U.S. patent application number 11/403488 was filed with the patent office on 2006-09-07 for method and device for treating ailments of the spine.
This patent application is currently assigned to St. Francis Medical Technologies, Inc.. Invention is credited to Daniel P. Borschneck, Gerald A. B. Saunders, Donald A. Soboleski.
Application Number | 20060200137 11/403488 |
Document ID | / |
Family ID | 23024810 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060200137 |
Kind Code |
A1 |
Soboleski; Donald A. ; et
al. |
September 7, 2006 |
Method and device for treating ailments of the spine
Abstract
This invention relates to a spinal facet cap for treating
scoliosis, the facet cap comprising a shim portion for inserting
into a facet joint of a spine, and an alignment portion for
maintaining alignment of the shim portion within the facet joint.
The invention also provides a method for treating scoliosis,
comprising implanting at least one spinal facet cap into at least
one facet joint of a subject in need thereof.
Inventors: |
Soboleski; Donald A.;
(Sydenham, CA) ; Saunders; Gerald A. B.;
(Sydenham, CA) ; Borschneck; Daniel P.;
(Glenburnie, CA) |
Correspondence
Address: |
FLIESLER MEYER, LLP
FOUR EMBARCADERO CENTER
SUITE 400
SAN FRANCISCO
CA
94111
US
|
Assignee: |
St. Francis Medical Technologies,
Inc.
Alameda
CA
|
Family ID: |
23024810 |
Appl. No.: |
11/403488 |
Filed: |
April 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10075373 |
Feb 15, 2002 |
|
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11403488 |
Apr 13, 2006 |
|
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60268860 |
Feb 16, 2001 |
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Current U.S.
Class: |
606/247 ;
606/276; 606/330 |
Current CPC
Class: |
A61F 2250/0007 20130101;
A61F 2002/3055 20130101; A61F 2/4405 20130101; A61F 2220/0025
20130101; A61B 17/7064 20130101; A61F 2002/30522 20130101 |
Class at
Publication: |
606/061 |
International
Class: |
A61F 2/30 20060101
A61F002/30 |
Claims
1. A spinal facet cap adapted to treat spinal ailments comprising:
a shim portion adapted to be inserted into a facet joint of a
spine; an alignment portion extending from the shim portion; said
alignment portion including a tongue with an orifice; and wherein
said orifice is positionable relative to the shim portion.
2. The spinal facet cap of claim 1 wherein said shim portion has a
shape that is at least partially complementary to at least a facet
joint contour.
3. The spinal facet cap of claim 1 including at least one pin
extending from the shim portion.
4. The spinal facet cap of claim 1 wherein said shim portion has a
shape that is at least partially complementary to at least a facet
joint contour, and said shim portion includes a pin extending from
said facet contact surface.
5. The spinal facet cap of claim 1 including at least two pins
extending from the shim portion.
6. The spinal facet cap of claim 1 including at least one hook
extending from the shim portion.
7. The spinal facet cap of claim 1 wherein said shim portion has a
shape that is at least partially complementary to at least a facet
joint contour, and said shim portion includes at least one hook
extending from a peripheral edge of the facet contact surface.
8. The spinal facet cap of claim 1 including a first hook extending
from a first surface of said shim portion and a second hood
extending from a second surface of said shim portion.
9. The spinal facet cap of claim 1 wherein said shim portion is at
least one of concave and convex.
10. The spinal facet cap of claim 1 wherein said shim portion
includes at least one boss extending therefrom.
11. The spinal facet cap of claim 1 wherein said shim portion
includes at least one ridge extending therefrom.
12. The spinal facet cap of claim 1 wherein said shim portion
includes a facet contact surface that is substantially a shape
complementary to an articulating surface of the facet joint, and
said shim portion includes at least one ridge extending from a
peripheral edge of the facet contact surface.
13. The spinal facet cap of claim 1 wherein said tongue is
positionable relative to the shim portion.
14. The spinal facet cap of claim 1 wherein said shim portion
includes a facet contact surface that is substantially a shape
complementary to an articulating surface of the facet joint, and
said facet contact surface includes a peripheral edge, and said
alignment portion extends from said peripheral edge and said
alignment portion is positionable relative to said peripheral
edge.
15. The spinal facet cap of claim 1 wherein said shim portion
includes a facet contact surface that is substantially a shape
complementary to an articulating surface of the facet joint, and
said orifice is positionable relative to said facet contact
surface.
16. The spinal facet cap of claim 1 wherein said alignment portion
and at least a part of said shim portion include separate elements
and said alignment portion is mounted on said at least a part of
said shim portion and said alignment portion is movable relative to
said at least a part of said shim portion.
17. The spinal facet cap of claim 1 wherein at least a part of said
shim portion is a separate element from said alignment portion with
said alignment portion mounted on said shim portion.
18. A spinal facet cap adapted to treat spinal ailments comprising:
a shim portion adapted to be inserted into a facet joint of a
spine; said shim portion being substantially a shape complementary
to an articulating surface of the facet joint; an alignment portion
which is a separate element from at least a part of said shim
portion and said alignment portion mounted on at least said part of
said shim portion; and said alignment portion being movable
relative to said at least said part of said shim portion.
19. The spinal facet cap of claim 18 wherein said alignment portion
is the only element extending from said shim portion
20. The spinal facet cap of claim 18 including at least one pin
extending from the shim portion.
21. The spinal facet cap of claim 18 wherein said shim portion
includes a pin extending from a facet contact surface of the shim
portion.
