U.S. patent application number 12/012359 was filed with the patent office on 2008-06-05 for flexible spine stabilization systems.
Invention is credited to Eric C. Lange.
Application Number | 20080132950 12/012359 |
Document ID | / |
Family ID | 23038413 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080132950 |
Kind Code |
A1 |
Lange; Eric C. |
June 5, 2008 |
Flexible spine stabilization systems
Abstract
A spine stabilization system includes a flexible member
attachable to a portion of the spinal column. The use of components
resist loading applied by extension and rotation of the spine,
while the flexibility of the member does not subject it to the
compressive loading of the spinal column segment to which it is
attached.
Inventors: |
Lange; Eric C.; (Germantown,
TN) |
Correspondence
Address: |
KRIEG DEVAULT LLP
ONE INDIANA SQUARE, SUITE 2800
INDIANAPOLIS
IN
46204-2709
US
|
Family ID: |
23038413 |
Appl. No.: |
12/012359 |
Filed: |
February 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11411452 |
Apr 26, 2006 |
7326249 |
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12012359 |
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11030550 |
Jan 5, 2005 |
7041138 |
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11411452 |
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10682695 |
Oct 9, 2003 |
6852128 |
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11030550 |
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10078522 |
Feb 19, 2002 |
6652585 |
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10682695 |
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60272102 |
Feb 28, 2001 |
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Current U.S.
Class: |
606/246 ;
606/280; 606/70 |
Current CPC
Class: |
A61B 2017/00867
20130101; A61F 2310/00017 20130101; A61B 17/7059 20130101; A61F
2002/448 20130101; A61B 17/86 20130101; A61F 2/08 20130101; A61F
2002/0068 20130101; A61F 2310/00179 20130101; A61F 2210/0014
20130101; A61F 2002/30092 20130101; A61F 2310/00029 20130101; Y10S
606/91 20130101; A61F 2002/30914 20130101; A61F 2310/00023
20130101; A61F 2/30767 20130101; Y10S 606/914 20130101; A61F
2310/00071 20130101; A61F 2/446 20130101; A61F 2/0077 20130101;
Y10S 606/908 20130101; A61F 2/442 20130101; Y10S 606/907 20130101;
A61B 17/8085 20130101 |
Class at
Publication: |
606/246 ;
606/280; 606/70 |
International
Class: |
A61B 17/58 20060101
A61B017/58 |
Claims
1. A spinal stabilization device, comprising: a flexible member
having opposite ends spaced from one another along an axis with a
length along said axis sized for attachment between at least a
first and a second vertebrae, said flexible member including a
plurality of interwoven components, said flexible member further
including at least one grommet positioned adjacent each of said
opposite ends, said at least one grommet defining a hole for
receiving a fastener to secure said flexible member to an
underlying one of the first and second vertebrae.
2. The device of claim 1, wherein said number of interwoven
components are arranged so that no apertures are formed between
said components.
3. The device of claim 2, wherein said number of interwoven
components of said flexible member include: a number of vertically
oriented components generally paralleling said axis; and a number
of horizontally oriented components extending transversely to said
vertically oriented components.
4. The device of claim 3, wherein said number of interwoven
components of said flexible member include: a number of first and
second diagonal components extending transversely to one another,
said first and second diagonal components extending in an oblique
orientation to said axis and in an oblique orientation to said
number of vertically oriented components and in an oblique
orientation to said number of horizontally oriented components.
5. The device of claim 4, wherein said vertically and horizontally
oriented components are interwoven with one another and said
diagonally oriented components are interwoven with one another.
6. The device of claim 4, wherein said vertically, horizontally and
diagonally oriented components are interwoven with one another.
7. The device of claim 1, wherein said flexible member comprises at
least one layer including a number of square shaped apertures, said
square shaped apertures extending through said first layer with a
first pair of sides generally paralleling said axis and a second
pair of side generally orthogonally oriented to said axis.
8. The device of claim 7, wherein said flexible member further
comprises a second layer including a number of diamond shaped
apertures extending through said second layer with sides of said
diamond shaped apertures obliquely oriented to said axis.
9. The device of claim 8, wherein said at least one grommet
adjacent each of said opposite ends secure said layers to one
another.
