U.S. patent application number 12/709243 was filed with the patent office on 2010-09-02 for compliant dynamic spinal implant.
Invention is credited to Anton E. Bowden, Peter A. Halveson, Larry L. Howell, Eric M. Stratton.
Application Number | 20100222821 12/709243 |
Document ID | / |
Family ID | 42560591 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100222821 |
Kind Code |
A1 |
Bowden; Anton E. ; et
al. |
September 2, 2010 |
Compliant Dynamic Spinal Implant
Abstract
A spinal implant comprises a plurality of contiguous segments in
which said contiguous segments form an angle at a location in which
two adjacent segments of the plurality of contiguous segments
intersect. At least one of said contiguous segments is prestressed
to form a selected radius of curvature prior to implantation. At
least one mounting connection is configured to connect said spinal
implant to a mounting mechanism, said mounting mechanism being
configured to attach said spinal implant to a degenerate spinal
segment.
Inventors: |
Bowden; Anton E.; (Lindon,
UT) ; Howell; Larry L.; (Orem, UT) ; Halveson;
Peter A.; (Alpine, UT) ; Stratton; Eric M.;
(Provo, UT) |
Correspondence
Address: |
THORPE NORTH & WESTERN, LLP.
P.O. Box 1219
SANDY
UT
84091-1219
US
|
Family ID: |
42560591 |
Appl. No.: |
12/709243 |
Filed: |
February 19, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61208018 |
Feb 19, 2009 |
|
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|
61210740 |
Mar 19, 2009 |
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Current U.S.
Class: |
606/260 |
Current CPC
Class: |
A61B 17/7026 20130101;
A61B 2017/00004 20130101; A61B 17/7011 20130101; A61B 17/7007
20130101 |
Class at
Publication: |
606/260 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Claims
1. A spinal implant comprising: a plurality of contiguous segments
in which said contiguous segments form an angle at a location in
which two adjacent segments of the plurality of contiguous segments
intersect, at least one of said contiguous segments being
prestressed to form a selected radius of curvature prior to
implantation; and, at least one mounting connection configured to
connect said spinal implant to a mounting mechanism, said mounting
mechanism being configured to attach said spinal implant to a
degenerate spinal segment.
2. The spinal implant of claim 1, wherein said at least one
prestressed contiguous segment is configured to apply a torque to a
degenerate spinal segment after implantation.
3. The spinal implant of claim 1, wherein each of said angles are
from about 80 degrees to about 110 degrees.
4. The spinal implant of claim 1, wherein said implant is made from
at least one of biocompatible plastics, polymers, metals, metal
alloys, laminates, shape-memory materials, and bioabsorbable
materials.
Description
PRIORITY CLAIM
[0001] This application claims the benefit of and priority from
U.S. Provisional Patent Application No. 61/208,018 filed on Feb.
19, 2009, and U.S. Provisional Patent Application No. 61/210,740
filed on Mar. 19, 2009, which are each incorporated herein in their
entirety for all purposes by this reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Research leading to this application was sponsored, in part,
through National Science Foundation Award No. CMMI-0800606, "Lamina
Emergent Mechanisms."
FIELD
[0003] Embodiments of the present invention relate generally to
mechanical spinal implants and, more particularly, to dynamic
spinal implants that relieve symptoms of degenerative spinal
diseases, that restore healthy motion to an unhealthy spine, and
that promote the healing of spinal tissues.
BACKGROUND
[0004] The human spine functions through a complex interaction of
several parts of the anatomy. FIGS. 1 and 2 (the cross-section A-A
of FIG. 1) illustrate a segment of the spine 4, with vertebra 5.
The vertebra 5 include the vertebral body 6, the spinous process 8,
transverse process 10, pedicle 12, and laminae 14. A functional
spine, comprising several vertebra 5, typically subcategorized as
being part of the cervical, thoracic, lumbar, sacral, and coccygeal
regions as known, provides support to the head, neck, trunk, and
transfer weight to lower limbs, protects the spinal cord 20, from
which peripheral nerves 32 extend, and maintain the body in an
upright position while sitting or standing.
[0005] Also illustrated in FIGS. 1 and 2, the spinal segment 4
includes intervertebral discs 20 that separate adjacent vertebra 5.
The intervertebral discs 20 provide motion, load bearing and
cushioning between adjacent vertebrae 5. Intervertebral discs 20
are the largest avascular structure in the body, relying on
diffusion for its nutrition. The diffusion of nutrients is aided by
the compression cycles that the intervertebral discs 20 undergo
during the course of normal movement, which drives out waste
products and cycles fluids. Lying down and resting reduces the load
on the intervertebral discs 20 allowing nutrients to diffuse into
the intervertebral discs 20.
[0006] Also illustrated in FIGS. 1 and 2, the spinal segment
includes spinal facet joints 16. Spinal facet joints 16 join the
adjacent vertebrae 6. The spinal facet joints 16 are synovial
joints that function much like those of the fingers. Together with
the intervertebral disc 20, the spinal facet joints 16 function to
provide proper motion and stability to a spinal segment 4. Thus,
each spinal segment 4 includes three joints: the intervertebral
disc 20 in the anterior aspect of the spinal segment 4 and the two
spinal facet joints 16 in the posterior aspect of the spinal
segment 4.
[0007] For the spinal segment 4 to be healthy, each of the
intervertebral disc 20 and the spinal facet joints 16 must be
healthy. To remain healthy these joints require motion. The
intervertebral disc 20 and the spinal facet joints 16 function
together to provide both quality and quantity of motion. The
quality of the motion is a exhibited by the non-linear energy
storage (force-deflection, torque-rotation) behavior of the spinal
segment 4. The quantity of motion is the range of segmental
rotation and translation.
[0008] Back pain due to diseased, damaged, and/or degraded
intervertebral discs 20 and/or spinal facet joints 16 is a
significant health problem in the United States and globally. A
non-exhaustive and non-limiting illustration of examples of
diseased and/or damaged intervertebral discs are shown in FIG. 3.
While a healthy intervertebral disc 20 is illustrated at the top of
the spine segment 18, diseased and/or damaged discs are also
illustrated. The diseased and/or damaged discs include a
degenerated disc 22, a bulging disc 24, a herniated disc 25, a
thinning disc 26, discs indicating symptoms of degeneration with
osteophyte formation 28, as well as hypertrophic spinal facets
29.
[0009] A degenerating spinal segment 18 is believed to be the
product of adverse changes to its biochemistry and biomechanics.
These adverse changes create a degenerative cascade affecting the
quality and/or quantity of motion and may ultimately lead to pain.
