U.S. patent application number 10/762008 was filed with the patent office on 2005-07-21 for cervical facet resurfacing implant.
Invention is credited to Grob, Dieter, Winston Hale, Horace.
Application Number | 20050159746 10/762008 |
Document ID | / |
Family ID | 34750304 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050159746 |
Kind Code |
A1 |
Grob, Dieter ; et
al. |
July 21, 2005 |
Cervical facet resurfacing implant
Abstract
The present invention relates to prostheses for treating spinal
pathologies, and more specifically to a system and method for
treating articulating surfaces of cervical vertebrae facet joints.
The system includes a superior implant for placement on a superior
articulating surface and an inferior implant for placement on an
inferior articulating surface. In addition, described is a method
for providing articulating surfaces for cervical vertebrae facet
joint articular facets.
Inventors: |
Grob, Dieter; (Erlenbach,
CH) ; Winston Hale, Horace; (Degersheim, CH) |
Correspondence
Address: |
Mark C. Johnson
Renner, Otto, Boisselle & Sklar, LLP
Nineteenth Floor
1621 Euclid Avenue
Cleveland
OH
44115-2191
US
|
Family ID: |
34750304 |
Appl. No.: |
10/762008 |
Filed: |
January 21, 2004 |
Current U.S.
Class: |
606/247 ;
606/279; 606/86A; 606/907; 606/909 |
Current CPC
Class: |
A61F 2230/0054 20130101;
A61F 2310/00161 20130101; A61B 17/7064 20130101; A61F 2002/30578
20130101; A61F 2310/00023 20130101; A61F 2310/00131 20130101; A61B
17/1659 20130101; A61B 17/1757 20130101; A61B 17/1671 20130101;
A61F 2310/00239 20130101; A61F 2310/00796 20130101; A61F 2002/4631
20130101; A61F 2310/00029 20130101; A61F 2002/30769 20130101; A61F
2002/30649 20130101; A61F 2002/2817 20130101; A61F 2002/30176
20130101; A61F 2002/30884 20130101; A61F 2/4405 20130101 |
Class at
Publication: |
606/061 |
International
Class: |
A61B 017/56 |
Claims
What is claimed is:
1. A cervical facet resurfacing implant comprising: a superior
implant having an articulating surface and a fixation surface and
configured for secured placement on a resurfaced superior articular
facet of a selected cervical vertebra; and an inferior implant
having an articulating surface and a fixation surface and
configured for secured placement on a resurfaced inferior articular
facet of a cervical vertebra immediately above the selected
cervical vertebra such that the articulating surface of the
inferior implant interacts with the articular surface of the
superior implant.
2. The cervical facet resurfacing implant of claim 1 wherein the
superior implant and inferior implant are each generally
disk-shaped.
3. The cervical facet resurfacing implant of claim 1 wherein the
superior implant further comprises a tab extending from the
generally disk-shaped portion of the superior implant.
4. The cervical facet resurfacing implant of claim 3 wherein the
tab is configured for attachment to the lateral mass of the
selected cervical vertebra.
5. The cervical facet resurfacing implant of claim 4 wherein the
tab is attached to the lateral mass of the selected cervical
vertebra with a screw.
6. The cervical facet resurfacing implant of claim 3 wherein the
tab and the disk-shaped portion of the superior implant form an
angle of from about 110 degrees to about 160 degrees.
7. The cervical facet resurfacing implant of claim 1 wherein the
inferior implant further comprises a tab extending from the
generally disk-shaped portion of the inferior implant.
8. The cervical facet resurfacing implant of claim 7 wherein the
tab is configured for attachment to the inferior articular process
of the cervical vertebra immediately above the selected cervical
vertebra.
9. The cervical facet resurfacing implant of claim 7 wherein the
tab is attached to the inferior articular process of the cervical
vertebra immediately above the selected cervical vertebra with a
screw.
10. The cervical facet resurfacing implant of claim 7 wherein the
tab and the disk-shaped portion of the inferior implant form an
angle of from about 10 degrees to about 70 degrees.
11. The cervical facet resurfacing implant of claim 1 wherein at
least one of the superior implant and the inferior implant
comprises a surface fixation mechanism.
12. The cervical facet resurfacing implant of claim 11 wherein the
surface fixation mechanism comprises at least one of: at least one
peg, at least one pip, at least one fin, ridges, and at least one
screw hole.
13. The cervical facet resurfacing implant of claim 12 wherein the
surface fixation mechanism comprises multiple regions and wherein
each of the regions has at least one ridge oriented in a different
direction than the other regions.
14. The cervical facet resurfacing implant of claim 1 wherein the
fixation surface of at least one of the inferior implant and the
superior implant has at least one of: a porous coating, a porous
onlay material, a biologic coating, a surface treatment, and a
material facilitating ingrowth of bone.
15. The cervical facet resurfacing implant of claim 1 wherein the
articulating surface of at least one of the inferior implant and
the superior implant is composed of at least one of:
cobalt-chromium alloy, ceramic, UHMWPE, pyrolytic carbon, and
Ti/Al/V.
16. The cervical facet resurfacing implant of claim 1 wherein the
inferior implant and superior implant each range from about 1 mm
thick to about 6 mm thick.
