U.S. patent application number 15/863716 was filed with the patent office on 2018-05-10 for sacral tether anchor and methods of use.
This patent application is currently assigned to Empirical Spine, Inc.. The applicant listed for this patent is Empirical Spine, Inc.. Invention is credited to Todd Alamin, Ian Bennett, Louis Fielding, Darin Gittings, Hugues Malandain, Anand Parikh, Eller Torres.
Application Number | 20180125556 15/863716 |
Document ID | / |
Family ID | 42396068 |
Filed Date | 2018-05-10 |
United States Patent
Application |
20180125556 |
Kind Code |
A1 |
Alamin; Todd ; et
al. |
May 10, 2018 |
SACRAL TETHER ANCHOR AND METHODS OF USE
Abstract
A system for restricting flexion of a spinal segment in a
patient comprises a constraint device having a tether structure and
a compliance member coupled with the tether structure. The tether
structure is adapted to be coupled with a superior spinous process
and a sacrum. The system also includes an anchor member that is
anchored to the sacrum. The anchor member has an attachment feature
that is adapted to couple with the constraint device.
Inventors: |
Alamin; Todd; (Woodside,
CA) ; Fielding; Louis; (San Carlos, CA) ;
Gittings; Darin; (Sunnyvale, CA) ; Malandain;
Hugues; (Mountain View, CA) ; Parikh; Anand;
(San Diego, CA) ; Torres; Eller; (Vista, CA)
; Bennett; Ian; (San Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Empirical Spine, Inc. |
Woodside |
CA |
US |
|
|
Assignee: |
Empirical Spine, Inc.
Woodside
CA
|
Family ID: |
42396068 |
Appl. No.: |
15/863716 |
Filed: |
January 5, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15279046 |
Sep 28, 2016 |
|
|
|
15863716 |
|
|
|
|
14598932 |
Jan 16, 2015 |
|
|
|
15279046 |
|
|
|
|
13963786 |
Aug 9, 2013 |
|
|
|
14598932 |
|
|
|
|
13193441 |
Jul 28, 2011 |
8529607 |
|
|
13963786 |
|
|
|
|
PCT/US2010/022767 |
Feb 1, 2010 |
|
|
|
13193441 |
|
|
|
|
61149224 |
Feb 2, 2009 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 17/7053 20130101;
A61B 17/7056 20130101; A61B 17/1606 20130101; A61B 17/7055
20130101; A61B 17/1604 20130101; A61B 17/88 20130101; A61B 17/7059
20130101; A61B 17/846 20130101; A61B 17/7067 20130101; A61B 17/8863
20130101; A61B 17/1671 20130101; A61B 17/8605 20130101 |
International
Class: |
A61B 17/88 20060101
A61B017/88; A61B 17/70 20060101 A61B017/70; A61B 17/16 20060101
A61B017/16; A61B 17/84 20060101 A61B017/84 |
Claims
1. A method for restricting flexion of a spinal segment of a
patient, said method comprising: providing a constraint device
having a tether structure, the tether structure comprising an upper
portion and a lower portion, the tether structure configured to
restrict flexion of the spinal segment while allowing substantially
unrestricted spinal extension; coupling the upper portion of the
tether structure to a spinous process of a superior vertebra in the
spinal segment; anchoring an anchor element to a sacrum of the
patient inferior to the superior vertebra, wherein the anchor
element comprises a plate having a plurality of protrusions, the
plurality of protrusions configured to penetrate the sacrum,
wherein anchoring the anchor element comprises anchoring the anchor
element to the sacrum without using screws, and wherein anchoring
the plurality of protrusions only penetrates cortical bone on a
dorsal surface of the sacrum; and coupling the lower portion of the
tether structure to an attachment feature on the anchor
element.
2. The method of claim 1, wherein anchoring the anchor element
comprises nailing the plurality of protrusions into the sacrum.
3. The method of claim 1, wherein anchoring the anchor element
comprises hammering the plurality of protrusions into the sacrum
with a mallet.
4. The method of claim 1, wherein the plurality of protrusions
comprise a plurality of nail-like protrusions.
5. The method of claim 1, wherein the plurality of nail-like
protrusions are inclined relative to a surface of the plate.
6. The method of claim 1, wherein the attachment feature on the
anchor element comprises an aperture for receiving the lower
portion of the tether structure.
7. The method of claim 1, wherein the attachment feature on the
anchor element comprises a hook for hooking the lower portion of
the tether structure.
8. The method of claim 1, wherein the constraint device further
comprises a compliance member disposed between the upper and lower
portions of the tether.
9. The method of claim 1, further comprising inserting the anchor
element through a minimally invasive incision.
10. The method of claim 1, further comprising moving the anchoring
element cranially or caudally.
11. The method of claim 1, further comprising passing a free end of
the upper portion or a free end of the lower portion through a
locking mechanism.
12. The method of claim 1, further comprising adjusting length or
tension in the tether structure.
13. The method of claim 1, further comprising promoting
osseointegration of the anchor element with the spinal segment.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/279,046 (Attorney Docket No. 48626-712.304)
filed Sep. 28, 2016 which is a continuation of U.S. patent
application Ser. No. 14/598,932 (Attorney Docket No. 48626-712.303)
filed Jan. 16, 2015, which is a continuation of U.S. patent
application Ser. No. 13/963,786 (Attorney Docket No. 48626-712.302)
filed Aug. 9, 2013, which is a continuation of U.S. patent
application Ser. No. 13/193,441 (Attorney Docket No.
48626-712.301), filed Jul. 28, 2011, which is a continuation of PCT
Application No. PCT/US2010/022767 (Attorney Docket No.
48626-714.601), filed Feb. 1, 2010, which claims the benefit of
U.S. Provisional Patent Application No. 61/149,224 (Attorney Docket
No. 48626-714.101) filed Feb. 2, 2009; the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention generally relates to medical methods
and apparatus. More particularly, the present invention relates to
methods and apparatus used to couple a prosthesis to a spinal
segment. Often, a portion of the prosthesis may be coupled to the
sacrum. The methods and apparatus disclosed herein may be used
during orthopedic internal fixation procedures. This includes but
is not limited to treatment of patients having back pain or other
spinal conditions.
[0003] A major source of chronic low back pain is discogenic pain,
also known as internal disc disruption. Patients suffering from
discogenic pain tend to be young, otherwise healthy individuals who
present with pain localized to the back. Discogenic pain usually
occurs at the discs located at the L4-L5 or L5-S1 junctions of the
spine. Pain tends to be exacerbated when patients put their lumbar
spines into flexion (i.e. by sitting or bending forward) and
relieved when they put their lumbar spines into extension (i.e. by
standing or arching backwards). Flexion and extension are known to
change the mechanical loading pattern of a lumbar segment. When the
segment is in extension, the axial loads borne by the segment are
shared by the disc and facet joints (approximately 30% of the load
is borne by the facet joints). In flexion, the segmental load is
borne almost entirely by the disc. Furthermore, the nucleus shifts
posteriorly, changing the loads on the posterior portion of the
annulus (which is innervated), likely causing its fibers to be
subject to tension and shear forces. Segmental flexion, then,
increases both the loads borne by the disc and causes them to be
borne in a more painful way. Discogenic pain can be quite
disabling, and for some patients, can dramatically affect their
ability to work and otherwise enjoy their lives.
[0004] Pain experienced by patients with discogenic low back pain
can be thought of as flexion instability, and is related to flexion
instability manifested in other conditions. The most prevalent of
these is spondylolisthesis, a spinal condition in which abnormal
segmental translation is exacerbated by segmental flexion. The
methods and devices described herein should as such also be useful
for these other spinal disorders or treatments associated with
segmental flexion, for which the prevention or control of spinal
segmental flexion is desired. Another application for which the
methods and devices described herein may be used is in conjunction
with a spinal fusion, in order to restrict motion, promote healing,
and relieve pain post-operatively. Alternatively, the methods and
devices described should also be useful in conjunction with other
treatments of the anterior column of the spine, including
kyphoplasty, total disc replacement, nucleus augmentation and
annular repair.
[0005] Patients with discogenic pain accommodate their syndrome by
avoiding positions such as sitting, which cause their painful
segment to go into flexion, preferring positions such as standing,
which maintain their painful segment in extension. One approach to
reducing discogenic pain involves the use of a lumbar support
pillow often seen attached to office chairs. Biomechanically, the
attempted effect of the ubiquitous lumbar support pillow is also to
maintain the painful lumbar segment in the less painful extension
position.
[0006] Current treatment alternatives for patients diagnosed with
chronic discogenic pain are quite limited. Many patients follow a
conservative treatment path, such as physical therapy, massage,
anti-inflammatory and analgesic medications, muscle relaxants, and
epidural steroid injections, but typically continue to suffer with
a significant degree of pain. Other patients elect to undergo
spinal fusion surgery, which commonly requires discectomy (removal
of the disk) together with fusion of adjacent vertebra. Fusion may
or may not also include instrumentation of the affected spinal
segment including, for example, pedicle screws and stabilization
rods. Fusion is not lightly recommended for discogenic pain because
it is irreversible, costly, associated with high morbidity, and has
questionable effectiveness. Despite its drawbacks, however, spinal
fusion for discogenic pain remains common due to the lack of viable
alternatives.
