Note: Descriptions are shown in the official language in which they were submitted.
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INTER-FACET IMPLANT
CLAIM OF PRIORITY
This application claims priority to the following applications, which are all
incorporated herein by
reference:
United States Provisional Application No. 60/635,453 entitled INTER-CERVICAL
FACET
IMPLANT AND METHOD, by James F. Zucherman et al., filed December 13, 2004
(Attorney Docket
No. KLYC-01118US0);
United States Provisional Application No. 60/668,053 entitled INTER-CERVICAL
FACET
IMPLANT DISTRACTION TOOL, by Scott A. Yerby et al., filed April 4, 2005
(Attorney Docket No.
KLYC-01125US0);
United States Provisional Application No. 60/679,363 entitled INTER-CERVICAL
FACET
IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al., filed May 10,
2005 (Attorney
Docket No. KLYC-01118US7);
United States Provisional Application No. 60/679,361 entitled INTER-CERVICAL
FACET
IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al., filed May 10,
2005; (Attorney
Docket No. KLYC-01118US 8);
United States Provisional Application No. 60/679,377 entitled INTER-CERVICAL
FACET
IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al., filed May 10,
2005 (Attorney
Docket No. KLYC-01118US9);
United States Provisional Application No. 60/687,765 entitled INTER-CERVICAL
FACET
IMPLANT WITH MULTIPLE DIRECTION ARTICULATION JOINT AND METHOD FOR
IMPLANTING, by James F. Zucherman et al., filed June 6, 2005 (KLYC-0 11
18US6);
United States Provisional Application No. 60/717,369 entitled INTER-CERVICAL
FACET
IMPLANT WITH SURFACE ENHANCEMENTS, by James F. Zucherman et al., filed
September 15,
2005; (Attorney Docket No. KLYC-01133US0);
United States Utility Patent Application No. 11/053,399 entitled INTER-
CERVICAL FACET
IMPLANT AND METHOD, by Charles J. Winslow et al., filed February 8, 2005
(Attorney Docket No.
KLYC-01118US 1);
United States Utility Patent Application No. 11/053,624 entitled INTER-
CERVICAL FACET
IMPLANT AND METHOD, by Charles J. Winslow et al., filed February 8, 2005
(Attorney Docket No.
KLYC-01118US2);
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United States Utility Patent Application No. 11/053,735 entitled INTER-
CERVICAL FACET
IMPLANT AND METHOD, by Charles J. Winslow et al., filed February 8, 2005
(Attorney Docket No.
KLYC-0 111 8US3);
United States Utility Patent Application No. 11/053,346 entitled INTER-
CERVICAL FACET
IMPLANT AND METHOD, by Charles J. Winslow et al., filed February 8, 2005
(Attorney Docket No.
KLYC-01122US0);
United States Utility Patent Application No. 11/093,557 entitled INTER-
CERVICAL FACET
IMPLANT WITH LOCKING SCREW AND METHOD, by Charles J. Winslow et al., filed
March 30,
2005 (KLYC-01118US5); and
United States Utility Patent Application No. 11/093,689 entitled INTER-
CERVICAL FACET
IMPLANT AND METHOD FOR PRESERVING THE TISSUES SURROUNDING THE FACET
JOINT, by Carl Lauryssen et al., filed March 30, 2005 (KLYC-01124US0).
TECHNICAL FIELD
This invention relates to interspinous process implants.
BACKGROUND OF THE INVENTION
The spinal column is a bio-mechanical structure composed primarily of
ligaments, muscles,
vertebrae and intervertebral disks. The bio-mechanical functions of the spine
include: (1) support of the
body, which involves the transfer of the weight and the bending movements of
the head, trunk and arms to
the pelvis and legs, (2) complex physiological motion between these parts, and
(3) protection of the spinal
cord and the nerve roots.
As the present society ages, it is anticipated that there will be an increase
in adverse spinal
conditions which are characteristic of older people. By way of example only,
with aging comes an increase
in spinal stenosis (including, but not limited to, central canal and lateral
stenosis), and facet arthropathy.
Spinal stenosis results in a reduction foraminal area (i.e., the available
space for the passage of nerves and
blood vessels) which compresses the cervical nerve roots and causes radicular
pain. Humpreys, S.C. et al.,
Flexion and traction effect on C5-C6foraminal space, Arch. Phys. Med.
Rehabil., vol. 79 at 1105 (Sept.
1998). Another symptom of spinal stenosis is myelopathy, which results in neck
pain and muscle
weakness. Id. Extension and ipsilateral rotation of the neck further reduces
the foraminal area and
contributes to pain, nerve root compression, and neural injury. Id.; Yoo, J.U.
et al., Effect ofcervical spine
motion on the n.euroforaminal dimensions ofhuinan cervical spine, Spine, vol.
17 at 1131 (Nov. 10, 1992).
In contrast, neck flexion increases the foraminal area. Humpreys, S.C. et al.,
supra, at 1105.
In particular, cervical radiculopathy secondary to disc hemiation and cervical
spondylotic
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foraminal stenosis typically affects patients in their fourth and fifth
decade, and has an annual incidence
rate of 83.2 per 100,000 people (based on 1994 information). Cervical
radiculopathy is typically treated
surgically with either an anterior cervical discectomy and fusion ("ACDF") or
posterior
laminoforaminotomy ("PLD"), with or without facetectomy. ACDF is the most
commonly performed
surgical procedure for cervical radiculopathy, as it has been shown to
increase significantly the foramina
dimensions when compared to a PLF.