17. The cervical facet resurfacing implant of claim 1 wherein the
inferior implant and superior implant each range from about 3 mm in
diameter to about 14 mm in diameter.
18. The cervical facet resurfacing implant of claim 1 further
comprising a trans-lateral mass fixation mechanism for securing the
inferior implant to the inferior articular facet.
19. The facet implant of claim 18 wherein the trans-lateral mass
fixation mechanism comprises at least one of: a translaminar screw,
a bolt and a fixation pin.
20. A facet implant comprising: a generally disk-shaped superior
implant having an articulating surface and a fixation surface and
being configured for placement on a resurfaced superior articular
facet of a selected cervical vertebra, the superior implant having
a tab extending from the generally disk-shaped portion of the
superior implant, the tab being configured for secured attachment
to the lateral mass of the selected vertebra; and a generally
disk-shaped inferior implant having an articulating surface and a
fixation surface and being configured for placement on a resurfaced
inferior articular facet of a cervical vertebra immediately above
the selected cervical vertebra such that the articulating surface
of the inferior implant interacts with the articular surface of the
superior implant, the inferior implant having a tab extending from
the generally disk-shaped portion of the inferior implant, the tab
being configured for secured attachment to the inferior articular
process of the cervical vertebra immediately above the selected
vertebra.
21. The cervical facet resurfacing implant of claim 20 wherein at
least one of the superior implant and the inferior implant
comprises a surface fixation mechanism.
22. The cervical facet resurfacing implant of claim 21 wherein the
surface fixation mechanism comprises at least one of: at least one
peg, at least one pip, at least one fin, ridges, and at least one
screw hole.
23. The cervical facet resurfacing implant of claim 20 wherein the
fixation surface of at least one of the inferior implant and the
superior implant has at least one of: a porous coating, a porous
onlay material, a biologic coating, a surface treatment, and a
material facilitating ingrowth of bone.
24. The cervical facet resurfacing implant of claim 20 wherein the
articulating surface of at least one of the inferior implant and
the superior implant is composed of at least one of:
cobalt-chromium alloy, ceramic, UHMWPE, pyrolytic carbon, and
Ti/Al/V.
25. A method for providing articulating surfaces for vertebrae
facet joint articular facets of comprising: creating a space
between a superior articular facet of a selected vertebra and an
inferior articular facet of a vertebra immediately above the
selected vertebra; using a rasp to prepare an articulating surface
of the inferior articular facet for an inferior implant; using a
rasp to prepare an articulating surface of the superior articular
facet for a superior implant; fixing the inferior implant on the
inferior articular facet such that a fixation surface of the
inferior implant interacts with the articulating surface of the
inferior articular facet; and fixing the superior implant on the
superior articular facet such that a fixation surface of the
superior implant interacts with the articulating surface of the
superior articular facet; wherein the articulating surface of the
superior implant and the articulating surface of the inferior
implant are configured to articulate with one another.
26. The method of claim 24 wherein each of the steps are repeated
on articular facets on a contralateral side of the vertebrae facet
joint.
27. The method of claim 24 wherein the created space is begun with
a curette.
28. The method of claim 24 wherein the created space is a space
sufficient for using a rasp on an articulating surface of an
articular facet.
29. The method of claim 24 wherein the created space ranges from
about 2 mm to about 5 mm.
30. The method of claim 24 wherein multiple rasps of increasing
thickness are used to prepare the articulating surfaces of the
superior and inferior articular facets.
31. The method of claim 24 wherein the articulating surfaces of the
superior and inferior articular facets are prepared such that the
created space is increased to accommodate the superior and inferior
implants.
32. The method of claim 30 wherein the articulating surfaces of the
superior and inferior articular facets are prepared such that the
shape and dimension of superior articular facet resembles the
superior implant and the shape and dimension of the inferior
articular facet resembles the inferior implant.
33. The method of claim 30 wherein the created space is increased
such that it ranges from about 4 mm to about 15 mm.
34. The method of claim 24 wherein the articulating surfaces of the
superior and inferior articular facets are prepared such that a
bleeding bone bed is created to facilitate bone ingrowth.
35. The method of claim 24 wherein the inferior and superior
articulating surfaces are prepared by the same rasp.
36. The method of claim 24 wherein at least one rasp is configured
to cut when moving in a first direction, but not when moving in a
direction opposite of the first direction.
37. The method of claim 24 further comprising securing the inferior
implant to the inferior articular facet with a trans-lateral mass
fixation mechanism.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to prostheses for
treating spinal pathologies, and more specifically to a system and
method for treating articulating surfaces of cervical facet
joints.
BACKGROUND OF THE INVENTION
[0002] Back and neck pain are common ailments. In many cases, the
pain severely limits a person's functional ability and quality of
life. A variety of spinal pathologies can lead to back pain.