[0007] An alternative method, that is not commonly used in
practice, but has been approved for use by the United States Food
and Drug Administration (FDA), is the application of bone cerclage
devices which can encircle the spinous processes or other vertebral
elements and thereby create a restraint to motion. Physicians
typically apply a tension or elongation to the devices so that they
apply a constant and high force on the anatomy, thereby fixing the
segment in one position and allowing effectively no motion. The
lack of motion allowed after the application of such devices is
thought useful to improve the likelihood of fusion performed
concomitantly; if the fusion does not take, these devices will fail
through breakage of the device or of the spinous process to which
the device is attached. These devices are designed for static
applications and are not designed to allow for dynamic elastic
resistance to flexion across a range of motion. The purpose of bone
cerclage devices and other techniques described above is to almost
completely restrict measurable motion of the vertebral segment of
interest. This loss of motion at a given segment gives rise to
abnormal loading and motion at adjacent segments, which can lead
eventually to adjacent segment morbidity.
[0008] An alternative solution that avoids some of the challenges
associated with cerclage devices involves the use of an elastic
structure, such as tether structures, coupled to the spinal
segment. The elastic structure can relieve pain by increasing
passive resistance to flexion while often allowing substantially
unrestricted spinal extension. This mimics the mechanical effect of
postural accommodations that patients already use to provide
relief.
[0009] Spinal implants using tether structures are currently
commercially available. One such implant couples adjacent vertebrae
via their pedicles. This implant includes spacers, tethers and
pedicle screws. To install the implant, muscles are retracted to a
wide extent to expose the pedicles, and selected portions of the
disc and vertebrae bone may be removed. Implants are then placed to
couple two adjacent pedicles on each side of the spine. The pedicle
screws secure the implants in place. The tether is clamped to the
pedicle screws with set-screws, and limits the extension/flexion
movements of the vertebrae of interest, as well as limiting other
motions such as axial compression, later bending, and rotation.
Because significant tissue is displaced and/or removed and because
of screw placement into the pedicles, the implant and accompanying
surgical methods are highly invasive and the implant is often
irreversibly implanted. There is also an accompanying significant
chance of nerve root damage. Additionally, the tip of the set-screw
clamps the tethers, and this may result in abrasion of the tethers
along with generation of particulate wear debris.
[0010] Other implants employing tether structures couple adjacent
vertebrae via their processes instead. These implants include a
tether and a spacer. To install the implant, the supraspinous
ligament is temporarily lifted and displaced. The interspinous
ligament between the two adjacent vertebrae of interest is then
permanently removed and the spacer is inserted in the interspinous
space. The tether is then wrapped around the processes of the two
adjacent vertebrae, through adjacent interspinous ligaments, and
then mechanically secured in place by the spacer or also by a
separate component fastened to the spacer. The supraspinous
ligament is then restored back to its original position. Such
implants and accompanying surgical methods are not without
disadvantages. These implants may subject the spinous processes to
frequent, high loads during everyday activities, sometimes causing
the spinous processes to break or erode. Furthermore, the spacer
may put a patient into segmental kyphosis, potentially leading to
long-term clinical problems associated with lack of sagittal
balance. The process of securing the tethers is often a very
complicated maneuver for a surgeon to perform, making the surgery
much more invasive. And, as previously mentioned, the removal of
the interspinous ligament is permanent. As such, the application of
the device is not reversible.
[0011] More recently, less invasive spinal implants have been
introduced. Like the aforementioned implant, these spinal implants
are placed over one or more pairs of spinous processes and provide
an elastic restraint to the spreading apart of the spinous
processes occurring during flexion. However, extension-limiting
spacers are not used and interspinous ligaments need not be
permanently removed. As such, these implants are less invasive and
may be reversibly implanted. The implants typically include a
tether structure and a securing mechanism for the tether. The
tether may be made from a flexible polymeric textile such as woven
polyester (PET) or polyethylene (e.g. ultra high molecular weight
polyethylene, UHMWPE); multi-strand cable, or other flexible
structure. The tether is wrapped around the processes of adjacent
vertebrae and then secured by the securing mechanism. Securing
mechanisms are described in greater detail below.
[0012] While the constraint devices described above appear to be
promising, in some situations, attachment of the device to a
spinous process can be challenging. For example, if the constraint
device is attached to a small spinous process that does not
protrude enough or has geometry unsuitable to engage a tether, such
as steeply sloping surfaces, the constraint device could migrate or
disengage from the spinous process after implantation. Furthermore,
it may be necessary to couple the constraint device with an upper
spinous process disposed on a superior vertebra and an inferior
spinous process, crest or tubercle disposed on the sacrum (e.g. for
implantation at the L5-S1 level). Often, the spinous processes in
these regions are small and do not protrude sufficiently to provide
an adequate attachment point for the constraint device. In other
cases where a spinous process of sufficient size is present, the
surfaces may slope such that the constraint device would tend to
migrate or slip off the process. Therefore, it would be desirable
to provide apparatus and methods that facilitate attachment of the
constraint device to a small or sloping spinous processes, sacral
crest or tubercle, in particular one disposed on the sacrum or
directly to the sacrum. Moreover, it would also be desirable if
such devices and methods were easy to use and minimally invasive to
the patient.
2. Description of the Background Art
[0013] Patents and published applications of interest include: U.S.
Pat. Nos. 3,648,691; 4,643,178; 4,743,260; 4,966,600; 5,011,494;
5,092,866; 5,116,340; 5,180,393; 5,282,863; 5,395,374; 5,415,658;
5,415,661; 5,449,361; 5,456,722; 5,462,542; 5,496,318; 5,540,698;
5,562,737; 5,609,634; 5,628,756; 5,645,599; 5,725,582; 5,902,305;
Re. 36,221; 5,928,232; 5,935,133; 5,964,769; 5,989,256; 6,053,921;
6,248,106; 6,312,431; 6,364,883; 6,378,289; 6,391,030; 6,468,309;
6,436,099; 6,451,019; 6,582,433; 6,605,091; 6,626,944; 6,629,975;
6,652,527; 6,652,585; 6,656,185; 6,669,729; 6,682,533; 6,689,140;
6,712,819; 6,689,168; 6,695,852; 6,716,245; 6,761,720; 6,835,205;
7,029,475; 7,163,558; Published U.S. Patent Application Nos.
2002/0151978; 2004/0024458; 2004/0106995; 2004/0116927;
2004/0117017; 2004/0127989; 2004/0172132; 2004/0243239;
2005/0033435; 2005/0049708; 2005/0192581; 2005/0216017;
2006/0069447; 2006/0136060; 2006/0240533; 2007/0213829;
2007/0233096; 2008/0009866; 2008/0108993; 2008/0177264;
2008/0108993; 2008/0262549; Published PCT Application Nos. WO
01/28442 A1; WO 02/03882 A2; WO 02/051326 A1; WO 02/071960 A1; WO
03/045262 A1; WO2004/052246 A1; WO 2004/073532 A1; WO2008/051806;
WO2008/051423; WO2008/051801; WO2008/051802; and Published Foreign
Application Nos. EP0322334 A1; and FR 2 681 525 A1. The mechanical
properties of flexible constraints applied to spinal segments are
described in Papp et al. (1997) Spine 22:151-155; Dickman et al.
(1997) Spine 22:596-604; and Garner et al. (2002) Eur. Spine J.
S186-S191; Al Baz et al. (1995) Spine 20, No. 11, 1241-1244;
Heller, (1997) Arch. Orthopedic and Trauma Surgery, 117, No.
1-2:96-99; Leahy et al. (2000) Proc. Inst. Mech. Eng. Part H: J.
Eng. Med. 214, No. 5: 489-495; Minns et al., (1997) Spine 22 No.
16:1819-1825; Miyasaka et al. (2000) Spine 25, No. 6: 732-737;
Shepherd et al. (2000) Spine 25, No. 3: 319-323; Shepherd (2001)
Medical Eng. Phys. 23, No. 2: 135-141; and Voydeville et al (1992)
Orthop Traumatol 2:259-264.
BRIEF SUMMARY OF THE INVENTION
[0014] The present invention relates to methods and apparatus used
to couple a prosthesis to a spinal segment and adjust the
prosthesis during orthopedic internal fixation procedures. This
includes but is not limited to coupling a constraint device between
a superior spinous process and the sacrum during treatment of
patients having spinal pain, instability or other spinal
conditions.
[0015] In a first aspect of the present invention, a system for
restricting flexion of a spinal segment in a patient comprises a
constraint device having a tether structure and a compliance member
coupled with the tether structure. The tether structure comprises
an upper portion adapted to be coupled with a superior spinous
process and a lower portion adapted to be coupled with a sacrum.
The constraint device provides a force resistant to flexion of the
spinal segment. The system also has an anchor member comprising an
attachment member and a coupling member. The attachment member is
adapted to attach the anchor member to the sacrum, and the coupling
member is adapted to couple the tether structure with the anchor
member.
[0016] The system may further comprise a second compliance member
coupled with the tether structure. The compliance members may be
disposed substantially parallel to one another. They may be
disposed on opposite sides of a midline of the spinal segment. The
upper portion of the tether structure may comprise first and second
free ends. Each of the free ends may be coupled with one of the
compliance members. The lower portion of the tether structure may
comprise a loop which may be coupled to the coupling member.
[0017] The anchor member may comprise an elongate bar, and the bar
may be disposed across the midline of the spinal segment. The bar
may comprise a through hole that is adapted to receive the
attachment member, which attaches the bar to the sacrum. The bar
may have an adjustable length. The anchor member may comprise a
plate in engagement with the sacrum. The anchor may be disposed in
a recessed region of the sacrum so that an outer surface of the
anchor member is substantially flush with an outer surface of the
sacrum. The anchor member may comprise a staple, or a cable.
[0018] The attachment member may comprise a screw threadably
engaged with the sacrum. The screw may be axially threaded into
engagement with a crest of the sacrum in a generally caudal
direction. The attachment member may comprise a nail, a clip, or a
hook that is adapted to couple with the sacrum.
