U.S. patent application number 11/770802 was filed with the patent office on 2009-01-01 for spinous process spacer hammock.
Invention is credited to Michael Fisher, John Riley Hawkins, Michael J. O'Neil, Hassan Serhan, Michael Andrew Slivka.
Application Number | 20090005873 11/770802 |
Document ID | / |
Family ID | 40161529 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090005873 |
Kind Code |
A1 |
Slivka; Michael Andrew ; et
al. |
January 1, 2009 |
Spinous Process Spacer Hammock
Abstract
An interspinous spacer comprising: a) a first brace having an
upper throughhole and a lower throughhole, b) a second brace having
an upper throughhole and a lower throughhole, c) a ligament having
a first end and a second end, wherein the ligament extends from the
upper throughhole of the first brace through the upper throughhole
of the second brace.
Inventors: |
Slivka; Michael Andrew;
(Taunton, MA) ; O'Neil; Michael J.; (West
Barnstable, MA) ; Serhan; Hassan; (South Easton,
MA) ; Fisher; Michael; (Middleboro, MA) ;
Hawkins; John Riley; (Cumberland, RI) |
Correspondence
Address: |
PHILIP S. JOHNSON;JOHNSON & JOHNSON
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
08933-7003
US
|
Family ID: |
40161529 |
Appl. No.: |
11/770802 |
Filed: |
June 29, 2007 |
Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61B 17/8869 20130101;
A61B 2017/681 20130101; A61B 17/7062 20130101; A61B 17/7053
20130101; A61B 17/7068 20130101 |
Class at
Publication: |
623/17.16 |
International
Class: |
A61F 2/44 20060101
A61F002/44; A61B 17/58 20060101 A61B017/58 |
Claims
1. An interspinous spacer comprising: a) a first brace having an
upper throughhole and a lower throughhole, b) a second brace having
an upper throughhole and a lower throughhole, c) a ligament having
a first end and a second end, wherein the ligament extends from the
upper throughhole of the first brace through the upper throughhole
of the second brace.
2. The spacer of claim 1 wherein the ligament extends from the
upper throughhole of the second brace through the lower throughhole
of the second brace.
3. The spacer of claim 2 wherein the ligament extends from the
lower throughhole of the second brace through the lower throughhole
of the first brace.
4. The spacer of claim 3 wherein the first end of the ligament is
in mechanical connection with the second end of the ligament
between the upper throughhole and a lower throughhole of the first
brace.
5. The spacer of claim 1 wherein the ligament has a cross-section
having a height and a width, wherein the width is greater than the
height.
6. The spacer of claim 1 further comprising: d) a ligament
tensioning element.
7. The spacer of claim 6 wherein the ligament tensioning element
comprises a wheel around which the ligament is wound as the wheel
is turned, thereby creating tension in the ligament.
8. The spacer of claim 7 wherein the wheel comprises a locking
element.
9. The spacer of claim 6 further comprising e) a sleeve placed over
a portion of the ligament.
10. The spacer of claim 6 wherein the ligament tensioning element
comprises a crimpable sleeve.
11. A method of implanting an interspinous implant, comprising the
steps of: a) implanting a first brace having an upper throughhole
and a lower throughhole on a first side of a spinous process, b)
implanting a second brace having an upper throughhole and a lower
throughhole on a second side of the spinous process, c) passing a
ligament from the upper throughhole of the first brace through the
upper throughhole of the second brace.
12. The method of claim 11, further comprising the step of: d)
passing the ligament from the upper throughhole of the second brace
through the lower throughhole of the second brace.
13. The method of claim 12, further comprising the step of: e)
passing the ligament from the lower throughhole of the second brace
through the lower throughhole of the first brace.
14. The method of claim 12, further comprising the step of: f)
mechanically connecting a first end of the ligament with a second
end of the ligament between the upper throughhole and a lower
throughhole of the first brace.
15. The method of claim 11 wherein the first brace is implanted
through a first incision on the first side of the spinous process,
and the second first brace is implanted through the first
incision.