For example, as the health of a spinal segment 18 degenerates
and/or changes, the space through which the spinal cord 30 and
peripheral nerves 32 (FIGS. 1 and 2) pass can become constricted
and thereby impinge a nerve, causing pain. For example, the spinal
cord 30 or peripheral nerves 32 may be contacted by a bulging disc
24 or herniated disc 25 or hypertrophic spinal facet 29 as
illustrated in FIG. 3. As another example, a change in the spinal
segment 18, such as by a thinning disc 26 may alter the way in
which the disc functions, such that the disc and spinal facets may
not provide the stability or motion required to reduce muscle,
ligament, and tendon strain. In other words, the muscular system is
required to compensate for the structural deficiency and/or
instability of the diseased spinal segment 18, resulting in muscle
fatigue, tissue strain, and hypertrophy of the spinal facets,
further causing back pain. The pain this causes often leads
patients to limit the pain-causing motion; but this limited motion,
while offering temporary relief, may result in longer-term harm.
because the lack of motion limits the ability of the disc to expel
waste and obtain nutrients as discussed above.
[0010] Of course, other diseases of the disc and other back related
problems and/or maladies afflict many people. For example, as the
disc degenerates the spinal facet joints undergo a change in motion
and in loading. This causes the spinal facet joints to begin to
degenerate. Spinal facet joint arthritis is an additional source of
pain. Also, scoliosis, or a lateral curvature of the spine, is
illustrated in FIG. 4. A patient's body 40 is illustrated in
outline. Also illustrated is the lateral curvature of a scoliotic
spine 42 that is afflicted with scoliosis. The scoliotic center
line 44 of the scoliotic spine 42 is illustrated, as compared to a
healthy centerline or axis 46 of a healthy spinal column or
functional spine unit. Conditions such as kyphosis, an exaggerated
outward-posterior curvature of the thoracic region of the spine
resulting in a rounded upper back, lordosis, an exaggerated forward
curvature of the lumbar and cervical regions of the spine, and
other conditions also afflict some patients.
[0011] In many instances of degenerative disc disease, fusion of
the vertebrae is the standard of care for surgical treatment,
illustrated in FIG. 5. In the U.S. alone, approximately 349,000
spinal fusions are performed each year at an estimated cost of
$20.2 billion. The number of lower back, or lumbar, fusions
performed in the U.S. is expected to grow to approximately 5
million annually by the year 2030 as the population ages, an
increase of 2,200%.
[0012] Spinal fusion aims to limit the movement of the vertebra
that are unstable or causing a patient pain and/or other symptoms.
Spinal fusion typically involves the removal of a diseased disc 50,
illustrated in outline in FIG. 5. The removed disc 50 is replaced
by one or more fusion cages 52, which are filled or surrounded by
autograft bone that typically is harvested by excising one or more
spinal facet joints 57. Vertebral bodies 51 adjacent the removed
disc 50 are stabilized with one or more posterior supports 58 that
are fixedly connected to the vertebral bodies 51 with the use of
pedicle screws 54 that are screwed--such as by use of a bolt-style
head 56 to turn the pedicle screw 54--into a hole drilled into the
pedicle 12 of the vertebral bodies 51.
[0013] Fusion, however, often fails to provide adequate or
sufficient long-term relief in about one-half of the treatments,
resulting in low patient satisfaction. Further, fusion, by
definition, restricts the overall motion of the treated functional
spine unit, imposing increased stresses and range of motion on
those portions of the spinal segment adjacent to the fused
vertebral bodies 51. Fusion of a spinal segment has been indicated
as a potential cause of degeneration to segments adjacent to the
fusion. The adjacent spinal facet joints 57 and adjacent discs 59
often have to bear a greater load as a result of the fusion than
would typically be the case, leading to possible overloading and,
in turn, degeneration. Thus, surgical fusion often provides
short-term relief, but possibly greater long-term spinal
degradation than would otherwise have occurred.
[0014] Thus, a challenge to alleviating the back pain associated
with various ailments is to find a remedy that, ideally, does not
involve removing the diseased disc or damaging the spinal facet
joints, and that provides sufficient stability to the diseased
segment to alleviate pain and/or other symptoms, while still
providing sufficient freedom of movement to allow the disc and
spinal facet joints to return to health.
[0015] A further challenge is simply the complex, multi-dimensional
nature of movement associated with a functional spine unit.
Illustrated in FIG. 6 are the varying, orthogonal axes around which
a functional spine unit moves. For example, a vertebra 5 is
illustrated with an X-axis 60, around which a forward bending
motion, or flexion, 61 in the anterior direction occurs. Flexion 61
is the motion that occurs when a person bends forward, for example.
A rearward bending motion, or extension, 62 is also illustrated.
The Y-axis 63 is the axis around which lateral extension, or
bending, 64, left and right, occurs. The Z-axis 65 is the axis
around which axial rotation 66, left and right, occurs. Spinal
fusion, as discussed above, limits or prevents flexion 61-extension
62, but also limits or prevents motion in lateral extension, or
bending, 64 and axial rotation 66. Thus, an improved alternative
remedy to fusion preferably allows for movement with improved
stability around each of the three axes, 60, 63, and 65.
[0016] Another difficulty associated with the complex motion of the
spine is that the center-of-rotation for movement around each of
the X-axis 60, Y-axis 63, and Z-axis 65 differs for each axis. This
is illustrated in FIG. 7, in which the center-of-rotation for the
flexion 61-extension 62 motion around the X-axis 60 is located at
flexion-extension center-of-rotation 70. The center-of-rotation for
the lateral extension, or bending, 64 motion around the Y-axis 63
is located at lateral extension, or bending, center-of-rotation 73.
The center-of-rotation for the axial rotation 66 around the Z-axis
65 is located at axial rotation center-of-rotation 75. For more
complex motion patterns (e.g., combined flexion, lateral
extension/bending, etc.) a two-dimensional representation of the
center-of-rotation is inadequate, but the three-dimensional
equivalent called the helical axis of motion, or instantaneous
screw axis can be employed. Spinal remedies which force rotation of
a spinal segment around any axis other than the natural helical
axis impose additional stresses on the tissue structures at both
the diseased spinal segments and the adjacent spinal segments.
Compounding the issue for the centers-of-rotation is that they
actually change location during the movement, i.e., the location of
the centers-of-rotation are instantaneous. Thus, a preferable
remedy to spinal problems would account for the different
instantaneous centers-of-rotation throughout the range of motion.