[0019] The coupling member may comprise one of a hook, an eyelet, a
slot, and a pin. The coupling member may comprise a channel
disposed in a portion of the anchor member. The channel may be
adapted to receive the tether structure therethrough. The system
may further comprise a liner element disposed in the channel. The
coupling member may comprise a protuberance adapted to engage the
tether structure, or the coupling member may comprise a pin that is
adapted to engage the tether structure. The coupling member may
comprise a gate mechanism having an open position and a closed
position. In the open position, the coupling member may receive the
tether structure and in the closed position, the tether structure
may be captured by the coupling member.
[0020] The system may further comprise a bone removal tool. The
bone removal tool may be configured to remove bone from the sacrum
thereby facilitating attachment of the anchor member thereto. The
bone removal tool may comprise a rongeur tool, or a drill. The bone
removal tool may comprise an elongate shaft, a handle coupled with
the shaft, and a cutting element having a crescent shaped
cross-section. The cutting element may extend laterally from the
shaft, and it may be adapted to remove bone from the sacrum. The
bone removal tool may comprise a knurled cutting surface adapted to
remove bone from the sacrum.
[0021] The anchor member may comprise a surface that is adapted to
promote osseointegration of the anchor with the sacrum. The surface
may comprise hydroxyapatite or titanium.
[0022] In another aspect of the present invention, a system for
restricting flexion of a spinal segment in a patient comprises a
constraint device comprising a tether structure and a compliance
member coupled with the tether structure. The tether structure
comprises an upper portion and a lower portion. The upper portion
is adapted to be coupled with a superior spinous process and the
lower portion is adapted to be coupled with a coccyx. The
constraint device provides a force resistant to flexion of the
spinal segment. The lower portion may comprise a loop and the loop
may be disposed around the coccyx. The lower portion may be longer
than the upper portion.
[0023] In still another aspect of the present invention, a method
for restricting flexion in a spinal segment comprises providing a
constraint device having a tether structure, a compliance member
coupled with the tether structure, and an anchor member. The tether
structure comprises an upper portion and a lower portion. The upper
portion of the tether structure is engaged with a superior spinous
process, and the anchor member is attached to a sacrum. The lower
portion of the tether structure is coupled with the anchor
member.
[0024] The method may further comprise resisting flexion of the
spinal segment. The step of engaging the upper portion of the
tether structure may comprise disposing the upper portion of the
tether structure over a superior surface of the spinous
process.
[0025] The step of attaching the anchor member may comprise
removing bone from the sacrum. Attaching the anchor member may
comprise forming a recessed region in the sacrum. Attaching the
anchor member may comprise creating a notched region or a channel
in a crest of the sacrum. The attaching step may also comprise
adjusting length of the anchor member. Attaching the anchor member
may comprise threadably engaging a fastener with the sacrum. The
fastener may be threadably engaged in a generally caudal direction
so as to avoid penetration of the fastener into a spinal canal or
into an anterior cortex of the sacrum. Attaching may comprise
stapling or nailing the anchor member to the sacrum, or clipping a
portion of the anchor member to a sacral crest or a spinous process
of the sacrum. Attaching the anchor member may comprise hooking a
portion of the anchor member with a neural foramen of the sacrum,
or with a lateral edge of the sacrum.
[0026] The anchor member may comprise a through hole, and the step
of coupling the lower portion of the tether structure comprises
advancing the lower portion of the tether structure through the
through hole. The anchor member may comprise an elongate channel,
and the step of coupling the lower portion of the tether structure
may comprise advancing the lower portion of the tether structure
through the elongate channel. The step of coupling the lower
portion of the tether structure may comprise at least partially
encircling the lower portion of the tether structure around a
portion of the anchor member or the coupling member. Coupling the
lower portion of the tether structure may comprise opening a gate
in the anchor member thereby permitting the anchor member to
receive the tether structure. The gate may also be closed, thereby
capturing the tether structure. The method may further comprise
promoting osseointegration of the anchor member with the sacrum, or
adjusting length or tension in the constraint device.
[0027] In another aspect of the present invention, a method for
restricting flexion of a spinal segment in a patient comprises
providing a constraint device having a tether structure that has an
upper portion and a lower portion. The upper portion of the tether
structure is engaged with a superior spinous process, and bone is
removed from the sacrum in order to form an attachment region in
the bone. The lower portion of the tether structure is coupled with
the attachment region.
[0028] The method may further comprise resisting flexion of the
spinal segment. The constraint device may further comprise a
compliance member coupled with the tether structure. The step of
engaging the upper portion of the tether structure may comprise
disposing the upper portion of the tether structure over a superior
surface of the spinous process.
[0029] The step of removing bone may comprise creating a channel
extending through a crest of the sacrum. The channel may be lined
with a liner element. Removing bone may comprise notching the
sacrum, or it may comprise one of cutting, grinding, drilling,
filing, rasping, sawing, and abrading the sacrum. Removing bone may
comprise removing the bone with one of a rongeur tool, a cutting
tool, a file, a rasp, a saw, and a drill.
[0030] The step of coupling the lower portion of the tether
structure may comprise advancing the lower portion through a
channel in the sacrum. The method may further comprise preserving
ligaments or other anatomical structures disposed along a midline
of the spinal segment.
[0031] In still another aspect of the present invention, a method
for restricting flexion of a spinal segment in a patient comprises
providing a constraint device having a tether structure, and a
compliance member coupled with the tether structure. The tether
structure comprises an upper portion and a lower portion. The upper
portion of the tether structure is engaged with a superior spinous
process, and the lower portion of the tether structure is coupled
with a coccyx. Coupling the lower portion may comprise encircling
at least a portion of the coccyx with the lower portion of the
tether structure. The lower portion of the tether structure may
comprise a loop, and the step of coupling the lower portion may
comprise placing the loop around the coccyx.
[0032] These and other embodiments are described in further detail
in the following description related to the appended drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A is a schematic diagram illustrating the lumbar and
sacral regions of the spine.
[0034] FIG. 1B a schematic illustration showing a portion of the
lumbar region of the spine taken along a sagittal plane.
[0035] FIG. 2A illustrates a spinal implant of the type described
in U.S. Patent Publication No. 2005/0216017A1.
[0036] FIG. 2B illustrates the sacrum.
[0037] FIGS. 3A-3B illustrate the use of an undercut in the sacrum
for anchoring a constraint device.
[0038] FIGS. 4A-4C illustrate the use of an anchor member for
securing a constraint device to the sacrum.
[0039] FIGS. 5A-5F illustrate use of a notched region in the sacrum
for anchoring a constraint device.
[0040] FIG. 6 illustrates an exemplary embodiment of a notching
tool.
[0041] FIGS. 7A-7B illustrates use of an aperture in the sacrum for
attachment of a constraint device.
[0042] FIGS. 8A-8B illustrate an exemplary embodiment of a punch
tool.
[0043] FIGS. 8C-8F illustrate additional embodiments of bone
removal tools.
[0044] FIGS. 9A-9E illustrate various embodiments of a
crossbar.
[0045] FIG. 10 illustrates use of a screw as an anchor.
[0046] FIGS. 11A-11D illustrate an anchor coupled with the
sacrum.
[0047] FIG. 12 illustrates use of a screw or pin as an anchor.
[0048] FIG. 13 illustrates another embodiment of a screw or pin as
the anchor.
[0049] FIGS. 14A-14B illustrate still other embodiments of a screw
or pin as the anchor.
[0050] FIGS. 15A-15D illustrate additional embodiments of a screw
or pin as the anchor.
[0051] FIGS. 16A-16F illustrate various embodiments of pins or
posts that may be used as the anchor.
[0052] FIGS. 17A-17B illustrate two exemplary embodiments of screws
that may be used as the anchor.
[0053] FIGS. 18A-18B illustrate a liner.
[0054] FIG. 19 illustrates another embodiment of a liner.
[0055] FIGS. 20A-20B illustrate another embodiment of a liner.
[0056] FIG. 21 illustrates a reinforcement device.
[0057] FIG. 22 illustrates the use of a retaining pin.
[0058] FIGS. 23A-23B illustrate retaining bar embodiments.
[0059] FIG. 24A-24C illustrate retaining clips.
[0060] FIGS. 25A-25E illustrate additional retaining clip
embodiments.
[0061] FIGS. 26A-26D illustrate still other retaining clip
embodiments.
[0062] FIG. 27 illustrates a gate mechanism.
[0063] FIGS. 28A-28C illustrate a retention plate.
[0064] FIG. 29 illustrates a hook embodiment.
[0065] FIGS. 30A-30D illustrate the anatomy of a neural foramen and
various embodiments of neural foramina hooks.
[0066] FIG. 31 illustrates additional embodiments of sacral
hooks.
[0067] FIG. 32 illustrates attachment of a constraint device with
the coccyx.
[0068] FIGS. 33A-33B illustrate several embodiments of constraint
devices which may be attached to the coccyx.
[0069] FIGS. 34A-34B illustrate surgical methods of coupling a
constraint device with the coccyx.
DETAILED DESCRIPTION OF THE INVENTION
[0070] FIG. 1A is a schematic diagram illustrating the lumbar
region of the spine including the spinous processes (SP), facet
joints (FJ), lamina (L), transverse processes (TP), and sacrum (S).
FIG. 1B is a schematic illustration showing a portion of the lumbar
region of the spine taken along a sagittal plane and is useful for
defining the terms "neutral position," "flexion," and "extension"
that are often used in this disclosure.