16. The method of claim 11 wherein the first brace is implanted
through a first incision on the first side of the spinous process,
and the second first brace is implanted through a second incision
on the second side of the spinous process.
17. An interspinous spacer comprising: a) a first brace having an
upper end portion and a lower end portion, b) a second brace having
an upper end portion and a lower end portion, c) an upper ligament
having a first end and a second end, d) a lower ligament having a
first end and a second end, wherein the upper ligament connects the
upper end portion of the first brace to the upper end portion of
the second brace, and wherein the lower ligament connects the lower
end portion of the first brace to the lower end portion of the
second brace.
18. The spacer of claim 17 wherein each of the first and second
braces further comprises an intermediate portion, and wherein the
spacer further comprises a distance adjustment element attached to
each of the intermediate portions.
19. The spacer of claim 18 wherein the distance adjustment element
comprises a threaded rod.
20. The spacer of claim 19 wherein the intermediate portion of each
brace has a threaded hole adapted for threaded mating with the
threaded rod.
21. The spacer of claim 20 wherein a first threaded hole is
threaded in a first direction and a second threaded hole is
threaded in a second opposite direction.
22. The spacer of claim 17 further comprising e) a sleeve placed
over a portion of the upper ligament.
Description
BACKGROUND OF THE INVENTION
[0001] Patients suffering from low back or leg pain frequently have
stenosis of the vertebral and/or neural foramen that constricts
their spine-related nerves. It has been shown that applying
traction to the spinous processes may alleviate this pain and
several devices have been developed that accomplish this. However,
many of these devices are either difficult to implant, do not stay
in place, or wear away the bone of the spinous process due to poor
conformance of the device.
[0002] US Published Patent Application No. US20060122620 ("Kim I")
discloses a posterior element distraction system for implantation
at a spinal motion segment comprising a superior vertebra, an
inferior vertebra, each vertebra comprising a posterior element
comprising a spinous process, laminal portions and a set of facet
joints, and further comprising an interspinous space between the
spinous processes, the system comprising: at least one lateral
member for positioning on a side of the spinal motion segment and
outside the interspinous space, wherein the at least one lateral
member has an unexpanded configuration and an expanded
configuration; and first and second transverse members extending
transversely from the at least one lateral member, wherein when the
system is operatively implanted at a spinal motion segment and the
at least one lateral member is in an expanded configuration, the
transverse members are caused to contact a portion of either the
superior or inferior posterior elements thereby providing
distraction between the superior and inferior posterior
elements.
[0003] US Published Patent Application No. US20060085070 (Kim II)
discloses a device for stabilizing at least one spinal motion
segment comprising a first vertebra having a first spinous process
and a second vertebra having a second spinous process, the device
comprising: an undeployed configuration having an axial dimension
and a radial dimension substantially transverse to the axial
dimension; and a deployed configuration having an axial dimension
and a radial dimension substantially transverse to the axial
dimension; wherein the radial dimension of the undeployed
configuration is less than the radial dimension in the deployed
configuration.
[0004] US Published Patent Application No. 2005-0203512 ("Hawkins")
discloses an interspinous implant for insertion into an
interspinous space between a first and second spinous process, the
first spinous process having a first and second side, the implant
comprising: a) a first base having a side surface adapted for
fixation to a first side of the first spinous process, b) a second
base having a side surface adapted for fixation to a second side of
the first spinous process, c) a first flexible ligament having a
first end connected to the first base and a second end connected to
the second base.
[0005] U.S. Pat. No. 6,582,433 (Yun) discloses a device and method
that immobilizes the vertebral bodies by immobilizing the
respective spinous process extending therefrom. The device contains
a spacer extending from a body with the spacer adapted to be
positioned between adjacent spinous processes so that the spacer
may be located close to the spine. A strap connected with the body
is designed to engage the spinous processes, such that the device
may be adjusted to be positioned about the spinous processes. The
device ensures that the spacer remains positioned between adjacent
spinous processes. The method to insert the device minimizes
destruction to body tissue, thus it is less traumatic to the
patient and allows for the patient to recover from the procedure
faster than conventional methods.