Stated differently, a preferable remedy to spinal problems would
allow the diseased spinal segment and adjacent spinal segments to
under motion approximate that of the natural helical axis through
the range of motions.
[0017] Many previous efforts have been made to solve at least some
of the problems associated with spinal fusion, but with varying
degrees of success. For example, U.S. Pat. No. 7,632,292 (the '292
Patent) to Sengupta and Mulholland, discloses an arched-shaped
spring mechanism that is attached to adjacent vertebrae via pedicle
screws. This device relies on the extension and compression of the
spring to accommodate flexion 61 and extension 62 about the X-axis
60 illustrated in FIG. 6. The device disclosed in the '292 Patent
addresses only flexion-extension and neither lateral
extension/bending nor axial rotation, which would both still be
improperly supported. Further, the '292 Patent does not account for
the instantaneous centers-of-rotation; in other words, the
centers-of-rotation will be misplaced for motions other than
flexion. In addition, it may be anticipated that the device is
either too stiff to provide proper motion or that the
extension-compression cycles may lead to fatigue failure of the
device.
[0018] Another example is U.S. Pat. No. 6,966,910 (the '910 Patent)
and its associated family of applications to Ritland. As with the
'292 Patent, the '910 Patent relies on the extension-compression
cycle of a spring mechanism--specifically the reverse curves within
the mechanism--to accommodate flexion 61 and extension 62 about the
X-axis 60 illustrated in FIG. 6. Lateral extension/bending and
axial rotation are not addressed.
[0019] Thus, there exists a need for a spinal implant that protects
the spinal cord and the peripheral nerves from damage.
[0020] Further, there exists a need for a spinal implant that
reduces the stress on a diseased and/or damaged disc without
overloading the adjacent discs and vertebrae that could initiate
progressive degeneration or diseases in the adjacent discs and
vertebrae.
[0021] Another need exists for a spinal implant that minimizes or
avoids wear. Previous spinal implants that have parts that move
against each other may cause wear particles or debris--i.e., small
pieces of the implant--to come free, potentially loosening the
implant and/or decreasing the stability of the implant, and/or
potentially causing adjacent bone or tissue to degrade because of
contamination. Further, wear particles may change the chemical
structure and/or chemical stability of biocompatible devices such
that the resultant chemical structure and/or chemical stability
becomes non-biocompatible or causes the implant to degrade at an
accelerated rate.
[0022] A need also exists for a spinal implant that provides for
proper force-deflection behavior of the spinal implant
(kinetics)--as noted above in the discussion of FIG. 6--preferably
to approximate those of a normal, functional spine unit to relieve
the load and strain on the intervertebral discs, to protect the
spinal facet joints, to reduce the risk of damage to segments of
the spine adjacent to the diseased segment, to reduce muscle
fatigue and reduce and/or eliminate subsequent pain.
[0023] A need also exists for a spinal implant that exhibits
kinematics--such as the limits of the ranges-of-motion and the
centers-of-rotation noted above in the discussion of FIG. 7--that,
preferably, are maintained near those of a functional spine unit to
maintain an effective range of motion for the intervertebral discs,
spinal facet joints, muscles, ligaments, and the tendons around the
spine and to reduce the amount of neural element strain, e.g., the
strain on the spinal cord and/or other parts of the nervous
system.
[0024] A need still exists for a spinal implant that relieves a
portion of the load that would otherwise be borne by the diseased
disc. In addition, a compliant spinal implant preferably distracts
(or extends) the space--including the space anteriorly and/or
posteriorly--between the vertebrae adjacent to the diseased
discs.
[0025] In addition, a need exists for a spinal implant that
preferably restores a torque-rotation signature near that of a
healthy, functional spine unit.
[0026] Spinal implants including one or more of the recited
features and benefits could improve the opportunity for the
diseased spinal segment and/or intervertebral discs and/or spinal
facet joints to heal.
SUMMARY
[0027] Various features and embodiments of the invention disclosed
herein have been the subject of substantial ongoing experimentation
and have shown a significant improvement over the prior art. Among
other improvements, the embodiments of the invention provide robust
and durable compliant spinal implants that have a smaller profile
and accommodate motion in three axes as compared to a single axis
of motion of the prior art. It is believed that the embodiments,
collectively and/or individually, represent an unexpected advance
in the field and will enable physicians to provide spinal implants
that can be selected and individually adjusted pre-operatively,
intra-operatively (i.e., during the operation), and
post-operatively to restore the normal or near normal function of a
damaged or diseased spinal segment.
[0028] Embodiments of the compliant dynamic spinal implant include
a geometry that, once implanted, is configured to allow
flexion-extension, and/or lateral extension/bending, and/or axial
rotation with an instantaneous or near-instantaneous
centers-of-rotation for the diseased and/or damaged disc and
adjacent vertebrae that are similar to that of a healthy spinal
segment. Thus, the implant restores, to a degree, close to normal
movement of the diseased and/or damaged discs and adjacent
vertebrae, which, in turn, promotes healing of the diseased and/or
damaged disc.
[0029] Other embodiments of the spinal implant provide protection
to the spine, discs, spinal cord, and peripheral nerves by reducing
the risk of harmful, damaging, and/or painful movements while still
providing a sufficient range of motion to promote healing and while
reducing the risk of damage and/or disease to adjacent discs and
vertebrae. Embodiments of the spinal implant do so by reducing the
stresses on a diseased and/or damaged spinal segment without
overloading the adjacent spinal segments, including the adjacent
intervertebral discs, spinal facet joints, and vertebrae, that
could initiate progressive degeneration or diseases in the adjacent
spinal segments. For example, embodiments of a spinal implant
preferably relieve a portion of the compressive load that would
otherwise be borne by the diseased disc and, preferably, distracts
(or increases) the space between the vertebrae adjacent to the
diseased discs, which improves the opportunity for the diseased
disc to heal.
[0030] Embodiments of the spinal implant preferably provide for
force-deflection behaviors near those of a normal, functional spine
unit--such as the healthy discs and/or spinal facet joints near the
damaged and/or diseased spinal segments of a patient--to reduce
muscle fatigue and subsequent pain. Additionally, embodiments of
the spinal implant preferably provide proper motion--such as the
centers-of-rotation, whether instantaneous or otherwise, limits of
the ranges-of-motion, and the types of motion--that are maintained
near those of a functional spine unit to maintain an effective
range of motion for the muscles and the tendons around the spine
and to reduce the amount of spinal cord strain. For instance,
embodiments of the compliant spinal implant preferably restore a
torque-rotation signature near that of a healthy, functional spine
unit.