[0071] As used herein, "neutral position" refers to the position in
which the patient's spine rests in a relaxed standing position. The
"neutral position" will vary from patient to patient. Usually, such
a neutral position will be characterized by a slight curvature or
lordosis of the lumbar spine where the spine has a slight anterior
convexity and slight posterior concavity. In some cases, the
presence of the constraint of the present invention may modify the
neutral position, e.g. the device may apply an initial force which
defines a "new" neutral position having some extension of the
untreated spine. As such, the use of the term "neutral position" is
to be taken in context of the presence or absence of the device. As
used herein, "neutral position of the spinal segment" refers to the
position of a spinal segment when the spine is in the neutral
position.
[0072] Furthermore, as used herein, "flexion" refers to the motion
between adjacent vertebrae in a spinal segment as the patient bends
forward. Referring to FIG. 1B, as a patient bends forward from the
neutral position of the spine, i.e. to the right relative to a
curved axis A, the distance between individual vertebrae L on the
anterior side decreases so that the anterior portion of the
intervertebral disks D are compressed. In contrast, the individual
spinous processes SP on the posterior side move apart in the
direction indicated by arrow B. Flexion thus refers to the relative
movement between adjacent vertebrae as the patient bends forward
from the neutral position illustrated in FIG. 1B.
[0073] Additionally, as used herein, "extension" refers to the
motion of the individual vertebrae L as the patient bends backward
and the spine extends from the neutral position illustrated in FIG.
1B. As the patient bends backward, the anterior ends of the
individual vertebrae will move apart. The individual spinous
processes SP on adjacent vertebrae will move closer together in a
direction opposite to that indicated by arrow B.
[0074] FIG. 2A shows a spinal implant of the type described in
related U.S. Patent Publication No. 2005/0216017 A1 (now U.S. Pat.
No. 7,458,981), the entire contents of which are incorporated
herein by reference. As illustrated in FIG. 2A, an implant 10
typically comprises a tether structure having an upper strap
component 12 and a lower strap component 14 joined by a pair of
compliance elements 16. The upper strap 12 is shown disposed over
the top of the spinous process SP4 of L4 while the lower strap 14
is shown extending over the bottom of the spinous process SP5 of
L5. The compliance element 16 will typically include an internal
element, such as a spring or rubber block, which is attached to the
straps 12 and 14 in such a way that the straps may be "elastically"
or "compliantly" pulled apart as the spinous processes SP4 and SP5
move apart during flexion. In this way, the implant provides an
elastic tension on the spinous processes which provides a force
that resists flexion. The force increases as the processes move
further apart. Usually, the straps themselves will be essentially
non-compliant so that the degree of elasticity or compliance may be
controlled and provided solely by the compliance elements 16.
Additional details on constraint devices is disclosed in U.S.
patent application Ser. No. 12/106,103 (Attorney Docket No.
026398-000410US) which is incorporated herein by reference. Any of
these constraint devices may be used with the anchoring methods and
apparatus disclosed herein. In other embodiments, the constraint
device may be a tether structure with or without a compliance
member or element. The tether structure may be elastic.
[0075] The flexion-limiting device may also be attached to an upper
spinous process disposed on a vertebra and the sacrum in order to
limit flexion between the sacrum and the upper vertebra. However,
the sacrum often has spinous processes that are very short and
rounded; these are also referred to as spinous tubercles. The
sacrum may only have a low crest along the dorsal midline. These
regions are often insufficient for a tether to loop around since
the bone protruding from the sacrum may be too short and the
oblique angle of the sacral surfaces around which the device would
loop may permit the device to migrate dorsally, and potentially
slide off. FIG. 2B illustrates the spinous processes SP on the
sacrum.
[0076] Referring now to FIG. 3A, a top view of the sacrum shows how
an undercut 302 may be formed by carving, cutting, sawing, grinding
or other suitable means, into the sacrum S. Undercut 302 in this
exemplary embodiment is a T-shaped slot that is adapted to receive
a pin or other anchor. FIG. 3B is a cross-sectional sideview of the
sacrum and undercut 302. In FIG. 3B, a constraint device having a
tether 304 is anchored to the sacrum S by engaging the tether 304
with the undercut 302. A free end 310 of tether 304 is wrapped
around a pin 306 and the free end 310 is then fastened to the
tether using methods well known in the art such as stitching,
thermal welding, suturing, bonding, riveting, etc. Alternatively,
the free end 310 may return to an attachment point on the
constraint device. Tether 304 and pin 306 are then slidably
received in the T-shaped slot 302, with the tether 304 exiting the
central portion of slot 302. The tether 304 and pin 306 are
advanced in the cranial direction until the pin 306 bottoms out in
the slot thereby capturing the pin 306 and tether 304. An optional
fastener 308, such as a screw or pin may be advanced through the
sacrum and tether/pin in order to further secure the device into
the slot 302. In this exemplary embodiment a T-shaped slot is used,
however one will appreciate that other geometries may also be used.
The remainder of the constraint device may be secured to a superior
portion of the affected spinal segment such as a spinous process,
pedicle, transverse process, etc. Tools which may be used to create
the undercut are described below.
[0077] FIGS. 4A-4C illustrate the use of a washer to attach a
constraint device to the sacrum S. In FIG. 4A a circular washer 402
has a central aperture 404 and a tab 406 for engagement with the
constraint device. Tab 406 has an oblong aperture 408 for receiving
a tether of the constraint device. A fastener such as a screw may
be received in aperture 404 and threadably engaged with the sacrum
S in order to secure the washer 402 to the bone. In FIG. 4B,
optional recessed regions 410 are formed on either side of the
spinal segment midline so that the outer surface of washer 402 will
be substantially flush with the outer surface of the sacrum.
Recessed regions 410 may be formed by cutting, carving, grinding,
or other means known in the art and these recessed regions are also
useful in helping to distribute loading more evenly along the
interface between the anchor and the bone, thereby reducing the
likelihood of mechanical failure. In this embodiment coatings such
as hydroxyapatite or titanium may be deposited over an outer
surface of the washer in order to improve fixation through
osseointegration. Surface features such as beading may also be used
to enhance integration of the anchor with the bone. These coatings
and surface features may be used in any of the implants described
in this disclosure where bone ingrowth is desirable. While a
circular washer is disclosed in this embodiment, one of ordinary
skill in the art will appreciate that many other geometries may be
substituted, some of which may provide even better fixation of the
anchor to the sacrum. FIG. 4C is a cross-section of the sacrum S
showing the washer 402 disposed in a recess 410 formed in the
sacrum S. A fastener 416, here a screw, is disposed through
aperture 404 and threadably engaged with the sacrum S. Tether 412
has a free end 414 that is fed through aperture 408 and then fixed
to itself using any of the means previously disclosed with
reference to FIGS. 3A-3B. Exemplary screws which may be used
include, but are not limited to those disclosed in FIGS. 17A-17B
described in greater detail below. Tools which may be used to
create the recessed region are also described below.
[0078] FIGS. 5A-5F illustrate how a notch may be created in the
sacrum S and used to anchor a tether or a strap of a constraint
device. The notch may be created in the sacral crest, a spinous
process or a tubercle. In FIG. 5A a notched region 502 is formed in
a crest of the sacrum S. The notch 502 lengthens the surface of
engagement available for a strap if a spinous process is present
but insufficient to restrain the strap, or the notch creates a
raised region 504 that is similar to a naturally occurring spinous
process. FIG. 5B is a side view showing notch 502 cut into the
sacrum S, thereby forming the raised region 504. A tether may then
be secured to the sacrum S by looping the tether directly through
the notch 502 and thus no additional hardware is required. In some
embodiments it is desirable to place hardware into the notch 502 in
order to protect the tether/bone interface. In FIG. 5C, a plate or
sheave 508 is fixed in the notch 502. The plate 508 in this
embodiment is secured to the notch with a screw 506. FIG. 5D
illustrates an exemplary embodiment of a plate 508 having a curved
region 510 that forms a hook for engaging a tether structure. The
plate or sheave 508 may be fabricated from any number of materials
including metals such as stainless steel or titanium, ceramics,
polymers or other biocompatible materials. One of skill in the art
will appreciate that a variety of geometries may be used as a
protective liner element such as the plate, sheave, or other liners
described below. FIG. 5E shows how the constraint device is coupled
with the notch in the sacrum S, with or without the protective
sheave. In FIG. 5E, a constraint device 512 has a compliance member
514 and a tether structure 516. The tether 516 is passed through
the notch 502, thereby securing the constraint device to the
sacrum. An upper portion of the constraint device 512 may be
coupled with a superior spinous process (not illustrated).
[0079] FIG. 5F illustrates an alternative embodiment of a notched
sacrum used to retain the tether. In FIG. 5F a notch is created in
the sacrum having a keyway which includes a narrow slotted region
522 that opens up into an enlarged aperture or slotted region 520.
The narrow slotted region 522 is sized to receive the tether 516.
In this exemplary embodiment, the tether is a rectangular shaped
strap having upper and lower planar surfaces that represent the
width of the strap and the tether also has front and back side
walls generally perpendicular to the upper and lower planar
surfaces that represent the strap thickness. Thus, when the tether
516 is oriented in a desired position, the tether may be advanced
into the slotted region. In this embodiment, the aperture can
receive the tether when the tether is advanced such that the tether
leading edge is one of the side walls. This embodiment is also
advantageous because when the tether structure is in tension,
forces are distributed evenly along the surface of the enlarged
slotted region 520. The enlarged aperture 520 may be drilled or
otherwise cut in the sacrum and the narrow slotted region 522 may
be cut with a saw or other bone removing tools. Additional details
on tether structures and compliance members which may be applied to
the embodiments disclosed in FIGS. 5A-5F or any of the tether
structures or compliance members disclosed herein, are disclosed in
U.S. patent application Ser. No. 12/106,103 (Attorney Docket No.
