U.S. patent application number 10/955207 was filed with the patent office on 2006-04-20 for posterior stabilization systems and methods.
This patent application is currently assigned to DePuy Spine, Inc.. Invention is credited to Amie Borgstrom, William Dunbar, J. Riley Hawkins, S. Daniel Kwak.
Application Number | 20060084976 10/955207 |
Document ID | / |
Family ID | 36146361 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060084976 |
Kind Code |
A1 |
Borgstrom; Amie ; et
al. |
April 20, 2006 |
Posterior stabilization systems and methods
Abstract
Various methods and devices for repairing and/or restoring
function to a damaged, injured, diseased, or otherwise unhealthy
facet joint, lamina, posterior ligament, and/or other features of a
patient's spinal column are provided. In an exemplary embodiment,
the methods and devices are effective to mimic the natural function
of the posterior elements, preferably without necessarily mimicking
the anatomy, by allowing a high degree of flexibility between two
adjacent vertebrae when the vertebrae are moved within a first
range of motion, and by controlling movement of the adjacent
vertebrae within a second range of motion beyond the first range of
motion.
Inventors: |
Borgstrom; Amie; (North
Attleborough, MA) ; Hawkins; J. Riley; (Cumberland,
RI) ; Kwak; S. Daniel; (Grafton, MA) ; Dunbar;
William; (Norton, MA) |
Correspondence
Address: |
NUTTER MCCLENNEN & FISH LLP
WORLD TRADE CENTER WEST
155 SEAPORT BOULEVARD
BOSTON
MA
02210-2604
US
|
Assignee: |
DePuy Spine, Inc.
Raynham
MA
02767
|
Family ID: |
36146361 |
Appl. No.: |
10/955207 |
Filed: |
September 30, 2004 |
Current U.S.
Class: |
606/54 |
Current CPC
Class: |
A61B 17/7043 20130101;
A61B 17/7031 20130101; A61B 2017/7073 20130101; A61B 17/7025
20130101; A61B 17/7049 20130101; A61B 17/7023 20130101; A61B
17/7001 20130101 |
Class at
Publication: |
606/054 |
International
Class: |
A61B 17/60 20060101
A61B017/60 |
Claims
1. An implantable device for stabilizing the spine, comprising: at
least one flexible member adapted to span across at least two
adjacent vertebrae in a patient's spinal column; a superior
connector adapted to be coupled to a superior vertebra and an
inferior connector adapted to be coupled to an inferior vertebra,
the superior and inferior connectors extending through the at least
one flexible member such that the superior and inferior connectors
and the at least one flexible member are effective to control
movement between the superior and inferior vertebrae.
2. The implantable device of claim 1, wherein the superior
connector is movable relative to the at least one flexible
member.
3. The implantable device of claim 1, further comprising first and
second flexible members.
4. The implantable device of claim 1, wherein each flexible member
includes at least two thru-bores formed therein for receiving the
superior and inferior connectors therethrough.
5. The implantable device of claim 4, wherein each thru-bore
includes a bushing disposed therein and adapted to receive a
connector therethrough.
6. The implantable device of claim 4, wherein each thru-bore
includes a bearing formed therein and adapted to receive a
connector therethrough.
7. The implantable device of claim 4, wherein a region surrounding
each thru-bore is adapted to provide stability to the connector
extending therethrough.
8. The implantable device of claim 7, wherein each region is
substantially rigid.
9. The implantable device of claim 1, wherein each connector
comprises a substantially rigid rod.
10. The implantable device of claim 1, wherein the superior
connector includes opposed terminal ends that are adapted to be
coupled to pedicles of a superior vertebra, and a mid-portion that
is adapted to extend around and be positioned inferior to a spinous
process of a superior vertebra, and wherein the inferior connector
includes opposed terminal ends that are adapted to be coupled to
pedicles of an inferior vertebra, and a mid-portion that is adapted
to be positioned proximate and superior to a spinous process of an
inferior vertebra.
11. The implantable device of claim 10, wherein the superior
connector is substantially v-shaped and the inferior connector is
generally linear with a v-shaped portion formed therein.
12. The implantable device of claim 11, wherein the v-shaped
portion in the inferior connector is formed at a substantial
mid-point thereof.
13. The implantable device of claim 12, wherein the v-shaped
portion in the inferior connector is adapted to fit around a
spinous process of an inferior vertebra.
14. The implantable device of claim 11, wherein the v-shaped
superior connector includes a central linear portion and first and
second lateral arms extending at an angle relative to the central
linear portion.
15. The implantable device of claim 1, wherein each connector
includes first and second terminal ends adapted to be fixedly mated
to opposed sides of a vertebra.
16. The implantable device of claim 15, further comprising a
plurality of spinal anchors, each being adapted to be implanted in
a vertebra and to fixedly mate a terminal end of a connector to the
vertebra.
17. The implantable device of claim 16, wherein each spinal anchor
comprises a spinal screw having a rod-receiving head formed
thereon, and wherein each connector comprises a rod.
18. The implantable device of claim 1, wherein the at least one
flexible member is formed from a material selected from the group
consisting of polyurethane, composite reinforced polyurethane, and
silicones.
19. The implantable device of claim 1, wherein the at least one
flexible member comprises a single flexible member having a
substantially hour-glass shape.