10. The device of claim 1, wherein said components of said flexible
member are comprised of a soft fiber material.
11. The device of claim 1, wherein said opposite ends define
horizontal edges of said flexible member and said flexible member
further includes opposite vertical edges extending between said
horizontal edges, said flexible member including a corner where
each of said vertical edges joins a respective one of said
horizontal edges, said flexible member including at least one
grommet adjacent each of said corners, each of said at least one
grommets defining a hole to receive a fastener through said
flexible member to secure said flexible member to an underlying one
of the first and second vertebrae.
12. A spinal stabilization device, comprising: a flexible member
including opposite ends spaced from one another along an axis with
a length along said axis sized for attachment between at least a
first and a second vertebrae, said flexible member comprising at
least one layer of interwoven components, wherein said interwoven
components are arranged to provide a substantially solid wall
between said opposite ends.
13. The device of claim 12, wherein said flexible member comprises
a plurality of vertical components extending along said axis and a
plurality of horizontal components that are generally orthogonally
oriented to said axis and said vertical components.
14. The device of claim 13, wherein said flexible member further
comprises a plurality of diagonal components obliquely oriented to
said axis and transversely oriented to each of said vertically and
horizontally oriented components.
15. The device of claim 12, further comprising at least one grommet
positioned adjacent each of said opposite ends, said grommets each
defining a hole through said at least one layer for receiving a
fastener to secure said flexible member to an underlying one of the
first and second vertebrae.
16. The device of claim 12, wherein said flexible member is
comprised of a soft fiber material.
17. The device of claim 12, wherein said opposite ends define
horizontal edges of said flexible member and said flexible member
further includes opposite vertical edges extending between said
horizontal edges, said flexible member including a corner where
each of said vertical edges joins a respective one of said
horizontal edges, said flexible member including at least one
grommet adjacent each of said corners, each of said at least one
grommets defining a hole to receive a fastener through said
flexible member to secure said flexible member to an underlying one
of the first and second vertebrae.
18. A spinal stabilization device, comprising: a flexible member
having opposite ends spaced from one another along an axis with a
length along said axis sized for attachment between at least a
first and a second vertebrae, said flexible member including a
number of interwoven components that form a substantially solid
wall between said opposite ends, said flexible member further
including at least one grommet positioned adjacent each of said
opposite ends, said a least one grommet defining a hole for
receiving a fastener to secure said flexible member to an
underlying one of the first and second vertebrae.
19. The device of claim 18, wherein said interwoven components are
arranged so that said interwoven components form no apertures
through said flexible member.
20. The device of claim 18, wherein said flexible member comprises
a plurality of vertical components extending along said axis and a
plurality of horizontal components that are generally orthogonally
oriented to said axis and to said vertical components.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/411,452, issuing as U.S. Pat. No.
7,326,249, which is a continuation of U.S. patent application Ser.
No. 11/030,550 filed on Jan. 5, 2005, issued as U.S. Pat. No.
7,041,138; which is a continuation of U.S. patent application Ser.
No. 10/682,695 filed Oct. 9, 2003, and issued as U.S. Pat. No.
6,852,128; which is a continuation of U.S. patent application Ser.
No. 10/078,522 filed on Feb. 19, 2002, and issued as U.S. Pat. No.
6,652,585; which claims the benefit of the filing date of
Provisional Patent Application Ser. No. 60/272,102 filed on Feb.
28, 2001. Each of the referenced applications is incorporated
herein by reference in its entirety.
BACKGROUND
[0002] The present invention relates to orthopedic implants, and
more particularly, to flexible spinal stabilization systems.
[0003] Interbody fusion device, artificial discs, interbody spacers
and other devices have been inserted in a spinal disc space or
engaged to a vertebral body. For example, as shown in FIG. 1, a
pair of interbody fusion devices I1 and I2 are inserted into an
intradiscal space between the L5 and S1 levels of the spinal
column. Aorta A1 and vena cava A2 along with other tissue and
vasculature also extend along the anterior aspect of the spinal
column. As shown in FIG. 2, the anterior longitudinal ligament AL
extends along the anterior portion of the disc space. The disc
space is surrounded by annulus fibrosus or annulus fibers AF.
Insertion of implants I1 and I2 into the disc space can be
facilitated by the removal of all or a portion of the anterior
longitudinal ligament AL and the annulus fibers AF.