0216398-000410US), entitled "Methods and Devices for Controlled
Flexion Restriction of Spinal Segments," filed Apr. 18, 2008, the
entire contents of which are incorporated herein by reference.
[0080] Various tools and fixtures may be used to create the notch
in FIGS. 5A-5F. One exemplary embodiment is illustrated in FIG. 6
and includes a forceps-like tool such as a rongeur tool 602 having
a pair of jaws 604 that are adapted to remove bone and create the
desired notch. The notch may also be created with files, chisels,
rasps, grinders or other bone removal instruments. These
instruments may be manual or power tools, such as a drill, burr or
saw. FIGS. 8C-8F illustrate other embodiments of bone removal tools
which may be used to create various features in the sacrum. In FIG.
8C, a crescent shaped cutting edge 824 is attached to a shaft 822
having a handle 820 for a surgeon to grasp. The crescent shaped
cutting edge 824 is used to rongeur bone such as creating an
undercut notch in a sacral crest which may be difficult for
currently commercially available curettes. The cutting motion is a
combination of both lateral and rotational movements as indicated
by the arrows in FIGS. 8C-8D. The embodiment of FIG. 8C facilitates
bone removal since the cutting edge 824 is offset from the shaft
822 of the tool, allowing deeper penetration into the bone as the
undercut is created and preservation of midline tissues and
structures. For example, it may be beneficial to create a notch,
while maintaining the supraspinous ligament along the midline. An
instrument that laterally accesses the bone removal site (such as
those described with a cutting surface offset from the shaft) will
facilitate bone removal while maintaining the midline structures.
An adjustment mechanism such as a set screw 826 may be used to
change the handle 820 orientation to facilitate use. FIG. 8D is an
enlarged view of the cutting edge 824 in FIG. 8C.
[0081] Another tool which may facilitate bone removal or creating
attachment features in the sacrum is illustrated in FIGS. 8E-8F. In
FIG. 8E, a curette tool has a knurled cutting surface 836 coupled
to and offset from a shaft 834 having a handle 830 for grasping. An
adjustment mechanism 832 such as a set screw allows adjustment of
the handle position relative to the cutting edge 836. The knurled
curette tool may also be used to debride bone for creating notches
such as undercuts in the sacrum. A sharp tip or cutting edge 838 on
the tip may be used to help the tool penetrate tissue. The knurled
surface removes bone by abrading it away, similar to a file.
[0082] FIGS. 7A-7B illustrate an attachment method similar to that
previously described with respect to FIGS. 5A-5F, with the major
difference being that instead of creating a notch in a sacral
crest, spinous process or tubercle of the sacrum, in this
embodiment, an aperture is created in these regions of the sacrum.
In FIG. 7A, an aperture 708 is created in a crest or spinous
process or tubercle of the sacrum, here the aperture is a circular
hole. A constraint device 702 having a tether 706 and a compliance
member 704 may be coupled with the sacrum S by passing at least a
portion of the tether structure 706 through the aperture 708. FIG.
7B shows a side view of the aperture 708 in the sacrum S. The
aperture 708 may be drilled into the sacrum S or a punch tool may
be used to create the hole. For example, in FIG. 8A, a forceps-like
tool 802 similar to the rongeur tool of FIG. 6 has a pair of jaws
804 that are adapted to create the aperture. In the embodiment of
FIG. 8A, the punch creates a round hole, although other shapes may
also be created. FIG. 8B illustrates the forceps-like punch tool
802. The punch tool may include a handle 806 for grasping in a
surgeon's hand and the jaws 804 which punch the aperture. A
double-action mechanism 808 creates greater leverage in use,
thereby providing higher punch forces than a single-action
mechanism would. The punching jaws 804 in this embodiment could
easily be substituted with the notching jaws in FIG. 6 and the
tools illustrated in FIGS. 8C-8F may also be used to create the
aperture.
[0083] In some embodiments where an aperture or notch has been
created in a portion of the sacrum, it may be advantageous to line
the aperture or notch with a protective liner element such as a
bearing, liner, ferrule or grommet type of device. The liner is
advantageous since it prevents direct contact between the tether
and the bone thereby minimizing wear and tear on the bone or
tether. Furthermore, a liner can help to more evenly distribute
forces from the tether across the aperture or notch. FIGS. 18A-18B
illustrate one embodiment of a liner. In FIG. 18A, aperture 1804
extends through a crest 1802 of the sacrum S. A two-piece liner is
inserted into the aperture 1804. Both halves 1806 and 1808 may then
be coupled together by press fitting, snap fitting, threading,
bonding, welding, ratcheting mechanism, etc. to form a smooth
channel 1810 through the sacral aperture 1804. The liner may have
flanged ends to conform with the outer surface of the aperture 1804
and the liner may also be malleable in order to conform with the
anatomy. The liner may be fabricated from many different metals
such as stainless steel or titanium, as well as many different
polymers. Surface treatments such as those disclosed in this
specification may also be used to enhance osseo-integration of the
liner with the bone. Additionally, the channel 1810 may be coated
with various materials to provide desired characteristics for the
tether, for example a Teflon lining may be used to provide a
lubricious surface. The corners/edges of the liner may further be
designed and processed to reduce friction at the points at which
the tether exits the liner. FIG. 18B illustrates a perspective view
of the assembled liner.
[0084] FIG. 19 illustrates an alternative embodiment of a liner or
grommet. In FIG. 19, the grommet includes a main body section 1906,
here a cylindrical body that is sized to fit the aperture in the
sacrum. The main body 1906 also has a central channel or passage
1904 that passes through the body and accommodates the tether of
the constraint device. In this embodiment, the grommet also has a
number of fingers 1902 which extend from either the proximal or
distal end of the grommet. These fingers are fabricated from a
superelastic or shape memory alloy such as Nitinol. Therefore, the
grommet may be placed in a sleeve for introduction through the
sacral aperture. Once the grommet is positioned in the sacral
aperture, the sleeve may be retracted and the fingers either
self-expand around the edges of the aperture or self-expand upon
reaching a desired temperature (e.g. above body temperature). Thus,
the fingers 1902 form flanges which lock the grommet into the
sacral aperture. Any of the coatings or surface treatments
described herein may also be used in conjunction with this
liner.
[0085] FIG. 20A illustrates a threaded liner 2002 that may be used
to line apertures and notches created in portions of the sacrum. In
FIG. 20A, a cylindrical tube having threads 2006 and a central
channel 2004 may be threaded into the sacral aperture. The liner
may be threaded into the sacral aperture and the threads allow more
secure anchoring of the liner 2002 with the sacrum than other
embodiments. FIG. 20B illustrates the use of the threaded liner
from FIG. 20A. In FIG. 20B, a constraint device has an upper tether
2010 coupled with an upper spinous process SP and a lower tether
2012 passes through the central channel 2004 of liner 2002 that has
been threaded into an aperture in the sacrum S. The liner 2002 may
have any of the surface treatments or coating described herein.
[0086] In addition to lining the internal surfaces of sacral
apertures, the external surfaces of the aperture may also be
reinforced. In FIG. 21, an aperture is created in a sacral crest or
a spinous process or tubercle of the sacrum, and the tether
structure 2104 of the constraint device is passed through the
aperture. In this embodiment, one or both of the external surfaces
of the sacral aperture are reinforced so that loads are not
entirely borne by the bone. Here, a washer 2106 having a central
opening 2102 is positioned adjacent the sacral aperture. The washer
2106 may be positioned in a groove cut into the bone similar to the
embodiment described in FIGS. 4A-4C above so that it is flush with
the outer surface, or the washer 2106 may be secured to the bone
forming a raised region. The washer may be sutured, strapped,
fixtured, buckled, tied, twisted, ratcheted or bonded to the bone.
In this embodiment, the washer 2106 is held in position using a
wire 2110 which passes through an aperture 2108 in the washer and
the other end of the wire may be secured to the bone. External
reinforcement may also be combined with internal lining. The washer
2106 may also include any of the surface treatments or coatings
described in this application.
[0087] FIGS. 9A-9E illustrate a crossbar engaged with the sacrum as
an anchor member for constraint device attachment. In FIG. 9A, a
crossbar 902 is coupled with the sacrum S transverse to the midline
of the spinal segment. This allows fixtures such as screws which
penetrate the wings or ala of the sacrum to avoid the spinal canal
and also allows the fixtures to be placed deeper into the bone for
improved purchase. The crossbar 902 may have a fixed length that
matches the sacral anatomy or the crossbar may have a sliding,
telescoping or otherwise adjustable length. Also, the crossbar may
be malleable so that it may be formed to match the surface contours
of the sacrum. Fixtures such as screws 906 may be used to
threadably attach the crossbar to the sacrum. In this embodiment,
four screws 906 are used to secure the crossbar with the bone.
Other means for attaching the anchor member to the bone may also be
used in conjunction with screws or by themselves, such as using
bone cement, dowel pins, etc. In FIG. 9A, the crossbar 902 has an
attachment feature 904 for engaging and holding the constraint
device. Here, the attachment feature comprises two slots for
receiving and holding a portion of the constraint device, such as
the tether. The attachment feature could include other options such
as passages, hooks or retention features such as clamps, some of
which are disclosed below.
[0088] In FIG. 9B a constraint device comprises a tether 908
coupled with two compliance members 910. A lower portion of the
tether 908 is advanced through an aperture 916 in a tube 914
coupled with the crossbar 902. Apertures 918 on either end of the
crossbar 902 are used to receive a fastener such as a screw 912 so
that the crossbar 902 is secured to the sacrum. In FIG. 9C, a post
920 is disposed on the crossbar 902 and the lower portion of the
tether may then be wrapped around the post. Additional details
involving the use of a post coupled either directly with the sacrum
or coupled to a crossbar are described below in other exemplary
embodiments.