[0031] Embodiments of the present invention exhibit reduced or
limited wear compared to prior art devices. Such reduced wear is
provided, preferably, by having few to no parts within the implant
itself that move or wear against other parts of the spinal implant
or against the vertebrae and/or other skeletal tissue that might
cause the implant to wear. Thus, embodiments of the spinal implant
produce few to no wear particles when compared to prior
devices.
[0032] Further embodiments include spinal implants that have a
geometry engineered and configured to provide one or more of the
above benefits. Embodiments of the spinal implant include a first
attachment on a first length and a second attachment on a second
length. Each attachment is configured for connecting and attaching
to a device (typically, although not necessarily, pedicle screws
and other similar devices) for temporarily or permanently fixing
the spinal implant to one or more vertebrae. The first length and
the second length are joined by a third section having a geometry
engineered to provide one or more of the above benefits. The spinal
implant preferably relies upon the geometry and the material from
which the implant is manufactured to provide torque to oppose the
flexion-extension of the spine, rather than compression-extension
as in prior art devices. In addition, the spinal implant preferably
relies upon the geometry and the material from which the implant is
manufactured to provide compression and extension to oppose the
lateral extension/bending of the spine.
[0033] Embodiments of the spinal implant are preferably made of
biocompatible materials, including, but not limited to,
biocompatible polymers and plastics, bioabsorbable materials,
stainless steel, titanium, nitinol, shape-memory materials and/or
alloys, and other similar materials. Additionally, embodiments of
the spinal implant can be manufactured with materials that provide
for pre-operative, operative, and post-operative adjustment of the
implant and the manner in which it responds to a given input such
as stress and/or torque, and, in the instance of post-operative
adjustment, preferably adjustment through minimally invasive
techniques and, more preferably, through non-invasive techniques.
Embodiments of methods of adjusting the spinal implant are also
disclosed.
[0034] Embodiments of methods of implanting the spinal implant are
also disclosed.
[0035] Methods of using the above described system to detect leaks
are also disclosed.
[0036] As used herein, "at least one," "one or more," and "and/or"
are open-ended expressions that are both conjunctive and
disjunctive in operation. For example, each of the expressions "at
least one of A, B and C," "at least one of A, B, or C," "one or
more of A, B, and C," "one or more of A, B, or C" and "A, B, and/or
C" means A alone, B alone, C alone, A and B together, A and C
together, B and C together, or A, B and C together.
[0037] Various embodiments of the present inventions are set forth
in the attached figures and in the Detailed Description as provided
herein and as embodied by the claims. It should be understood,
however, that this Summary does not contain all of the aspects and
embodiments of the one or more present inventions, is not meant to
be limiting or restrictive in any manner, and that the invention(s)
as disclosed herein is/are and will be understood by those of
ordinary skill in the art to encompass obvious improvements and
modifications thereto.
[0038] Additional advantages of the present invention will become
readily apparent from the following discussion, particularly when
taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] To further clarify the above and other advantages and
features of the one or more present inventions, reference to
specific embodiments thereof are illustrated in the appended
drawings. The drawings depict only exemplary embodiments and are
therefore not to be considered limiting. One or more embodiments
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0040] FIG. 1 is a segment of a functional spine unit;
[0041] FIG. 2 is a cross-section of the segment of the functional
spine unit illustrated in FIG. 1, taken along section A-A of FIG.
1;
[0042] FIG. 3 is a segment of a spine illustrating various
pathologies of intervertebral discs;
[0043] FIG. 4 is a scoliotic spine;
[0044] FIG. 5 is a prior art discectomy and spinal fusion;
[0045] FIG. 6 illustrates the three axes of motion around which
functional spine unit moves;
[0046] FIG. 7 illustrates the centers-of-motion of a functional
spine unit;
[0047] FIG. 8 illustrates an embodiment of an unimplanted compliant
dynamic spinal implant, shown from the rear/posterior view, i.e.,
as it would appear from the rear of a person when implanted;
[0048] FIG. 9 is a lateral/side view of the spinal implant shown in
FIG. 8;
[0049] FIG. 10 shows embodiments of the spinal implant as they
would appear implanted in a pair of lumbar vertebrae as viewed from
the rear;
[0050] FIG. 11 is a lateral/side view of one of the spinal implants
of FIG. 10;
[0051] FIG. 12 is a posterior view of the spinal implant of FIG. 8
undergoing a torsional load;
[0052] FIG. 13 is a lateral view of the spinal implant of FIG. 9
undergoing a torsional load;
[0053] FIG. 14 is a posterior view of the spinal implant of FIG. 8
undergoing a compressive load and a torsional load;
[0054] FIG. 15 is a lateral view of the spinal implant of FIG. 9
undergoing a compressive load and a torsional load;
[0055] FIG. 16 is a graph of the rotation that occurs for a given
torque for an exemplary healthy spine and an exemplary degenerative
spine undergoing flexion and extension;
[0056] FIG. 17 is a graph of the moment difference between the
response of the degenerative spine and the healthy spine graphed in
FIG. 16 and a linear curve fit of the moment difference; and,
[0057] FIG. 18 is a graph of the healthy spine of FIG. 16 and the
resultant rotation that occurs for a given torque of the
degenerative spine (shown in FIG. 16) that has had an embodiment of
the spinal implant that has been adjusted to exhibit a torque
response that is the negative slope of the linear curve fit shown
in FIG. 17.
[0058] The drawings are not necessarily to scale.
DETAILED DESCRIPTION
[0059] As noted above, the kinetics and kinematics of the spine are
quite complex, involving three separate axes around which motion
occurs and three separate centers-of-rotation for the different
motions. Applicants have recognized that previous spinal implants
often address just one form of motion, typically flexion and
extension, often through the use of springs of some type that flex
and compress. Efforts to address more than one mode of rotation or
motion typically tend to be complex, large, and often do not
address each individual motion as effectively as devices dedicated
to a single motion.
[0060] Through significant experimentation and engineering work,
Applicants have discovered geometries that rely, in part, on the
concept of torsion, rather than primarily compression and extension
of springs, to provide a seemingly simple, yet decidedly complex,
geometry that accommodates motion and stiffness around the three
axis and accommodates the separate centers-of-rotation for each
motion (flexion-extension, lateral extension or bending, and axial
rotation). A compliant mechanism gains its motion from the
deflection of flexible, resilient members. Such devices move
without the aid of traditional sliding joints and bearings, thus
increasing precision and eliminating friction and wear. They also
integrate spring and hinge functions, allowing for the design of
desired force-deflection behavior.
