a cavity for the
fixation element 200. The guide wire and bone preparation
instrument are then removed and the fixation element 200 is guided
into the prepared cavity in the pedicle bone P by a driver (not
shown) engaged with the drive feature 212 on the proximal post 230
of the fixation element 200. Like in the first method, the fixation
element 200 is driven into the vertebra until a connection feature
213 (e.g., a screw thread) is just above the first resection
surface 112. This connection feature 213 is eventually used to
secure the superior facet prosthesis 300 to the vertebra 100.
[0176] In yet a third method of placing the fixation element 200 in
the pedicle, the surgeon aligns the fixation element 200 with
anatomic landmarks and simply drives the fixation element 200
through the first resected surface 112 and into the pedicle bone P.
As with the first and second methods, the fixation element 200 is
driven into the vertebra until a connection feature 213 (e.g., a
screw thread) is just above the first superior resection surface
112.
[0177] In FIG. 22, a superior facet prosthesis 300 is shown placed
around the fixation element 200. The superior facet prosthesis 300
has a facet articulating component 320 that articulates with the
inferior facet articulating surface of the vertebra above it. Facet
articulating component 320 is preferably formed in the general
shape of a blade or wing ear. The superior facet prosthesis 300
also has a bone apposition surface 322 that has been placed on the
first resection surface 112 and an opening 324 in a flange 323 that
surrounds the fixation element 200. The superior facet articulating
component 320 has an articulating surface 321 generally adjacent to
the flange 323 that is orientated in a direction that faces
approximately the same direction that the original anatomic
superior articulating surface 145 faced prior to resection. This
orientation of the articulating surface 321 allows the superior
facet prosthesis 300 to function as either a hemiplasty implant and
articulate against a natural anatomic inferior facet 6 or act as a
unilateral prosthesis and articulate against an inferior facet
prosthesis 400 on the vertebra superior (cephalad) to it. No
portion of superior facet prosthesis 300 rests on the lamina.
[0178] FIG. 23 shows the addition of the inferior facet prosthesis
400 to the construct described in FIG. 22. The inferior facet
prosthesis 400 generally has a shape similar to a longitudinal rod
that is curved to match the contour of the inferior resection 121
(FIGS. 19 and 20). The inferior facet prosthesis 400 has an opening
410 through its superior end 420 that is shaped to surround the
portion of the fixation element 200 that protrudes from the first
resection surface 112. In FIG. 23, the inferior facet prosthesis
400 is placed over the superior facet prosthesis 300. However, the
order of the placement of the prostheses can be reversed such that
the inferior prosthesis 400 is placed on the fixation element 200
first followed by the superior prosthesis 300. When only the
inferior facet 6 or the superior facet 43 is being replaced, only
the appropriate (superior or inferior) facet prosthesis is placed
on the fixation element 200 without the other (inferior or
superior) facet prosthesis.
[0179] Because the various components of the implant are modular,
many combinations of configurations and implant size, structure and
shapes are feasible. For example, in a patient with unusual
anatomy, the inferior facet prosthesis 400 may need to be larger
than expected to conform to a particularly unusual or exceptionally
large morphology of the inferior resection surface 121, and the
superior facet prosthesis 300 may need to have an unusual angle to
its articulating surface to conform to particular anatomic
constraints. If this is the case, the modularity of the system
allows for the surgeon to assemble an implant specifically designed
to match the patient's anatomic structures during the surgery. This
flexibility of a modular implant design allows the implant
manufacturer to accommodate a large variation in anatomic
structures with a limited selection of implant component sizes,
shapes, and material types.
[0180] The modularity of the implant design also allows different
components of the implant to be fabricated from different
materials. Traditionally bone fixation implants such as the
fixation element 300 are fabricated from biocompatible metals or
alloys that provide sufficient strength and fatigue properties,
such as cobalt chrome alloys, titanium and titanium alloys, and
stainless steels. However, the fixation element 300 may be
fabricated from ceramics, polymers, or biological materials such as
allograft bone, composites, or other biocompatible structural
materials. Likewise the superior facet prosthesis 300 and the
inferior facet prosthesis 400 may be fabricated from metals,
alloys, ceramics, polymers, biological materials, composites, or
other biocompatible structural materials.