[0089] In FIG. 9D, the tether structure 908 has two free ends which
may be threaded through apertures 922 in the crossbar 902. The ends
may then be secured by knotting the free ends, pinning them in
place, locking them, or by using other methods well known in the
art. Other applicable locking mechanisms are disclosed below. In
FIG. 9D, the crossbar 902 may be secured to the sacrum with screws
912 that pass through apertures 918 on either end of the crossbar.
FIG. 9E illustrates another embodiment of attachment of the
constraint device to the sacrum. In FIG. 9E, a crossbar 902 is
fixed to the sacrum S with pins or screws 930 on either end of the
crossbar 902. The crossbar 902 has an elongated, elliptically
shaped aperture 932 which may receive a portion of the constraint
device. In this embodiment, the constraint device comprises an
upper tether 924 which is disposed around a superior surface of a
superior spinous process SP. The upper tether 924 has a fixed end
and a free end 926 which is engaged with a first compliance member
934. The free end 926 may be pulled through a locking mechanism on
the compliance member 934, thereby adjusting length or tension in
the constraint device. The fixed end is fixedly coupled with the
second compliance member in this embodiment, although it also could
be adjustable. A lower portion of the tether 936 also has a fixed
end and a free end 928. The fixed end may be fixed with the first
compliance member or it may be adjustable. The free end is similar
to the upper tether free end 926, and it may be adjustably coupled
with the second compliance member. The lower portion of the tether
is threaded through the aperture 932, thereby securing the tether
and constraint device to the sacrum S. While this method of
attaching the constraint device to the sacrum is relatively easy to
perform, in some situations the method may result in twisting of
the constraint device which causes asymmetry in the device along
with unbalanced forces applied to the spinal segment.
[0090] FIG. 10 illustrates the use of a screw as the sacral anchor
member. In FIG. 10, an anchor screw 1002 is threadably engaged with
the sacrum. In this exemplary embodiment, the screw 1002 may be
screwed into a crest of the sacrum axially in the caudal direction.
This allows the screw to be much longer than if it were threaded
perpendicularly in an anterior direction into the bone. A screw
directed in the anterior direction could penetrate either the
spinal canal or the anterior cortex of the sacrum and the colon. By
directing the screw axially in the caudal direction permits a
longer screw to be used without fear of penetrating the regions
listed above, and allows a longer portion of the screw threads to
be engaged with the bone, thereby providing greater purchase. A
tether structure 1004 may be threaded through an aperture 1006,
eyelet, hook or other attachment feature on the screw. The
orientation of the screw also helps distribute loads primarily in
the direction of the screw's longitudinal axis which is desirable
since it results in less bending moments exerted on the screw which
can cause screw fatigue, loosening and "toggling," all which are
commonly associated with bone screws. In alternative embodiments,
the screw may be oriented in a cranial direction.
[0091] Instead of using a screw as in FIG. 10, a pin may be used to
help create or enhance the sacral attachment region. In FIG. 22, a
pin 2202 that is inserted in the cranial direction into a crest,
spinous process or tubercle 2204 of the sacrum S. A portion of the
pin is embedded in the bone while a portion is left unembedded. The
unembedded portion of the pin forms an overhang and the tether 2206
of the constraint device is captured between the overhang and the
sacrum. Thus the tether is captured on an inferior side of the
sacral crest. Here, a single pin is used, although more than one
pin may be used if required. In other embodiments, the pin may
include a flanged rim, boss or land that prevents the pin from
further penetration into the bone. The flange may be fixed or it
may be adjustable so that penetration depth may be varied.
Additionally, the pin may have threads on the shaft in order to
facilitate implantation into the bone and enhance fixation. Still
other embodiments of the pin may have an arcuate section such that
as the pin is advanced into the bone, the curve forces the pin in a
direction away from and prevents penetration of the pin into the
sacral canal.
[0092] Lateral retaining bars may also be used to retain the tether
to the sacrum. In FIG. 23A, a rectangular shaped retaining bar 2306
is laterally positioned in a crest, spinous process or tubercle
2302 of the sacrum S. In this embodiment, a single bar extends from
one side of the crest 2302 to the other side and a portion of the
retaining bar 2306 extends past each side of the crest 2303,
forming a flange. Tether 2304 may then be held in position by the
flanged portion of the retaining bar 2306. In FIG. 23A, the
retaining bar may be a single bar pushed through the crest 2302 or
two separate bars may be pressed into the crest 2302 from opposite
sides. Additionally, the retaining bar 2306 may be pressed directly
into the bone, or a channel may be drilled or otherwise cut into
the bone before receipt of the bar. In FIG. 23B, a single retaining
bar 2308 is pushed through the crest 2302. One end of the retaining
bar has a T-shaped end 2312 which serves as a stop to prevent the
bar from penetrating too deeply into the bone and also creates the
flanged region for retaining the tether 2304. A pin, spline or
other elongate element 2310 may then be placed through the opposite
end of the bar in order to lock the bar into position and to create
a second flanged region for retaining the tether 2304.
Additionally, in other embodiments, the retaining bar ends may be
curved to help enhance retention of the tether by forming hook-like
regions as well as preventing sharp or long ends from protruding as
well as producing a profile that may approximate the sacral surface
more closely.
[0093] Retaining clips are also useful way of engaging a tether
with the sacrum, as seen in FIGS. 24A-24C. In FIG. 24A a retaining
clip 2402 has two legs 2408 and a pair of flanges 2404 or wings.
Sharpened fingers 2406 help engage the clip with bone without
requiring deep penetration into the bone. The fingers 2406 may
comprise hooks, barbs or teeth to improve purchase on the sacral
surface. In use, the clip may be stretched open and then allowed to
spring back and close around a spinous process, tubercle or crest
of the sacrum S. Alternatively, the clip 2402 may be pressed and
deformed against these regions. In either case, the clip is then
securely attached to the raised area of the sacrum S and a portion
of the tether is captured under the flanges 2404 and secured to the
sacrum S. FIG. 24B illustrates a side view of a constraint device
having an upper tether portion 2410 coupled with a superior spinous
process SP and a lower tether portion 2414 captured between the
wings or flanges 2404 of the retaining clip 2402 and the sacrum S.
Compliance members 2412 join the upper and lower tethers. FIG. 24C
illustrates a back view of the FIG. 24B. Any of the
osseo-integration surface treatments or coatings disclosed herein
may also be used with retaining clip 2402 to help engagement of the
clip with the bone.
[0094] Additional embodiments of retaining clips are illustrated in
FIGS. 25A-25E. In FIG. 25A, the clip may be attached to a crest,
spinous process or tubercle of a sacrum in the same manner as
previously described with respect to FIGS. 24A-24C. Retaining clip
2502 has two legs 2504, 2506 which may spring into engagement with
the sacrum S or which may be deformed into engagement with the
sacrum S. Fingers 2508 which may take the same form as the fingers
2406 help the clip engage the bone. The retaining clip has an
aperture 2510 extending through both legs 2504, 2506. The tether
may be passed through this aperture, thereby securing the tether to
the clip and sacrum. FIG. 25B illustrates an alternative embodiment
of a retaining clip similar to that of FIG. 25A, except this
embodiment does not have aperture 2510 and instead has an overhang
2516 which forms a lip for retaining the tether. FIG. 25C
illustrates a side view of the retaining clip in FIG. 25B when
clipped to the sacrum S and how overhang 2516 retains tether 2518.
FIG. 25D is a back view of FIG. 25C. FIG. 25E is a side view
showing the retaining clip of FIG. 25A when clipped to the sacrum
S. Tether 2518 is secured to the clip 2504 by passing through
aperture 2510. Any of these retaining clips may also include the
osseo-integration coatings and surface treatments described herein
to help engagement of the clip with the bone.
[0095] Other clip-on anchors may include wire-like staples such as
those illustrated in FIGS. 26A-26D. In FIG. 26A, a wire-like clip
or staple 2602 is attached to a spinous process, tubercle or crest
SP of the sacrum. The clip may be applied with a staple-like gun or
the device may be applied manually by a surgeon. A tether may be
coupled with the wire-like clip 2602 by passing it through a looped
portion 2606 in the clip. FIG. 26B is an enlarged view of FIG. 26A.
The staple-type anchor may include a series of contact points such
as seen in FIG. 26C. Here, the retaining clip 2610 is applied with
a staple-type gun or manually by the surgeon and a hook or overhang
region 2612 allows the clip to retain the tether 2614. FIG. 26D
represents a cross-section of FIG. 26C taken along line A-A.
[0096] Any of the retaining clips or other devices disclosed herein
may further comprise a carabiner-style gate for receiving and
retaining a part of the constraint device. FIG. 27 illustrates one
such embodiment. In FIG. 27, a gate 2702 is movable from a closed
position to an open position. In the open position, a portion of a
constraint device such as a tether may be passed into the receiver
2704. Once the gate is closed, the tether is captured by the clip.
The gate may be spring loaded so that it is biased into the closed
position.
[0097] Other mechanisms for retaining a tether to the sacrum
include the use of a retaining plate that is coupled to adjacent
crests, spinous processes or tubercles of the sacrum. For example,
in FIG. 28A, a retaining plate includes an elongate middle section
2802 having an enlarged fork-like head and tail sections 2804,
2806. Each fork-like section is U-shaped with the arms of the U
forming a receptacle in which a portion of the sacrum may rest.