[0003] Through disease or injury, the laminae, spinous process,
articular processes, or facets of one or more vertebral bodies can
become damaged, such that the vertebrae no longer articulate or
properly align with each other. This can result in an undesired
anatomy, loss of mobility, and pain or discomfort. With respect to
vertebral articular surface degeneration, facet joints may show a
reduced thickness of cartilage and may advance to entire
disappearance thereof. Furthermore, surrounding the degenerated
articular surfaces, there is bony formation capable of causing
neurological compressions inside either the foramenae or spinal
canal. These facts induce pain which affect a large part of the
population.
[0004] The vertebral facet joints, for example, can be damaged by
either traumatic injury or by various disease processes, such as
osteoarthritis, ankylosing spondylolysis, and degenerative
spondylolisthesis. The damage to the facet joints often results in
pressure on nerves, also called a "pinched" nerve, or nerve
impingement. The result is pain, misaligned anatomy, and a
corresponding loss of mobility. Pressure on nerves can also occur
without facet joint pathology, e.g., a herniated disc.
[0005] Degenerative spinal diseases can involve articular surfaces
only, but may also have a more invasive pathology including
traumatic, infectious, tumorous or dysmorphic (spondylolisthesis,
for example) effecting the destruction of all or part of the
articular process. The locking of vertebral motions by spinal
arthrodesis or ligamentoplasty induces, beyond a spinal stiffness,
an increased force on the joint facets of the adjacent vertebrae
above and below the fusion, usually sustained by the considered
intervertebral space and therefore an increase of degeneration of
these joint facets.
[0006] One type of conventional treatment of facet joint pathology
is spinal stabilization, also known as intervertebral
stabilization. By applying intervertebral stabilization, one can
prevent relative motion between the vertebrae. By preventing this
movement, pain can be reduced. Stabilization can be accomplished by
various methods. One method of stabilization is spinal fusion.
Another method of stabilization is fixation of any number of
vertebrae to stabilize and prevent movement of the vertebrae. Yet
another type of conventional treatment is decompressive
laminectomy. This procedure involves excision of the laminae to
relieve compression of nerves. With regard to discal prostheses,
they provide a "space" between two vertebral bodies while
preserving some motion. They solve the aging intervertebral disc
problem but do not function to reduce the force on posterior joint
facets.
[0007] These traditional treatments are subject to a variety of
limitations and varying success rates. Furthermore, none of the
described treatments puts the spine in proper alignment or returns
the spine to a desired anatomy. In addition, stabilization
techniques, by holding the vertebrae in a fixed position,
permanently limit a person's mobility. Some procedures involving
motion devices have a high incidence of spontaneous fusion. There
is thus a need in the art for a system and procedure capable of
increasing the percentage of good results in disc replacement
surgery. In addition, there is a need in the art for better results
than are commonly achieved through spinal fusions. Further, there
is a need in the art for a system and procedure that permits
greater mobility in cases of spinal problems involving only the
facet joints, and for obviating the need for spinal fusion
associated with degenerative and congenital problems of the
spine.
BRIEF SUMMARY OF THE INVENTION
[0008] According to an aspect of the invention, there is provided a
cervical facet resurfacing implant comprising: a superior implant
having an articulating surface and a fixation surface and
configured for secured placement on a resurfaced superior articular
facet of a selected cervical vertebra; and an inferior implant
having an articulating surface and a fixation surface and
configured for secured placement on a resurfaced inferior articular
facet of a cervical vertebra immediately above the selected
cervical vertebra such that the articulating surface of the
inferior implant interacts with the articular surface of the
superior implant.
[0009] According to another aspect of the invention, there is
provided a facet implant comprising: a generally disk-shaped
superior implant having an articulating surface and a fixation
surface and being configured for placement on a resurfaced superior
articular facet of a selected cervical vertebra, the superior
implant having a tab extending from the generally disk-shaped
portion of the superior implant, the tab being configured for
secured attachment to the lateral mass of the selected vertebra;
and a generally disk-shaped inferior implant having an articulating
surface and a fixation surface and being configured for placement
on a resurfaced inferior articular facet of a cervical vertebra
immediately above the selected cervical vertebra such that the
articulating surface of the inferior implant interacts with the
articular surface of the superior implant, the inferior implant
having a tab extending from the generally disk-shaped portion of
the inferior implant, the tab being configured for secured
attachment to the inferior articular process of the cervical
vertebra immediately above the selected vertebra.