It is desirable to eliminate the need for major surgery for all individuals,
and in particular, for the
elderly. Accordingly, a need exists to develop spine implants that alleviate
pain caused by spinal stenosis
and other such conditions caused by damage to, or degeneration of, the
cervical spine.
The present invention addresses this need with implants and methods for
implanting an apparatus
into at least one facet joint of the cervical spine to distract the cervical
spine while preferably preserving
mobility and normal lordotic curvature.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a lateral view of two adjacent cervical vertebrae and spinous
processes, highlighting
the cervical facet joint.
FIG. 2 depicts a lateral view of the cervical spine with spinal stenosis.
FIG. 3A depicts correction of cervical stenosis or other ailment with a wedge-
shaped embodiment
of the implant of the invention positioned in the cervical facet joint.
FIG. 3B depicts correction of cervical kyphosis or loss of lordosis with a
wedge-shaped
embodiment of the invention with the wedge positioned in the opposite
direction as that depicted in FIG.
3A.
FIG. 4 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention including a screw fixation device for attaching to a
single vertebra.
FIG. 5 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising screw fixation of two implants, one
implant fixed to each of two
adjacent vertebrae.
FIG. 6 shows cervical spine kyphosis, or loss of lordosis.
FIG. 7 shows correction of cervical kyphosis, or loss of lordosis, with a
further embodiment of the
implant of the invention comprising two facet implants with screw fixation.
FIG. 8 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising a facet implant and a keel.
FIG. 9 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the inverition, comprising facet implant, a keel, and screw
fixation.
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FIG. 10 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising a facet implant with teeth.
FIG. 11 depicts correction of cervical stenosis or other ailment with a
further embodiment of the
implant of the invention, comprising a facet implant with teeth and screw
fixation.
FIG. 12 depicts correction of cervical stenosis or other ailment with a
further embodiment of the
implant of the invention, comprising two facet implants having bony ingrowth
surfaces.
FIG. 13 depicts correction of cervical stenosis or other ailment with a
further embodiment of the
implant of the invention, comprising two facet implants having bony ingrowth
surfaces and posterior
alignment guide.
FIG. 14 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet implants with increased facet
joint contact surfaces.
FIG. 15 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet implants having bony ingrowth
surfaces and screw fixation.
FIG. 16 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet implants with articular inner
surfaces.
FIG. 17 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising a facet joint implant with a roller.
FIG. 18 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising a facet joint implant with a plurality of
rollers.
FIG. 19 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet joint implants, screw fixation,
and elastic restraint.
FIG. 20 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet joint implants, screw fixation,
and spring restraint.
FIG. 21 shows correction of cervical stenosis or other ailment with a further
embodiment of the
implant of the invention, comprising two facet joint implants, screw fixation,
and magnetic restraint.
FIG. 22A shows a perspective view of a further embodiment of implant of the
invention.
FIG. 22B shows a perspective exploded view of the embodiment of the invention
shown in FIG.
22A.
FIG. 23A depicts a posterior view of the embodiment of the implant of the
invention shown in
FIG. 22A.
FIG. 23B shows a posterior view of a locking plate of the embodiment of the
implant of the
invention shown in FIG. 22A.
FIG. 24A depicts a lateral side view of the embodiment of the implant of the
invention shown in
FIG. 22A.
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FIG. 24B shows a lateral side view of the keel of the locking plate of the
embodiment of the
implant of the invention shown in FIG. 22A.
FIG. 25A shows a perspective view of a further embodiment of the implant of
the invention.
FIG. 25B shows a side view of the embodiment of the implant of the invention
in FIG. 25A,
having a curved, uniformly-thick artificial facet joint spacer or inter-facet
spacer including a tapered end
FIG. 26A shows a perspective view of a further embodiment of the implant of
the invention
having a locking cam in a first position.
FIG. 26B shows a posterior view of the embodiment of the implant of the
invention depicted in
FIG. 26A.
FIG. 27A depicts a side view of the embodiment of the implant of the invention
shown in FIGS.
26A and 26B, implanted in the cervical spine.
FIG. 27B shows a posterior perspective view of the embodiment of the implant
of the invention
shown in FIGs. 26A, 26B, and FIG. 27A.
FIG. 28A depicts a posterior perspective view of a further embodiment of the
implant of the
invention.
FIG. 28B depicts a side view of the embodiment of the implant of the invention
shown in FIG.
28A.
FIG. 29A depicts a side view of an embodiment of a sizing tool of the
invention.
FIG. 29B depicts a top view of an embodiment of the sizing tool of the
invention depicted in FIG.
29A.
FIG. 29C depicts a perspective view of an embodiment of the sizing tool of the
invention depicted
in FIGs. 29A and 29B.
FIG 29D depicts a side view of the head of the sizing tool of the invention
depicted in FIG. 29A.
FIG. 29E depicts a cross-sectional view of the head of the sizing tool of the
invention depicted in
FIGS. 29A-29C.
FIG. 30 is a flow diagram of an embodiment of a method of the invention.
FIG. 31A is posterior view of a further embodiment of the implant of the
invention.