[0061] An embodiment of a compliant dynamic spinal implant 100 is
illustrated in FIGS. 8 and 9, which is an embodiment of a geometry
that accomplishes, in part, the objectives provided above and in
the background section. A posterior view of the spinal implant 100
is presented in FIG. 8--reference being made to the direction the
spinal implant would be viewed from when implanted in a patient. In
other words, the spinal implant 100 in FIG. 8 appears as it would
as viewed it from the patient's back. A lateral, or side, view, of
the implant is presented in FIG. 9. It will be understood that
while these references to view are presented for clarity, it should
be understood the spinal implants 100 shown in FIGS. 8 and 9 appear
in their unstressed, pre-implant condition, as will be explained in
further detail below. In this particular embodiment, the spinal
implant 100 comprises a plurality of contiguous segments. In one
embodiment, these contiguous segments include a first segment 101,
having a first length 107, a first width 111, and a first height or
thickness 118; a second segment 102 having a second length 108, a
second width 112, and a second height or thickness 119; a third
segment 103 having a third length 109, a third width, and a third
height or thickness; a fourth segment 104 having a fourth length, a
fourth width 113, and a fourth height or thickness. The spinal
implant 100 also includes a fifth segment 105 having a fifth length
110, a fifth width 114, and a fifth height or thickness 120. Of
course, one having skill in the art would understand that other
geometries and configurations exist--including greater or fewer
segments--that accomplish, in part, the recited objectives.
[0062] In this particular embodiment, the third width is the same
width as the fourth width 113. Likewise, the fourth length is the
same length as the third length 109. Furthermore, the heights of
each segment discussed, including, the third and fourth heights,
are the same as the first height 118, second height 119, and fifth
height 120, respectively. Of course, the specific
dimensions--including those not individually discussed--may be the
same or they may differ from each other as one having skill in the
art would understand.
[0063] As illustrated, the plurality of segments form angles at the
location in which adjacent segments intersect. In other words, a
plurality of angles exist, one angle for each intersection between
two adjacent segments. For example, the first segment 101 is joined
to the third segment 103, creating a first angle 115 between the
first segment 101 and the third segment 103. The third segment 103
is joined to the fifth segment creating a second angle 117. The
fifth segment 105 is, in turn, joined to the fourth segment 104,
creating a third angle that, in this instance, is the same angle as
the second angle 117. The fourth segment 104, in turn, is joined to
the second segment 102, creating a fourth angle 116.
[0064] When reference is made to that the individual segments being
"joined," it is understood that the segments may be temporarily
joined, through a removable connection, such as bolts, screws,
biocompatible adhesives, and the like. Alternatively, one or more
of the segments may be joined permanently, such as through the use
of biocompatible epoxies, polymers, and other known methods of
joining the segments. In yet another embodiment, the individual
segments may be formed as a single, unitary piece, such as by
laminating, molding, pressing, stamping, milling, and other known
methods.
[0065] In the embodiment illustrated, each of the angles 115, 116,
and 117 are each right angles, thus forming a "U" configuration or
shape of the contiguous segments, with each of the segments lying
within proximately the same plane before implantation, although the
measurement of each angle may differ from the others and fall
within a variety of ranges. For example, the measurement of one or
more of the angles may range from about 80.degree. to about
100.degree.; from about 70.degree. to about 110.degree.; and from
about 45.degree. to about 135.degree.; and so forth.
[0066] As noted, embodiments of the spinal implant 100 use, in
part, torsion to apply a force or load to the vertebrae of a
patient. Typically, although not necessarily, the spinal implant
100 has an initial curvature to the device, as indicated in FIG. 9
by torsion angle 122 with a radius of curvature 121. FIG. 9, in the
pre-implanted condition, includes this torsion angle 122, thus, as
will be discussed below when explaining the procedure to implant
the device, the spinal implant will provide a known or selected
torque when it is straightened for implantation. Of course, the
magnitude of this torque is a function of the radius of curvature
121, the material from which the spinal implant 100, is
manufactured, and the specific geometry of each of the individual
segments.
[0067] The spinal implant 100 optionally includes at least one
mounting connection for connecting the spinal implant 100 to a
mounting mechanism. For example, an embodiment of a mounting
connection includes through holes 106 (FIG. 8), through which a
mounting mechanism, typically, although not necessarily, pedicle
screws, are positioned to hold the spinal implant in position in
the patient--i.e., the mounting mechanism attaches the spinal
implant 100 to at least a portion of a spinal segment, such as a
vertebra, a pedicle, or other bony structure of a patient as will
be discussed below. Of course, pedicle screws are merely one
example of a mounting mechanism for attaching the spinal implant
100 to a patient's vertebrae. Other mounting mechanisms, such as
the use of pins, biocompatible adhesives, straps, and the like,
fall within the scope of this disclosure.
[0068] The spinal implant 100 can be formed of biocompatible
plastics, polymers, metals, metal alloys, laminates, shape-memory
materials, and other similar materials, either wholly as one
material or as a combination of materials--i.e., different segments
may be manufactured from different materials. Optionally,
embodiments of the spinal implant can be made from bioabsorbable
materials that a patient's body will naturally breakdown over time,
thus potentially avoiding the need for a second surgery to remove
the spinal implant 100, should such an option prove necessary
and/or desirable.
[0069] An embodiment of the spinal implant 100 can optionally be
made with nitinol, a metal alloy of nickel and titanium, that
provides the ability of shape-memory. A spinal implant 100 made
from such materials would be manufactured into a first shape or
geometry or configuration (e.g., the length of the first and second
segments 101 and 102, the radius of curvature 121, etc.) having a
known and desired first torque response. The spinal implant 100
would then be manipulated into a second shape or geometry having a
known and desired second torque response. The spinal implant 100,
in the second shape or geometry or configuration, then would be
implanted in the patient. After implantation, a physician can apply
an activating agent, such as heat, current, or other parameter, to
cause the spinal implant 100 to revert back to its original, first
shape or geometry, allowing the material to consequently revert to
its first torque response. Thus, a measure of adjustability in the
torque response of the spinal implant 100--even post-surgery--can
be manufactured into the spinal implant 100. For example, in the
case of nitinol, applying a parameter such as heat to the spinal
implant and, in so doing, raising the spinal implant to a
temperature above the transition temperature of the nitinol causes
the spinal implant to revert to its first shape or geometry. In so
doing, the stiffness of the spinal implant could be altered by, for
example, making the spinal implant significantly stiffer so that it
approximates more closely the stiffness provided by a spinal fusion
procedure.