[0181] In FIG. 24, an enlarged head 500 is added to the fixation
element 200 and is tightened down to force the prosthesis or
prostheses into the bone to stabilize them. The enlarged head 500
shown in FIG. 24 has a hexagonal geometry on its external surface
that is shaped to accept a driver (not shown) that is used to force
an internal connection feature 520 (e.g., a screw thread) of the
enlarged head 500 onto the connection feature 213 of the fixation
element 200. In the case of the threaded embodiment of the
connection feature 213, the enlarged head 500 is provided with a
threaded connection feature 520 and is driven onto the fixation
element 200 by turning the enlarged head 500 and allowing the
threads to drive all components of the implant between the enlarged
head 500 and the first resection surface 112 into the bone at or
near the resection surface 112.
[0182] FIG. 25 is an isometric posterior view of the assembly of
the fixation element 200, the superior facet prosthesis 300, and
the enlarged head 500 placed on the first resection surface 112.
FIG. 26 is the same construct shown in FIG. 25, but with the
implants and the vertebra 100 cut by a cross-sectioning plane 150
placed along an axis that passes through the center of the fixation
element 200. The cross-section plan 150 shown cutting through the
vertebra 100 and the implant in FIG. 26 is shown for visualization
purposes to illustrate, using a cross-sectioned view, how the
vertebra 100, fixation element 200, superior facet prosthesis 300
and the enlarged head 500 engage with each other. In actual
surgery, it is highly unlikely that a surgeon would make a cut as
illustrated by the cross-section 150 shown in FIG. 26.
[0183] FIG. 27 is a view of the vertebra 100 and the implant
wherein the cross-section 150 shown in FIG. 26 is orientated such
that the cross-section plane is facing the viewer. In FIG. 27, the
fixation element 200 is in the vertebra 100. The embodiment of the
fixation element 200 in FIG. 27 comprises a distal end 220 that is
shaped to guide the fixation element 200 into bone tissue, a bone
stabilizing portion 210 adjacent and proximal to the distal end, a
shaft portion 240 adjacent and proximal to the bone stabilizing
portion 210, a connection feature 213 adjacent and proximal to the
shaft portion 240, and a drive feature 212.
[0184] The distal end 220 shown in FIG. 27 has a frustro-conical
shape that allows the fixation element 200 to be driven or guided
into the vertebra 100. The distal end 220 could be shaped in the
form of a spade tip, trochar tip, or twist drill tip to assist in
the guidance of the fixation element 200 in the vertebra 100. The
fixation element 200 may also have a cutting flute (not shown)
formed in the distal end 220 to help remove bone tissue and
accommodate the guidance of the fixation element 200 in the
vertebra 100. The fixation element 200 has a stabilizing portion
210 to help secure the fixation element 200 to the vertebra 100.
This stabilizing portion 210 is a structure that can be the shape
of various features that are designed to anchor into bone such as
threads, ribs, grooves, slots, fins, barbs, splines, bone ingrowth
surfaces, roughened surfaces, or any geometric feature that helps
to engage the fixation element 200 with the bone tissue to help
stabilize the fixation element 200. In FIG. 27, the stabilizing
portion 210 is shown as a unitary continuous bone thread 231.
However, other types of threads such as multiple lead threads,
variable pitched thread, non-uniform pitch thread, buttress thread,
or other thread forms used on bone screws may be used. Because FIG.
27 is a cross-sectional view, the full length of the cannulation
211 is seen passing from the distal end 220 of the fixation element
200 to the proximal post 230 of the fixation element 200.