FIG. 31B is a side view of an embodiment of a locking screw of the implant of
the invention
depicted in FIG. 31A.
FIG. 32 is a posterior view of a further embodiment of the implant of the
invention.
FIGs. 33A and 33B depict initial and final insertion positions of the
embodiment of the
invention depicted in FIG 32.
FIGs. 34A and 34B illustrate a top and bottom plan view of an alternative
embodiment of an
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inter-cervical facet implant in accordance with the present invention.
FIG. 35 is a partially exploded perspective view of the implant of FIGs. 34A
and 34B.
FIGs. 36A and 36B illustrate side views of the implant of FIGs. 34A and 34B
illustrating a
general range of motion of the implant.
FIG. 37 is a side view of still another embodiment of an implant in accordance
with the
present invention.
FIG. 38 is a flow diagram of an embodiment of a method in accordance with the
present invention.
FIG. 39A is a posterior view of a further embodiment of the implant of the
invention.
FIG. 39B is a side view of a further embodiment of the implant of the
invention.
FIG. 40A is a perspective view of an embodiment of the implantation tool of
the invention.
FIG. 40B is a perspective view of the engagement head of the implantation tool
of the
invention.
FIG. 41A shows a perspective view of a further embodiment of the implant of
the invention
having a locking cam in a first position.
FIG. 41B shows a perspective view of a further embodiment of the implant of
the invention
having a locking cam in a second position.
FIG. 42A is a side view of still another embodiment of an implant in
accordance with the
present invention.
FIG. 42B is a top view of the implant of FIG. 42A.
FIG. 42C is a bottom view of the implant of FIG. 42A.
FIG. 42D-F are side views of the implant of FIG. 42A illustrating the various
arrangements of
a bone screw associated the implant.
FIG. 42G is an end view of the implant of FIG. 42F illustrating the
arrangement of the bone
screw associated the implant from an alternative viewing angle.
FIG. 43 is a side view of still another embodiment of an implant in accordance
with the
present invention.
FIG. 44 illustrates a side view of a distraction tool in accordance with one
embodiment of the
present invention.
FIG. 45 illustrates a side view of the distraction tool in accordance with one
embodiment of
the present invention.
FIG. 46A illustrates a perspective view of a distraction head of the
distraction tool in
accordance with one embodiment of the present invention.
FIG. 46B illustrates a perspective view of the distraction head of the
distraction tool in
accordance with one embodiment of the present invention.
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FIG. 47A illustrates a side view of a curved distraction head of the
distraction tool in
accordance with one embodiment of the present invention.
FIG. 47B illustrates a side view of the curved distraction head of the
distraction tool in
accordance with one embodiment of the present invention.
FIG. 48A illustrates a perspective view of a distraction tool in accordance
with one
embodiment of the present invention.
FIG. 48B illustrates a top view of the distraction tool in accordance with one
embodiment of
the present invention.
FIGs. 49A-49C illustrate one distraction process using the distraction tool of
the present
invention.
FIG. 49D illustrates a flow chart of one implantation method in accordance
with one
embodiment of the present invention.
FIG. 50A illustrates a perspective view of a distraction and insertion tool in
accordance with
one embodiment of the present invention.
FIG. 50B illustrates a top view of the distraction and insertion tool shown in
FIG. 50A in
accordance with one embodiment of the present invention.
FIG. 51 illustrates a perspective view of a distraction tool with sizing
mechanism in
accordance with one embodiment of the present invention.
Detailed Description
Embodiments of the present invention provide for a minimally invasive surgical
implantation
method and apparatus for cervical spine implants that preserves the physiology
of the spine. In particular,
embodiments provide for distracting the cervical spine to increase the
foraminal dimension in extension
and neutral positions. Such implants, when implanted in the cervical facet
joints, distract, or increase the
space between, the vertebrae to increase the foraminal area or dimension, and
reduce pressure on the nerves
and blood vessels of the cervical spine.
The facet joints in the spine are formed between two vertebrae as follows.
Eachvertebra has four
posterior articulating surfaces: two superior facets and two inferior facets,
with a superior facet from a
lower vertebra and an inferior facet of an upper vertebra forming a facet
joint on each lateral side of the
spine. In the cervical spine, the upward inclination of the superior articular
surfaces of the facet joints
allows for considerable flexion and extension, as well as for lateral
mobility. Each facetjoint is covered by
a dense, elastic articular capsule, which is attached just beyond the margins
of the articular facets. The
capsule is larger and looser in the cervical spine than in the thoracic and
lumbar spine. The inside of the
capsule is lined by a synovial membrane which secretes synovial fluid for
lubricating the facet joint. The
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exterior of the joint capsule is surrounded by a capsular ligament. It is this
ligament and the joint capsule
that must be cut in the embodiments of the method described herein for
inserting the artificial facet joint
spacer or inter-facet spacer.
In a specific preferred embodiment, an implanted interfacet spacer of 1.5 mm
to 2.5 mm in width
can result in interfacet distraction that increases foraminal dimension in
extension and neutral. Other
interfacet spacer dimensions also are contemplated by the invention described
herein below. The present
embodiments also preserve mobility of the facet joints.
Further embodiments of the present invention accommodate the distinct
anatomical structures of
the spine, minimize further trauma to the spine, and obviate the need for
invasive methods of surgical
implantation. Embodiments of the present invention also address spinal
conditions that are exacerbated by
spinal extension.