[0006] It is an object of the present invention to provide an
interspinous spacer that is easy to implant, remains in place after
it is implanted, and whose excellent conformance to the adjacent
spinous processes prevents wearing away of the adjacent spinous
processes during use.
SUMMARY OF THE INVENTION
[0007] In a first embodiment of the present invention, there is
provided an interspinous spacer that comprises a flexible strap or
ligament that is threaded through two slotted plates positioned on
either side of the spinous processes and a means for tensioning the
strap and holding it in place once the desired distraction has been
achieved. Distraction of the spinous processes is achieved by
locating the slots on the straps such that the distance between the
slots on each plate is larger than the distance between the spinous
processes. Adjustable distraction of the spinous processes may also
be achieved by varying the level of tension in the strap.
Increasing the level of tension in the strap increases the
distraction of the spinous processes (up to the distance between
the upper and lower throughholes), while decreasing the level of
tension decreases the distraction. In addition, as the ligament is
tensioned, the two braces automatically become snugly opposedly
positioned against the sides of the spinous processes, thereby
helping to keep the device from migrating during use.
[0008] In another embodiment, the spacer comprises two straps or
ligaments, one located at the cranial and one at the caudal
portions of the device, with each strap being fixed to the
respective inner surfaces of two plates positioned on opposing
sides of the spinous processes. For this embodiment, there is
preferably a centrally located distance adjustment element that
connects the two plates and may be adjustable in a medial-lateral
direction such that the adjustment changes the tension of the
straps and thereby enables distraction of the spinous processes. In
one preferred embodiment, the central distance adjustment element
is a threaded rod and the plates have threaded holes for mating
with the threaded rod. Preferably, the opposed holes are threaded
in the opposite direction (right hand versus left hand threads)
such that upon turning the threaded rod, the plates will move
either away from each other or towards each other, thus either
tightening or loosening the strap.
DESCRIPTION OF THE FIGURES
[0009] FIG. 1 discloses a first embodiment of the interspinous
spacer of the present invention.
[0010] FIGS. 2a-2f disclose a method of implanting the spacer of
FIG. 1.
[0011] FIG. 3 discloses a preferred first embodiment of the
interspinous spacer of the present invention.
[0012] FIG. 4 discloses a second embodiment of the interspinous
spacer of the present invention.
[0013] FIG. 5 discloses an embodiment of the present invention
having a transverse bolt.
[0014] FIG. 6 discloses an embodiment of the present invention
having a prosthetic ligament connecting to each plate and extending
up and over the upper spinous process.
[0015] FIG. 7 discloses an embodiment of the present invention
having two J-shaped plates.
[0016] FIG. 8 discloses a crimp block revision tool of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Now referring to FIG. 1, there is provided an interspinous
spacer comprising: [0018] a) a first brace 1 having an upper
throughhole 3 and a lower throughhole 5, [0019] b) a second brace
11 having an upper throughhole 13 and a lower throughhole 15,
[0020] c) a ligament 21 having a first end 23 and a second end 25,
wherein the ligament extends from the upper throughhole of the
first brace through the upper throughhole of the second brace, then
through the lower throughhole of the second brace, then through the
lower throughhole of the first brace, and wherein the first end of
the ligament is in mechanical connection with the second end of the
ligament between the upper throughhole and a lower throughhole of
the first brace.
[0021] Now referring to FIGS. 2a-2f, the spacer is assembled in
situ as follows: First, and now referring to FIG. 2a, the ligament
is drawn through each of the upper and lower holes of a first
brace, with each end of the ligament exiting the respective holes
in the same direction. Next, and now referring to FIG. 2b, the
ligament and brace combination is inserted on a first side of the
spine, is passed through the space between adjacent spinous
processes SP and exits on the second side of the spine. The first
brace is then oriented so that the portion of the ligament that
runs between the holes of the first brace is located on the outer
face 7 of the first brace, while the inner face 9 abuts the spinous
processes.
[0022] Next, if needed, each end of the ligament is passed back
through the space between the adjacent interspinous processes and
extended back into the first half of the spine.