22. The spinal facet cap of claim 18 including at least two pins
extending from the shim portion.
23. The spinal facet cap of claim 18 including at least one hook
extending from the shim portion.
24. The spinal facet cap of claim 18 wherein said shim portion
includes at least one hook extending from a peripheral edge of a
facet contact surface of the shim portion.
25. The spinal facet cap of claim 18 wherein said shim portion is
at least one of concave and convex.
26. The spinal facet cap of claim 18 wherein said shim portion
includes at least one boss extending therefrom.
27. The spinal facet cap of claim 18 wherein said shim portion
includes at least one ridge extending therefrom.
28. The spinal facet cap of claim 18 wherein said shim portion
includes at least one ridge extending from a peripheral edge of a
facet contact surface of the shim portion.
29. The spinal facet cap of claim 18 wherein said alignment portion
includes a tongue and said tongue is positionable relative to the
shim portion.
30. The spinal facet cap of claim 18 wherein said shim portion
includes a peripheral edge and said alignment portion extends from
said peripheral edge and said alignment portion is positionable
relative to said peripheral edge.
31. The spinal facet cap of claim 18 wherein said alignment portion
includes an orifice and said orifice is positionable relative to
said shim portion.
32. The spinal facet cap of claim 1 wherein said alignment portion
is the only element extending from said shim portion
33. The spinal facet cap of claim 18 wherein said alignment portion
includes an orifice, said orifice being movable relative to said at
least said part of said shim portion.
34. The spinal facet cap of claim 1 wherein a shape of the shim
portion is adjustable.
35. The spinal facet cap of claim 1 wherein an angle of the shim
portion relative to the remainder of the spinal facet cap can be
adjusted.
36. The spinal facet cap of claim 18 wherein a shape of the shim
portion is adjustable.
37. The spinal facet cap of claim 18 wherein an angle of the shim
portion relative to the remainder of the spinal facet cap can be
adjusted.
38. A spinal facet cap adapted to treat ailments of the spine
comprising: a shim portion adapted to be inserted into a facet
joint of a spine; said shim portion at least partially
complementary to an articulating surface of the facet joint; a pin
extending from the shim portion; an alignment portion extending
from said shim portion; and said alignment portion being movable
relative to said at least said part of said shim portion.
39. The spinal facet cap of claim 38 wherein said alignment portion
is a separate element from at least a part of said shim portion and
said alignment portion is mounted on at least said part of said
shim portion.
40. A spinal facet cap adapted to treat ailments of the spine
comprising: a shim portion adapted to be inserted into a facet
joint of a spine; said shim portion being at least partially
complementary to an articulating surface of the facet joint; a pin
extending from the shim portion; and an alignment portion extending
from said shim portion.
41. The spinal facet cap of claim 40 wherein said alignment portion
is movable relative to said at least said part of said shim
portion.
42. A spinal facet cap adapted to treat ailments of the spine
comprising: a shim portion adapted to be inserted into a facet
joint of a spine; said shim portion being at least partially
complementary to an articulating surface of the facet joint; a pin
extending from the shim portion; an alignment portion extending
from said shim portion; said alignment portion including a tongue
with an orifice; and said orifice being movable relative to said at
least said part of said shim portion.
43. The spinal facet cap of claim 40 wherein said tongue is movable
relative to said at least said part of said shim portion.
44. A spinal facet cap adapted to treat ailments of the spine
comprising: a shim portion adapted to be inserted into a facet
joint of a spine; said shim portion including a first surface
adapted to be positioned in contact with a first facet of a facet
joint and a second surface adapted to be positioned in contact with
a second facet of facet joint; at least one pin extending from said
first surface with at least one pin extending from said second
surface; and an alignment portion extending from said shim
portion.
45. The spinal facet cap of claim 44 wherein said alignment portion
is positionable relative to said shim portion.
46. The spinal facet cap of claim 44 wherein said alignment portion
is a separate element and mounted to at least a part of said shim
portion.
Description
CLAIM TO PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/075,373, filed on Feb. 15, 2002 which
claims the benefit of U.S. Provisional Patent Application No.
60/268,860, filed on Feb. 16, 2001, the disclosures of which are
incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] Scoliosis is an orthopedic condition characterized by
abnormal curvature of the spine, with varying degrees of lateral
curvature, lordosis and rotation. Despite extensive research, the
pathogenesis of scoliosis remains obscure in the majority of
cases.
[0003] The vertebral column is composed of vertebra, discs,
ligaments and muscles. Its function is to provide both mobility and
stability of the torso. Mobility includes rotation, lateral
bending, extension and flexion. Scoliotic curvature is associated
with pathologic changes in the vertebra and related structures.
Vertebral bodies become wedge-shaped, pedicles and laminas become
shorter and thinner on the concave aspect of the curve. Apart from
the obvious physical deformity, cardiopulmonary problems may also
present. As curvature increases, rotation also progresses causing
narrowing of the chest cavity. In severe deformities, premature
death is usually caused by respiratory disease and superimposed
pneumonia.
[0004] Treatment options have varied little over the past few
decades, and only two treatments effectively help correct
scoliosis: spinal bracing with exercises and surgery. A properly
constructed Milwaukee or low-profile brace will aid some patients
with minor scoliosis. However, if the scoliosis progresses despite
such bracing, or if there is substantial discomfort, surgical
correction involving fusion of vertebra may be required. Surgery
has traditionally involved procedures such as the Harrington, Dwyer
and Zielke, and Luque procedures which rely on implanted rods,
laminar/pedicle hooks, and screws to maintain the correction until
stabilized by fusion of vertebrae.