FIG. 1 shows a simplified diagram of a portion of the cervical spine, focusing
on a cervical facet
joint 1 formed between two adjacent cervical vertebrae. The spinous processes
3 are located posteriorly
and the vertebral bodies 5 are located anteriorly, and a nerve root canal 7 is
visible. Each vertebra has four
posterior articulating surfaces: two superior facets and two inferior facets,
with a superior facet from a
lower vertebra and an inferior facet of an upper vertebra forming a facet
joint on each lateral side of the
spine. In the cervical spine, the upward inclination of the superior articular
surfaces of the facet joints
allows for considerable flexion and extension, as well as for lateral
mobility. Each facet joint is covered by
a dense, elastic articular capsule, which is attached just beyond the margins
of the articular facets. The
capsule is large and looser in the cervical spine than in the thoracic and
lumbar spine. The inside of the
capsule is lined by a synovial membrane which secretes synovial fluid for
lubricating the facet joint. The
exterior of the joint capsule is surrounded by a capsular ligament. It is this
ligament that may be pushed
out of the way in the embodiments of the method for inserting the facet joint
spacer or inter-facet spacer,
described herein.
FIG. 2 depicts cervical foraminal stenosis. From the drawing, the nerve root
canal 7 is narrowed
relative to the nerve root canal 7 depicted in FIG. 1. The spinal canal and/or
intervertebral foramina also
can be narrowed by stenosis. The narrowing can cause compression of the spinal
cord and nerve roots.
FIG. 3A shows a first embodiment 100 of the present invention, which is meant
to distract at least
one facet joint, in order to increase the dimension of the neural foramen
while retaining facet joint
mobility. The wedge-shaped embodiment or inter-facet spacer 100 is a wedge-
shaped implant that can be
positioned in the cervical facet joint 101 to distract the joint and reverse
narrowing of the nerve root canal
107. In this embodiment or inter-facet spacer 100, the implant is positioned
with the narrow portion of the
wedge facing anteriorly. However, it is also within the scope of the present
invention to position
embodiment or inter-facet spacer 100 (FIG. 3B) with the wide portion of the
wedge facing anteriorly, to
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correct for cervical kyphosis or loss of cervical lordosis.
Referring to FIG. 4, the embodiment 200 of the implant has ajoint insert or
inter-facet spacer 210,
also herein referred to as a facet joint spacer or inter-facet spacer, that.is
positioned in the cervical facet
joint 101. The joint insert or inter-facet spacer 210 can be wedge-shaped with
the narrow part of the
wedge facing anteriorly. Alternatively, the joint insert or inter-facet spacer
210 need not be wedge-shaped
but can be of substantially uniform thickness, the thickness determined by an
individual patient's need for
distraction of the cervical facet joint 201. As with embodiment 100, one
objective of this embodiment is
facet joint distraction, and joint mobility after implantation. The joint
insert or inter-facet spacer 210 is
continuous with a posterior sheath 220 bent at an angle from the joint insert
or inter-facet spacer 210 to
align substantially parallel with the bone. The posterior sheath can lie
against the lamina, preferably
against the lateral mass. The posterior sheath 220 can have a bore 230 which
can accept a bone screw 240.
Alternatively, the bore 230 can accept any other appropriate and/or equivalent
fixation device capable of
fixing the embodiment 200 to the spine. The device is thereby affixed to the
vertebra, preferably by fixing
to the lateral mass.
FIG. 5 shows embodiment 300, which is the use of two embodiments 200, each
fixed to one of
two adjacent cervical vertebrae. As with embodiment 200, the implanted facet
joint is distracted and joint
mobility is retained. A joint insert or inter-facet spacer 310 from each of
the two implants is inserted and
positioned in the cervical facet joint 301. In this embodiment, the joint
inserts or inter-facet spacers 310
are substantially flat and parallel to each other and are not wedge-shaped.
Alternatively, the joint inserts or
inter-facet spacers 310 can together define a wedge-shaped insert that is
appropriate for the patient. The
two joint inserts or inter-facet spacers 310 combined can have, by way of
example, the shape of the joint
insert or inter-facet spacer 210 in FIG. 4. Embodiment 300 then can be fixed
to the spine with a screw 340
or any other appropriate fixation device, inserted through a bore 330 in the
posterior sheath 320. The
posterior sheath 320 can be threaded to accept a screw. The screw can be
embedded in the lamina,
preferably in the lateral mass, where possible.
It is within the scope of the present invention to use and/or modify the
implants of the invention to
correct cervical spine kyphosis, or loss of lordosis. FIG. 6 depicts a
cervical spine lordosis. FIG. 7
demonstrates an embodiment 400 which contemplates positioning two implants to
correct for this spinal
abnormality while retaining facet joint mobility. The joint insert or inter-
facet spacer 410 of each implant
is shaped so that it is thicker at its anterior portion. Alternatively, the
implants can be shaped to be thicker
at the posterior ends, for example as depicted in FIG. 3A. The posterior
sheath 420 of each implant is bent
at an angle from the joint insert or inter-facet spacer 410 to be positioned
adjacent to the lateral mass and/or
lamina, and has a bore 430 to accept a screw 440 or other appropriate and/or
equivalent fixation means to
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fix the embodiment 400 to the spine, preferably to the lateral mass. The
placement of two joint inserts or
inter-facet spacers 410 in the cervical facet joint 401 distracts the facet
joint, which shifts and maintains the
vertebrae into a more anatomical position to preserve the physiology of the
spine..