[0023] Next, and now referring to FIG. 2c, one end of the ligament
is passed through the upper throughhole of the second brace, while
the second end of the ligament is passed through the lower
throughhole of the second brace. Each end of the ligament enters
its respective throughhole from the same inner face 19 of the
second brace.
[0024] Next, and now referring to FIG. 2d, the second brace is then
inserted into the first half of the spine and oriented so that its
inner face 19 abuts the spinous processes, and the ends of the
ligament are closer to the outer face 17 of the second brace.
[0025] Next, and now referring to FIG. 2e, the respective end
portions of the ligament are then pulled in unison so as to create
tension in the ligament and thereby cause distraction of the upper
and lower spinous processes. Since the distance D between the upper
and lower slots on each plate (shown in FIG. 2c) is larger than the
gap G between the spinous processes (shown in FIG. 2c), distraction
is achieved when the ligament is tensioned.
[0026] Lastly, and now referring to FIG. 2f, the respective end
portions of the ligament are then mechanically connected by a
connection means 27 (such as a crimpable tube) to make a permanent
and continuous loop that extends through each of the upper and
lower throughholes of each brace.
[0027] Therefore, in accordance with the present invention, there
is provided a method of implanting an interspinous implant,
comprising the steps of: [0028] a) implanting a first brace having
an upper throughhole and a lower throughhole on a first side of a
spinous process, [0029] b) implanting a second brace having an
upper throughhole and a lower throughhole on a second side of the
spinous process, [0030] c) passing a ligament from the upper
throughhole of the first brace through the upper throughhole of the
second brace, [0031] d) passing the ligament from the upper
throughhole of the second brace through the lower throughhole of
the second brace, [0032] e) passing the ligament from the lower
throughhole of the second brace through the lower throughhole of
the first brace, and [0033] f) mechanically connecting a first end
of the ligament with a second end of the ligament between the upper
throughhole and a lower throughhole of the first brace.
[0034] In some embodiments, the first brace is implanted through a
first incision on the first side of the spinous process, and the
second first brace is implanted through the first incision. In some
embodiments, the first brace is implanted through a first incision
on the first side of the spinous process, and the second first
brace is implanted through a second incision on the second side of
the spinous process.
[0035] In one preferred embodiment, the means for tensioning the
strap comprises a wheel around which the strap can wind as the
wheel is turned, thus creating the tension in the strap. The wheel
may be either a part of the implant or a part of an instrument.
[0036] Once the desired distraction is achieved, the position may
be locked in place either by locking the wheel (in the case where
the wheel is part of the implant) or by securing a blocking member
on the strap. One such blocking member could be a metallic sleeve
that is crimped into place, or a hardenable polymer formed in
place. In some embodiments, the strap may be crimped and then glued
in place. In other embodiments, the strap may be tied and then
glued in place.
[0037] Now referring to FIG. 3, there is provided an interspinous
spacer comprising: [0038] a) a first brace 31 having an upper
throughhole 33, a lower throughhole 34, an intermediate section 35,
and a wheel 36 and a crimpable tube 37 each mechanically connected
to the intermediate section [0039] b) a second brace 39 having an
upper throughhole 41 and a lower throughhole 43, [0040] c) a
ligament 45 having a first end 47 and a second end 49, wherein the
ligament extends from the wheel through upper throughhole of the
first brace, through the upper throughhole of the second brace,
then through the lower throughhole of the second brace, then
through the lower throughhole of the first brace, and into the
crimpable tube.
[0041] Now referring to FIG. 4, there is provided an interspinous
spacer comprising: [0042] a) a first brace 51 having an upper end
portion 53, a lower end portion 55, and an intermediate portion 57,
[0043] b) a second brace 61 having an upper end portion 63, a lower
end portion 65 and an intermediate portion 67, [0044] c) a distance
adjustment element 71 connected to each of the intermediate
portions, [0045] d) an upper ligament 81 having a first end 83 and
a second end 85, [0046] e) a lower ligament 91 having a first end
93 and a second end 95, wherein the upper ligament connects the
upper end portion of the first brace to the upper end portion of
the second brace, and wherein the lower ligament connects the lower
end portion of the first brace to the lower end portion of the
second brace.