[0185] The drive feature 212 in the embodiment shown in FIG. 27 is
an internal hex. However, any shape of drive feature 212 that
transmits the loads necessary to drive the fixation element 200
into the vertebra can be formed on the proximal post 230 of the
fixation element 200. The depth of the drive feature 212 formed in
the proximal post 230 of the fixation element 200 is seen in the
cross-sectional view of FIG. 27. The drive feature 212 may be an
internal drive feature such as the hex socket shown in this
embodiment, or an external drive feature with geometry on the
periphery of the proximal post 230 of the fixation element 200 that
engages with a corresponding internal drive feature on a driver
tool (not shown). In this embodiment the depth of the drive feature
212 is slightly longer than its cross-section is wide. This depth
can be adjusted based on the material properties of the fixation
element 200 and the drive tool (not shown).
[0186] The fixation element 200 is fabricated from biocompatible
base materials that allow for the structural rigidity and strength
needed. Examples of base materials that the fixation element 200
are made from include titanium, titanium alloys, cobalt-chrome
alloys, stainless steel alloys, zirconium alloys, other
biocompatible metal materials, biocompatible ceramics,
biocompatible composites, and biocompatible polymers. The fixation
element 200 may also have surface materials formed on the base
material that allow for material properties specific to a
particular portion of the fixation element 200. For example, the
bone stabilization portion 210 could be coated with materials that
allow for improved bone ingrowth into the implant surface such as a
hydroxylapatite, bioceramic, Bioglass.RTM., or other calcium
phosphate derived material. The tribological bearing properties of
the material in the areas that the fixation element 200 interfaces
with other artificial elements may be improved by applying surface
hardening techniques to the material of the fixation element 200 in
these areas. Surface hardening techniques known in the materials
science and materials engineering arts such as anodizing, ion
implantation, and other techniques could be applied to these
isolated areas.
[0187] A connection feature 213 is formed on the portion of the
fixation element 200 that protrudes from the first resection
surface 112. This connection feature 213 is designed to connect the
enlarged head 500 to the fixation element 200. In the embodiment of
the connection feature 213 shown in FIG. 21, threads 260 are on the
external surface of this proximal section of the fixation element
200. These threads 260 engage with the threads on the internal
connection feature 520 (FIG. 27) of the enlarged head 500. Although
this connection feature 213 in this embodiment is threaded, other
mechanical locking features (not shown) capable of locking the
fixation element 200 and the enlarged head 500 together, such as
press fit, taper fit, bonding fit by cement or glue, interference
fit, expansion fit and mechanical interlocking fit such as a
bayonet connection, can be used as the connection feature 213 (and
a corresponding construction used on connection feature 520 of head
500).
[0188] Also shown in FIG. 27 is a cross-sectional view of an
embodiment of the superior facet prosthesis 300. This embodiment of
the superior facet prosthesis 300 has a flange 323 that has an
opening 324 that wraps around the fixation element 200. In the
assembled and implanted configuration of this embodiment, the
flange 323 is positioned such that its bone contacting surface 322
makes contact with the first resection surface 112. Although not
shown in this embodiment, other embodiments of the superior facet
prosthesis 300 have structures (e.g., spikes) that protrude into
the first resection surface 112 to help resist torsion and other
anatomic loads. Protruding from the flange 323 at a given angle
.alpha., and a given distance X from the opening 324, is an
articulating component 320. The articulating component 320 has an
articulating surface 321 that replicates the natural articular
surface of the replaced facet. Once the surgeon assesses the
anatomy of the superior facet 43 that is being replaced, a
particular superior facet prosthesis 300 is selected that has the
angle .alpha. and the distance X that best fits the anatomy of the
level of vertebra, the left or right side, and the size of the
patient's anatomy being replaced. Thus a kit containing various
sizes and shapes of superior facet prostheses 300 are provided to
the surgeon and the surgeon selects the superior facet prosthesis
300 that best suits the situation.
[0189] After the fixation element 200 and the superior facet
prosthesis 300 are selected and placed, they are locked to the
vertebra by the enlarged head 500. As shown in FIG. 24, the
enlarged head 500 in this embodiment has an internal connection
feature 520 and a hexagonal shaped external drive feature 510 that
is used to drive the enlarged head 500 over the fixation element
200 and against the superior facet prosthesis 300. The specific
shape of the external drive feature 510 is dependent on the mating
shape of the driver (not shown).