FIG. 8 shows a further embodiment 500 of the implant of the invention, wherein
the joint insert or
inter-facet spacer 510 has a keel 550 on an underside of the joint insert or
inter-facet spacer 510. The keel
550 can be made of the same material or materials set forth above. The
surfaces of the keel 550 can be
roughened in order to promote bone ingrowth to stabilize and fix the implant
500. In other embodiments,
the keel 550 can be coated with materials that promote bone growth such as,
for example, bone
morphogenic protein ("BMP"), or structural materials such as hyaluronic acid
"HA," or other substances
which promote growth of bone relative to and into the keel 550.
The keel 550 can be embedded in the facet bone, to facilitate implant
retention. The keel 550 can
be placed into a channel in the facet bone. The channel can be pre-cut. Teeth
(not shown), preferably
positioned posteriorly, also may be formed on the kee1550 for facilitating
retention of the implant 500 in
the cervical facet joint 501. As noted above, the joint insert or inter-facet
spacer 510 can be substantially
flat or wedge-shaped, depending upon the type of distraction needed, i.e.,
whether distraction is also
necessary to correct abnormal curvature or lack of curvature in the cervical
spine. Because the joint is not
fused, mobility is retained, as with the embodiments described above and
herein below.
FIG. 9 illustrates that a further embodiment 600 of the implant of the
invention can have both
screw fixation and a keel 650 for stability and retention of the implant 600.
On embodiment 600, the joint
insert or inter-facet spacer 610 is continuous with a posterior sheath 620
having a bore hole 630 to accept a
screw 640 which passes through the bore 630 and into the bone of the
vertebrae, preferably into the lateral
mass, or the lamina. The bore 630 can be threaded or not threaded where it is
to accept a threaded screw or
equivalent device. Alternatively, the bore 630 need not be threaded to accept
a non-threaded equivalent
device. The kee1650 is connected with the joint insert or inter-facet spacer
610 and embeds in the bone of
the cervical facet joint 601 to promote implant retention.
A further alternative embodiment 700 is illustrated in FIG. 10. In this
embodiment 700, the joint
insert or inter-facet spacer 710 has on a lower side at least one tooth 760.
It should be clear to one of
ordinary skill in the art that a plurality of teeth 760 is preferable. The
teeth 760 are able to embed in the
bone of the cervical facet joint 701 to facilitate retention of the implant
700 in the joint 701. The teeth 760
can face in a direction substantially opposite the direction of insertion, for
retention of the implant 700. As
above, the joint insert or inter-facet spacer 710 can be wedge-shaped or
substantially even in thickness,
depending upon the desired distraction. Because the implant distracts and is
retained without fusion, facet
joint mobility is retained.
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FIG. 11 depicts a further embodiment 800 of the implant of the invention. In
this embodiment
800, the joint insert or inter-facet spacer 810 is continuous with a posterior
sheath 820 having a bore 830
for accepting a fixation device 840, as described above. The fixation device
840 can be a screw which fits
into a threaded bore 830; alternatively, the fixation device 830 can be any
other compatible and appropriate
device. This embodiment 800 further combines at least one tooth 860 on an
underside of the joint insert or
inter-facet spacer 810 with the posterior sheath 820, bore 830 and fixation
device 840 to address fixation of
the implant 800 in a cervical facet joint 801. It will be recognized by one of
ordinary skill in the art that
the implant 800 can have a plurality of teeth 860 on the underside of the
joint insert or inter-facet spacer
810.
FIG. 12 shows yet another embodiment 900 of an implant of the present
invention. In this
embodiment 900, the joint inserts or inter-facet spacers 910 of two implants
900 are positioned in a
cervical facet joint 901. As described above, the joint inserts or inter-facet
spacers 910 can be wedge-
shaped as needed to restore anatomical curvature of the cervical spine and to
distract, or the joint inserts or
inter-facet spacers 910 can be of substantially uniform thickness. The
implants 900 each comprise a joint
insert or inter-facet spacer 910 with an outer surface 970 that interacts with
the bone of the cervical facet
joint 901. On the upper implant 900, the surface 970 that interacts with the
bone is the upper surface 970
and on the lower implant 900, the surface 970 that interacts with the bone is
the lower surface 970. Each
surface 970 can comprise a bone ingrowth surface 980 to create a porous
surface and thereby promote bone
ingrowth and fixation. One such treatment can be with plasma spray titanium,
and another, with a coating
of sintered beads. Alternatively, the implant 900 can have casted porous
surfaces 970, where the porous
surface is integral to the implant 900. As a further alternative, the surfaces
970 can be roughened in order
to promote bone ingrowth into these defined surfaces of the implants 900. In
other embodiments, the
surfaces 970 can be coated with materials that promote bone growth such as for
example bone
morphogenic protein ("BMP"), or structural materials such as hyaluronic acid
("HA"), or other substances
which promote growth of bone on other external surfaces 970 of the implant
900. These measures
facilitate fixation of the implants 900 in the facet joint, but do not result
in fusion of the joint, thereby
retaining facet joint mobility, while also accomplishing distraction of the
joint.