20. The implantable device of claim 1, wherein the at least one
flexible member has a central portion that has an elasticity that
is greater than an elasticity of opposed superior and inferior
terminal ends thereof.
21. An implantable device for stabilizing the spine, comprising:
first and second dynamic stabilizing members adapted to be
positioned adjacent to opposed sides of a spinous process and to
extend along at least two adjacent vertebrae in a patient's spinal
column; and at least one pair of stabilizing rods adapted to extend
through the first and second dynamic stabilizing members and to
couple to two adjacent vertebrae to control movement between the
adjacent vertebrae.
22. The implantable device of claim 21, wherein the first and
second dynamic stabilizing members are substantially flexible.
23. The implantable device of claim 22, wherein the first and
second dynamic stabilizing members each have a flexibility that
varies along a length thereof.
24. The implantable device of claim 22, wherein the first and
second dynamic stabilizing members each have a mid-portion having a
flexibility that is greater than a flexibility of opposed terminal
ends thereof.
25. The implantable device of claim 21, wherein a pair of
stabilizing rods comprises a superior stabilizing rod and an
inferior stabilizing rod, and wherein the first and second dynamic
stabilizing members each include a superior hole formed therein and
adapted to receive the superior stabilizing rod, and an inferior
hole formed therein and adapted to receive the inferior stabilizing
rod.
26. The implantable device of claim 25, wherein the superior
stabilizing member includes opposed terminal ends that are adapted
to be coupled to pedicles of a vertebra, and a mid-portion that is
adapted to extend around and be positioned inferior to a spinous
process of a vertebra.
27. The implantable device of claim 25, wherein the inferior
stabilizing member includes opposed terminal ends that are adapted
to be coupled to pedicles of an inferior vertebra, and a
mid-portion that is adapted to be positioned proximate and inferior
to a spinous process of an adjacent superior vertebra.
28. The implantable device of claim 25, wherein the superior
stabilizing member has a generally elongate shape with a v-shaped
portion formed therein, and wherein the inferior stabilizing member
is substantially v-shaped.
29. The implantable device of claim 25, wherein the superior and
inferior holes in the first and second dynamic stabilizing members
each include a bearing element disposed therein and adapted to
receive the stabilizing rod.
30. The implantable device of claim 25, wherein the superior and
inferior holes in the first and second dynamic stabilizing members
are adapted to rigidly support the stabilizing rod relative to the
dynamic stabilizing member.
31. The implantable device of claim 30, wherein a region
surrounding the superior and inferior holes in the first and second
dynamic stabilizing members have an elasticity that is less than an
elasticity of the remainder of the first and second dynamic
stabilizing members.
32. A posterior element replacement implant, comprising: at least
one flexible member; and at least one connector adapted to be
coupled to adjacent vertebrae and adapted to extend through the at
least one flexible member; wherein the at least one connector is
adapted to move relative to the at least one flexible member
without substantially deforming the at least one flexible member
when the adjacent vertebrae are moved within a first range of
motion, and wherein the at least one connector is adapted to deform
the at least one flexible member when the adjacent vertebrae are
moved within a second range of motion beyond the first range of
motion.
33. The implant of claim 32, wherein the at least one connector
comprises a superior connector and an inferior connector.
34. The implant of claim 33, wherein the superior and inferior
connectors each comprise a substantially rigid rod.
35. The implant of claim 34, wherein the superior rod is
substantially v-shaped, and the inferior rod is substantially
linear with a v-shaped portion formed therein.
36. The implant of claim 33, wherein the at least one flexible
member comprises first and second flexible members.
37. The implant of claim 36, wherein the first and second flexible
members each have a substantially elongate shape with first and
second thru-bores formed therein for receiving the superior and
inferior connectors.
38. The implant of claim 37, wherein each thru-bore includes a
bearing formed therein and adapted to receive a connector extending
therethrough.
39. An implantable posterior element repair kit, comprising: a
plurality of pairs of dynamic stabilizing members, each pair
comprising first and second dynamic stabilizing members adapted to
be positioned adjacent to opposed sides of a spinous process and to
extend along at least two adjacent vertebrae in a patient's spinal
column; and a plurality of pairs of stabilizing rods, each pair of
stabilizing rods being adapted to couple to a pair of dynamic
stabilizing members and to couple to two adjacent vertebrae to
control movement between the adjacent vertebrae.
40. The kit of claim 39, wherein each of the plurality of pairs of
dynamic stabilizing members has an elasticity that differs from one
another.
41. The kit of claim 39, wherein each of the plurality of pairs of
dynamic stabilizing members has a size that differs from one
another.
42. The kit of claim 39, wherein each of the plurality of pairs of
dynamic stabilizing members has a shape that differs from one
another.
43. A method for stabilizing the posterior element in adjacent
vertebrae, comprising: coupling at least one flexible member to two
adjacent vertebrae with at least one connector such that the at
least one connector is movable relative to the at least one
flexible member without substantially deforming the at least one
flexible member when the vertebrae are moved within a first range
of motion, and such that the at least one connector is effective to
deform the at least one flexible member when the vertebrae are
moved within a second range of motion beyond the first range of
motion.