[0010] According to another aspect of the invention, there is a
method for providing articulating surfaces for cervical vertebrae
facet joint articular facets comprising of: creating a space
between a superior articular facet of a selected cervical vertebra
and an inferior articular facet of a cervical vertebra immediately
above the selected cervical vertebra; using a rasp to prepare an
articulating surface of the inferior articular facet for an
inferior implant; using a rasp to prepare an articulating surface
of the superior articular facet for a superior implant; fixing the
inferior implant on the inferior articular facet such that a
fixation surface of the inferior implant interacts with the
articulating surface of the inferior articular facet; and fixing
the superior implant on the superior articular facet such that a
fixation surface of the superior implant interacts with the
articulating surface of the superior articular facet; wherein the
articulating surface of the superior implant and the articulating
surface of the inferior implant are configured to articulate with
one another.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a lateral elevation view of a normal human spinal
column;
[0012] FIG. 2A is an anterior view of a normal human cervical
vertebra;
[0013] FIG. 2B is a posterosuperior view of a normal human cervical
vertebra;
[0014] FIG. 3 is a posterior perspective view of a cervical
vertebral facet joint;
[0015] FIG. 4 is a lateral elevation view of a cervical vertebral
facet joint;
[0016] FIG. 5 illustrates a cervical facet implant;
[0017] FIGS. 6A-C illustrate a facet implant in conjunction with
cervical vertebrae;
[0018] FIG. 7 illustrates an alternate embodiment of a cervical
facet inferior implant in conjunction with a trans-lateral mass
screw;
[0019] FIG. 8 is a flow chart generally illustrating a method for
providing articulating surfaces for cervical facet joint articular
facets;
[0020] FIG. 9 is an illustration of a rasp being used to prepare an
articulating surface;
[0021] FIG. 10 is an illustration of a rasp; and
[0022] FIG. 11 is an illustration of an aiming device for use in
positioning a trans lateral mass screw.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring initially to FIG. 1, the human spinal column 10 is
illustrated. The spinal column 10 is comprised of a series of
thirty-three stacked vertebrae divided into five regions. The
cervical region includes seven vertebrae, known as C1-C7. The
thoracic region includes twelve vertebrae, known as T1-T12. The
lumbar region contains five vertebrae, known as L1-L5. The sacral
region is comprised of five vertebrae, known as S1-S5. The
coccygeal region contains four vertebrae 12, known as Co1-Cu4.
[0024] Turning now to FIGS. 2 and 3, normal human cervical
vertebrae 12 are illustrated. It will be understood by those
skilled in the art that while the cervical vertebrae 12 vary
somewhat according to location, they share many features common to
most vertebrae 12. Each vertebra 12 includes a vertebral body 14.
Two short bones, the pedicles 16, extend backward from each side of
the vertebral body 14 to form a vertebral arch 18. At the posterior
end of each pedicle 16, the vertebral arch 18 flares out into broad
plates of bone known as the laminae 20. The laminae 20 fuse with
each other to form a spinous process 22. The spinuous process 22
provides muscle and ligament attachment.
[0025] The transition from the pedicles 16 to the laminae 20 is
interrupted by a transverse process 24 that thrust out laterally on
each side from the junction of the pedicle 16 and the lamina 20.
The transverse processes 24 serve as guides for the attachment of
muscles to the vertebrae 12. Connecting the transverse process 24
on each side of the body 14 is a lateral mass 26. Two inferior
articular processes 28 extend downward from the junction of the
laminae 20 and the transverse processes 24. The inferior articular
processes 28 each have a natural bony structure known as an
inferior articular facet 32, which faces downward. On the superior
articular facet 30 is a superior articulating surface 38.
Similarly, a superior articular facet 30 faces upward from the
junction of the lateral mass 26 and the pedicle 16. On the inferior
articular facet 32 is an inferior articulating surface 40.
[0026] As shown in FIGS. 3 and 4, when adjacent vertebrae 12 are
aligned, the superior articular facet 30 and inferior articular
facet 32 interlock. Capped with a smooth articular cartilage, the
interlocked vertebrae form a facet joint 36, also known as a
zygapophysial joint. An intervertebral disc 34 between each pair of
vertebrae 12 permits gliding movement between vertebrae 12. Thus,
the structure and alignment of the vertebrae 12 permit a range of
movement of the vertebrae 12 relative to each other.
[0027] The facet joint 36 is composed of a superior half and an
inferior half. The superior half is formed by the vertebral level
below the intervertebral disc 34, and the inferior half is formed
by the vertebral level above the intervertebral disc 34. For
example, in the C3-C4 facet joint, the superior portion of the
joint is formed by bony structure on the C4 vertebra (e.g., a
superior articular surface and supporting bone on the C4 vertebra),
and the inferior portion of the joint is formed by bony structure
on the C3 vertebra (e.g., an inferior articular surface and
supporting bone on the C3 vertebra).
[0028] Turning now to FIG. 5, an exemplary cervical facet
resurfacing implant according to the present invention is
illustrated. The exemplary facet implant 100 generally has a
superior implant 102 and an inferior implant 104. The superior
implant 102 generally has a disk-shaped portion 106 and a tab 108
extending from the disk-shaped portion 106. The disk-shaped portion
106 includes an articulating surface 110 and a fixation surface
112.
[0029] The inferior implant 104 also generally has a disk-shaped
portion 114 and a tab 116 extending from the disk-shaped portion
114. The disk-shaped portion 114 includes an articulating surface
118 and a fixation surface 120.
[0030] It should be noted that the term "disk-shaped" is not
restricted to circular or ovular shapes. A generally disk-shaped
implant may have multiple sides, such as a square-shaped,
hexagonal-shaped, or octagonal-shaped implant. While each of these
shapes appear similar from a lateral perspective and are capable of
performing a similar function according to the present invention, a
circular or ovular disk-shape is preferred.
[0031] Turning now to FIGS. 6A-C, an exemplary cervical facet
resurfacing implant according to the present invention is
illustrated in conjunction with a facet joint. The superior implant
102 is configured for placement on superior articular facet 30. The
superior implant 102 may be fixed to the superior articulating
surface 38 using cemented and/or cementless fixation techniques. In
an exemplary embodiment, the superior implant 106 includes a
disk-shaped portion 106, which has an articulating surface 110 and
a fixation surface 112 and is configured for placement on a
specifically prepared superior articulating surface 38.