[0047] Preferably, the distance adjustment element comprises a
threaded rod 73 having a first end 75 threaded in one direction and
a second end 77 threaded in a second direction, and the
intermediate portion of each brace has a threaded hole 59, 69
adapted for threaded mating with the threaded rod. More preferably,
a first threaded hole is threaded in a first direction while a
second threaded hole is threaded in a second opposite
direction.
[0048] In use, the device of FIG. 4 is implanted so that the first
brace is located on a first side of the spinous processes, the
second brace is located on a second side of the spinous processes,
and the distance adjustment element is located in the gap between
the spinous processes. The distance adjustment element is then
actuated to decrease the distance between the braces. As the
distance between the braces decreases, the two braces automatically
become snugly opposedly positioned against the spinous processes,
thereby helping to keep the device from migrating during use. As
the distance increases, the two ligaments automatically become
tensioned and press against the inner portion of the spinous
processes, thereby causing distraction.
[0049] Preferably, when the strap or ligament contacts the spinous
process, it is relatively wide in the anterior-posterior direction
to maximize contact with the spinous processes, thus minimizing
stress risers and thereby the potential wear of the strap or the
bone. Thus, the strap preferably has a cross-section having a
height and a width, wherein the width is greater than the height.
Additionally, a protective guard may be placed over the contacting
portions of the spinous processes in order to minimize this wear.
Alternatively, a protective sleeve may be placed over the strap in
the region where it interfaces with the bone. Also, the strap is
preferably constructed of a wear-resistant material such as
ultra-high molecular weight polyethylene. Other biocompatible
materials may be used as well, including polyethylene
terephthalate, polyetheretherketone (PEEK), polyurethane, or
bioabsorbable materials such as poly(L-lactic acid), poly(glycolic
acid) and other biocompatible materials known in the art. The strap
may be constructed by weaving, braiding or knitting fibers or fiber
bundles into a typical fabric form. In one preferred embodiment, a
three-dimensional weaving pattern is used to create a thin and wide
strap.
[0050] In some embodiments, more than one strap may be used. The
straps may also be made of metal or elastormeric. They can be rigid
or flexible. They can be made of a fabric or non-fabric material.
They may comprise a belt, a weave, a composite or a laminate.
[0051] Some embodiments of the present invention may comprises a
belted strap. An alternative embodiment to a woven or braided
fabric ligament would be a composite or homogeneous belt of
material. Similar to an automotive belt that uses grooves or ribs
of material to help transfer load, the belted strap could use
composite internal materials, potting compounds, or external
surface features to enhance system performance. For example, a
composite belted ligament could have a layer of steel or Kevlar.TM.
material that would help to prevent material creep. Similarly,
surface features on the belt could articulate with the spinous
processes to prevent device migration or assist device
placement.
[0052] As noted above, the device of the present invention may
comprise multiple ligaments. There are many benefits to having
multiple ligaments in the device of the present invention. One
ligament with a cross-sectional width that is significantly larger
in dimension than its cross-sectional thickness constrains the
width of the ligament relative to the side plate width. For a plate
where the ligament passes through a through-hole, the plate must be
wider than the ligament unless it is acceptable to compress or fold
the ligament where it passes through the plate. Another benefit to
incorporating a plurality of ligaments between the side plates is
redundancy. If one ligament within the plurality fails, the other
ligaments can assume the load. Multiple ligaments can travel
multiple pathways from one side plate to the other side plate--much
like a traditional hammock. This splay of ligaments can enable the
mechanical load to be spread over a larger area of the spinous
process. A splay of ligaments may also allow for differential
tightening between the ligaments. Differential tightening can be
used to preferentially load bone at different regions of the
spinous process. For example, three ligaments could be applied
where the majority of the load is carried on the first and last
ligaments and the middle ligament is only used in a modest
capacity. Some degree of bone resorption and ligament settling can
be expected. The first and third ligaments would create slight
depressions in the local bone due to overload and subsequent
Wolff's Law remodeling. This overload would be resolved by the
second central ligament assuming more load during the settling. A
positive consequence of this arrangement is that the device is now
positively fixed in place between the spinous processes due to the
remodeled bone depressions that prevent device migration. A
multiplicity of ligaments might also mitigate the consequences of
this situation by "over-loading" some ligaments with the
expectation that they will cause bone resorption while the other
ligaments osseo-integrate and assume a more "natural" load bearing
status. Multiple smaller ligaments of material are easier to handle
from a surgical perspective than one large strap or belt of
material. Smaller ligaments would be more akin to traditional
sutures. Multiple ligaments can be tied-off like sutures, and
systems for fixing the ultimate length of these small ligaments is,
again, more akin to the systems used to fix the length of
traditional braided suture materials.