44. The method of claim 43, wherein the step of coupling at least
flexible member to two adjacent vertebrae with at least one
connector comprises coupling a superior connector to a superior
vertebra, the superior connector extending through first and second
flexible members, and coupling an inferior connector to an inferior
vertebra, the inferior connector extending through the first and
second flexible members.
45. The method of claim 44, wherein the step of coupling the
superior connector to the superior vertebra comprises implanting
first and second spinal anchors in the superior vertebra and
locking the superior connector to the first and second spinal
anchors, and wherein the step of coupling the inferior connector to
the inferior vertebra comprises implanting first and second spinal
anchors in the inferior vertebra and locking the inferior connector
to the first and second spinal anchors.
46. A method for mimicking the normal function of adjacent
vertebrae in a patient's spinal column, comprising: implanting a
first pair of spinal anchors in opposed pedicles of a first
vertebra, and implanting a second pair of spinal anchors in opposed
pedicles of an adjacent second vertebra; coupling opposed terminal
ends of a first rigid member to the first pair of spinal anchors in
the first vertebra, and coupling opposed terminal ends of a second
rigid member to the second pair of spinal anchors in the second
vertebra, the first and second rigid members extending through at
least one flexible member.
47. The method of claim 46, wherein the at least one flexible
member comprises first and second flexible members positioned on
opposed sides of a spinous process of each vertebra.
48. The method of claim 46, wherein the first rigid member is
substantially v-shaped, and the second rigid member is
substantially linear with a v-shaped portion formed therein.
49. The method of claim 46, wherein the first rigid member extends
from the opposed pedicles inferior to a spinous process of the
first vertebra, and wherein the second rigid member extends from
the opposed pedicles superior to a spinous process of the second
vertebra.
50. The method of claim 46, wherein each spinal anchor comprises a
spinal screw having a receiver head formed thereon and adapted to
seat a terminal end of a rigid member.
51. The method of claim 46, further comprising the steps of
implanting a third pair of spinal anchors in opposed pedicles of a
third vertebra adjacent to the second vertebra, coupling opposed
terminal ends of a third rigid member to the second pair of spinal
anchors in the second vertebra, and coupling opposed terminal ends
of a fourth rigid member to the third pair of spinal anchors in the
third vertebra, the third and fourth rigid members extending
through the at least one flexible member.
52. A method for providing stability to adjacent vertebrae,
comprising coupling a superior stabilizing rod to opposed sides of
a superior vertebra and coupling an inferior stabilizing rod to
opposed sides of an inferior vertebra such that movement between
the superior and inferior vertebrae is controlled by at least one
flexible member coupled to each of the superior and inferior
stabilizing rods.
53. The method of claim 52, wherein the superior stabilizing rod is
adapted to move relative to the at least one flexible member
without substantially deforming the at least one flexible when the
superior and inferior vertebrae are moved relative to one another
within a first range of motion, and wherein the superior
stabilizing rod is adapted to deform the at least one flexible
member when the superior and inferior vertebrae are moved relative
to one another within a second range of motion beyond the first
range of motion.
54. A spinal stabilization device, comprising: a first elongate
connector adapted to couple to opposed lateral sides of a first
vertebra; a second elongate connector adapted to couple to opposed
lateral sides of a second vertebra adjacent to the first vertebra;
and at least one flexible member movably coupled to the first and
second elongate connectors such that, when the connectors are mated
to adjacent first and second vertebrae, the connectors and the at
least one flexible member are effective to allow controlled
movement of the adjacent first and second vertebrae.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to spinal instrumentation, and
in particular to various devices that are adapted to mimic the
natural function of the structural posterior elements.
BACKGROUND OF THE INVENTION
[0002] The vertebrae in a patient's spinal column are linked to one
another by the disc and the facet joints, which control movement of
the vertebrae relative to one another. Each vertebra has a pair of
articulating surfaces located on the left side, and a pair of
articulating surfaces located on the right side, and each pair
includes a superior articular surface, which faces upward, and an
inferior articular surface, which faces downward. Together the
superior and inferior articular surfaces of adjacent vertebra form
a facet joint. Facet joints are synovial joints, which means that
each joint is surrounded by a capsule of connective tissue and
produces a fluid to nourish and lubricate the joint. The joint
surfaces are coated with cartilage allowing the joints to move or
articulate relative to one another.
[0003] Diseased, degenerated, impaired, or otherwise painful facet
joints and/or discs can require surgery to restore function to the
three joint complex. Subsequent surgery may also be required after
a laminectomy, as a laminectomy predisposes the patient to
instability and may lead to post-laminectomy kyphosis (abnormal
forward curvature of the spine), pain, and neurological
dysfunction. Damaged, diseased levels in the spine were
traditionally fused to one another. While such a technique may
relieve pain, it effectively prevents motion between at least two
vertebrae. As a result, additional stress may be applied to the
adjoining levels, thereby potentially leading to further
damage.
[0004] More recently, techniques have been developed to restore
normal function to the facet joints. One such technique involves
covering the facet joint with a cap to preserve the bony and
articular structure. Capping techniques, however, are limited in
use as they will not remove the source of the pain in
osteoarthritic joints. Caps are also disadvantageous as they must
be available in a variety of sizes and shapes to accommodate the
wide variability in the anatomical morphology of the facets. Caps
also have a tendency to loosen over time, potentially resulting in
additional damage to the joint and/or the bone support structure
containing the cap.