[0032] The disk-shaped portion 106 of the superior implant 102 may
range from about 1 mm thick to about 6 mm thick. In an exemplary
embodiment, the thickness of the superior implant 102 ranges from
about 2 mm to about 4 mm. In another exemplary embodiment, the
thickness of the superior implant 102 ranges from about 1.5 mm to
about 2.5 mm. The disk-shaped portion 106 of the superior implant
102 may also range from about 3 mm in diameter to about 14 mm in
diameter. In an exemplary embodiment, the diameter of the superior
implant 102 ranges from about 6 mm to about 12 mm. In another
exemplary embodiment, the diameter of the superior implant 102
ranges from about 8 mm to about 10 mm.
[0033] The fixation surface 112 may be generally flat or generally
curved and is configured to interact with the superior articulating
surface 38. The articulating surface 110 may be generally curved
and may be configured to interact with an articulating surface 118
of the inferior implant 104.
[0034] Extending from the disk-shaped portion 106 of the superior
implant is a tab 108 configured to interact with or for attachment
to the lateral mass 26 of the vertebra 12. The tab 108 may be
generally curved so that it matches the natural curvature of the
vertebra 12. For example, the tab 108 and the disk-shaped portion
106 of the superior implant 102 may form an angle ranging from
about 110 degrees to about 160 degrees. In one exemplary
embodiment, the tab 108 and the disk-shaped portion 106 of the
superior implant 102 form an angle ranging from about 120 degrees
to about 150 degrees. In another exemplary embodiment, the tab 108
and the disk-shaped portion 106 of the superior implant 102 may
form an angle ranging from about 130 degrees to about 145
degrees.
[0035] The tab 108 may include a hole or a slot or the like
configured to receive a fixation device, such as a screw or the
like. In other words, the fixation device passes through the hole
or slot of the tab 108 and into the lateral mass 26 of the vertebra
12.
[0036] The superior implant 102 may have a surface fixation
mechanism for fixing the superior implant 102, such as by fixing
the fixation surface 112, to the superior articulating surface 38.
The surface fixation mechanism may be any fixation mechanism known
in the art, such as at least one of: one or more pegs, one or more
pips, ridges, one or more grooves, one or more fins, and one or
more screws. In an exemplary embodiment, the surface fixation
mechanism includes at least one fin 122. The fin 122 helps prevent
the superior implant 102 from migrating along the superior
articulating surface. In another exemplary embodiment, the surface
fixation mechanism may include a plurality of ridges, grouped in
regions such that the ridges in different regions are oriented in
different directions. For example, the surface fixation mechanism
may include four regions on the fixation surface 112 where each of
the four regions has ridges oriented in a different direction. The
various orientations of the ridges prevent the inferior implant 104
from moving in different directions with respect to the superior
articulating surface 38.
[0037] The fixation surface 112 of the superior implant 102 may
also have a porous coating; a porous onlay material; a biologic
coating; a surface treatment, such as to facilitate bone ingrowth
or cement fixation; a material facilitating bone ingrowth; and
combinations thereof. For example, the fixation surface 112 may
have a porous surface that is beaded, threaded, textured, etc.
Further, the fixation surface 112 may have a hydroxyapatite coating
or may be plasma-sprayed. In addition to the examples listed, any
known method of improving fixation of biologic implants may be used
to improve the interaction of the fixation surface 112 and the
superior articular facet 30.
[0038] In one exemplary embodiment, the fixation surface 112 of the
superior implant 102 is configured to interact only with the
superior articulating surface 38 and does not interact directly
with any other aspect of the superior articular facet 30 or the
facet joint 36. The fixation surface 112 of the superior implant
102 may be generally flat or generally curved for improved
interaction with the superior articulating surface 38.
[0039] The articulating surface 110 in one exemplary embodiment is
generally configured to articulate or interact with the
articulating surface 118 of the inferior implant 104. Accordingly,
the articulating surface 110 of the superior implant 102 may be
generally flat or generally curved. The superior implant 102
articulating surface 110 may be configured such that it acts as a
"female" surface wherein it is concave or configured to accept a
"male" articulating surface 118 of an inferior implant 104.
Conversely, the superior implant 102 articulating surface 110 may
also be configured such that it acts as a "male" surface wherein it
is convex or configured to be accepted by "female" articulating
surface 118 of an inferior implant 104.
[0040] The superior implant 102 may be composed of any material
commonly used in the art for articulating medical implants. Such
materials include, but are not limited to, cobalt-chromium alloys,
ceramics (alumina ceramic, zirconia ceramic, yttria zirconia
ceramic, etc.), titanium, ultra high molecular weight polyethylene
(UHMWPE), pyrolytic carbon, titanium/aluminum/vanadium (Ti/Al/V)
alloys, Tantalum, Carbon composite materials and combinations
thereof. For example, the superior implant 102 may be generally
composed of titanium, but have a UHMWPE articulating surface. Some
materials are more appropriate for articulating surfaces and some
more appropriate for fixation surfaces, but any materials known in
the art for use with articulating and fixation surfaces can be used
in the present invention. Such materials are commonly used in joint
arthroplasty and the like.