[0070] Another embodiment of the spinal implant 100 can be made
from bioabsorbable materials, as mentioned. The patient's body
would slowly absorb the spinal implant 100 and, in the process of
so doing, the compressive load or force and torque provided or born
by the spinal implant 100 would slowly be transferred to the
intervertebral discs and/or vertebrae of the patient as the
patient's spine healed and/or improved in health and strength.
Thus, a bioabsorbable device contemplates and allows for a patient
to regain his or her spinal health, an adjustment and transfer of
force and torque from the spinal implant to the patient's body, and
the eventual removal of the spinal implant through absorption
rather than surgery.
[0071] An advantage of embodiments of the spinal implants
disclosed--provided that they are manufactured as single, unitary
piece--is that they do not have any joints or surfaces that might
rub or wear against each other because the embodiments rely on
deflection of the segment(s) to provide a force and/or torque. The
relative lack of rubbing or movement against other elements as
compared to prior art devices minimizes or prevents the formation
of wear particles that might otherwise be generated. This is the
case for those prior art devices that have biocompatible surfaces
that might wear off to expose non-biocompatible surfaces or, in
some instances, the wear causes the biocompatible surface to become
non-biocompatible, leading to additional wearing of the prior art
devices at an accelerated rate.
[0072] For context, FIGS. 10 and 11 illustrate embodiments of the
spinal implant 200 as they might appear implanted on a lumbar
portion of the spine of a patient. The spinal implants 200 are
fixed to the vertebrae 204 adjacent to a diseased disc 206. In this
embodiment, pedicle screws 202 are used to fix the spinal implants
200 to the vertebrae 204. (The method of surgical implantation will
be discussed in more detail below.) Once implanted, the spinal
implants 200 optionally provide an extension force 210, if they are
prestressed, as will be discussed below, to help distract the
vertebrae 204 from the diseased disc 206. Alternatively, the spinal
implants 200 resist a compressive force 214 from the normal action
of gravity upon the person, thus supporting a portion of the load
that would otherwise have been born by the diseased disc 206. In
addition, the spinal implants provide a torque 212 (about an axis
perpendicular to the page of FIG. 10) that distracts the diseased
disc 206 and, preferably, distracts an anterior portion 207 of the
diseased disc 206. The torque 212 applied by the spinal implants
200 can be selected and adjusted to compensate at least partially
and, preferably, almost fully, for the diseased disc 206, as will
be explained further below.
[0073] Turning to FIGS. 12 and 13, these figures illustrate the
spinal implants 100 from FIGS. 8 and 9 as they might appear during
surgical implantation. As noted in the discussion of FIG. 9 above,
the spinal implant 100 optionally is manufactured (or shaped, in
the case of shape-memory materials like nitinol) to have a first
geometry, which may include a first radius of curvature 121, the
radius of curvature is about an axis orthogonal to the axis of the
spinal column (e.g., axis 44 in FIG. 4). To implant the spinal
implant 100, a surgeon could use a positioning tool that provides a
torque 130 that causes the radius of curvature 121 to increase,
potential to infinity, in the illustrated instance. In such a
position, the surgeon can fix the spinal implants 100 to the
patient's vertebrae (vertebrae 204 in FIGS. 10 and 11) with pedicle
screws or other methods. Once the positioning tool is released and,
consequently, torque 130 removed, the spinal implant 100 tends to
return to its original, unstressed state and, in so doing, applies
a torque 212 to the vertebrae 204 as illustrated in FIGS. 10 and
11.
[0074] FIGS. 14 and 15 illustrate the spinal implant 100 under a
compressive force 142. This load could be caused by the normal
action of gravity when implanted in a patient as the spinal implant
100 bears some of the compressive load. Alternatively or in
addition to the load of gravity, such a force may occur as a result
of lateral extension--i.e., the patient is leaning toward that side
as a result of rotation 64 around the Y-axis 63 illustrated in FIG.
6. As FIG. 14 indicates, the third segment 103 and the fourth
segment 104 deflect, causing a change in the first, second and
fourth angles, 115, 117, and 116, respectively. The deflection of
the segments 103 and 104 creates a torque that balances the
compressive force 142.
[0075] In addition, a torque 140 can be applied to the spinal
implant 100, a situation that might occur when the patient is
leaning forward, causing flexion, i.e. a rotation around the X-axis
60 in the forward direction (flexion 61) in the spinal region in
which the spinal implant 100 has been fixed. Such a movement would
cause compression of the anterior region 207 of a diseased disc 206
as illustrated in FIG. 11. The spinal implant 100, by bending,
applies a torque that would counteract, at least in part, the
torque 142 caused by flexion. As one having skill in the art would
understand, embodiments of the spinal implants 100 having a
selected geometry such as that illustrated, would provide similar
torque to balance and/or offset other forces incurred through
flexion-extension, lateral extension/bending, and axial
rotation.
[0076] A benefit of embodiments of the spinal implant are that it
can be individually adjusted to a specific patient and that
patient's pathologies, rather than relying on prior art devices
that were manufactured for a predetermined subset of the
population. The disadvantages of the latter approach are that it is
rare that an individual patient's pathologies, by coincidence, are
an exact match for a device. Thus, the patient must compromise, to
a greater or lesser extent, on the performance and the relief that
may be obtained through the use of some prior art devices.
[0077] Referring to FIGS. 16-18, a process for selecting and
adjusting a spinal implant to a patient's pathology will be
discussed. FIG. 16 is a graph of the torque-rotation response of a
healthy and a diseased or degenerative disc undergoing flexion and
extension, i.e., rotation in flexion 61 and extension 62 around the
X-axis 60 as illustrated in FIG. 6 and corresponding to bending or
leaning over and bending or leaning backwards. The X-axis 300 of
the graph is the torque measured in Newton.cndot.meters (Nm). The
Y-axis 305 of the graph is a measurement of the range of motion in
rotation in degrees. The solid (healthy) curve 310 is the response
of a healthy functional spine unit which, for example, can include
the disc 208 illustrated in FIG. 11. The dotted (degenerate) curve
315 is the response of a diseased or degenerative disc, such as
disc 206 illustrated in FIG. 11. Qualitatively, FIG. 16 indicates
that the diseased disc rotates more at lower torque than the
healthy disc, indicating that there is a greater degree of laxity
in the diseased disc, which may present as the disc bulging
anteriorly and pressing against the spinal cord, causing pain,
and/or other similar pathology. These measurements can be taken for
the spine, as a whole, but, more preferably, the measurements are
made at the vertebrae adjacent to the diseased disc. This is so
because the torque-rotation response of the adjacent healthy
vertebrae and discs should be the most similar to the response of
the diseased disc when it was once healthy, a consideration since
it is desired to restore the diseased disc to health.