[0005] Other techniques for restoring the normal function to the
posterior element involve arch replacement, in which superior and
inferior prosthetic arches are implanted to extend across the
vertebra typically between the spinous process. The arches can
articulate relative to one another to replace the articulating
function of the facet joints. While these techniques can be
effective in replacing the bony elements, they do not specify a
means to replace the function of the soft tissues and more
specifically a means to mimic the load deformation curve of the
natural spine.
[0006] Accordingly, there remains a need for improved systems and
methods that are adapted to mimic the natural function of the facet
joints.
SUMMARY OF THE INVENTION
[0007] The present invention provides various methods and devices
for repairing and/or replacing a damaged facet joint, and
optionally for replacing other posterior elements, including, for
example, the lamina, the posterior ligaments, and/or other features
of a patient's spinal column. In one exemplary embodiment, an
implantable device for replacing and/or stabilizing one or more
facet joints in a patient's spinal column is provided and it
generally includes at least one dynamic stabilizing member, e.g., a
flexible member, and at least one stabilizing rod or connector that
is adapted to couple to adjacent vertebrae and that is adapted to
extend through the at least one flexible member. In an exemplary
embodiment, the device includes superior and inferior connector
members that are adapted to mate to superior and inferior
vertebrae, respectively, and the flexible member(s) is adapted to
span across at least two adjacent vertebrae in a patient's spinal
column. In use, the superior and inferior connectors and the
flexible member(s) are effective to control movement between the
superior and inferior vertebrae. More preferably, the connector(s)
are adapted to slidably and/or rotatably move relative to the
flexible member(s), preferably without deforming the flexible
member(s), when the adjacent vertebrae are moved within a first
range of motion, and they are preferably adapted to deform the
flexible member(s) when the adjacent vertebrae are moved within a
second range of motion beyond the first range of motion.
[0008] The flexible member(s) can have a variety of configurations,
shapes, and sizes. In one embodiment, the implant includes two
flexible members and each flexible member has a substantially
elongate shape. The flexible members can also have a shape that is
in the form of an hour-glass. In another embodiment, the implant
can include a single flexible member, and the flexible member can
optionally have a shape that is substantially in the form of an
hour-glass. The flexible member(s) can also have an elasticity that
varies. For example, the flexible member can have a central portion
that has an elasticity that is greater than an elasticity of
opposed superior and inferior terminal ends thereof. In another
embodiment, each flexible member can include at least two
thru-bores formed therein for receiving the superior and inferior
connectors therethrough. Each thru-bore can include a bushing or
bearing disposed therein and adapted to receive a connector. The
region surrounding the thru-bores can have properties or
characteristics that vary, or that are at least different than the
properties of the central region. In one embodiment, a region
surrounding each thru-bore is adapted to provide stability to the
connector extending therethrough. As such, each region surrounding
the thru-bores can be substantially rigid or have less elasticity
than the central portion.
[0009] Each connector can also have a variety of configurations,
and in one embodiment each connector is in the form of a
substantially rigid rod. More preferably, the superior connector
includes opposed terminal ends that are adapted to couple to the
pedicles of the superior vertebra, and a mid-portion that is
adapted to extend around and be positioned inferior to the spinous
process of the superior vertebra, and the inferior connector
includes opposed terminal ends that are adapted to couple to the
pedicles of the inferior vertebra, and a mid-portion that is
adapted to be positioned proximate and superior to the spinous
process of the inferior vertebra. In an exemplary embodiment, the
superior connector is substantially v-shaped and the inferior
connector is generally linear with a v-shaped portion formed
therein. More preferably, the v-shaped superior connector includes
a central linear portion and first and second lateral arms
extending at an angle relative to the central linear portion, and
the v-shaped portion in the inferior connector is preferably formed
at a substantial mid-point thereof. In use, the v-shaped portion of
the inferior connector can be adapted to fit around the spinous
process of the inferior vertebra, and the v-shaped superior
connector can be adapted to extend around the spinous process of
the superior vertebra. Each connector can also include first and
second terminal ends that are adapted to be fixedly mated to
opposed sides of a vertebra. By way of non-limiting example, a
spinal anchor, such as a spinal screw, can be used to fixedly a
terminal end of a connector to the vertebra.
[0010] The present invention also provides methods for replacing
and/or stabilizing the posterior elements in adjacent vertebrae. In
one embodiment, the method can include the steps of coupling at
least one flexible member to two adjacent vertebrae with at least
one connector such that the at least one connector is slidably
and/or rotatably movable relative to the at least one flexible
member, preferably without substantially deforming the flexible
member, when the vertebrae are moved within a first range of
motion, and such that the at least one connector is effective to
stretch and/or deform the at least one flexible member when the
vertebrae are moved within a second range of motion beyond the
first range of motion. Preferably, the step of coupling at least
flexible member to two adjacent vertebrae with at least one
connector comprises coupling a superior connector to a superior
vertebra, and coupling an inferior connector to an inferior
vertebra. The superior connector and the inferior connector can
extend through first and second flexible members. In one
embodiment, the superior and inferior connectors can be coupled to
the superior and inferior vertebrae, respectively, by implanting
first and second spinal anchors in each of the superior and
inferior vertebra and locking the superior and inferior connectors
to the spinal anchors.