[0004] In order to stabilize the spinal column, it is known to
secure a rigid metal construct to each of the vertebral bodies on
either side of the spinal disc space after inserting devices or
performing surgical procedures in the disc space or on the
vertebral bodies. For example, a rigid metal plate can be placed
along the anterior aspect of the vertebrae and secured to the L5
and S1 levels after insertion of implants I1 and I2 into the disc
space therebetween. In another example, a rigid rod or plate can be
secured to the posterior portions of vertebrae V1 and V2 after
anterior insertion of implants I1 and I2.
[0005] While rigid metal constructs provide adequate load
resistance, there can be drawbacks, such as the intrusion of the
construct into the adjacent tissue and vasculature, stress
shielding, multiple surgeries for installation, and fatigue. What
are needed are systems that do not require posterior hardware to
support the spinal column or rigid anterior, antero-lateral, or
lateral plates and constructs. The systems should be resistant to
fatigue, stress shielding and tensile and rotational loads that are
typically applied to the spinal column. The present invention is
directed toward meeting these needs, among others.
SUMMARY
[0006] The present invention is directed to spine stabilization
systems that are flexible and resist loading applied by extension
and rotation of the spine, while the flexibility of the components
does not subject them to the compressive loading of the spinal
column segment to which it is secured.
DESCRIPTION OF THE FIGURES
[0007] FIG. 1 is an elevational view of a spinal column segment
having a pair of interbody fusion devices inserted into a disc
space.
[0008] FIG. 2 is a plan view of a disc space of a spinal column
segment and the surrounding tissue and vasculature.
[0009] FIG. 3 is a perspective view a spinal column segment with
its associated ligaments.
[0010] FIGS. 4(a) and 4(b) illustrate various features of a spinal
disc space.
[0011] FIGS. 5(a) and 5(b) illustrate various structural properties
of the annulus fibrosous.
[0012] FIG. 6 is a flexible spine stabilization system according to
one embodiment secured to a spinal column segment.
[0013] FIGS. 7(a) through 7(c) show various components of the
system of FIG. 6.
[0014] FIG. 8 is an elevational view of another embodiment flexible
spine stabilization system secured to a spinal column segment.
[0015] FIG. 8a is an enlarged detail view of a portion of the
system of FIG. 8.
[0016] FIG. 9 is elevational view of yet another embodiment
flexible spine stabilization system secured to a spinal column
segment.
[0017] FIG. 10(a) is an elevational view of a further embodiment
flexible spine stabilization system.
[0018] FIG. 10(b) is the system of FIG. 10(a) secured to a spinal
column segment.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0019] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
illustrated embodiments and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended. Any
such alterations and further modifications of the invention, and
any such further applications of the principles of the invention as
illustrated herein are contemplated as would normally occur to one
skilled in the art to which the invention relates.
[0020] The present invention is directed to flexible spine
stabilization systems for placement on the anterior aspect of the
vertebrae of a spinal column segment. It is contemplated the
systems may also be placed on the antero-lateral aspect or the
lateral aspect of the vertebrae. It is also contemplates that the
systems can extend across one or more vertebral levels. The systems
are configured to replicate, substitute and/or augment the
structure and function of the natural occurring fibers that protect
the intervertebral disc space. It is further contemplated that the
systems can be used in lieu of the placement of a rigid anterior
plate across one or more disc spaces after insertion of an
interbody fusion device into the disc space. It is also
contemplated that the systems can be used in non-interbody fusion
procedures.
[0021] The spine stabilization systems include a member having a
first set of one or more components oriented generally in the
direction of the annulus fibers, and a second set of components
oriented generally in the direction of the fibers of the anterior
longitudinal ligament. The use of components having such
orientations provides resistance to loading applied by extension,
lateral bending, and rotation of the spine. The flexibility of the
member does not subject it to stress shielding caused by the
compressive loading of the spinal column segment to which it is
secured. Thus, the spine stabilization systems of the present
invention replicate, augment and/or substitute the load resistant
properties capabilities of the annulus fibers and anterior
longitudinal ligament.
[0022] Further description of flexible spinal stabilization systems
is provided after the following discussion of the anatomical
features of the annulus and anterior longitudinal ligament.