[0005] Thus the goal of current surgery is to strip the paraspinal
muscles from the lamina of vertebra to be fused, and effect
correction and spinal fusion in one step. The general technique is
as follows: [0006] 1. The outer cortex of the lamina and spinous
processes is removed so that raw cancellous bone is exposed. [0007]
2. Posterior facet joints are destroyed and usually autogenous bone
graft added. Graft is usually placed along the entire fusion area.
The fusion extends from one vertebra above the superior
end-vertebra involved in the curvature to two below the inferior
end-vertebra of the curve. [0008] 3. Spinal instrumentation is
applied. A distraction rod allows the spine to be jacked' up on the
concave side of the curve. A compression assembly may be used on
the convex side of the curve to `pull` the curve straight.
--Anchors, laminar hooks, and/or wires are placed around the lamina
to provide fixation for the rods.
[0009] Yet other surgical procedures involve memory metal implants
(Sanders, A Memory Metal Based Scoliosis Correction System,
CIP-Data Koninklijke Bibliotheek, Den Haag, 1993), fusion of
vertebra anteriorly, using anterior cages (e.g., Harms cage, from
DePuy-AcroMed Inc.). Nevertheless, it is clear that available
procedures have drawbacks including the requirement for substantial
prosthetic implants (see Mohaideen et al., Pediatr.
Radios.sub.--30:110-118 (2000) for a review) and complicated
surgical procedures, often only partly correct scoliotic
deformities, and result in reduced flexibility of the spine.
SUMMARY OF THE INVENTION
[0010] According to one aspect of the present invention there is
provided a spinal facet cap for treating ailments of the spine
including scoliosis, comprising a shim portion for inserting into a
facet joint of a spine, and an alignment portion for maintaining
alignment of said shim portion within said facet joint. The shim
portion of the spinal facet cap comprises two opposed surfaces for
engaging articular surfaces of the facet joint. In one embodiment,
the shim portion is of substantially uniform thickness. In another
embodiment, the shim portion is wedge-shaped.
[0011] In one embodiment of the spinal facet cap, the alignment
portion comprises a tongue. In some embodiments, the tongue is
provided with an orifice.
[0012] In another embodiment, the alignment portion comprises a
boss along at least one edge of the shim portion.
[0013] In yet another embodiment, the alignment portion comprises
at least one facet hook disposed along at least one edge of the
shim portion, for receiving either one of the superior facet or the
inferior facet of a vertebra. In a further embodiment, the
alignment portion comprises two facet hooks disposed along two
edges of the shim portion, one said facet hook for receiving the
superior facet of a first vertebra, a second said facet hook for
receiving the inferior facet of a second vertebra. In further
embodiments in which facet hooks are provided, the alignment
portion further comprises a tongue having an orifice. In yet
further embodiments, the thickness of the wedge-shaped shim
portion, and/or the distance between alignment portions disposed on
either side of the shim portion, is adjustable.
[0014] According to another aspect of the present invention there
is provided a method for treating scoliosis in a subject in need
thereof comprising implanting in a facet joint of the subject a
spinal facet cap, said spinal facet cap comprising a shim portion
and an alignment portion for maintaining alignment of said facet
cap within said facet joint, such that scoliosis in the subject is
treated. In some embodiments, a spinal facet cap is implanted in
each of two or more facet joints of the subject, such that
scoliosis in the subject is treated.
[0015] In some embodiments of the method of the invention, the
alignment portion comprises at least one facet hook disposed along
at least one edge of the shim portion, for receiving either one of
the superior facet or the inferior facet of a vertebra.
[0016] In other embodiments, the method further comprises
evaluating the subject for the number, size, shape, location, and
placement of spinal facet caps required to treat scoliosis in the
subject. In yet other embodiments, an imaging system is used to so
evaluate the subject. In some embodiments, the imaging system is a
computed tomography (CT) system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The file of this patent contains at least one drawing
executed in colour. Copies of this patent with colour drawing(s)
will be provided by the Patent and Trademark Office upon request
and payment of the necessary fee.
[0018] The invention will be described, by way of example, with
reference to the accompanying drawings, wherein:
[0019] FIG. 1 shows a posterior view of a typical scoliotic
spine;
[0020] FIG. 2 shows a posterior view of a scoliotic spine corrected
with spinal facet caps according to the invention;
[0021] FIGS. 3A to 3F show further embodiments of a spinal facet
cap according to the invention;
[0022] FIGS. 4A to 4C show a further embodiment of a spinal facet
cap according to the invention;
[0023] FIG. 5 shows a further embodiment of a spinal facet cap
according to the invention;
[0024] FIG. 6A shows a posterior view of a scoliotic spine;
[0025] FIG. 6B shows a posterior view of the scoliotic spine of
FIG. 5A corrected with spinal facet caps according to the
invention; and
[0026] FIG. 7A shows a side view of a scoliotic spine; and
[0027] FIG. 7B shows a side view of the scoliotic spine of FIG. 7A
corrected with 30 spinal facet caps according to the invention;
[0028] FIG. 8A is a radiograph of a prosthetic model of a spine
with scoliosis at the mid-lumbar level;
[0029] FIG. 8B is a radiograph of the model of FIG. 8A, with the
scoliosis corrected using spinal facet caps of the invention;
[0030] FIGS. 9A and 9B show embodiments of a facet caps according
to the invention; and
[0031] FIGS. 10A and 10B are photographs showing the facet caps of
FIGS. 9A and 9B, respectively, inserted into facet joints of a
patient,
DETAILED DESCRIPTION OF THE INVENTION
[0032] Surgical procedures for correction of scoliosis has changed
little in the last forty years. Current procedures still rely on
surgical principals established in the 1960's, and involve fusion
of one or more vertebrae.