[0011] In yet another embodiment, a method for restoring normal
function to the posterior elements and/or replacing the posterior
elements of adjacent vertebrae in a patient's spinal column is
provided and it includes the steps of implanting a first pair of
spinal anchors in opposed pedicles of a first vertebra, implanting
a second pair of spinal anchors in opposed pedicles of an adjacent
second vertebra, coupling opposed terminal ends of a first rigid
member to the first pair of spinal anchors in the first vertebra,
and coupling opposed terminal ends of a second rigid member to the
second pair of spinal anchors in the second vertebra. The first and
second rigid members preferably extend through at least one
flexible member. In an exemplary embodiment, the first and second
rigid members extend through first and second flexible members that
are preferably positioned on opposed sides of a spinous process of
each vertebra.
[0012] The method can also include the step of implanting a third
pair of spinal anchors in opposed pedicles of a third vertebra
adjacent to the second vertebra, coupling opposed terminal ends of
a third rigid member to the second pair of spinal anchors in the
second vertebra, and coupling opposed terminal ends of a fourth
rigid member to the third pair of spinal anchors in the third
vertebra. The third and fourth rigid members preferably extend
through the at least one flexible member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0014] FIG. 1A is a perspective view illustration of two adjacent
vertebrae coupled to one another by a facet joint stabilizing
device in accordance with one embodiment of the present
invention;
[0015] FIG. 1B is a side view illustration of the vertebrae and
device shown in FIG. 1A;
[0016] FIG. 1C is a front view illustration of the vertebrae and
device shown in FIG. 1A;
[0017] FIG. 2A is a side view illustration of the superior
connector of the device shown in FIGS. 1A-1C;
[0018] FIG. 2B is a side view illustration of the inferior
connector of the device shown in FIGS. 1A-1C;
[0019] FIG. 2C is an exploded view illustration of one of the
flexible members of the device shown in FIGS. 1A-1C;
[0020] FIG. 2D illustrates another embodiment of a posterior
element stabilizing device having hour-glass shaped flexible
members;
[0021] FIG. 3 is a chart showing a typical load-deformation curve
of a human functional spine unit; and
[0022] FIG. 4 is a perspective view of another embodiment of a
posterior element stabilizing device in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides various methods and devices
for replacing damaged, injured, diseased, or otherwise unhealthy
posterior elements, such as the facet joints, the lamina, the
posterior ligaments, and/or other features of a patient's spinal
column. In an exemplary embodiment, the methods and devices are
effective to mimic the natural function of the spine by allowing a
high degree of flexibility between two adjacent vertebrae when the
vertebrae are moved within a first range of motion, and by
controlling or limiting movement of the adjacent vertebrae within a
second range of motion beyond the first range of motion. A person
skilled in the art will appreciate that, while the methods and
devices are especially configured for use in restoring and/or
replacing the facet joints and optionally other posterior elements
of a patient's spine, the methods and devices can be used for a
variety of other purposes in a variety of other surgical
procedures.
[0024] FIGS. 1A-1C illustrate one exemplary embodiment of a
posterior element replacement implant connected between adjacent
vertebrae 60, 62. As shown, the implant 10 generally includes first
and second flexible members 12, 14, also referred to as dynamic
stabilizing elements, and first and second connectors 16, 18, also
referred to as stabilizing rods. The implant 10 is preferably
effective to mimic the natural function of the spine. As shown in
FIGS. 1A-1C, the implant 10 is coupled to superior and inferior
vertebrae 60, 62 such that it is effective to perform the function
of the posterior elements that connect the vertebrae, or to
otherwise control movement of the vertebrae 60, 62. More
particularly, the first connector 16, hereinafter referred to as
the superior connector 16, is coupled to the superior vertebra 60,
and the second connector 18, hereinafter referred to as the
inferior connector 18, is coupled to the inferior vertebra 62. The
superior and inferior connectors 16, 18 extend through the first
and second flexible members 12, 14, such that the connectors 16, 18
are coupled to one another via the flexible members 12, 14. As a
result, the connectors 16, 18 and the flexible members 12, 14 are
effective to control movement of the vertebrae 60, 62 relative to
one another, thereby functioning in place of the posterior
elements. In an exemplary embodiment, the flexible members 12, 14
are movable, e.g., rotatable and/or slidable, but preferably not
deformable, relative to at least one of the connectors, e.g., the
superior connector 16, when the vertebrae 60, 62 are moved within a
first range of motion, and at least one of the connectors, e.g.,
the superior connector 16, is effective to deform, e.g., stretch,
rotate, etc., the flexible members 12, 14, or otherwise create
resistance, when the superior and inferior vertebrae 60, 62 are
moved within a second range of motion beyond the first range of
motion.
[0025] A person skilled in the art will appreciate that while FIGS.