[0190] Referring to FIG. 28, six different embodiments of the bone
stabilization portion 210 of the fixation element 200 are shown
that are labeled A, B, C, D, E, and F. The figure shows a side view
of each fixation element 200 embodiment and a cross-sectional view
of each embodiment to the right of the respective side view. To the
left of the six embodiments is a representative enlarged head 500.
Embodiment A is the threaded fixation element 200 embodiment shown
in FIGS. 26 and 27 and described above. Embodiments B through E are
various designs of fixation elements with non-circular
cross-sections. Embodiment B is a four rib cruciate design with
four longitudinal fins configured to resist torsion when the
fixation element 200 is in the vertebra 100. Embodiment C is an
oval shaped cross-section design that is wider in the first
direction than the second direction to resist torsion. If the
dimension of the width in the first and second directions is equal,
the cross-section shape becomes more of a circle and bone
stabilization portion 210 becomes more of a press-fit peg.
Embodiment D is a square cross-section design with four
approximately perpendicular sides. The corners of the sides help to
resist torsion. Embodiment E is a triangular cross-section design
with three sides to resist torsion. Embodiment F is an anchor-like
design that is driven into the vertebra, with the wire arches or
barbs 290 being compressed against the host bone and applying a
radial expansion force so as to lock the structure to the bone.
[0191] Referring to FIG. 28A, six more different embodiments of the
bone stabilization portion 210 of the fixation element 200 are show
that are labeled G, H, J, K, L, and I. FIG. 28A shows a side view
of each fixation element 200 embodiment and a cross-sectional view
of each embodiment to the right of the respective side view. Each
embodiment has an attached enlarged head 500. Embodiment G is
similar to the threaded fixation element 200 embodiment shown in
FIGS. 10, 11, 12 and 24 and described above. Embodiments H through
K are various designs of fixation elements 200 with non-circular
cross-sections. Embodiment H is a four rib cruciate design with
four longitudinal fins 285 configured to resist torsion when the
fixation element 200 is in the vertebra 100. Embodiment I is an
oval shaped cross-section design that is wider in the first
direction 286 than the second direction 287 to resist torsion. If
the dimension of the width in the first direction 286 and second
direction 287 is equal, the cross-section shape becomes more of a
circle and bone stabilization portion 210 becomes more of a
press-fit peg. Embodiment J is a square cross-section design with
four approximately perpendicular sides 288. The corners 289 of the
sides 288 help to resist torsion. Embodiment K is a triangular
cross-section design with three sides 291 to resist torsion.
[0192] Embodiment L is an anchor-like design that is similar to
Embodiment F in FIG. 28, but with an attached enlarged head 500'.
As embodiment L is driven into the vertebra, wire arches or barbs
290 are compressed and apply radial expansion force against the
wall of the prepared bone and into the pedicle bone P resulting in
a locking anchor.
[0193] FIG. 29 is an isometric view of a radially expanding
fixation element 600. The radially expanding fixation element 600
comprises two main elements, an expansion sleeve 620 and a central
element 610 that is inside of the expansion sleeve 620. The
radially expanding fixation element 600 is placed into the vertebra
and then the central element 610 is pulled relative to the
expansion sleeve 620 resulting in radial expansion of the fixation
element 600. This is shown in FIG. 30. As the proximal post 630 of
the central element 610 is pulled axially along its longitudinal
axis, and the expansion sleeve is held axially in the bone by
compression fit, talons 621 on the expansion sleeve 620 are
radially expanded outward by a mandrel 660 on the central element
610. The talons or fingers 621 provide both torsional and axial
stability to the radially expanding fixation element 600. This
provides a secure fixation element for fixation of the remaining
components of the implant.