[0033] Selection for the level of fusion requires analysis about a
plum line from the sacral spinous process superior. Vertebrae that
pass outside this line identify the curve. The most superior of the
inferior vertebrae, which bisect this line, is the inferior extent
for fusion and the most inferior of the superior vertebrae that
bisect this line is the superior extent of fusion. All levels
in-between these two identified levels require fusion.
[0034] After the curve is identified, all posterior ligaments and
facet joints are destroyed by decortication and cartilage is
removed at each level of fusion. Instrumentation for correction of
the scoliosis is placed in such a manner to apply a distractive
force on the concavity of the curve and compression on the
convexity of the curve. All current systems rely on some vertebral
fixation to a rod. Compressive and distractive forces are then
applied along the rod at the points of vertebrae to rod fixation.
Three forms of fixation of the posterior spine are currently
available: pediclellaminar hooks, wires and screws. Laminar hooks
are placed around vertebrae lamina. Distractive hooks are placed
pointing away from the apex of the curve and compressive hooks
placed facing towards the apex of the curve. Pedicle screws are
placed posterior to anterior in the vertebrae and can either have a
distractive or compressive force applied through the rod. Laminar
wires wrap around the lamina and connect to a rod at each level.
The corrective force is applied as the wire tightens around a rigid
rod. The lamina and thus the vertebrae are dragged to the rod.
[0035] The spinal facet cap of the invention differs from the
above-described standard instrumentation in a number of ways. For
example, as discussed above, during standard procedures for
correcting scoliosis, facet joints are generally destroyed. In
contrast, the spinal facet caps of the invention require that the
facet joints are substantially or entirely intact. This procedure
is thus expected to preserve mobility of the facet joint. Further,
rather than applying a distractive or compressive force through a
rod, the facet cap effectively reshapes the facet joint. Such
reshaping affords symmetry between left and right facet joints
which corrects abnormal curvature. Thus, no fixation of the
vertebrae is required; rather, there is modulation of the vertebral
(facet) shape, This reshaping is expected to allow for the omission
of fusing the intervening vertebral levels and multiple levels of
vertebrae, which is the result of rod fixation, thus preserving
flexibility of the spine. Also, the use of conventional
instrumentation with a rod concentrates the load (i.e., weight of
the torso) on the portion of the spine to which the rod is
attached, as well as on the rod itself. The resulting stress
sometimes results in failure of the conventional instrumentation.
In contrast, in providing for the correction of individual facet
joints of the spine, the facet cap of the invention maintains the
natural load distribution along the spine. Accordingly, there is no
load concentration at any point of the spine, and low likelihood of
failure of the implanted facet cap.
[0036] As used herein, the term "scoliosis" is intended to mean any
abnormal curvature of the spine. Such abnormal curvature can exist
in any one of all three planes, or in any combination thereof, and
hence can be manifested by inappropriate lateral curvature,
lordosis, kyphosis, and/or rotation. Scoliosis can be congenital or
idiopathic, or induced by injury, trauma, infection, inflammation,
or degenerative changes in the spine.
[0037] As used herein, the term "treating scoliosis" is intended to
mean correcting or reducing curvature of the spine of a subject,
such that the subject experiences an improvement in condition,
comfort (e.g., reduction or amelioration of pain), appearance,
posture, and/or flexibility of the spine. The term "treating
scoliosis" is also intended to mean preventing scoliosis from
progressing to a more severe state, or inhibiting the degree to
which scoliosis progresses.
[0038] As used herein, the term "subject" is intended to mean any
vertebrate that can have scoliosis. Typically, such subjects are
primates. Preferably, the subject is human.
[0039] According to one theory, many forms of scoliosis result from
asymmetry between left and right facet joints of vertebrae.
According to another theory, many forms of scoliosis cause
asymmetry between left and right facet joints of vertebrae. While
not holding to one particular theory at the exclusion of others,
the present invention provides for the treatment of scoliosis by
substantially or completely correcting such asymmetry.
[0040] In one aspect, the invention provides a prosthetic device
for treating scoliosis by substantially or completely correcting
asymmetry between left and right facet joints of vertebrae. The
prosthetic device, generally referred to as a spinal facet cap, is
surgically implanted into a spinal facet joint at any level in the
spine. Surgically implanting one or more spinal facet cap(s) is
carried out with minimal or no modification of the facet joint(s)
involved; thus, the invention provides for the correction of
left-right asymmetry of facet joints while preserving the facet
joints. In this respect the invention is unlike any known
procedures for treating scoliosis.
[0041] FIG. 1 shows a posterior view of a typical scolictic spine,
with asymmetry between left and right facet joints, and spinal
curvature convex left. FIG. 2 shows the spine of FIG. 1 in which
the asymmetry between left and right facet joints has been
corrected with two spinal facet caps according to an embodiment of
the present invention. As can be seen in FIG. 2, a spinal facet cap
10 according to the invention comprises a shim portion 12 which is
implanted between the superior facet 22 of a first (lower) vertebra
20 and the corresponding inferior facet 32 of a second overlying
vertebra 30. The shim portion has two opposed surfaces, a first
(lower) surface 14 engaging the superior articular surface of the
superior facet 22, and a second (upper) surface 16 engaging the
inferior articular surface of the corresponding inferior facet 32.