[0078] Referring now to FIG. 17, this graph uses the same axes and
scale as the graph in FIG. 16. In this instance, FIG. 17 plots the
solid (moment difference) curve 320, which is the calculated
difference in the response between the solid (healthy) curve 310
and the dotted (degenerate) curve 315 in FIG. 16. The dashed
(linear) curve 325 is a linear curve fit of the solid (moment
difference) curve 320.
[0079] A difference and improvement in the embodiments of the
spinal implant disclosed herein is that the geometry of the spinal
implant optionally uses this calculated moment difference as an
input in the design process. The spinal implant 200 of FIGS. 10 and
11, for example, can be designed to have a radius of curvature 121
(illustrated in FIG. 9) that provides a desired and known torque
response when implanted in the patient as discussed above. In this
example, the spinal implant 200 would have a linear torque-rotation
response in flexion-extension that has a slope that is the negative
of the dashed (linear) curve 200.
[0080] FIG. 18 illustrates the reason for creating a spinal implant
that relies, in part, on the moment difference between the healthy
disc and the diseased disc. Again, the same axes and scale are used
in FIG. 18 as in FIG. 16. In this graph, the original solid
(healthy) curve 310 is plotted. Now, however, a spinal implant
designed and adjusted for the patient's pathology, has been
implanted as described above with respect to FIGS. 10 and 11. In
other words, a spinal implant 200 is now supporting the diseased
disc 206 and the adjacent vertebrae 204. As can be seen in FIG. 18,
the spinal implant provides a desired stiffness, restoring the
response of the dotted (degenerate) curve 315 to that of the dashed
(linear and degenerate) curve 330 that is similar to the solid
(healthy) curve 210. Qualitatively, it can be seen that with the
spinal implant, the rotational response for a given torque is quite
near that of the healthy disc. While this example is provided for
flexion and extension, one having skill in the art would understand
that similar measurements can be made for lateral extension and
axial rotation so that the results can be used, in part, as an
input into the geometry of the spinal implant and, therefore, to
allow the spinal implant to accommodate and support the motion of
the spine in the three axes as discussed above. In brief,
embodiments of the spinal implant can be designed and adjusted, in
part, pre-operatively for an individual patient's pathology.
Embodiments of the spinal implant can restore, at least in part, a
healthy torque-rotation signature to a diseased spine.
[0081] A further advantage of the above approach of measuring
torque-rotation and similar data for use as an input is that it
avoids a problem that appears in prior art devices. As briefly
alluded to, many prior art devices have a limited range over which
they function, typically force-displacement in compression and
extension for the devices that commonly rely upon springs. These
devices are not typically calibrated to an individual. As a result,
it is not uncommon for these prior art devices to use an extension
force to distract the diseased disc that is too large for a given
individual, causing undue strain on the surrounding muscles and
ligaments, which may result in undue pain. In severe cases, the
pain this causes might result in the patient unduly limiting his or
her range of motion, resulting in nutritional deficiencies and
other problems associated with minimal or a lack of movement in the
spine and the disc, which was the outcome to be avoided
initially.
[0082] Embodiments of the spinal implant disclosed herein provide
additional benefits, such as:
[0083] Treating scoliosis, kyphosis, lordosis, and/or similar
pathologies: For example, with reference to FIG. 4 which
illustrates a spine presenting with scoliosis, embodiments of the
disclosed spinal implant can treat the scoliosis. This is done by
using spinal implants that have different torque-rotation
signatures from each other. That is, rather than using spinal
implants 200 having the same torque-rotation signature as
illustrated in FIG. 10, in the instance of scoliosis one of the
spinal implants would have a different and, possibly, opposite,
torque-rotation signature than the other. In addition, a
prestressed force may be applied to one or both of the spinal
implants so that they apply a force to one or both sides of the
scoliotic spine. In other words, the torque and/or any force
applied by the spinal implants would be unbalanced in order to
counteract the curvature of the scoliotic spine. For example, in
FIG. 4 an extensive force 82 can be applied on the right side of
the lumbar area of the spine by one spinal implant, while on the
left side another spinal implant could apply a compressive force on
the left side of the lumbar area of the spine, tending to cause the
lumbar spine to straighten. Alternatively, or in addition to, the
unbalanced forces, torques 84 and 86 could be applied to the spine
by the spinal implants. A similar strategy could be used to treat
other conditions of the spine that present similar pathology to
scoliosis, such as kyphosis, lordosis, and the like.
[0084] Provide distraction of the vertebrae to allow healing of the
diseased disc: As noted, a spinal implant can be prestressed to
provide a torque and/or extensive force to distract, either
anteriorly, posteriorly, or both, the portion the vertebrae
adjacent to a diseased disc. In so doing, the spinal implants carry
or bear a portion of the force normally borne by the diseased disc,
as well as an additional force that static devices such as the
prior art posterior support 58 in FIG. 5 do not carry. This
arrangement allows sufficient support and space for the diseased
disc to heal while still providing for sufficient moment that
static prior art devices and procedures (such as spinal fusion) do
not provide. In other words, embodiments of the spinal implant
provide an opportunity for the diseased disc to heal, which may
allow the spinal implants to eventually be removed.
[0085] Protect spinal cord and periphery nerves: The embodiments
disclosed provide, in part, a measure of protection to the spinal
cord and peripheral nerves from being impinged by bulging and/or
herniated discs and/or parts of the skeletal structure and other
parts of the anatomy afflicted with various pathologies as
described above.
[0086] Limit range of motion and provide stiffness: The embodiments
disclosed, as shown graphically in FIGS. 16-18, restore a measure
of stiffness and limit the range of motion that might otherwise be
causing pain, such as through muscles overexerting themselves to
compensate for the laxity caused by a diseased disc. By limiting
the range of motion, the strain on muscles and ligaments is
reduced, thereby reducing risk of injury to those muscles. Further,
laxity is reduced, thereby improving the structural stiffness (as
opposed to the colloquial muscle stiffness caused by over-exertion)
of the spine.
[0087] Kinetics similar to a healthy spine: Related to limiting the
range of motion discussed above, the motion that embodiments of the
spinal implant provide in the three axes discussed above regarding
FIG. 6 is similar to that of a healthy spine. What this provides is
that the patient's muscles and ligaments do not have to compensate
for an unnatural motion of the spinal implant, unlike the case with
prior art devices. In other words, the spinal implant provides more
natural motion, which would encourage patients to move more with
less attendant pain as their muscles would not be compensating or
overworking for a prior art spinal implant that does not provide
such natural motion around all three axes. In so doing, the
movement provides further nutrition to the discs, increasing the
likelihood that the discs will heal.