FIG. 13 depicts yet another embodiment 1000 of the implant of the present
invention. In this
embodiment 1000, the joint inserts or inter-facet spacers 1010 of two implants
1000 are positioned in a
cervical facet joint 1001. As described above, the joint inserts or inter-
facet spacers 1010 can be wedge-
shaped as needed to restore anatomical curvature of the cervical spine and to
distract, or the joint inserts or
inter-facet spacers 1010 can be of substantially uniform thickness. The
implants 1000 each comprise a
joint insert or inter-facet spacer 1010 with an outer surface 1070 that
interacts with the bone of the cervical
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facet joint 1001. On the upper implant 1000, the surface 1070 that interacts
with the bone is the upper
surface and on the lower implant 1000, the surface 1070 that interacts with
the bone is the lower surface.
As set forth above, each outer surface 1070 can comprise a bone ingrowth
surface 1080 to create a porous
surface and thereby promote bone ingrowth and fixation, without facetjoint
fusion and loss of mobility. In
one preferred embodiment, the bone ingrowth surface 1080 can be created with
plasma spray titanium,
and/or with a coating of sintered beads. In an alternative preferred
embodiment, the implant 1000 can have
casted porous surfaces 1070, where the porous surface is integral to the
implant 1000. In a further
alternative preferred embodiment, the surfaces 1070 can be roughened in order
to promote bone ingrowth
into these defined surfaces of the implants 1000. In other preferred
embodiments, the surfaces 1070 can be
coated with materials that promote bone growth such as for example BMP, or
structural materials such as
HA, or other substances which promote growth of bone on other external
surfaces 1070 of the implant
1000.
The implant 1000 can have a posterior alignment guide 1090. The posterior
alignment guides
1090 of each implant 1000 can be continuous with the joint inserts or inter-
facet spacers 1010. The
posterior alignment guides substantially conform to the bone of the vertebrae
when the joint inserts or
inter-facet spacers 1010 are inserted into the cervical facet joint 1001. The
posterior alignment guides
1090 are used to align the implants 1000 so that the joint inserts or inter-
facet spacers 1010 contact each
other and not the bones of the cervical facet joint 1001 when the joint
inserts or inter-facet spacers 1010 are
positioned in the cervical facet joint 1001.
FIG. 14 depicts a further embodiment 1100 of the implant of the present
invention. In this
embodiment 1100, the joint inserts or inter-facet spacers 1110 of two implants
1100 are inserted into the
cervical facet joint 1101. Each of the joint inserts or inter-facet spacers
1110 is continuous with a cervical
facet joint extender or facet-extending surface 1192. The bone contacting
surfaces 1170 ofthe joint inserts
or inter-facet spacers 1110 are continuous with, and at an angle to, the bone
contacting surfaces 1193 of the
cervical facet joint extenders 1192, so that the cervical facet joint
extenders 1192 conform to the bones of
the vertebrae exterior to the cervical facet joint 1101. The conformity of the
cervical facet joint extenders
1192 is achieved for example by forming the cervical facet joint extenders
1192 so that when the join
inserts 1110 are positioned, the cervical facet joint extenders 1192 curve
around the bone outsider the
cervical facet joint 1101.
The cervical facet joint extenders have a second surface 1184 that is
continuous with the joint
articular surfaces 1182 of the joint inserts or inter-facet spacers 1110. The
second surfaces 1184 extend the
implant 1100 posteriorly to expand the joint articular surfaces 1182 and
thereby to increase contact and
stability of the spine at least in the region of the implants 1100. It is to
be understood that such facet joint
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extenders 1192 can be added to the other embodiments of the invention
described and depicted herein.
The embodiment depicted in FIG. 15 shows two implants 1200 positioned in a
cervical facet joint
1201, having bony ingrowth surfaces as one preferred method of fixation, and
using screws as another
preferred method of fixation. In this embodiment, each of two implants 1200
has a joint insert or inter-
facet spacer 1210 positioned in a cervical facet joint 1201. As described
above, the joint inserts or inter-
facet spacers 1210 can be wedge-shaped as needed to restore anatomical
curvature of the cervical spine and
to distract, or the joint inserts or inter-facet spacers 1210 can be of
substantially uniform thickness. The
implants 1200 each comprise a joint insert or inter-facet spacer 1210 with an
outer surface 1270 that
interacts with the bone of the cervical facet joint 1001. On the upper implant
1200, the surface 1270 that
interacts with the bone is the upper surface and on the lower implant 1200,
the surface 1270 that interacts
with the bone is the lower surface. As set forth above, each outer surface
1270 can comprise a bone
ingrowth surface 1280 to create a porous surface and thereby promote bone
ingrowth and fixation. In one
preferred embodiment, the bone ingrowth surface 1280 can be created with
plasma spray titanium, and/or
with a coating of sintered beads. In an alternative preferred embodiment, the
implant 1200 can have casted
porous surfaces 1270, where the porous surface is integral to the implant
1200. In a further alternative
embodiment, the surfaces 1270 can be roughened in order to promote bone
ingrowth into these defined
surfaces of the implants 1200. In other preferred embodiments, the surfaces
1270 can be coated with
materials that promote bone growth such as for example BMP, or structural
materials such as HA, or other
substances which promote growth of bone on other external surfaces 1270 of the
implant 1200.