[0194] FIG. 31 shows a cross-pin element 700 engaged with the
fixation element 200 to help secure the fixation element 200 both
torsionally and axially. The cross-pin element 700 is columnar in
shape having a distal end 710, mid section 730 (with a length along
its longitudinal axis that is longer than its transverse
cross-sectional width), and a proximal post 720. The distal end 710
is shaped to penetrate through bone tissue and into a cross hole
280 formed in the fixation element 200. Instrumentation (not shown)
is used to align the cross-pin element 700 with the cross-hole 280
by fixing to the drive feature 212 or the cannulation 211 on the
fixation element 200 and aligning the direction of insertion of the
cross-pin element 700 with the cross-hole 280. Once the cross-pin
element 700 is in place in the bone and through the fixation
element 200, the torsional and axial stability of the fixation
element 200 is improved.
[0195] The various embodiments of the fixation element 200
described above and shown in FIG. 28 through FIG. 31 function in
conjunction with the enlarged head 500 to hold the inferior facet
prosthesis 400 and/or the superior facet prosthesis 300 to their
respective resection surfaces. Various combinations of this modular
implant will be described below and shown in FIGS. 32 through 37.
Although these figures show a fixation element 200 and enlarged
head 500 as the means of securing the prostheses to the vertebra,
other clamping means such as the screw fastener 17 (FIG. 10) may be
used to mount the prosthesis to the bone. For example, the screw
prostheses 17 shown in FIGS. 10 through 12 passes through either
the opening 324 (FIG. 22) in the superior facet prosthesis 300 or
the opening 410 (FIG. 23) in the inferior facet prosthesis 400 or
through both of these openings wherein the head of the screw
fastener 17 acts as the securing means pressing the inferior facet
prostheses 400 and the superior facet prosthesis 300 against their
respective resection surfaces.
[0196] FIGS. 32 through 37 demonstrate different combinations of
assemblies of the facet replacement prosthesis. The basic
components of the prosthesis are the fixation element 200, superior
facet prosthesis 300, inferior facet prosthesis 400, and the
enlarged head 500. However, as described above, a screw fastener 17
can replace the fixation element 200 and the enlarged head 500.
[0197] Referring to FIG. 32, three sequential layers of vertebra
are shown, the top vertebra 101 is above the middle vertebra 102
that is shown above the bottom vertebra 103. Portions of some of
the facets on the right side of the vertebrae are replaced by
prostheses. Looking at the facet joint between the top vertebra 101
and the middle vertebra 102, inferior facet prosthesis 401 is
articulating against superior facet prosthesis 302 to form an
artificial unilateral joint. The inferior facet of the middle
vertebra 102 is replaced by inferior facet prosthesis 402 and the
superior facet of the bottom vertebra 103 is replaced by superior
facet prosthesis 303. Thus, a second unilateral prosthetic joint is
formed that is also on the right side and is located at the level
between the middle vertebra 102 and the bottom vertebra 103. FIG.
32 demonstrates the difference in shape of the inferior facet
prosthesis 401 that is implanted around the fixation element 201
without a superior facet prosthesis 300 and an inferior facet
prosthesis 402 that is implanted around a fixation element 202 and
over a superior facet prosthesis 302. The opening 410 of the
inferior facet prosthesis 401 on the top vertebra 101 in this
assembly is offset more laterally than the opening 410 in the
inferior facet prosthesis 402 for the middle vertebra 102. This is
because the fixation element 201 is implanted more laterally on the
top vertebra 101 to preserve more of the superior facet since it is
not replaced by a prosthesis at this level.
[0198] Referring to FIG. 33, the top vertebra 101 is left intact
without resection of the facets. Portions of both the superior and
inferior facets on the right side of the middle vertebra 102 are
replaced by superior facet prosthesis 302 and an inferior facet
prosthesis 402. Only the right superior facet of the bottom
vertebra 103 is replaced (i.e., by a superior facet prosthesis 303)
in FIG. 33. Thus, a hemiplasty replacement results on the right
facet joint between the top vertebra 101 and the middle vertebra
102 and a unilateral replacement results between the middle
vertebra 102 and the bottom vertebra 103. This assembly shown in
FIG. 33 demonstrates how the superior facet prosthesis 302 can
articulate against a natural inferior facet 6 or superior facet
prosthesis 303 can articulate against an inferior facet prosthesis
402.