1A-1C illustrate two flexible members 12, 14 and two connectors 16,
18, that any number of flexible members can be used. By way of
non-limiting example, the implant 10 can include only one flexible
member that is similar to flexible member 12 or 14. In another
embodiment, shown in FIG. 4, the implant can include a single
flexible member 13 that performs the function of flexible members
12 and 14. More particularly, the single flexible member 13 can
have an hour-glass shape such that the narrow region of the hour
glass extends between the spinous process of two adjacent
vertebrae, and the widened ends of the hour glass extends at or
adjacent to the location of the facet joints. This configuration is
particularly useful in laminectomy procedures in which the spinous
processes are removed. A person skilled in the art will also
appreciate that the function of the flexible members 12, 14 and the
connectors 16, 18 can be reversed. For example, the connectors 16,
18 can be formed from a flexible or deformable material, and
members 12, 14 can be substantially rigid.
[0026] Each flexible member can have a variety of configurations,
shapes, and sizes. In an exemplary embodiment, as shown, each
flexible member 12, 14 has a generally elongate shape such that it
is adapted to span across two or more adjacent vertebrae. While
FIGS. 1A-1C illustrate substantially rectangular-shaped or oblong
members 12, 14, in other exemplary embodiments the flexible members
12, 14 can have an oval shape, a cylindrical shape, etc. By way of
non-limiting example, FIG. 2D illustrates two flexible members 12',
14' having an hour-glass shape. The length of the flexible members
12, 14 will vary depending on the number of levels being repaired
and/or replaced, and thus the number of vertebrae to which the
implant is to be attached to. As shown in FIGS. 1A-1C, each
flexible member 12, 14 has a length that is adapted to span across
two adjacent vertebrae 60, 62. The flexible members 12, 14 can also
be adapted to be positioned on opposed sides of the spinous
process, such that the flexible members 12, 14 can be positioned in
or near the location of the facet joints, as is also shown in FIGS.
1A-1C.
[0027] Each flexible member 12, 14 also preferably includes at
least one thru-bore formed therethrough for receiving the
connectors 16, 18. As best shown in FIG. 1C, each flexible member
12, 14 includes a superior thru-bore 12s, 14s, and inferior
thru-bore 12i, 14i. Each thru-bore 12s, 12i, 14s, 14i should have a
size that is adapted to receive the connector 16, 18 therethrough
preferably without allowing significant movement of the connector
16, 18 relative thereto, i.e., such that the connectors 16, 18 are
in close contact with the thru-bores 12s, 12i, 14s, 14i. The
thru-bores 12s, 12i, 14s, 14i are, however, preferably effective to
allow at least one of the connectors 16, 18, and preferably both of
the connectors 16, 18, to slide freely therethrough. Such a
configuration allows the flexible members 12, 14 to slide along
and/or rotate with respect to the connectors 16, 18, at least
during a particular range of motion which will be discussed in more
detail below.
[0028] Each thru-bore 12s, 12i, 14s, 14i can also be adapted to
facilitate sliding and/or rotating movement of the flexible members
12, 14 relative to the connectors 16, 18. In an exemplary
embodiment, the thru-bores 12s, 12i, 14s, 14i are preferably
configured to prevent or reduce wearing thereof during use of the
implant. While various techniques can be used to achieve this, in
one exemplary embodiment each thru-bore 12s, 12i, 14s, 14i can
include a bushing or bearing element disposed therein and adapted
to slidably receive a connector 16, 18. In one exemplary
embodiment, shown in FIG. 2C which illustrates flexible member 12,
the superior thru-bore 12s can include a superior bushing 20s and
the inferior thru-bore 12i can include an inferior bushing 20i.
Each bushing 20s, 20i is in the form of a generally hollow,
cylindrical member that is adapted to fit within the thru-bore 12s,
12i in the flexible member 12 and that functions as a bearing
surface for the connectors 16, 18. The bushings 20s, 20i can,
however, have virtually any shape and size.
[0029] In another embodiment (not shown), the flexible members 12,
14 can include a bearing surface formed within or integrally with
the thru-bores 12s, 12i, 14s, 14, and/or the thru-bores 12s, 12i,
14s, 14i can at least be modified to achieve properties that will
facilitate movement of the connectors 16, 18 relative thereto.
Alternatively, the thru-bores 12s, 12i, 14s, 14i, or at least a
region surrounding the thru-bores 12s, 12i, 14s, 14i, can have a
stiffness that is greater than a remainder of the flexible members
12, 14, or at least that is sufficient to minimize wear on the
thru-bores 12s, 12i, 14s, 14i when the device 10 is implanted and
in use. The bushings 20s, 20i, the thru-bores 12s, 12i, 14s, 14i,
or bearing surface formed within the thru-bores 12s, 12i, 14s, 14i
can be formed from any material. Suitable materials include, by way
of non-limiting example, metals, ceramics, polymers, etc. A person
skilled in the art will appreciate that a variety of techniques can
be used to facilitate slidable and/or rotatable movement of the
flexible members 12, 14 relative to the connectors 16, 18.
[0030] Each flexible member 12, 14 can also be formed from a
variety of materials, but each flexible member 12, 14 is preferably
effective to mimic the flexion/extension, rotation, lateral
bending, and load carrying requirements of the posterior elements
of the spine. In an exemplary embodiment, each flexible member 12,
14 is formed from a polymer, and more preferably a biocompatible
polymer, such as polyurethane, composite reinforced polyurethane,
silicone, etc. A person skilled in the art will appreciate that the
material can vary depending on the intended use. For example, a
material can be selected, based on a patient's size and condition,
to have a particular stiffness.