Screw fixation or other appropriate fixation also can be used with implants
1200 for fixation in the
cervical facet joint 1201. The joint insert or inter-facet spacer 1210 is
continuous with a posterior sheath
1220 bent at an angle from the joint insert or inter-facet spacer 1210 to
align substantially parallel with the
bone, preferably the lateral mass or lamina. The posterior sheath 1220 can
have a bore 1230 which can
accept a bone screw 1240, preferably into the lateral mass or lamina.
Alternatively, the bore 1230 can
accept any other appropriate and/or equivalent fixation means for fixing the
embodiment 1200 to the spine.
FIG. 16 depicts a further preferred embodiment of the present invention. In
this embodiment
1300, two joint inserts or inter-facet spacers 1310 are positioned in the
cervical facet joint 1301. The joint
inserts or inter-facet spacers each have outer surfaces 1370 that interact
with the bone of the vertebrae
forming the cervical facet joint. These outer surfaces 1370 of the embodiment
1300 can be treated to
become bone ingrowth surfaces 1380, which bone ingrowth surfaces 1380
contribute to stabilizing the two
joint inserts or inter-facet spacers 1310 of the implant 1300. In one
preferred embodiment, the bone
ingrowth surface 1380 can be created with plasma spray titanium, and/or with a
coating of sintered beads.
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In an alternative preferred embodiment, the implant 1300 can have casted
porous surfaces 1370, where the
porous surface is integral to the implant 1300. In a further alternative
embodiment, the surfaces 1370 can
be roughened in order to promote bone ingrowth into these defined surfaces of
the implants 1300. In other
preferred embodiments, the surfaces 1370 can be coated with materials that
promote bone growth such as
for example BMP, or structural materials such as HA, or other substances which
promote growth of bone
on other external surfaces 1370 of the implant 1300. This fixation stabilizes
the implant 1300 in the facet
joint without fusing the joint, and thus the implant preserves joint mobility,
while accomplishing
distraction and increasing foraminal dimension.
Also shown in FIG. 16 are articular inner surfaces 1382 of the implants 1300.
These surfaces can
be formed from a metal and polyethylene, the material allowing flexibility and
providing for forward
bending/flexion and backward extension of the cervical spine. The embodiment
1300 of FIG. 16 can be
made in at least two configurations. The first configuration includes a
flexible spacer 1382 made, by way
of example, using polyethylene or other suitable, flexible implant material.
The flexible spacer 1382 can
be permanently affixed to the upper and lower joint insert or inter-facet
spacer 1310. The spacer 1382 can
be flat or wedge-shaped or have any other shape that would correct the
curvature of the spine. In other
configurations, the spacer 1382 can be affixed to only the upper insert 1310
or to only the lower insert
1310. Alternatively, a spacer 1382 can be affixed to each of an upper insert
1310 and a lower insert 1310
with the upper insert 1310 and the lower insert 1310 being separate units.
FIG. 17 shows a further preferred embodiment of the implant of the present
invention. In this
embodiment 1400, the implant has a roller 1496 mounted on a joint insert or
inter-facet spacer 1410, the
roller being a further means of preserving joint mobility while accomplishing
distraction. Both the roller
1496 and the joint insert or inter-facet spacer 1410 are positioned in the
cervical facet joint 1401. The joint
insert or inter-facet spacer 1410 as in other embodiments has a bone-facing
surface 1470 and joint articular
surface 1482. The bone-facing surface 1470 can interact with the lower bone of
the cervical facet joint
1401. Alternatively, the bone-facing surface can interact with the upper bone
of the cervical facet joint
1401. Between the bone-facing surface 1470 and the joint articular surface
1482 is an axisabout which the
roller 1496 can rotate. The roller 1496 rotates in a cavity in the joint
insert or inter-facet spacer 1410, and
interacts with the top bone of the cervical facet joint 1401. Alternatively,
where the bone- facing surface
1470 of the joint insert or inter-facet spacer 1410 interacts with the top
bone of the cervical facet joint
1401, the roller 1496 rotates in a cavity in the joint insert or inter-facet
spacer 1410 and interacts with the
lower bone of the cervical facet joint 1401. The rotation of the roller 1496
allows flexion and extension of
the cervical spine. Alternatively, a roller such as roller 1496 can be secured
to an upper and a lower insert
such as inserts 410 in FIG. 7. As depicted in FIG. 18, a plurality of rollers
1496 also is possible.
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FIG.19 depicts a further embodiment of the implant of the present invention.
In this embodiment,
two implants 1500 are implanted in the cervical facet joint 1501. Screw
fixation or other appropriate
fixation is used with implants 1500 for fixation in the cervical facet joint
1501. The joint insert or inter-
facet spacer 1510 is continuous with a posterior sheath 1520 bent at an angle
from the joint insert or inter-
facet spacer 1510 to align substantially parallel with the bone, preferably
the lateral mass or lamina. The
posterior sheath 1520 of each implant 1500 can have a bore 1530 which can
accept a bone screw 1540,
preferably into the lateral mass or lamina. Alternatively, the bore 1530 can
accept any other appropriate
and/or equivalent fixation means for fixing the embodiment 1500 to the spine.
The head of the screw 1540
in each posterior sheath 1520 of each implant 1500 has a groove 1598 or other
mechanism for retaining an
elastic band 1597. The elastic band 1597 is looped around each of the two
screws 1540 to restrain
movement of the cervical spine without eliminating facet joint mobility. The
band 1597 preferably can
restrain flexion and lateral movement. The elastic band 1597 can be made of a
biocompatible, flexible
material.