Referring now to FIG. 3, a spinal column segment including an upper
vertebra V1 and lower vertebra V2 is illustrated. The spinal column
segment includes anterior longitudinal ligament AL extending along
the anterior aspects of vertebra V1 and vertebra V2 and across the
intervertebral disc space between vertebrae V1 and V2. The nucleus
of the disc space is protected by annulus fibers AF. The spinal
column segment further includes posterior longitudinal ligament PL,
intertransverse ligament IL, facet capsular ligament FC,
interspinous ligament ISL, superspinous ligament SSL, and
ligamentum flavum LF. The spine is designed in such a way that when
the functional spinal unit is subjected to different complex force
and torque vectors, the individual ligaments provide tensile
resistance to external loads by developing tension. When a surgical
procedure interrupts or removes a portion of these ligaments, the
ability of the spinal unit to resist these complex force and torque
vectors is compromised.
[0023] The anterior longitudinal ligament AL is an uni-axial
structure, and is most effective in carrying loads along the
direction in which the fibers run. The anterior longitudinal
ligament AL has a fibrous tissue structure that arises from the
anterior aspect of the basioccipital and is attached to the atlas
and the anterior surfaces of all vertebrae, down to and including a
part of the sacrum. It is firmly attached to the edges of the
vertebral bodies, but is less firmly affixed to the annulus fibers
AF. The width of the anterior longitudinal ligament AL diminishes
at the level of disc and is narrower and thicker in the thoracic
region of the spine. The fibers of the anterior longitudinal
ligament run along the length of the spinal column in the direction
of the central spinal column axis and transverse to axial plane H.
The fibers of the anterior longitudinal ligament AL are much like
rubber bands in that they readily resist tensile forces, but buckle
when subjected to compressive forces.
[0024] Referring now to FIGS. 4(a) and 4(b), further properties of
the spinal disc space D will be discussed. The nucleus pulposus N
of the disc space is surrounded by the annulus fibrosus AF. The
annulus fibrosus AF includes a number of concentric laminated
bands, designated as annulus laminates AN1, AN2, AN3, and AN4 as
shown in FIG. 4(a). As shown further in FIG. 4(b), these annulus
laminates AN have fibers oriented either +30 degrees or -30 degrees
with respect to axial plane H of the spinal column. Stated another
way, the AN fibers are oriented about +60 degrees or about -60
degrees with respect to the fibers of the anterior longitudinal
ligament AL. The fibers of the adjacent annulus laminates AN are
non-orthogonal with respect to axial plane H and to one another,
forming a criss-cross pattern as shown by AN1 and AN2 of FIG. 2(b).
When interbody fusion devices or other implants are inserted
between the vertebrae, or when the disc space is access for
surgical procedures, the resection, removal and other cutting
required of the annulus laminates AN and anterior longitudinal
ligament AL disrupts fiber orientation and continuity.
[0025] Referring now to FIGS. 5(a) and 5(b), the tensile properties
and strength properties of the annulus fibrosis will now be
discussed. The annulus fibers AF resist tensile forces and torque
or rotational forces applied to the spinal column segment. In FIG.
5(a), the tensile stiffness of the annulus AF in different
directions is shown. The stiffness of annulus fibrosus AF is
highest along a direction oriented 15 degrees with respect to axial
plane H. In FIG. 5(b), the strength of the annulus AF has been
found to be greatest along a direction oriented 30 degree with
respect to horizontal axis H extending through the disc space. It
has further been found that the strength of the annulus AF is three
times greater along this 30 degree axis as compared to the strength
along axial plane H.
[0026] Referring now to FIG. 6, a spine stabilization system 20 is
illustrated. System 20 is secured to vertebra V1 and vertebra V2
and extends across the disc space D. It is contemplated that one or
more interbody fusion devices, interbody spacers, artificial discs
or other implant can be inserted into disc space D in a procedure
prior to attachment of system 20 to vertebrae V1 and V2. It is also
contemplated that a surgical procedure can be performed in or on
disc space D such as, for example, removal of discal material to
repair a herniated disc. In such procedures, the excision or
disruption to the annulus fibrosus AF and the anterior longitudinal
ligament AL compromises the ability of these spinal structures to
resist extension, torsion, and lateral bending of the spinal
column. System 20 can restore this ability and can cover the entry
made through the annulus fibrosis AF and anterior longitudinal
ligament AL, preventing devices inserted into the disc space from
backing out or protruding through the created opening.