[0041] The inferior implant 104 is configured for placement on
inferior articular facet 32. The inferior implant 104 may be fixed
to the inferior articulating surface 40 using cemented and/or
cementless fixation techniques. In an exemplary embodiment, the
inferior implant 104 has a disk-shaped portion 114, which has an
articulating surface 118 and a fixation surface 120 and is
configured for placement on a specifically prepared inferior
articulating surface 40.
[0042] The disk-shaped portion 116 of the inferior implant 104 may
range from about 1 mm thick to about 6 mm thick. In an exemplary
embodiment, the thickness of the inferior implant 104 ranges from
about 2 mm to about 4 mm. In another exemplary embodiment, the
thickness of the inferior implant 104 ranges from about 1.5 mm to
about 2.5 mm. The disk-shaped portion 114 of the inferior implant
104 may also range from about 3 mm in diameter to about 14 mm in
diameter. In an exemplary embodiment, the diameter of the inferior
implant 104 ranges from about 6 mm to about 12 mm. In another
exemplary embodiment, the diameter of the inferior implant 104
ranges from about 8 mm to about 10 mm.
[0043] The fixation surface 120 may be generally flat or generally
curved and is configured to interact with the inferior articulating
surface 40. The articulating surface 118 may be generally curved
and may be configured to interact with an articulating surface 110
of the superior implant 104.
[0044] Extending from the disk-shaped portion 114 of the inferior
implant is a tab 116 configured to interact with or for attachment
to the inferior articular process 28 of the vertebra 12. The tab
116 may be generally curved so that it matches the natural
curvature of the vertebra 12. For example, the tab 116 and the
disk-shaped portion 114 of the inferior implant 104 may form an
angle ranging from about 10 degrees to about 70 degrees. In one
exemplary embodiment, the tab 116 and the disk-shaped portion 114
of the inferior implant 104 form an angle ranging from about 20
degrees to about 60 degrees. In another exemplary embodiment, the
tab 116 and the disk-shaped portion 114 of the inferior implant 104
may form an angle ranging from about 30 degrees to about 50
degrees.
[0045] The tab 116 may include a hole or a slot or the like
configured to receive a fixation device, such as a screw or the
like. In other words, the fixation device passes through the hole
or slot of the tab 116 and into the inferior articular process 28
of the vertebra 12.
[0046] The inferior implant 104 may have a surface fixation
mechanism for fixing the inferior implant 104, such as by fixing
the fixation surface 120, to the inferior articulating surface 40.
The surface fixation mechanism may be any fixation mechanism known
in the art, such as at least one of: one or more pegs, one or more
pips, ridges, one or more grooves, one or more fins, and one or
more screws. In an exemplary embodiment, the surface fixation
mechanism includes at least one fin, such as the fin shown as 122
on the superior implant 102. The fin helps prevent the inferior
implant 104 from migrating along the superior articulating surface.
In another exemplary embodiment, the surface fixation mechanism may
include a plurality of ridges, grouped in regions such that the
ridges in different regions are oriented in different directions.
For example, the surface fixation mechanism may include four
regions on the fixation surface 120 where each of the four regions
has ridges oriented in a different direction. The various
orientations of the ridges prevent the inferior implant 104 from
moving in different directions with respect to the inferior
articulating surface 40.
[0047] The fixation surface 120 of the inferior implant 104 may
also have a porous coating; a porous onlay material; a biologic
coating; a surface treatment, such as to facilitate bone ingrowth
or cement fixation; and combinations thereof. For example, the
fixation surface 120 may have a porous surface that is beaded,
threaded, textured, etc. Further, the fixation surface 120 may have
a hydroxyapatite coating or may be plasma-sprayed. In addition to
the examples listed, any known method of improving fixation of
biologic implants may be used to improve the interaction of the
fixation surface 120 and the inferior articular facet 32.
[0048] In one exemplary embodiment, the fixation surface 120 of the
inferior implant 104 is configured to interact only with the
inferior articulating surface 40 and does not interact directly
with any other aspect of the inferior articular facet 32, the
inferior articular process 28, or even the facet joint 36. The
fixation surface 120 of the inferior implant 104 may be generally
flat or generally curved for improved interaction with the inferior
articulating surface 40.
[0049] The articulating surface 118 in one exemplary embodiment is
generally configured to articulate or interact with the
articulating surface 110 of the superior implant 102. Accordingly,
the articulating surface 118 of the inferior implant 104 may be
generally flat or generally curved. The inferior implant 104
articulating surface 118 may be configured such that it acts as a
"female" surface wherein it is concave or configured to accept a
"male" articulating surface 110 of a superior implant 102.
Conversely, the inferior implant 104 articulating surface 118 may
also be configured such that it acts as a "male" surface wherein it
is convex or configured to be accepted by "female" articulating
surface 110 of an superior implant 102.