The opposed surfaces of the shim portion of the spinal facet cap
can be substantially-planar, as shown in FIG. 2, or they can be
formed (e.g., concave or convex) to receive and at least partially
complement or parallel superior and inferior facet contours.
[0042] From FIG. 2 it will be appreciated that the shim portion of
the spinal facet cap must be properly aligned or positioned in the
facet joint, and that this alignment must be maintained. An
alignment portion is provided for this purpose. The alignment
portion can be provided numerous ways in accordance with the
invention. For example, the alignment portion can comprise an
extension or tongue 18, having an orifice 19, to accept a screw or
the like which is driven into the cortex of the vertebral pedicle.
The alignment portion can also comprise one or more facet hooks
and/or a ridge or boss disposed along the perimeter or margin of
the shim portion, to engage the superior and/or inferior facets.
The alignment portion at least partially encompasses the superior
and/or inferior facet(s).
[0043] In some embodiments, the opposed surfaces are parallel
(i.e., coplanar), such that the shim portion is of substantially
uniform thickness. In other embodiments, the opposed surfaces are
not coplanar, such that the shim portion is not of uniform
thickness and is generally wedge-shaped. In embodiments where the
opposed surfaces are not coplanar, the surfaces can be sloped along
a common axis so as to form a simple angle. The angle separating
the opposed surfaces can be, for example, from 0.degree. (coplanar)
to about 40.degree., preferably about 0.degree. to about
20.degree.. In other embodiments, the slopes of the opposed
surfaces form a compound angle in which the slopes are not aligned
on a common axis. It will be appreciated that the direction of
slope is appropriately chosen to correct a facet joint for a given
abnormality of curvature (e.g., kyphosis, lordosis, etc.).
[0044] It will be appreciated that a spinal facet cap according to
the invention can be produced in a range of sizes and shapes by
varying the thickness of the shim portion (i.e., distance between
the opposed surfaces), the angle of the shim portion (i,e., angle
between the opposed surfaces), the area of the shim portion (Le.,
surface area of the opposed surfaces), and the shape of the shim
portion and/or opposed surfaces so as to provide any desired amount
of correction to a facet joint, and to accommodate any size of
facet joint. Further, a facet cap according to the invention can be
symmetrical or asymmetrical with respect to the angle, area, and
shape of opposed surfaces.
[0045] Each opposed face of the shim portion is sized to
accommodate the generally circular or oblong (i.e., oval) shape of
the articulating surface of a facet joint into which the facet cap
is inserted. The size or area of the opposed faces of a facet cap
will depend on factors such as where in the spine the facet cap Is
implanted (e.g., cervical being smaller than lumbar), the age and
size of the subject, and the condition of the facet joint. The size
of the opposed faces Is generally described herein as circular,
having a diameter; however, it is to be understood that the opposed
faces can be of any shape and the diameter refers to that portion
of an opposed surface that substantially corresponds to an
articular surface of a facet joint, The diameter of each opposed
face of the shim portion ranges from about 5 mm to about 30 mm,
preferably from about 10 mm to about 20 mm, still more preferably
from about 12 mm to about 18 mm.
[0046] It will be appreciated that patients receiving facet caps
can vary in age/size, and in degree of severity of scoliosis. Thus,
the present invention contemplates a range of sizes and shapes of
facet caps, to suit any facet joint in need of treatment, so as to
correct any or all of a reduction in height, an abnormality in
tilt, and an abnormality in angulation (e.g., kyphosis, lordosis)
of the inferior or superior vertebral body. The facet caps can be
provided ready for implanting (e.g., sterilized and appropriately
packaged), or they can be sterilized prior to implanting using
methods well-known in the art.
[0047] A spinal facet cap according to the invention can be made of
any suitable biologically inert material. Examples of suitable
materials are cobalt chrome, stainless steel, and titanium. Cobalt
chrome is preferred owing to its biocompatibility with tissues and
cartilage.
[0048] Several embodiments of the spinal facet cap of the present
invention are shown in FIG. 3. For example, FIG. 3A shows a spinal
facet cap like that shown in FIG. 2. In FIG. 3B, the shim portion
50 has an alignment portion comprising a ridge 54 disposed along
the edge of and partially surrounding the surface 56 that engages
the inferior facet, toward the tongue 52. As shown in FIGS. 3C and
3D, in which FIG. 3D shows a longitudinal section of the embodiment
of FIG. 3C, the shim portion 60 similarly has an alignment portion
comprising a ridge 68 on the edge of the surface 67 that engages
the superior facet, opposite the tongue 62. The embodiment of FIGS.
3C and 3D also has a further ridge 64 on the edge of the surface 66
that engages the inferior facet, toward the tongue 62. It will be
appreciated that the provision of an alignment portion comprising
ridges on the first, second, or both surfaces of the facet cap
helps to maintain alignment of the facet cap with the superior and
inferior facets, and helps to keep the facet cap registered in the
facet joint.