[0027] System 20 includes diagonal components and vertical
components. The diagonal components can be oriented in the range of
15 degrees to 60 degrees with respect to axial plane H when the
devices are secured to the vertebrae. The vertical components
extend generally perpendicular to axial plane H. Stated another
way, a first set of diagonal components extends at an angle A1 in
the range of +30 degrees to +75 degrees relative to the vertical
components, and a second set of diagonal components extends
transverse to the first set and at an angle A2 in the range of -30
degrees to -75 degrees relative to the vertical components. In
another form, the first set of diagonal components extends at an
angle A1 in the range of +45 degrees to +60 degrees relative to the
vertical components, and the second set of diagonal components
extends transverse to the first set and at an angle A2 in the range
of -45 degrees to 60 degrees relative to the vertical components.
In a further form, the first set of diagonal components extends at
an angle A1 of about +60 degrees relative to the vertical
components, and the second set of diagonal components extends
transverse to the first set and at an angle A2 of about -60 degrees
relative to the vertical components.
[0028] Referring now to FIGS. 7(a) through 7(c), there are shown
various components of system 20. System 20 includes a member
extending between the first and second vertebrae V1 and V2. The
member includes a first layer 30 which has a number of vertically
oriented components 34 and a number of horizontally oriented
components 32. Components 32, 34 are interwoven or otherwise
attached to form a grid-like or mesh pattern having a number of
square apertures therethrough. The member further includes a second
layer 35 as shown in FIG. 7(b) having a number of first diagonal
components 36 and a number of second diagonal components 38.
Diagonal components 36 and 38 are interwoven or otherwise attached
to form a grid-like or mesh pattern having a number of
diamond-shaped apertures. Each layer 30, 35 is flexible in
compression yet inelastic or substantially inelastic to resist
tensile loading.
[0029] The individual components 32, 34, 36, 38 of each layer can
be made from a small diameter or cross-section wire, fiber, rod,
strand or other elongated component. As shown in FIG. 7(c), first
layer 30 is placed on top of second layer 35 and secured thereto
via grommets 26. Other securement devices and techniques are also
contemplated, including, for example, other fasteners such as
rivets, clamps, cables, sutures, staples, and hooks; and
chemical/thermal bonding, such as welding or adhesives. Other
embodiments contemplate that layers 30, 35 are not engaged to one
another, but rather simply placed on top of one another when
secured to the spinal column.
[0030] A number of openings 24 are formed through the layers to
accommodate fasteners 22. In the illustrated embodiment, four such
openings are formed, with one opening positioned adjacent each
corner. Eyelets or grommets 26 extend around each hole 24. As shown
in FIG. 6, bone engaging fasteners 22 can be placed through
corresponding ones of the holes 24 to secure layers 30, 35 to
vertebrae V1 and V2. The corners of layers 30, 35 can be rounded to
provide gradual transitions between the vertical and horizontal
edges thereof. Other embodiments contemplate one opening 24 at each
vertebra, and further embodiments contemplate more than two
openings 24 at each vertebra. Other embodiments also contemplate
that no openings are provided, but rather the fasteners extend
directly through the layers of material.
[0031] The vertically extending components 34 of first layer 30 are
oriented and function in a manner similar to the longitudinal
fibers of the anterior longitudinal ligament AL. Diagonal
components 36, 38 of second layer 35 are non-orthogonally oriented
with respect to the vertical components 34, and are oriented and
function similar to annulus fibers AF. Thus, system 20 replaces,
substitutes, and/or augments the function of the naturally
occurring fibers of the anterior longitudinal ligament AL and the
annulus fibrosis AF. The orientation of the components of system 20
are such that forces caused by extension, rotation, and lateral
bending of the spinal column are resisted in a manner the same as
or similar to the natural occurring anatomical structures provided
to resist such forces.