[0053] The plates are preferably constructed of biocompatible,
wear-resistant materials known in the art such as titanium,
stainless steel, PEEK, or carbon fiber-reinforced PEEK. The plates
may be constructed such that they provide some flexibility once
implanted--by either using more flexible materials such as PEEK, or
making the plates sufficiently thin to allow for some flexing. For
embodiments where the strap threads through the plates, the slots
or holes in the plate preferably have rounded edges to prevent wear
of the strap on the plate.
[0054] In preferred embodiments, each plate is manufactured from a
material that possesses the desirable strength and stiffness
characteristics for use as an interspinous spacer. The plates of
the present invention may be made from any non-resorbable material
appropriate for human surgical implantation, including but not
limited to, surgically appropriate metals, and non-metallic
materials, such as carbon fiber composites, polymers and
ceramics.
[0055] The plates can be made of any structural biocompatible
material including non-resorbable polymers (CFRP, PEEK, UHMWPE),
resorbables (such as PLA, PLGA, PGA), metallics (SS, Ti-6Al-4V,
CoCr,) and ceramics. The plate material is preferably selected from
the group consisting of metal and composite (such as PEEK/carbon
fiber).
[0056] If a metal is chosen as the material of construction for a
component, then the metal is preferably selected from the group
consisting of titanium, titanium alloys (such as Ti-6Al-4V), chrome
alloys (such as CrCo or Cr--Co--Mo) and stainless steel.
[0057] The plate component may have teeth; porous beaded surfaces
to encourage bony ingrowth; or fixation features on the ingrowth
surfaces to prevent device migration.
[0058] If a polymer is chosen as a material of construction for a
component, then the polymer is preferably selected from the group
consisting of polyesters, (particularly aromatic esters such as
polyalkylene terephthalates, polyamides; polyalkenes; poly(vinyl
fluoride); PTFE; polyarylethyl ketone PAEK; and mixtures
thereof.
[0059] If a ceramic is chosen as the material of construction for a
component, then the ceramic is preferably selected from the group
consisting of alumina, zirconia and mixtures thereof. It is
preferred to select an alumina-zirconia ceramic, such as BIOLOX
delta.TM., available from CeramTec of Plochingen, Germany.
[0060] In some embodiments, the first plate consists essentially of
a metallic material, preferably a titanium alloy or a chrome-cobalt
alloy. In some embodiments, the second plate consists essentially
of the same metallic material as the first plate.
[0061] In some embodiments, the components are made of a stainless
steel alloy, preferably BioDur.RTM. CCM Plus.RTM. Alloy available
from Carpenter Specialty Alloys, Carpenter Technology Corporation
of Wyomissing, Pa.
[0062] The plates may be rigid or flexible.
[0063] In some embodiments, the plates are made from a composite
comprising carbon fiber. Composites comprising carbon fiber are
advantageous in that they typically have a strength and stiffness
that is superior to neat polymer materials such as a polyarylethyl
ketone PAEK. In some embodiments, each plate is made from a polymer
composite such as a PEKK-carbon fiber composite.
[0064] Preferably, the composite comprising carbon fiber further
comprises a polymer. Preferably, the polymer is a polyarylethyl
ketone (PAEK) or polyphenylene. More preferably, the PAEK is
selected from the group consisting of polyetherether ketone (PEEK),
polyether ketone ketone (PEKK) and polyether ketone (PEK). In
preferred embodiments, the PAEK is PEEK.