Apertures 2808 on both head and tail sections allow a pin 2812 or
other fixture to secure the retaining plate to the bone. FIG. 28B
illustrates a side-view of a retaining plate 2802 coupled to the
sacrum and retaining a portion of a constraint device. A constraint
device has an upper tether portion 2814 coupled with a superior
spinous process SP and a lower tether portion 2818 disposed and
retained under the retaining plate 2802. A compliance member 2816
is coupled between the upper and lower tether portions. The
retaining plate 2802 has opposite ends pinned to raised regions
2820 of the sacrum. The raised regions 2820 may be a crest, spinous
process or tubercle. FIG. 28C illustrates a dorsal view of FIG.
28C.
[0098] In some situations, it is preferable to use the existing
natural features of the sacrum for tether anchoring rather than
modifying the bone with notching or other bone removal procedures
or screwing, stapling or pinning anchors into the bone. Screws in
particular have many known limitations and co-morbidities such as
invasiveness, blood loss, toggling or loosening of the screw,
fatigue or fracture, etc. Therefore, anchors which directly appose
bone without resection may be advantageous. Hooks for example are
desirable since they are less invasive than screws or nails and
even anchors that do penetrate bone with teeth or nails may still
be preferable to screws if they require less bone resection and
penetration, or are easier to implant and distribute loads more
evenly or provide other beneficial features. FIG. 29 illustrates
the use of hooks engaged with neural foramina of the sacrum. FIG.
29 illustrates neural foramina 2912 in the sacrum S. Neural
foramina 2912 are often lateral of the spinal segment midline,
therefore two foramina on opposite sides of the midline may be
joined with a transverse retaining device. In FIG. 29, a retaining
device includes a pair of hooks 2914 engaged in neural foramina
2908 of the sacrum S. The hooks 2914 are coupled together with a
transverse member 2916 such as a bar, wire, tether or other cross
member. The retaining device is used to secure a portion of a
constraint device to the sacrum S and may straddle the paraspinal
muscles (see FIG. 31). Constraint device 2910 includes an upper
tether portion 2902 coupled with a superior spinous process SP and
a lower tether portion 2906 is looped around and captured by the
cross member 2916 of the retaining device 2910. A pair of
compliance members 2904 couple the upper and lower tether portions
2902 and 2906 together.
[0099] FIGS. 30A-30D illustrate the anatomy of a neural foramen and
various configurations of foramenal hooks. FIG. 30A illustrates a
cross section of a sacral foramen 3012. The foramen is an aperture
between an upper (cranial direction 3002) and lower (caudal
direction 3004) portion of the sacrum. A nerve 3006 coupled with
the nerve root running in the spinal canal, near the dorsal surface
of the spinal canal 3008 may exit the foramen and may run adjacent
the dorsal sacral surface 3010. Because of the presence of the
nerve 3006, care must be used to avoid injuring the nerve when
hooks are placed in the foramen. FIGS. 30B-30D illustrate various
configurations of neural foramina hooks which may be used to engage
the foramen. In FIG. 30B, a hook 3020 has a single arm which is
positioned in the foramen 3012 and cranially-oriented such that the
hook is retained when under tension. In FIG. 30C, hook 3022 has two
arms, one arm 3022 is positioned in the foramen 3012 and cranially
oriented and a second arm 3024 which is positioned in the foramen
3012 and caudally oriented, thus the hook 3020 is retained in the
foramen. FIG. 30D illustrates still another foramenal hook
embodiment, this embodiment includes a hook 3024 having a claw
configuration with the claw positioned in adjacent foramen so that
the claw grasps the bone in between the two foramina. Thus, in FIG.
30D, the hook remains engaged with the sacrum.
[0100] The foramina hooks previously described have many
advantages, but must be used with caution in order to avoid
pinching the nerves in the area. Therefore, in some situations, it
still may be advantageous to use hooks, but to engage them with
another portion of the sacrum that minimizes or avoids pinching
nerves. FIG. 31 illustrates a retaining device having a pair of
hooks 3108 that are engaged with a lateral edge 3110 of the sacrum
S. A transverse connector such as bar, rod, wire, tether or other
cross member 3112 joins the two hooks 3108 together. A lower tether
portion 3106 of the constraint device may then be looped around the
cross member 3112 and secured to the sacrum S. The remainder of the
constraint device includes an upper tether portion 3102 engaged
with a superior spinous process SP and a pair of compliance members
3104 joining the upper and lower tether portions together. In
addition to avoiding the nerves in the foramina, this embodiment
also allows the retaining device to straddle the paraspinal muscles
P thereby causing minimal disruption to the muscles. Any of the
hook embodiments previously described may be used to hold the
retaining device to the edges of the sacrum.
[0101] An anchor member may be attached to the sacrum without
screws as seen in FIGS. 11A-11D. In FIG. 11A, an anchor plate 1106
having a plurality of nail-like protrusions 1108 is engaged with
the sacrum S. In this embodiment, the nails are inclined relative
to the outer surface of the plate 1106 to help resist applied loads
from the constraint device which includes an upper tether portion
1116 coupled with a superior spinous process SP and a lower tether
portion 1112 coupled with the anchor plate 1106 via an aperture
1110. In other embodiments, the anchor plate 1106 may have a
plurality of apertures through which individual nails may be
passed. Using a plurality of nails distributed along the length of
the anchor allows loads to be distributed over more points
therefore shorter nails may be used, avoiding the need for deep
penetrating nails. Preferably, the nails only penetrate the
cortical bone on the dorsal surface of the sacrum, minimizing the
risk of neural injury, but penetration may be varied as required. A
compliance member 1114 is disposed between the upper 1116 and lower
1112 portions of the tether. In this exemplary embodiment, the
anchor plate 1106 may be inserted through a minimally invasive
incision through the skin SK and then hammered into position with a
custom placement tool 1104 and mallet 1102. In this embodiment, the
aperture 1110 allows coupling of the anchor plate 1106 with the
tether, although other attachment features such as a hook may be
used. One of the advantages of this type of anchor is that there is
greater flexibility in attachment of the tether structure in the
cranial or caudal direction. Attaching the tether structure to
native anatomy such as a spinous process or a notch in the sacrum
is likely to be limited to specific areas of the sacrum. Using the
anchor plate allows the attachment region to be moved in the
cranial or caudal direction which will help accommodate the
compliance member and other portions of the tether structure.
[0102] An alternative embodiment of the anchor plate 1106 may be
seen in FIG. 11B. In FIG. 11B anchor plate 1106a comprises a hook
1118 for engaging the tether structure and instead of nails, a
plurality of hooks, claws or barbs 1108a are used to secure the
anchor plate 1106a to the sacrum S. FIG. 11C shows a constraint
device having an upper tether portion 1116 coupled with a superior
spinous process SP and a lower tether portion 1112 coupled with the
hook 1118 on anchor plate 1106a. A free end 1120 of the upper
tether 1116 and a free end 1120 of the lower tether 1112 pass
through a locking mechanism 1122 adjacent each compliance member
1114. Thus, length or tension in the tethers may be adjusted.
Additional details on the locking mechanism are disclosed elsewhere
in this application. FIG. 11D shows a side view of the constraint
device coupled with a spinous process SP and the anchor plate
1106a.
[0103] Additionally, the surfaces of anchor plate 1106 that engage
the sacrum S may be treated to create a surface that promotes
osseointegration of the plate with the bone. Exemplary treatments
include beading as well as hydroxyapatite and titanium coatings.
These surface treatments may be applied to any of the implants
disclosed in this specification.
[0104] Referring now to FIG. 12, pins or screws 1208 are placed in
the sacrum S and help to secure a constraint device to the bone. In
FIG. 12, a constraint device includes an upper tether portion 1202
that is disposed over a superior spinous process and a lower tether
portion 1206 is disposed around two screws 1208 threaded into the
sacrum S. Two compliance members 1204 join the upper and lower
tether portions together. Additionally, a free end 1210 of the
upper tether portion 1202 is received by one of the compliance
members 1204 and allows adjustment of the tension or length in the
constraint device.
[0105] In FIG. 13 a crossbar 1302 is anchored to the sacrum S with
two screws 1304 on either end of the crossbar 1302. In this
embodiment, the constraint device includes an upper tether 1306
looped around a superior spinous process SSP with a free end 1308
engaged with a locking mechanism 1312 on the compliance member
1310. The locking mechanism allows the length and tension of the
constraint device to be adjusted to accommodate different patients.
Various locking mechanisms are disclosed in U.S. patent application
Ser. No. 12/479,016 (Attorney Docket No. 026398-000710US) and PCT
Publication No. WO 2009/149407 (Attorney Docket No.
026398-000810US), the entire contents of both are incorporated
herein by reference. Also in this embodiment, a lower portion of
compliance member 1310 is coupled with a post or raised screw 1312
disposed on the crossbar 1302. The raised screw 1312 is preferably
located along the spinal segment midline, although it may be
located off center if desired.
[0106] FIGS. 14A-14B illustrate embodiments of constraint devices
anchored to the sacrum S with a pin or screw. In FIG. 14A, a
constraint device includes an upper tether 1402 disposed at least
partially around a superior surface of a superior spinous process
SP. One end of the upper tether 1402 is pre-attached to a first
compliance member 1408 while the opposite end of tether 1402 is a
free end 1404 that is received in a locking mechanism 1406 of a
second compliance member 1410. The locking mechanism 1406 allows
length and/or tension in the constraint device to be adjusted. Any
of the locking mechanisms previously described above may be used in
this embodiment. The first compliance member 1408 is coupled to a
loop 1412 in the tether structure and the loop 1412 is secured to a
post or screw 1414 in the sacrum S. An optional adjusting mechanism
1416 may be included in the first compliance member 1408 or the
second compliance member 1410 in order to allow further adjustment
of length and/or tension in the constraint device. A second loop
1412 is coupled with the second compliance member 1410 and a pin or
screw 1414 secures the second loop 1412 to the sacrum S.