[0049] The alignment portion of a spinal facet cap according to the
invention can also comprise one or more pins extending outwardly
from at least one of the two opposed surfaces. For example, the
spinal facet cap 70 shown in FIG. 3E has pins 72, 74 extending
outwardly from the opposed surfaces 73, 75, respectively. The pins
72, 74 engage holes prepared in the articular surfaces of the
superior and inferior facets during the implant procedure.
[0050] In FIG. 3F there is shown another embodiment of a spinal
facet cap according to the invention in which the shim portion 80
has an alignment portion comprising a facet hook 88 on the edge of
the surface 87 that engages the superior facet, substantially
opposite the tongue 82, and another facet hook 84 on the edge of
the surface 86 that engages the inferior facet, toward the tongue
82. In further embodiments, only one of either facet hook 84 or
facet hook 88 is present. The facet hook can vary in the extent of
the curvature of the hook and thus the extent to which the hook
encompasses the inferior/superior facet. For example, in some
embodiments the curvature of the facet hook can be reduced so that
the hook extends from the shim portion in a 90.degree. arc, whereas
in other embodiments the hook extends from the shim portion in a
180.degree. arc.
[0051] Although not shown in the drawings, it will be appreciated
that embodiments of the invention such as those shown in FIGS. 3A
to 3D and 3F can be provided with an orifice passing through the
shim portion, for accepting a pin, screw, or the like driven
through at least one of the inferior and superior facets, to
thereby contribute to maintaining alignment of the spinal facet
cap. In particular, in the embodiment of FIG. 3F, each of the facet
hook 84, shim portion 80, and facet hook 88 can be provided with an
orifice, the three orifices having a common longitudinal axis, so
as to accommodate a pin or screw disposed through the facet hook
84, the inferior facet, the shim portion 80, the superior facet,
and the facet hook 88. Also not shown in the figures are
embodiments in which the shim portion is sloped in the opposite
direction to that shown (i.e., a directive relative to the tongue
18 in FIG. 3A).
[0052] In the embodiment shown in FIGS. 4A to 4C, which is similar
to that of FIG. 317, the spinal facet cap 90 has a shim portion 92
with opposed surfaces 94, 96 provided with an alignment portion
comprising facet hooks 95, 97, respectively, and a tongue 98.
Tongue 98 extends outwardly from the shim portion 92, and has an
orifice 99 for accepting a screw. Facet hook 95 engages the
inferior facet, and facet hook 97 engages the superior facet. This
can be seen in FIG. 6, which shows a scoliotic spine (FIG. 6A) in
which the decrease in height and lateral tilt of the spine have
been corrected with spinal facet caps according to the present
embodiment (FIG. 66). A handle 100 is optionally provided to
facilitate implanting the facet cap. The handle 100 is attached to
the facet cap in a manner to allow it to be removed upon implanting
the cap. For example, the handle 100 can be crimped at the junction
with the facet cap, so that it can simply be broken off once the
facet cap is implanted.
[0053] It will be appreciated that the embodiment shown in FIG. 4
can be provided with only a single facet hook, in which case it is
preferable that the facet hook 95 that engages the inferior facet
is provided. However, the provision of two facet hooks 95 and 97
improves the stability of the implant. Also, the facet hooks can be
wider or narrower than those shown in FIG. 4. A wider facet hook
has the advantage of contacting more of the facet, and hence is
preferable. When a very wide facet hook is provided, it can be
curved so as to approximate the shape of the portion of the facet
that it contacts, and hence contact a greater portion of the facet.
As an alternative to a wide facet hook, a facet hook can comprise
two or more fingers, the fingers providing multiple points of
contact with a facet. An advantage of such fingers is that growth
of tissue around and between the fingers is possible, and such
growth improves the stability and reliability of the implant.
[0054] In a further embodiment, the distance between facet hooks,
and/or the angle of the shim portion (i.e., the extent to which the
shim portion is wedge-shaped) can be adjusted. An example of this
embodiment is shown in FIG. 5. FIG. 5A shows this embodiment,
denoted by reference numeral 120, in side and plan views, which
comprises two parts 130 and 150. FIG. 5B shows part 130 in side and
plan views, and FIG. 5C shows part 150 in side and plan views, Part
130 comprises a plate 134, an inferior facet hook 132 disposed on a
first surface of the plate 134, and a tongue 140 and two rows of
teeth 138 disposed on the opposite surface of the plate 134. An
orifice 136 accommodates a cortical screw (not shown). Part 150
comprises a plate 154, a superior facet hook 152 disposed on a
first surface of the plate 154, and two rows of teeth 158 disposed
on the opposite surface of the plate 154. A longitudinal opening
156 is provided in the plate 154, for accepting the tongue 140 of
part 130 in a sliding fit. As can be seen from FIG. 5A, part 130
mates with part 150 such that tongue 140 fits in opening 156 and
teeth 138 mesh with teeth 158, and the inferior and superior facet
hooks 132 and 152 are opposed. When mated, plates 134 and 154
comprise the shim portion. Preferably, the teeth comprising each
set of teeth 138 and 158 are asymmetrical, such that meshing of the
two sets of teeth forms a cachet that allows parts 130 and 150 to
slide relative to each other in one direction, but not the other.
Preferably, such rachet allows parts 130 and 150 to slide in a
direction which brings the inferior and superior facet hooks closer
together, and prevents the facet hooks from sliding farther apart.