[0199] FIG. 34 shows how an inferior facet prosthesis 401 can
articulate against a natural superior facet 43, or a inferior facet
prosthesis 402 can articulate against superior facet prosthesis
303. The right facet joint between the top vertebra 101 and the
middle vertebra 102 is a hemiplasty replacement with the inferior
facet replaced by an inferior facet prosthesis 401. The right facet
joint between the middle vertebra 102 and the bottom vertebra 103
is a unilateral replacement with the inferior facet replaced by an
inferior facet prosthesis 402 and the superior facet of the bottom
vertebra 103 replaced by a superior facet prosthesis 303.
[0200] FIG. 35 shows another example of how the superior facet
prosthesis 303 can articulate against a natural inferior facet 6 or
superior facet prosthesis 302 can articulate against an inferior
facet prosthesis 401. In this assembly of the implant, the right
side between the top vertebra 101 and the middle vertebra 102 is a
unilateral replacement and the right side between the middle
vertebra 102 and the bottom vertebra 103 is a hemiplasty
replacement.
[0201] FIG. 36 shows another example of how an inferior facet
prosthesis 402 can articulate against a natural superior facet 43,
or an inferior facet prosthesis 401 can articulate against superior
facet prosthesis 302. The right facet joint between the top
vertebra 101 and the middle vertebra 102 is an unilateral
replacement with the inferior facet replaced by an inferior facet
prosthesis 401 and the superior facet of the middle vertebra 102
replaced by a superior facet prosthesis 302. The right facet joint
between the middle vertebra 102 and the bottom vertebra 103 is a
hemiplasty replacement with the inferior facet replaced by an
inferior facet prosthesis 402.
[0202] The assembly of the implant shown in FIG. 37 demonstrates
only one level, that between the middle vertebra 102 and the bottom
vertebra 103, being replaced on the right side.
[0203] FIG. 38 and FIG. 39 show two embodiments of the superior
facet prosthesis. The embodiment shown in FIG. 38 is curved
superior facet prosthesis 305 with a curved articulating component
320 that has a curved articulating surface 321. This curved
articulating surface 321 allows for a more distributed contact load
between an inferior facet prosthesis 400 and the curved
articulating surface 321. This allows slightly more flexibility in
the position that the surgeon places the curved superior facet
prosthesis 305 than the superior facet prosthesis 300 previously
described. The articulating surface 321 of the superior facet
prosthesis 300 previously described is relatively flat. The
articulating surface 321 of the curved superior facet prosthesis
305 is curved. Since the bearing portion of the inferior facet
prosthesis 400 is columnar, the two prosthesis can be aligned on a
slight mismatch and make more of an anatomic contact if the
articulated surface is curved as in FIG. 38.
[0204] FIG. 39 illustrates bone ingrowth feature 390 on the
superior facet prosthesis 306. This bone ingrowth feature can be
any surface that allows bone to grow into the implant between the
first resection 111 of the vertebra and the 322 bone-contacting
surface 321 of the implant. Examples of bone ingrowth features 390
include porous coating of beads or meshes, electrochemically etched
shapes and porous pads pressed onto the implant surface made from
tantalum, titanium, cobalt chrome alloys or and other biocompatible
material such as hydroxylapatite or calcium phosphate ceramics.
[0205] FIG. 40 shows an isometric view of an inferior facet
prosthesis 400 formed in the general shape of a finger or talon.
More particularly, inferior facet prosthesis 400 is formed with a
flange 420 on its superior side shaped to either fit between the
superior facet prosthesis 300 and the enlarged head 500, or between
the first resection surface 112 and the enlarged head 500. The
flange 420 has an opening 410 through it that is dimensioned to
allow the inferior facet prosthesis 400 to fit over the proximal
end 210 of the fixation element 200 and around the post of the
fixation element 200. The inferior facet prosthesis 400 also has an
inferior portion 450 on the opposite side of the flange 420 that
has a bone apposition side 440 that is shaped to contact the
surface of the resected bone 121 (FIG. 19) and joint articulation
side 430 that is shaped to articulate with a natural or prosthetic
superior facet.