[0107] The embodiment of FIG. 14B is similar to that in FIG. 14A
with the major difference being that the tether structure in FIG.
14B has two free ends that may be adjusted. In FIG. 14B, the
constraint device includes an upper tether 1402 disposed at least
partially around a superior surface of a superior spinous process
SP. Both free ends 1404, 1405 of the upper tether are received in a
locking mechanism 1406 in each of the two compliance members 1408,
1410. The locking mechanism 1406 may be any of those previously
disclosed above. Similar to the embodiment of FIG. 14A, looped ends
1412 of the tether are coupled on one end to a compliance member,
either 1408, 1410 and secured at the other end to a pin or screw
1414 in the sacrum S. In alternative embodiments the looped ends
1412 may be coupled to one notch or aperture in the sacrum (similar
to FIG. 5E, 5F or 7A), or in still other embodiments the looped
ends are individually coupled to a notch or aperture, one on each
side of the spinal segment midline.
[0108] The embodiments of FIGS. 15A-15E use a pin or post secured
to a sacral crossbar as an attachment point for the constraint
device. In FIG. 15A, a crossbar 1522 is secured to the sacrum S
with two screws 1512 on either end of the crossbar. A central pin
or post 1516 is coupled with the crossbar 1522 and is used to
attach a constraint device to the sacrum. The constraint device in
FIG. 15A includes an upper tether 1502 disposed around an upper
surface of a superior spinous process SP. A free end 1506 of the
upper tether 1502 is received in a locking mechanism 1504 of a
first compliance member 1508 so that tension and/or length may be
adjusted. The opposite end of upper tether 1502 is pre-attached
with a second compliance member 1508. A lower tether 1514 is
disposed around a central pin or post 1516 and includes a free end
1510 that is also received in a locking mechanism 1520 of the
second compliance member 1508 to allow additional adjustment of
length and/or tension in the constraint device. The opposite end of
the lower tether 1514 is pre-attached with the first compliance
member. FIG. 15B illustrates the central pin or post 1516 in
greater detail. The post 1516 comprises a central concave region
1520 disposed between two enlarged shoulder or head regions 1518.
This helps prevent the tether 1514 from sliding off the post.
[0109] The embodiment of FIGS. 15C-15D is similar to the embodiment
illustrated in FIGS. 15A-15B with the major difference being how
the compliance device is coupled to a central post. As in FIG. 15A,
a crossbar 1522 is secured to the sacrum S with two screws 1512 on
either end of the crossbar 1522. The constraint device in this
embodiment generally takes the same form as the device described
with respect to FIG. 15A. In FIG. 15C, central post 1513 has an
aperture and the lower tether 1514 may be advanced through this
aperture and then secured to the compliance members 1508. FIG. 15D
illustrates the central post 1513 in greater detail. The aperture
may be elliptical or rectangular or any other shape that may
receive the tether structure 1514. An additional lower aperture
1526 allows the central post 1513 to engage the crossbar 1522 and a
set screw 1530 may be used to secure the components together.
[0110] Various embodiments of posts or pins are illustrated in
FIGS. 16A-16F. Any of these may be fabricated from metals such as
titanium or stainless steel, or they may be made from other
materials such as polymers or ceramics. Additionally, any of these
may be used in any of the embodiments disclosed above where the
constraint device is either wrapped around a post, pin, or screw or
threaded through an aperture in the post, pin, or screw. These
posts or pins may be secured directly into the sacrum or to an
anchor member such as a crossbar that is secured to the sacrum. The
posts/pins may be press fit into engagement with the sacrum or the
anchor member, or they may be coupled with another fastener such as
a screw that is threadably engaged with the bone or anchor.
Referring now to FIG. 16A, a pin has a elongate cylindrically
shaped body 1602 having a substantially constant diameter. A hex
head 1604 is provided so that a tool may engage and rotate the pin.
One of skill in the art will appreciate that other heads such as a
slot, Phillips, Torx, etc. may easily be substituted for the hex
head in this embodiment as well as any of the screw, pin or post
embodiments disclosed herein. In FIG. 16B, the pin has an elongate
cylindrical body 1606 also with a constant diameter, except that
this embodiment also includes an enlarged head/shoulder region 1608
that is coupled with the cylindrical body 1606 in order to prevent
a tether from slipping off the post. This embodiment also includes
a hex head 1604. The embodiment of FIG. 16C includes a concave
central region 1610 disposed between two enlarged head/shoulder
regions 1612, one of which includes a hex head 1604. Again, the
enlarged regions help prevent slipping of a tether off the
post.
[0111] FIG. 16D illustrates yet another embodiment of a pin or post
that may be used to help secure a constraint device either directly
or indirectly with a sacrum. In FIG. 16D, the central region of the
pin is concave and it is surrounded on either side by an enlarged
head/shoulder region 1616. One end of the post includes a hex head
1604. The transition from the concave region to the enlarged
head/shoulder region includes an annular flange 1618 on both ends
and this feature is also helpful for preventing slippage of the
tether structure off the pin/post. In FIG. 16E, the pin/post has a
cylindrical body 1620 with a central slot 1622 or aperture for
receiving the tether structure. Often, one end of the tether is
free so that it may be threaded through the slot and then secured
to the remainder of the constraint device with a locking mechanism
Once the tether is fed through the slot, it is captured and cannot
slip off the post. In this embodiment, the slot is elliptical in
shape, although one of skill in the art will appreciate that other
slot geometries may also be used. FIG. 16F illustrates still
another embodiment of a post/pin. In this embodiment, a central
cylindrically shaped region of constant diameter 1624 is surrounded
on either side by an enlarged head/should region 1626. The
transition from the central cylindrical region 1624 to the enlarged
head regions 1626 includes a step or flanged region 1628 on both
ends.
[0112] As previously mentioned, any of the post/pin embodiments may
be coupled with a screw for direct engagement with the sacrum.
FIGS. 17A-17B illustrate two exemplary embodiments of post/pins
having threaded regions that may be threadably engaged with the
sacrum. In FIG. 17A, a screw 1702 includes a head region having a
recessed step 1706 for holding a tether. A flange region 1708
prevents the tether from slipping off the post. A hex head or other
driver feature may be included on a top surface of the flange
region. A tapered head region 1710 allows better grip with cortical
bone and a tapered thread 1712 increases the grip of the screw with
bone. The dual lead 1704 design is also desirable since it allows
faster and more efficient penetration of the screw into the bone.
FIG. 17B illustrates an alternative embodiment of a screw 1714 that
can be threaded into the sacrum. In FIG. 17B, flanged region 1708
prevents slippage of the tether off the pin and provides an area
for a driver feature such as a hex head. An increased thread pitch
1718, dual lead 1704 and deeper thread 1720 permit more efficient
cutting into the bone. This embodiment also includes a tapered head
1716. Exemplary dimensions of these screws may include an outer
diameter from about 5 mm to about 8 mm, and more preferably from
about 6.5 mm to about 7.5 mm, with a thread length ranging from
about 20 mm to about 70 mm and more preferably from about 35 mm to
about 50 mm.
[0113] Many embodiments disclosed above relate to attachment of a
constraint device to the upper sacrum. An alternative attachment
location could be the lower sacrum such as the coccyx or
sacro-coccygeal junction. For example, in FIG. 32, a constraint
device has an upper tether portion 3202 coupled to a superior
spinous process SP and a long lower tether portion 3208 that passes
over the sacrum and is coupled to the coccyx 3210. A pair of
compliance members 3204 (only one illustrated in this side view)
join the upper and lower tether portions. This configuration is
desirable since the lower tether portion cannot slip off.
Additionally, the tethers are oriented parallel to the spinal
midline and medially oriented close to the midline which are
preferred positions for a flexion restricting device. Various
embodiments of constraint devices which may be coupled with the
lower sacrum are illustrated in FIGS. 33A-33B.
[0114] For example, the constraint device in FIG. 33A includes an
extra long lower tether portion 3306 that can accommodate the
additional distance required to be looped around the coccyx. The
upper tether portion 3302 is shorter than the lower portion, but
sized to be coupled with an upper spinous process. A pair of
compliance members 3304 join the upper and lower tether portions.
In FIG. 33B, the lower tether portion 3310 is a single tether
having a looped end 3312 for looping around the coccyx.
Additionally, a connector or shackle 3308 is attached to an upper
part of the lower tether portion 3310 and allows the lower tether
portion to be joined with a constraint device such as that
illustrated in FIG. 2A.
[0115] The constraint device may be coupled with the coccyx in
several different surgical procedures such as those illustrated in
FIGS. 34A-34B. For example, in FIG. 34A, an upper tether portion
3402 of the constraint device is coupled with a superior spinous
process SP. An extra long lower tether portion 3406 is then
advanced subcutaneously caudally toward the coccyx and then looped
around the coccyx 3410. The free end 3408 of the lower tether
portion is then advanced in the cranial direction and coupled with
a compliance member 3404 which is also coupled with the upper
tether portion 3402. In FIG. 34B, the upper tether portion 3402 is
coupled with an upper spinous process SP. A second incision may be
made and a lower tether portion 3414 is looped around the coccyx
3410 and the free end 3416 is advanced subcutaneously in the
cranial direction wherein it will be connected to a tail 3412 on
the compliance member 3404. Orthopedic cables, wires, sutures, band
passing instruments are well known in the art and may be used to
facilitate movement of the tethers
[0116] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
and equivalents may be used. Therefore, the above description
should not be taken as limiting the scope of the invention which is
defined by the appended claims.
* * * * *