[0032] Referring to FIGS. 8 and 8a, there is provided a spine
stabilization system 40 having a layer 46. Layer 46 includes a
number of interwoven components that include at least
longitudinally and diagonally oriented components. In the
illustrated embodiment, there are provided first diagonal
components 47, second diagonal components 48, vertical components
49, and horizontal components 45. The first and second diagonal
components 47, 48 are oriented and function similar to the fibers
of the annulus fibrosis AF, and the vertical components 49 are
oriented and function similar to the anterior longitudinal ligament
AL. Small apertures are provided through layer 46 between its
components. Eyelets or grommets 44 each surround a corresponding
one of the holes provided through layer 46. Bone engaging fasteners
42 extend through these holes to attach system 40 to vertebra V1
and vertebra V2.
[0033] Referring now to FIG. 9, there is shown another embodiment
spine stabilization system 50. The components of system 50 are
diagonally and vertically oriented to replicate the orientation of
the fibers of the anterior longitudinal ligament AL and annulus
fibers AF. System 50 includes a member formed by a layer 56 made
from components interwoven such that there are no apertures through
layer 56, providing a substantially solid wall across disc space D.
Layer 56 includes a number of holes formed therethrough surrounded
by grommets or eyelets 54. Fasteners 52 extend through the holes in
order to secure the flexible system 50 to vertebra V1 and V2 across
the annulus fibrosis AF.
[0034] Referring now to FIG. 10(a), another embodiment spine
stabilization system 60 is illustrated. System 60 includes member
having a first vertical component 66 and a second vertical
component 68. Vertical components 66 and 68 are interconnected by a
first diagonal component 70 and a second diagonal component 72. As
shown in FIG. 10(b), first diagonal component 70 extends from a
right lateral side of vertebral body V2 across the sagittal plane L
to a left lateral side of vertebral body V1. Second diagonal
component 72 extends from the left lateral side of vertebral body
V2 across the sagittal plane L to the right lateral side of
vertebral body V1. The first vertical component 66 extends from a
left lateral side of vertebral body V2 to the left lateral side of
vertebral body V1 offset to one side of sagittal plane L. Second
vertical component 68 extends from the right lateral side of
vertebral body V2 to the right lateral side of vertebral body V1
offset to the other side of sagittal plane L. In each corner of
system 60 there is formed a hole 64 for receiving a fastener 62 to
attach system 60 to vertebrae V1 and V2.
[0035] The vertically oriented components 66, 68 are oriented to
replace, substitute and/or augment the structure function of the
anterior longitudinal ligament AL and resist at least extension
forces applied to the spinal column segment. The diagonal
components 70, 72 are non-orthogonally oriented with respect to the
vertically oriented components 66, 68 and resist at least
rotational and torque forces on the spinal column segment. Thus,
diagonal components 70, 72 are oriented and function similar to the
fibers of the annulus fibrosis AF.
[0036] The components of the flexible spinal stabilization systems
can be made from one or a combination of metal material, polymeric
material, ceramic material, shape memory material, and composites
thereof. The components of the systems can also be coated or
impregnated with anti-adhesive material that will prevent tissue
and vasculature from attaching thereto. The components of the
systems can be provided in multiple layers each including one or
more components with the desired orientation and placed one on top
of the other, or the components can be provided in a single
interwoven layer that includes the desired component
orientation.
[0037] In one specific embodiment, the components are made from
metal wire mesh of suitable tensile strength and which is not
subject to substantial creep deformation or in vitro degradation.
It is contemplated that the wire can be made from stainless steel,
cobalt-chrome alloy, titanium, titanium alloy, or nickel-titanium,
among others.
[0038] In another specific embodiment, the components are made from
a soft fiber material. Soft fiber material can include polymeric
material, such as SPECTRA fiber, nylon, carbon fiber and
polyethylene, among others. Examples of suitable metal polymers
include DACRON and GORE-TEX. One advantage provided by a soft fiber
design is that the risk of tissue and vascular injury is further
mitigated by reducing the abrasive qualities of the component
material. A further advantage is that the components fibers can be
radiolucent, allowing radiographic imaging for assessment and
monitoring of the disc space and any implant, fusion devices, or
artificial disc inserted therein. Another advantage is that some
polymeric materials, such as spectra fiber, can be stronger than
metals and less susceptible to fatigue or creep.
[0039] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that the preferred embodiments have been shown and
described, and that all changes and modifications that come within
the spirit of the invention are desired to be protected.
* * * * *