[0206] FIG. 41 shows an isometric view of an inferior facet
prosthesis 400 also formed in the general shape of a finger or
talon. Inferior facet prosthesis 400 is formed with a superior end
420 having an opening 410 that is dimensioned and shaped to accept
the fixation element 200. The inferior facet prosthesis is
generally columnar in shape, having a curved length designed to
conform to the prepared anatomy of the vertebra 100. The inferior
facet prosthesis 400 of FIG. 41 has an inferior portion 450, which
is shown opposite the superior end 420, and slightly medially
offset from the superior end 420. This medial offset of the opening
410 relative to the inferior portion 450 allows the inferior facet
prosthesis 400 to be anchored to the bone by the fixation element
200 and secured to the bone by the enlarged head 500, or the
superior facet prosthesis 300 in combination with the enlarged head
500, at an anatomical position that allows optimal bone fixation.
The inferior facet prosthesis embodiment of FIG. 41 has a bone
ingrowth surface 441 and an articulating surface 430 on its
inferior end 450. In this embodiment, the bone ingrowth surface 441
is a textured structure that permits bone cells to grow into the
implant surface. The shape of the bone ingrowth surface 441 can be
a uniform textured surface as shown in FIG. 41, or can be a
non-uniform randomized structure such as a open cell foam
structure, a porous beaded structure, a wire mesh structure, an
electrochemical etched structure, or other bone ingrowth structures
known in the design of orthopedic implants. The bone ingrowth
surface is shaped to mate with the inferior resected bone surface
121 such as shown in FIG. 19 and FIG. 20.
[0207] FIG. 42 shows a posterior isometric view of an embodiment of
the superior facet implant 300 that has an additional locking
washer 800 to assist in stabilizing the superior facet implant to
the first resection surface 112. The construction of the implant
assembly shown in FIG. 42 is similar to that of the assembly shown
in FIG. 25 with the addition of the locking washer 800 that is
placed over and around the superior facet implant 300.
[0208] FIG. 43 shows the same implant of FIG. 42 with the enlarged
head 500 locked onto the fixation element 200 and pushing the
locking washer 800 against the superior prosthesis 300 and into the
bone tissue. This added bone penetration of the locking washer 800
helps to fix the superior prosthesis 300 such that the entire
assembly is more mechanically stable with respect to the vertebra
100.
[0209] FIG. 43 shows a further step in the assembly of the implant
construct described in FIG. 42. In FIG. 43, the locking washer 800
is secured over the fixation element 200 and into the bone tissue
by the enlarged head 500. Although this embodiment of the locking
washer 800 is only shown with the superior facet prosthesis 300,
the locking washer 800 can also be used to mechanically secure the
inferior facet prosthesis 400 and the combination of the inferior
facet prosthesis 400 and the superior facet prosthesis 300. In the
embodiment of the locking washer 800 shown in FIG. 42 and FIG. 43,
the locking washer 800 is placed over the superior facet prosthesis
300. However, the locking washer 800 may be placed under the
superior facet prosthesis 300 or under any other combination of
inferior facet prosthesis 400 and superior facet prosthesis 300, or
between the superior facet prosthesis 300 and the inferior facet
prosthesis 400 to stabilize the implant construct.
[0210] FIG. 44 shows an isometric view of the locking washer 800.
The locking washed 800 has an opening 810 in the body 805 that is
dimensioned to fit over the proximal post 230 of the fixation
element 200. The locking washer 800 also has an anti-rotation
feature 820 that mates with either the superior facet prosthesis
300 or the inferior facet prosthesis 400 or a combination of both
the inferior facet prosthesis 400 and the superior facet prosthesis
400. The anti-rotation feature 820 shown in this embodiment is a
flat surface, however, any feature that would rotationally
constrain the locking washer 800 to the other components of the
implant (such as a tab, groove, taper or other geometric shape) can
be formed on the washer as a anti-rotation feature 820. The locking
washer 800 also has prongs 830 that pass into the bone tissue of
vertebra 100 to help stabilize the implant construct. The prongs in
this embodiment of the locking washer 800 are elongated protrusions
that taper to a tissue penetration tip 840. The prongs have
sidewalls 850 that provide a surface to resist torsion once the
locking washer 800 penetrates the bone tissue. The prongs 830 may
also be simple spikes that are either symmetrical or nonsymmetrical
in cross-section that protrude from the locking washer body 805.