[0050] The inferior implant 104 may be composed of any material
commonly used in the art for articulating medical implants. Such
materials include, but are not limited to, cobalt-chromium alloys,
ceramics (alumina ceramic, zirconia ceramic, yttria zirconia
ceramic, etc.), titanium, ultra high molecular weight polyethylene
(UHMWPE), pyrolytic carbon, titanium/aluminum/vanadium (Ti/Al/V)
alloys, and combinations thereof. For example, the inferior implant
104 may be generally composed of a ceramic material or a
cobalt-chromium alloy. Some materials are more appropriate for
articulating surfaces and some more appropriate for fixation
surfaces, but any materials known in the art for use with
articulating and fixation surfaces can be used in the present
invention. Such materials are commonly used in joint arthroplasty
and the like.
[0051] Turning next to FIG. 7, there is provided an alternate
embodiment of a cervical facet inferior implant in conjunction with
a trans-lateral mass screw. In another exemplary embodiment, the
inferior implant 204 is configured to interact with or attach to a
trans-lateral mass fixation mechanism 202. As shown, the
trans-lateral mass fixation mechanism 202 is a screw, but may be
any like fixation mechanism.
[0052] For example, the inferior implant 204 may include a threaded
hole 212 either extending from or bored into the fixation surface
210 of the inferior implant 204. The manner in which the inferior
implant 204 and the trans-lateral mass fixation mechanism 202
interact may vary with different anatomies. For example, it may be
preferable to offset the trans-lateral mass screw 202 from the
inferior implant 204 such that when the trans-lateral mass screw
202 and inferior implant 204 interact, the trans-lateral mass screw
202 is not perpendicular to the inferior implant 204. The
trans-lateral mass screw 202 may range from about 0 degrees offset
from perpendicular to about 60 degrees offset from
perpendicular.
[0053] The articulating surface 208 of the inferior implant 204 is
generally configured to articulate or interact with the
articulating surface 110 of the superior implant 102 shown in FIG.
5. Accordingly, the articulating surface 208 of the inferior
implant 204 may be generally flat or generally curved. The inferior
implant 204 articulating surface 208 may be configured such that it
acts as a "male" surface wherein it is convex or configured to be
accepted by a "female" articulating surface 110 of a superior
implant 102. Conversely, the inferior implant 204 articulating
surface 208 may also be configured such that it acts as a "female"
surface wherein it is configured to accept a "male" articulating
surface 110 of a superior implant 102.
[0054] A trans-lateral mass fixation mechanism 202 is configured to
interact with the inferior implant 204. The trans-lateral mass
fixation mechanism 202 secures the inferior implant 204 to the
inferior articular facet 32. The trans-lateral mass fixation
mechanism 202 may be any fixation mechanism known in the art, such
as a translaminar screw. The trans-lateral mass fixation mechanism
202 may be made from any material known in the art for medical
fixation devices. For example, the trans-lateral mass fixation
mechanism 202 may be made from titanium, titanium/aluminum/vanadium
(Ti/Al/V) alloys, Tantalum, CrCo, ceramic, carbon or carbon
composite materials.
[0055] Turning next to FIG. 8, there is provided a flow diagram
generally illustrating a method for providing articulating surfaces
for facet joint articular facets. The overall flow begins at
process block 802 wherein a space is created between the superior
articular facet 30 and the inferior articular facet 32. It will be
understood by those skilled in the art that prior to creating the
space, it may be preferable or even necessary to expose the facet
joint 36 at an effected level and remove the capsule. The effected
level may be exposed through use of any appropriate procedure, such
as a modified "Wiltse" approach. The creation of the space at
process block 602 may be accomplished by using a curette or similar
device and by removing the cartilaginous surfaces of the facet
joint 36. In one exemplary embodiment, the created space is
sufficient for using a rasp on an articulating surface of an
articular facet. The space created between the superior articular
facet 30 and the inferior articular facet 32 may range, for
example, from about 2 mm to about 15 mm. In one exemplary
embodiment, the space ranges from about 4 mm to about 8 mm. It
should be understood that a rasp can be any tool used to scrape,
grate, or file the facets.
[0056] Flow progresses to process block 804 wherein the
articulating surface 40 of the inferior articular facet 32 is
prepared for an inferior implant 104. Such preparation may be made
by a rasp, such as a rasp specifically designed for preparing a
surface for the cervical facet implant. Progression then continues
to process block 806 wherein the articulating surface 38 of the
superior articular facet 30 is prepared for a superior implant 102.
Again, such preparation may be made by a rasp, such as a rasp
specifically designed for preparing a surface for the cervical
facet implant.
[0057] Each of the rasps of process blocks 804 and 806 may be
either a single shaft rasp or a double action rasp, such as those
illustrated in FIGS. 10-12 and described in detail herein. The
process of preparing the articulating surfaces 38 and 40 of the
articular facets 28 and 30 may involve using multiple rasps of
increasing thickness while widening the space created in process
block 802. For example, a 2 mm rasp may initially be used, then a 4
mm rasp, then a 6 mm rasp, then an 8 mm rasp, etc., until a desired
result is achieved. In addition, the rasps of process blocks 804
and 806 may be the same rasp. Further, a single rasp can be used to
prepare the articulating surfaces 38 and 40 concurrently. The
articulating surfaces 38 and 40 may be prepared such that a
bleeding bone bed is created to facilitate bone ingrowth for the
superior implant 102 and inferior implant 104.