[0065] In some embodiments, the carbon fiber comprises between 1
vol % and 60 vol % (more preferably, between 10 vol % and 50 vol %)
of the composite. In some embodiments, the polymer and carbon
fibers are homogeneously mixed. In others, the material is a
laminate. In some embodiments, the carbon fiber is present in a
chopped state. Preferably, the chopped carbon fibers have a median
length of between 1 mm and 12 mm, more preferably between 4.5 mm
and 7.5 mm. In some embodiments, the carbon fiber is present as
continuous strands.
[0066] In especially preferred embodiments, the composite
comprises: [0067] a) 40-99% (more preferably, 60-80 vol %)
polyarylethyl ketone (PAEK), and [0068] b) 1-60% (more preferably,
20-40 vol %) carbon fiber, wherein the polyarylethyl ketone (PAEK)
is selected from the group consisting of polyetherether ketone
(PEEK), polyether ketone ketone (PEKK) and polyether ketone
(PEK).
[0069] In some embodiments, the composite consists essentially of
PAEK and carbon fiber. More preferably, the composite comprises
60-80 wt % PAEK and 20-40 wt % carbon fiber. Still more preferably,
the composite comprises 65-75 wt % PAEK and 25-35 wt % carbon
fiber.
[0070] In some embodiments, the holes of the plates may be replaced
by positive features such as rungs, that can help anchor the
ligament.
[0071] In some embodiments, the device of the present invention
contains extra features that insure that the device stays in place
when set against the spinous processes. FIG. 5 discloses an
embodiment of the present invention having a transverse bolt 101
extending through a throughhole 102 in each of the plates. FIG. 6
discloses an embodiment of the present invention having a
prosthetic ligament 103 connected to each plate and extending up
and over the upper spinous process. FIG. 7 discloses an embodiment
of the present invention having two J-shaped plates 111, 113 that
encircle the spinous processes.
[0072] FIG. 8 discloses a crimp block revision tool 115 of the
present invention. Generally, the device's ligament is permanently
fixed at a certain length intraoperatively. However, it is expected
that a situation may present in some patients postoperatively that
requires further shortening of the ligament. To address this need
to post-operatively shorten an implanted ligament, an implantable
crimp block 115 is provided that captures a greater amount of
ligament material between two points than is represented by the
linear distance between those points. For example, the ligament
material must travel a tortuous pathway between the two points such
that the length of tether material between the points is greater
than the fixed linear distance between the points. In the
embodiment of FIG. 8, two hinged plates with stand-offs of height A
placed along the length of the plate at a distance 2B are closed
around a ligament of material. The stand-offs nest together,
thereby creating a tortuous pathway for the intervening ligament
material. For a plate with one central stand-off of height A that
nests between two stand-offs placed at the ends of the other plate
of length 2B (total crimp block length of 2B), the amount of
ligament material captured between these stand-offs is
2*(A.sup.2+B.sup.2).sub.1/2>2*B. Additional stand-offs can be
added. Thus, the reduction in ligament length for a crimp block
containing N stand-off segments of height A with distance 2*B
between the standoffs is characterized as
.DELTA.1=N*2*[(A.sup.2+B.sup.2).sup.1/2-B].
[0073] Preferably, the device of the present invention is placed
between the spinous processes using a minimally invasive approach
that spares the supraspinous ligament. For the first embodiment
described above having a continuous ligament, the first plate with
the strap woven through is threaded through the muscle, bone and
ligamentous structures from the contralateral side, followed by
threading of the second plate with the strap woven through to the
ipsilateral side. The tensioning and position locking can then be
accomplished through the same insertion approach used to place the
plates. Thus, the entire procedure can be accomplished using a
percutaneous technique.
[0074] Preferably, the device of the present invention is used in
patients who have stenosis of the vertebral and/or neural foramen
that constricts their spine-related nerves and thereby suffer from
low back or leg pain.
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