The shape and length of the locking washer prongs 830 is dependent
on how the locking washer is used. The prongs 830 of the locking
washer 800 that holds only one of the inferior facet prosthesis 400
or the superior facet prosthesis 300 to the vertebra 100 may be
shorter than the prongs 830 of the locking washer 800 that holds
both the inferior facet prosthesis 400 and the superior facet
prosthesis 300 to the vertebra 100.
[0211] FIG. 45 shows the superior facet prosthesis 300 and inferior
facet prosthesis 400 held to the vertebra 100 by adjunctive
flexible fixation element 900 and secondary flexible fixation
element 910. These flexible fixation elements 900 and/or 910 may be
made from such constructs as suture, braided cable, wire, ribbon,
and other constructs that have longer lengths than cross-sections
and withstand larger loads in tension than in compression. The
flexible fixation element 900 and/or 910 may be manufactured from
biocompatible metals, alloys such as cobalt chrome alloys, titanium
alloys, stainless steel alloys, polymers, bioabsorbale materials,
composites, or other materials that are biocompatible and can be
formed into a flexible element structure 900 and/or 910 such as
those shown in FIG. 45. The adjunctive flexible element 900 shown
in FIG. 45 is shown attached to and securing the elongated head
500. A flexible element attachment portion 580 (e.g., including an
opening) mates the flexible element 900 to the elongated head.
However, the adjunctive flexible fixation element 900 may attach to
and add adjunctive fixation element 900 to the fixation element
200, the superior facet prosthesis 300, the inferior facet
prosthesis 400 or a combination of the above listed elements of the
prosthesis. A flexible fixation attachment portion 480 (e.g.,
including an opening) in the inferior facet prosthesis 400 allows
the secondary flexible fixation element 910 to secure the inferior
facet prostheses 400 to the vertebra 100. The flexible fixation
elements 900 and/or 910 may be secured to the vertebra 100 by
physically wrapping around anatomic features such as the posterior
arch 35, the spinous process 46, or transverse process 105 or a
combination of these anatomic features. The flexible element 900
and secondary flexible element 910 may also be secured to the
vertebra by bone anchors such as anchors designed to anchor
flexible fixation elements (such as suture) to bone. Suture anchors
such as threaded suture anchors, barbed suture anchors, toggle
suture anchors or any other means of anchoring a flexible fixation
element to bone may be used to anchor the flexible fixation element
900 or the secondary flexible fixation element 910 to the vertebra
100.
[0212] FIG. 46 is a dorsal view of a bilateral inferior facet
prosthesis 1000. The bilateral inferior facet prosthesis 1000 is a
one-piece inferior facet prosthesis that has both a right inferior
side 1040 and a left inferior side 1020 connected by a stabilizing
bar 1010. Both the right inferior side 1040 and the left inferior
side 1020 are designed to fix to the vertebra at the respective
inferior resection surface 121 (FIG. 19) and the first resection
surface 112. The bilateral inferior prosthesis is a design that
allows replacement of both the left and the right inferior facet.
In this embodiment, the bilateral inferior prosthesis is placed
over the left and right fixation elements 200 which extend into the
top vertebra 101. In this embodiment shown in FIG. 46, the right
inferior side is articulating with a right superior facet
prosthesis 300 attached to the lower vertebra 102. Also in this
embodiment, the left inferior side 1020 is articulating with the
left natural superior facet 43 of the lower vertebra 102. The
stabilizing bar 1010 of the bilateral inferior prosthesis 1000 is
designed to stabilize the left side 1020 and the right side 1040 so
that they are secure.
[0213] Having described preferred embodiments of the invention with
reference to the accompanying drawings, it is to be understood that
the embodiments shown herein are by way of example, and that
various changes and modifications may be effected by one skilled in
the art without departing from the scope or spirit of the invention
as defined in the following claims.
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