Thus, to use this embodiment to correct a facet joint, parts 130
and 150 are first mated such that the facet hooks are farthest
apart, and the so-assembled facet cap is inserted into a facet
joint of a patient. The distance between the facet hooks is then
reduced by sliding parts 130 and 150 together, to fit the facet
joint being corrected and to provide the desired amount of
correction. In variations of this embodiment, either or both of
plates 134 and 154 can be wedge-shaped, so that as parts 130 and
150 slide relative to each other, the amount of shim provided to a
facet joint can be adjusted. Further, such wedge-shape of part 130
and/or part 150 can be tapered in any direction relative to the
facet hook, so as to provide correction for any type of facet joint
asymmetry (e.g., lordosis, kyphosis, etc.). It will be appreciated
that the facet hooks in this embodiment could be substituted for
ridges, bosses, etc, as discussed in respect of the alignment
portion of the above embodiments.
[0055] FIG. 7A shows a side view of a scoliotic spine with
pronounced lordosis. In FIG. 76, the scoliosis shown in FIG. 7A has
been corrected by inserting spinal facet caps 90 between facet
joints. Here, spinal facet caps according to the embodiment shown
in FIG. 3F or FIG. 4 are employed.
[0056] In another aspect, the invention provides a method for
treating scoliosis by surgically implanting at least one spinal
facet cap into at least one spinal facet joint, such that asymmetry
between left and right facet joints of vertebrae is substantially
or completely corrected.
[0057] Treating a subject exhibiting mild scoliosis might involve
implanting only a single facet cap. Treating more severe scoliosis
might involve implanting two or more spinal facet caps at various
locations in the spine to achieve the desired correction. In such
severe cases, spinal facet caps of various sizes and shapes are
expected to be employed. As mentioned above, the invention provides
for treating scoliosis while preserving facet joints. However, in
some cases, some minor modification (e.g., providing a hole for a
pin) or more extensive modification (e.g., removal of bone) of
either or both of the inferior and superior facets might be
necessary or desirable to ensure proper seating and alignment of a
spinal facet cap, and hence improve the subject's prognosis.
Treating a subject with scoliosis involves evaluating the subject
prior to surgery and during surgery for the number, size, shape,
location, and placement of spinal facet caps to achieve the desired
correction. An imaging system (e.g., computed tomography (CT),
radiography, or magnetic resonance imaging (MRI)) can
advantageously be used to evaluate the subject prior to surgery, to
help determine the number, size, shape, location, and placement of
spinal facet caps to achieve the desired correction. Further, data
obtained from such evaluation of a subject prior to surgery can be
used to prepare a custom suite of facet caps of, for example,
various sizes and shapes, to suit a particular subject.
WORKING EXAMPLES
Example 1
Cadaveric Implantation
[0058] A spinal facet cap based on the embodiment shown in FIGS. 2
and 3A, having a diameter of about 12 mm, was surgically implanted
into the scoliotic spine of a cadaver (female, elderly) at the
Department of Anatomy and Cell Biology at Queen's University,
Kingston, Ontario, Canada, to evaluate the ease or difficulty of
placement and the seating of the facet cap in the facet joint.
There were no complications in implanting the facet cap into the
spine, suggesting that use of the facet cap for treating scoliosis
could become a routine surgical procedure. Moreover, during this
exercise it was found that seating of the facet cap in the facet
joint was fully satisfactory. This exercise therefore provides a
strong indication that the spinal facet cap of the invention will
be effective in the treatment of scoliosis.
Example 2
Prosthetic Model
[0059] Osteotomies were performed on the mid-lumbar facets of a
prosthetic model of an adult human spine to create a scoliotic
model. This is shown in the radiograph of FIG. 8A, where reference
numeral 200 refers to pins used to hold the model together. Spinal
facet caps like that shown in FIG. 3F were then inserted into the
mid-lumbar facet joints, which substantially corrected the
scoliotic curvature of the spine. This can be seen in the
radiograph of Figure BB, where reference numeral 210 refers to the
facet caps.
Example 3
Formulation of in vivo Placement
[0060] The success of cadaveric implantation led to the formulation
of tempo in vivo application. During the course of standard
scoliosis surgery, all facet joints from the superior to inferior
aspect of the proposed fusion levels are stripped of the joint
capsule, the cartilage removed, and the joint decorticated. Prior
to destruction of the joints an in vivo model for facet cap
placement is present, as no further dissection of the spine is
necessary, in which the facet caps can be placed and removed in
minutes. This has allowed the formulation of a working model for
application of the facet caps. Thus, the below examples relate to
the temporary insertion of facet caps during the course of standard
corrective surgery, to establish an operative technique for their
insertion, and to evaluate their efficacy and ease of use.
Example 4
Operative Technique
Pre-operative
[0061] Pre-operative planning is based on the standard standing
radiograph of the spine. The most accessible inferior vertebral
body demonstrating tilting relative to pelvis is identified. The
inferior tilting of the vertebra is measured to determine the
appropriate thickness of the shim portion and distance between
facet hooks of the facet cap. The next superior adjacent facet may
also be targeted as a sight for correction. More superiously in the
spine the apex of the scoliotic curve is identified. A measurement
of the interior tilt of this vertebra is obtained along the concave
aspect of the scoliotic curvature. A facet cap having a shim of
appropriate thickness and distance between facet hooks is placed at
this level and the next superior adjacent facet may also be
targeted.