[0058] As shown in FIG. 9, when the single handed rasp is used to
prepare articulating surface 38 and/or articulating surface 40, the
working end of the tool may be positioned inside the space created
in process block 802. The rasp may then be moved from an anterior
to a posterior position inside the facet joint 36 in order to
effect a clean and uniform resection of the created space in the
shape and dimension of both implants. In other words, the
articulating surface 38 is prepared such that its shape and
dimension resembles the superior implant 102 and the articulating
surface 40 is prepared such that its shape and dimension resembles
the inferior implant 104. The anterior/posterior movement of the
rasp may be continued until the rasp is too small for the space
created. The rasp may be too small when the space created is so
wide that the rasp cannot prepare both the articulating surfaces 38
and 40 concurrently. A larger (thicker) rasp may then be used.
Increasingly larger rasps may be used until the created space is
increased such that it ranges from about 4 mm to about 8 mm. In one
exemplary embodiment, the rasps are designed to cut only when
moving in a posterior direction to help prevent injury during the
resurfacing process.
[0059] In one embodiment, the steps of process blocks 802, 804 and
806 are repeated on the contralateral side of facet joint 36 prior
to performing the steps of process block 808.
[0060] Progression then flows to process block 808 wherein the
inferior implant 104 is placed on the prepared/resurfaced
articulating surface 40 of the inferior articular facet 32. In one
exemplary embodiment, the inferior implant 104 is placed such that
the disk-shaped portion 114 interacts with the articulating surface
40 of the inferior articular facet 32, but not with other aspects
of the inferior articular facet 32.
[0061] In one alternative embodiment, a trans-lateral mass screw
202 is used to secure an inferior implant 204 to the inferior
articular facet 32. In this embodiment, the above method would also
include using the trans-lateral mass screw 202 to secure the
inferior implant 204 to the inferior articular facet 32.
[0062] To facilitate placement of the trans-lateral mass screw 106,
an aiming device such as the device illustrated in FIG. 11 may be
used. The aiming device can be used to position a drill for
creating a trans-lateral mass hole for the trans-lateral mass screw
202. A drill can then be used to create the hole, which may have a
diameter of about 2 mm, depending on the diameter of the
trans-lateral mass screw 202.
[0063] Once the hole is drilled, the trans-lateral mass screw 202
can be introduced into the hole and then used to secure the
inferior implant 104 to the inferior articular facet 32. In one
embodiment, the steps of process blocks 808, including any steps
associated with the drilling or placement of the trans-lateral mass
screw 202, are repeated on the contralateral side of facet joint 36
prior to performing the steps of process block 810.
[0064] Progression then continues to process block 810 wherein the
superior implant 102 is placed on the prepared/resurfaced
articulating surface 38 of the superior articular facet 30. In one
exemplary embodiment, the superior implant 102 is placed such that
the disk-shaped portion 106 interacts with the articulating surface
38 of the superior articular facet 30, but not with other aspects
of the superior articular facet 30.
[0065] In one embodiment, the steps of process blocks 802, 804,
806, 808 and 810 are then repeated on the contralateral side.
[0066] Turning now to FIG. 10, a single handed rasp is illustrated.
The rasp 1000 includes a handle 1002 and a shaft 1004 connecting
the handle 1002 to the working end of the rasp 1000. Attached to
the shaft 804 at the working end of the rasp 1000 is a head 1006.
The head 1006 has at least one cutting surface 1008. In one
exemplary embodiment, the cutting surface 1008 is configured to cut
when the cutting surface 1008 is moved in a first direction (e.g.
when the rasp is moved from the anterior to the posterior direction
of the facet joint) but not when the cutting surface 1008 is moved
in a direction opposite to the first direction (e.g. when the rasp
is moved from the posterior to the anterior direction of the facet
joint).
[0067] The rasp 1000 is configured to prepare the articulating
surfaces of a facet joint. In an exemplary embodiment, the rasp
1000 is configured to prepare articulating surfaces 38 and 40 of
the articular facets 28 and 30 such that the shape and dimension of
the prepared articulating surfaces resembles the shape and
dimension of the superior implant 1.02 and inferior implant 104.
For example, if the superior implant 102 and/or inferior implant
104 are curved, the head 1006 may be generally curved to properly
prepare the surface for the implant.
[0068] In addition, the rasp 1000 may be made from any appropriate
material commonly used for medical tools. In one exemplary
embodiment, at least part of the rasp 1000 is made from titanium,
although the rasp could also be made from any material known in the
art.
[0069] While the present invention has been described in
association with several exemplary embodiments, the described
embodiments are to be considered in all respects as illustrative
and not restrictive. Such other features, aspects, variations,
modifications, and substitution of equivalents may be made without
departing from the spirit and scope of this invention which is
intended to be limited solely by the scope of the following claims.
Also, it will be appreciated that features and parts illustrated in
one embodiment may be used, or may be applicable, in the same or in
a similar way in other embodiments.
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