[0031] The properties of the flexible members 12, 14 can also vary,
and they can be uniform or non-uniform throughout the body thereof.
In one embodiment, each flexible member 12, 14 can have a
mid-portion 12a, 14a that is more elastic than terminal ends 12b,
12c, 14b, 14c of the flexible members 12, 14. The flexible members
12, 14 can also have regions that are more or less elastic than the
remainder of the member 12, 14. In one exemplary embodiment, the
flexible members 12, 14 can be configured to have a first
elasticity during the first range of motion, and a second,
different elasticity in a second range of motion beyond the first
range of motion, as will be discussed in more detail below. In
another exemplary embodiment, as noted above, the regions
surrounding the thru-bores 12s, 12i, 14s, 14i can be formed from a
material having a stiffness that is greater than the remainder of
the flexible members 12, 14.
[0032] The connectors 16, 18 of the implant 10 can also have a
variety of configurations, but in an exemplary embodiment they are
adapted to allow the flexible members 12, 14 to slide and/or rotate
freely, preferably without deforming, relative thereto when the
superior and inferior vertebrae 60, 62 are moved within a first
range of motion, and they are adapted to deform the flexible
members 12, 14 when the superior and inferior vertebrae 60, 62 are
moved within a second range of motion beyond the first range of
motion. While various techniques can be used to achieve such a
configuration, FIGS. 1A-1C illustrate one exemplary embodiment of
superior and inferior connectors 16, 18.
[0033] The superior connector 16, which is shown in more detail in
FIG. 2A, is preferably adapted to couple to opposed pedicles 60a,
60b (FIG. 1A) of the superior vertebra 60 and to extend between the
pedicles 60a, 60b and inferior to the spinous process 60s. The
configuration of the superior connector 16 can, however, change
where a laminectomy is performed and the spinous process 60s has
been removed. The connector 16 can, for example, be substantially
linear. In the embodiment shown in FIG. 2A, the superior connector
16 is in the form of a substantially v-shaped rod and it preferably
includes a central linear portion 16a with two lateral arms 16b,
16c extending at an angle .alpha. relative to the central portion
16a. The angle .alpha. can vary depending on the size of the
patient, and in particular depending on the distance between the
opposed pedicles 60a, 60b and the angle necessary to allow the
superior connector 16 to extend around the spinous process 60s. The
angle .alpha. is also determinative of the range of sliding motion
between the flexible members 12, 14 and the connectors 16, 18. In
particular, the range of motion of the flexible members 12, 14
along the connectors 16, 18 will increase as the angle increases.
This will be discussed in more detail below. While the angle
.alpha. can vary, in an exemplary embodiment, the angle .alpha. is
in the range of about 95.degree. to 180.degree..
[0034] The inferior connector 18, which is shown in more detail in
FIG. 2B, is similarly adapted to couple to the opposed pedicles
62a, 62b (FIG. 1A) of the inferior vertebra 62 and to extend
between the pedicles 62a, 62b ands superior to the spinous process
62s. The connector 18, however, preferably has a substantially
linear configuration. In an exemplary embodiment, as shown in FIG.
2B, the connector 18 is in the form of a rod having a v-shaped
portion 18a formed therein, preferably at a substantially central
portion thereof. The v-shaped portion 18a is configured to extend
around, and be positioned superior to the spinous process 62s of
the vertebra 60.
[0035] Each connector 16, 18 can also be formed from a variety of
materials, but preferably the connectors 16, 18 are substantially
rigid. In an exemplary embodiment, the connectors 16, 18 are formed
from a bioimplantable metal, such as titanium, stainless steel, and
cobalt and nickel based alloys, such as cobalt-chromium-molybdenum
(Co--Cr Mo).
[0036] In use, the implant 10 can be used to replace one or more of
the posterior elements of the spine, including, for example, the
facet joints, the lamina, the posterior ligaments, and/or other
features of a patient's spinal column. The implant 10 can also be
adapted to function with either a natural vertebral disc, or with
an artificial disc. Regardless, as noted above, the implant 10 is
preferably adapted to mimic the function of the posterior elements,
without necessarily mimicking the anatomy. The device 10 is
implanted by first positioning the superior and inferior connectors
16, 18 through the thru-bores 12s, 12i, 14s, 14i in the flexible
members 12, 14. If necessary, other procedures, such as a
facetectomy and/or laminectomy, can be performed. The terminal ends
16t.sub.1, 16t.sub.2, 18t.sub.1, 18t.sub.2 of the connectors 16, 18
are then attached to the superior and inferior vertebrae 60, 62. As
noted above, the superior connector 16 is preferably attached to
the opposed pedicles 60a, 60b on the superior vertebra 60, and the
inferior connector 18 is preferably attached to the opposed
pedicles 62a, 62b on the inferior vertebra 62.
[0037] The connectors 16, 18 can be attached to the vertebrae 60,
62 using a variety of anchoring devices and other techniques known
in the art. In an exemplary embodiment, as shown in FIGS. 1A-1C,
the connectors 16, 18 are attached to the vertebrae 60, 62 using
spinal anchors, and in particular spinal screws. While only a
portion of the spinal screws are shown, each screw includes a
rod-receiving head 70, 72, 74, 76 that is configured to seat a
terminal end 16t.sub.1, 16t.sub.2, 18t.sub.1, 18t.sub.2 of a
connector 16, 18. A fastening element, such as a set screw, can be
used to lock the connectors 16, 18 to the screws 70, 72, 74,
76.