[0088] Kinematics similar to a healthy spine: Related to the
kinetics are the natural kinematics of embodiments of the spinal
implants. As discussed above, the centers-of-rotation for
flexion-extension, lateral extension/bending, and axial rotation,
are each located in different places. Prior art devices could not
accommodate these separate centers-of-rotation around more than one
axis, if even that, nor could they provide for the instantaneous or
near instantaneous change in the location of the centers-of-motion
as a spinal segment moves, nor could they provide for motion
approximate the motion of a natural helical axis. Stated
differently, the center-of-rotation of prior art devices often was
in a different location than the natural center-of-rotation of the
spine for a given movement. To compensate, patients with prior art
devices suffered strain upon the spinal cord and peripheral nerves,
muscle strain caused by the muscles overworking and compensating
for the two different centers-of-rotation (that of the prior art
device and that of the spine), ligament strain, and, consequently,
pain. In contrast, embodiments of the present spinal implant
provide centers-of-rotation in each of the three axes that is the
same, or nearly the same, as a patient's natural
centers-of-rotation for the spine. Thus, patients typically have
less pain and, consequently, greater movement, to the benefit of
the discs and the spine in general.
[0089] Adjust to the individual spine: As noted, embodiments of the
spinal implant can be designed and/or selected preoperatively for
an individual patient's torque-rotation response in order to
provide implants that restores the diseased disc/spine to near
healthy function. Related to this is the ability to prestress
embodiments of the implant prior to, or even during, surgery to
allow the surgeon to further individually tailor the
torque-rotation response of the spinal implant to the individual
patient as determined at the time.
[0090] Further, embodiments of the spinal implant are adjustable
post-surgically. As noted, spinal implants made of bioabsorbable
material will gradually degrade and, in the process, transfer ever
greater portions of the force and torque once borne by the spinal
implant back to the patient's spine as it heals. A further benefit
of this is that these embodiments do not need to be then be
surgically removed, reducing cost and risks to the patient.
Alternatively, embodiments of the spinal implant can be made from
shape-memory materials, such as nitinol. The use of shape memory
materials allows the spinal implant to be configured in a second
geometry or shape upon surgical implantation and then, upon
application of some transformation parameter, such as heat, the
spinal implant reverts to a first geometry or shape with different
mechanical properties (such as stiffness and/or torque), thus allow
a physician to subsequently alter the treatment of the patient
without surgical intervention.
[0091] Reduced wear: As noted, embodiments of the spinal implant do
not have moving components or components that rub against one
another, thereby reducing or eliminating the generation of wear
particles. Further, because embodiments of the spinal implant rely
upon torsion and/or torsion beams rather than compression and
extension that springs and other similar devices rely upon, reduces
or eliminates the risk of the material from which the spinal
implant is made suffers from fatigue and/or fatigue failure,
thereby increasing the reliability of the spinal implant.
[0092] Thus, disclosed above, in addition to the embodiments of the
spinal implant are methods of treating a spine with a spinal
implant configured to provide motion in three axes; methods of
treating a spine with a spinal implant that provides kinetics and
kinematics similar to that of a functional spine; methods of
treating pathologies that cause the spine to curve; methods of
healing a diseased or degenerated disc; methods of adjusting a
spinal implant without surgical intervention; methods of reducing
the wear of a spinal implant; methods of providing a near healthy
torque-rotation signature to a degenerate spine; and other methods
as will be recognized by one of skill in the art.
[0093] As alluded to above, embodiments of the spinal implant are
surgically implanted. While the spinal implants disclosed herein
can be implanted using either an anterior, posterior, or lateral
incision in the patient, a preferred method is to use a posterior
incision. Further, it is preferred that a minimally invasive
procedure be used, such as by laparoscopy in which only one or a
few, small incisions are made and the surgery is conducted with
laparoscopic tools. The methods include making an incision;
providing an embodiment of the spinal implant disclosed herein;
using a positioning tool to position the spinal implant and counter
and prestress designed into the spinal implant; and fixing the
spinal implant to two adjacent vertebrae. The surgical procedure
does not require that the disc space be distracted extensively to
install the spinal implant, thereby reducing the pain and recovery
time endured by the patient. The method optionally includes
implanting spinal implants with different characteristics, such as
different prestressed torques, for treating pathologies such as
scoliosis. Fixing the spinal implant to the vertebrae may be done
by applying straps, applying biocompatible adhesives, installing
pedicle screws, and the like, as known in the art.
[0094] Alternative methods and positions of placing the spinal
implant include locating them on the anterior side of the spine
rather than the posterior side. Spinal implants positioned to the
anterior side can be reached through an incision in the patient's
back and positioned between the transverse process of adjacent
vertebral bodies or mechanically attached to the anterior portion
of the vertebral body.
[0095] The present invention, in various embodiments, includes
providing devices and processes in the absence of items not
depicted and/or described herein or in various embodiments hereof,
including in the absence of such items as may have been used in
previous devices or processes, e.g., for improving performance,
achieving ease and/or reducing cost of implementation.
[0096] The foregoing discussion of the invention has been presented
for purposes of illustration and description. The foregoing is not
intended to limit the invention to the form or forms disclosed
herein. In the foregoing Detailed Description for example, various
features of the invention are grouped together in one or more
embodiments for the purpose of streamlining the disclosure. This
method of disclosure is not to be interpreted as reflecting an
intention that the claimed invention requires more features than
are expressly recited in each claim. Rather, as the following
claims reflect, inventive aspects lie in less than all features of
a single foregoing disclosed embodiment. Thus, the following claims
are hereby incorporated into this Detailed Description, with each
claim standing on its own as a separate preferred embodiment of the
invention.
[0097] Moreover, though the description of the invention has
included description of one or more embodiments and certain
variations and modifications, other variations and modifications
are within the scope of the invention, e.g., as may be within the
skill and knowledge of those in the art, after understanding the
present disclosure. It is intended to obtain rights which include
alternative embodiments to the extent permitted, including
alternate, interchangeable and/or equivalent structures, functions,
ranges or steps to those claimed, whether or not such alternate,
interchangeable and/or equivalent structures, functions, ranges or
steps are disclosed herein, and without intending to publicly
dedicate any patentable subject matter.
* * * * *