Operative Technique
[0062] The patient is placed prone, supported by bolsters over ASIS
and upper chest with care to keep pressure off the abdomen. After
preparing the skin the back is draped to expose the midline of the
back. A midline incision is made over the spinous processes over
the appropriate levels (see pre-operative planning). The linea
between the left and right paravertebral muscles is dissected down
to the spinous processes. Localization of the vertebral levels is
checked by AP radiograph. The paravertebral muscles are then
reflected laterally along the lamina to the facet joints. Care is
taken to maintain the integrity of the facet ligaments. Further
soft tissue dissection is then performed to expose the transverse
processes. The facet joint, which is to receive the facet cap, is
then stripped of the joint capsule and posterior pericapsuiar
ligament. Care is taken to leave the facet cartilage intact. The
contra lateral facet joint is then stripped of ligament and
capsule. The facet joint cartilage on the contra lateral facet
joint is excised to bleeding subchondral bone. A laminar spreader
is placed between the superior and inferior transverse processes on
the side of the spine to receive the facet cap. The laminar
spreader is distracted to open the space in the ipslateral facet
joint. The facet cap is then placed in the facet joint and laminar
spreader removed. Correct placement of the facet cap should allow
for maintenance of the distraction created by the laminar spreader.
The bone is then decorticated, autologus bone graft placed along
both sides of the transverse processes, facet and lamina. AP and
lateral radiographs are taken to assess position and affect of the
facet cap. The paravertebral muscle is then approximated and skin
closed.
Example 5
[0063] Male patient 16 years old with 70 degree thoracic curve and
95 degree neuromuscular kypho-scoliosis (Kingston, Ontario,
Canada). The pre-operative plan for facet cap placement was to
assess the possibility of seating a facet cap like that of FIG. 3F
in the lumbar facet joint between the L1 and L2 lumbar
vertebrae.
[0064] The posterior spine was prepared in the standard fashion,
described above. After the L1-L2 lumbar vertebrae facet was
stripped of the capsule the joint was inspected. No space was
available to open the facet joint so that the facet cap could be
inserted. However, it is expected that could the facet joint have
been opened, the facet position could be altered to allow the facet
cap to be seated.
Example 6
[0065] Female patient 14 years old with 54 degree King II
idiopathic scoliosis (Kingston, Ontario, Canada). The pre-operative
plan was for facet cap placement in the Lt-1-2 lumbar facet joint,
and the T6-T7 thoracic facet joint. The use of laminar spreader
distraction between the facet joint aided in facet joint alignment,
as did the addition of a small metal dissector into the joint for
space creation and facet cap placement.
[0066] The posterior spine was prepared in the standard fashion as
described above. After the L1-L2 lumbar vertebrae facet was
stripped of the capsule, a blunt osteotome was placed in the
inferior joint and wedged the joint open. Concurrently a laminar
spreader was placed between L1 and L2 and distracted. These two
maneuvers opened the facet joint and subjectively corrected the
scoliosis in this segment. However, the facet cap like that of FIG.
3B could not be inserted because it was the wrong size for this
patient. In particular, the facet hook pattern (radius) of the
superior and inferior facet hooks of the facet cap was too narrow
and the overall length of the facet cap too long. It is expected
that changing the radius of the facet hooks to a range of about 5
mm to about 1 cm, and the overall length of the facet cap to a
range of about 1.5 cm to about 2.5 cm would have been appropriate.
The thoracic facet was addressed, and it was found that the
superior facet hook obscured implantation of the facet cap in this
patient and the facet cap could not be inserted. It is expected
that rotation of the inferior facet hook by about 30 degrees from
parallel to the facet cap to the right, for right insertion, and to
the left for left insertion, would have facilitated implantation of
the facet cap in this patient.
Example 7
[0067] Female patient 16 years old with 45 degree thoracic curve
and 95 degree kyphosis neuromuscular kypho-scoliosis (Kingston,
Ontario, Canada). The pre-operative plan was to place modified
facet caps (FIGS. 9A and 9B) into the 1-2-1-3 lumbar facet joint
and T7-T8 thoracic facet joint.
[0068] The posterior spine was prepared in the standard fashion,
described above. Using the technique described above the 12-1-3
facet joint was opened and a facet cap like that shown in FIG. 9B
was inserted. This is shown in FIG. 10B, where reference numeral
400 refers to the facet cap, with superior facet hook 410 and
inferior facet hook 420 partially visible. Also shown in FIG. 10B
are several Moss.RTM. Miami (DePuy-AcroMed Inc.) laminar hooks 430
placed around vertebral laminae, for use with rods for the standard
corrective procedure. The facet cap subjectively corrected the
scoliosis at this level. The T7-T8 facet joint was prepared and a
facet cap like that shown in FIG. 9A was inserted, as shown in FIG.
10A where reference numeral 300 denotes the facet cap. The inferior
facet hook 320 can be seen clearly. Also visible are several
Moss.RTM. Miami (DePuy-AcroMed Inc.) laminar hooks 330 placed
around vertebral laminae, for use with rods for the standard
corrective procedure. The facet cap subjectively corrected the
scoliosis at this level. Dimensions of the facet caps used in this
example are provided in the below table. TABLE-US-00001 TABLE 1
Dimensions of facet caps used in Example 7 and shown in FIGS. 9A
and 913. Width of both facet caps was about 12.7 mm. Dimension mm A
2.0 B 1.5 C 25.0 D 28.0 E 14.7 F 8.7 G 8.4 H 0 I 3.2
Equivalents
[0069] Variants to the Id s described above will be apparent to
those skilled in he art. Such variants are within the scope of the
present invention and are covered by the below claims.
* * * * *