[0038] While not shown, several additional connectors can be
attached to adjacent vertebrae and positioned to extend through
flexible members 16, 18, or through separate flexible members,
thereby forming a multi-level replacement. The number of
connectors, and optionally the number of flexible members, will
vary depending on the number of levels being repaired. In attaching
additional connectors, each pair of spinal anchors, e.g., spinal
screws 70, 72, 74, 76, can be configured to mate to two connectors.
Thus, for example, if a third vertebra, located inferior to the
second vertebra 62, were coupled to the first and second vertebra
60, 62, a superior connector would mate to spinal anchors 74, 76,
and an inferior connector would mate to spinal anchors disposed
within the pedicles of the third vertebra. This procedure could be
repeated for multiple vertebrae. While not shown, the procedure can
also include the step of placing a sheath or protective member
partially or fully around the implant 10 for preventing tissue from
growing on the implant 10 and into the thru-bores 12s, 12i, 14s,
14i, and for preventing debris from migrating into the spinal
canal.
[0039] Once the connectors 16, 18 are fixedly attached to the
vertebrae 60, 62, the implant 10 is effective to control movement
of the vertebrae relative to one another. More particularly, the
implant 10 is effective to mimic the natural function of the spine.
FIG. 3 is a chart illustrating the load-deformation curve of a
functional spine unit (FSU). As shown, the FSU is highly flexible
at low loads, and it stiffens as the load increases. Thus, the FSU
becomes much less flexible as the range of motion increases. To
analyze this nonlinear biphasic behavior, the load-displacement
curve is divided into two parts: (1) the neutral zone, in which the
FSU is highly flexible, and (2) the elastic zone, in which the FSU
is much less flexible, and has a high degree of stiffness. The two
zones together constitute the physiological range of motion of a
zone. The implant 10 is adapted to mimic this behavior. In
particular, during flexion of the vertebrae 60, 62 relative to one
another in the neutral zone, referred to herein as the first range
of motion, the flexible members 12, 14 are free to slide along
and/or rotate with respect to the connectors 16, 18. Thus, as the
vertebrae flex away from one another, while in the neutral zone,
the connectors 16, 18 are moved apart from one another thereby
causing the flexible members 12, 14 to move toward one another.
Similarly, during extension, the flexible members 12, 14 are free
to slide and/or rotate, however they will move apart from one
another. Such movement is at least in part due to the shape of the
connectors 16, 1, and in particular the v-shape of the superior
connector 16. When the vertebrae 60, 62 are further flexed relative
to one another in the elastic zone, referred to herein as the
second range of motion (which is necessarily beyond than the first
range of motion), the flexible members 12, 14 are forced to deform,
which can include stretching, rotating, etc. This is a result of
the shape of the connectors 16, 18, which prevent the flexible
members 12, 14 from moving further toward one another. As a result,
in the first range of motion, the implant 10 mimics the natural
spine by allowing a greater degree of flexibility, as the
connectors 16, 18 allow the flexible members 12, 14 to slide
therealong and/or rotate relative thereto with minimal resistance,
and in the second range of motion, the implant 10 mimics the
natural spine by controlling flexibility, as the connectors 16, 18
cause the flexible members 12, 14 to deform, thereby resisting
flexion. As discussed above, the properties of the flexible members
12, 14 will necessarily affect the resistance to flexion, and the
flexible members 12, 14 can be especially adapted to have a first
flexibility in the first range of motion and a second flexibility
in the second range of motion. Since each patient's specific needs
will vary, the implant 10 can be provided as part of a kit having
several flexible members 12, 14 varying in shape, size, and
stiffness. The flexible members 12, 14 can also be particularly
tailored to different levels of a patient's spine.
[0040] The implant can also optionally include physical stops to
control when the flexible members stop sliding and/or rotating and
are forced to deform. In particular, the physical stops can be
formed on or attached to the connectors 16, 18 at a location that
will prevent the flexible members 12, 14 from sliding and/or
rotating at a particular point during flexion of the vertebrae. By
way of non-limiting example, FIG. 2D illustrates outer stops 12x',
14x' disposed on the superior connector 16' on opposed sides of the
flexible members 12', 14'. A central stop 16x' is also formed on
the connector 16' between the flexible members 12', 14'. The outer
stops 12x', 14x' are in the form of band clamps which can be
adjustably positioned at various locations along the connector 16'.
The central stop 16x' is in the formed of a stepped member, and it
can also optionally be adjustable. For example, the central stop
16x' can be in the form of a housing and the opposed sides of the
connector 16' can thread into the housing. A person skilled in the
art will appreciate that the stops can have any configuration and
that a variety of other techniques can be used to control movement
between the vertebrae in such a manner that mimics the natural
function of the spine.
[0041] One skilled in the art will appreciate further features and
advantages of the invention based on the above-described
embodiments. Accordingly, the invention is not to be limited by
what has been particularly shown and described, except as indicated
by the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
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