FIG. 20 shows an alternative to use of an elastic band as in FIG. 19. In the
embodiment in FIG.
20, the elastic band is replaced with a spring restraint 1699, which extends
between the heads of two
screws 1640, one screw fixing each of two implants 1600 in the cervical facet
joint 1601.
FIG. 21 shows another alternative to using an elastic band and/or a spring as
in FIGs. 19 or 20.
In FIG. 21, magnets 1795 is used for restraint between the two screws 1740.
The magnet 1795 can either
be comprised of two opposing magnetic fields or two of the same magnetic
fields to operate to restrain
movement. The head of one of the two screws 1740 is magnetized, and the head
of the other screw 1740 is
magnetized with either the same or opposite field. If the magnets 1795 have
the same polarity, the magnets
1795 repel each other and thus limit extension. If the magnets 1795 have
opposite polarities, the magnets
1795 attract each other and thus limit flexion and lateral movement.
FIGs. 22A-24B, depict a further embodiment 1800 of the implant of the present
invention. In this
embodiment, a facet joint spacer (or insert) or inter-facet spacer (or insert)
1810 is connected with a lateral
mass plate (also referred to herein as an anchoring plate) 1820 with a hinge
1822. The hinge 1822 allows
the lateral mass plate 1820 to bend at a wide range of angles relative to the
facet joint spacer or inter-facet
spacer and preferably at an angle of more than 90 degrees, and this
flexibility facilitates positioning and
insertion of the facet joint spacer or inter-facet spacer 1810 into a
patient's facet joint, the anatomy of
which can be highly variable among individuals. This characteristic also
applies to embodiments described
below, which have a hinge or which are otherwise enabled to bend by some
equivalent structure or material
property. The hinge 1822 further facilitates customizing the anchoring of the
implant, i.e., the positioning
of a fixation device. The hinge enables positioning of the lateral mass plate
1820 to conform to a patient's
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cervical spinal anatomy, and the lateral mass plate 1820 accepts a fixation
device to penetrate the bone.
The facet joint spacer or inter-facet joint spacer 1810 can be curved or
rounded at a distal end 1812 (FIG.
23A), and convex or dome-shaped on a superior surface 1813 to approximate the
shape of the bone inside
the facetjoint. The inferior surface 1815 can be flat or planar.
Alternatively, the inferior surface 1815 can
be concave. As another alternative, the inferior surface 1815 can be convex.
The lateral mass plate 1820, when implanted in the spine, is positioned
outside the facet joint,
preferably against the lateral mass or against the lamina. The lateral mass
plate 1820 has a bore 1830
therethrough. The bore 1830 can accept a bone screw 1840, also referred to as
a lateral mass screw, to
secure the lateral mass plate 1820 preferably to the lateral mass or
alternatively to another part of the spine,
and thus to anchor the implant. The lateral mass screw 1840 preferably has a
hexagonal head to accept an
appropriately-shaped wrench. As described below, the head accepts a compatible
probe 1826 from a
locking plate 1824.
The locking plate 1824 includes a kee11828 with a wedge shaped distal end to
anchor the implant,
preferably in the lateral mass or in the lamina, outside the facet joint and
to prevent rotation of the lateral
mass plate 1820 and the locking plate 1824. The keel 1828 aligns with a groove
1823 through an edge of
the lateral mass plate 1820 to guide and align the keel 1828 as the keel 1828
cuts into a vertebra.
As noted above, the locking plate 1824 includes a probe 1826 that fits against
the head of the
lateral mass screw 1840. The locking plate further includes a bore 1831 that
can accept a machine screw
(not shown) which passes through to an aligned bore 1829 in the lateral mass
plate 1820 to hold the
locking plate 1824 and the lateral mass plate 1820 together without rotational
displacement relative to each
other. The locking plate 1824 thus serves at least two functions: (1)
maintaining the position of the lateral
mass screw 1840 with the probe 1826, so that the screw 1840 does not back out;
and (2) preventing
rotation of the implant with the keel 1828 and machine screw relative to the
cervical vertebra or other
vertebrae.
It is to be understood that other mechanisms can be used to lock the locking
plate 1824 to the
lateral mass plate 1820. For example, the locking plate can include a probe
with barbs that can be inserted
into a port in the lateral mass plate. The barbs can become engaged in ribs
that define the side walls of the
port in the lateral mass plate
In the preferred embodiment depicted in FIGs. 25A, 25B, the lateral mass plate
1920 includes a
recessed area 1922 for receiving the locking plate 1924 so that the locking
plate 1924 is flush with the
upper surface 1925 of the lateral mass plate 1920 when the probe 1926 is urged
against the lateral mass
screw 1940 and the keel 1928 is inserted into the lateral mass or the lamina
of the vertebra. In the
preferred embodiment depicted in FIGs. 25A, 25B, the shape and contours of the
facet joint spacer or
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inter-facet joint spacer 1910 can facilitate insertion of the facet joint
spacer or inter-facet joint spacer 1910
into the cervical facet joint. In this embodiment, the facet joint spacer or
inter-facet joint spacer 1910 has a
rounded distal end 1912. The distal end 1912 is tapered in thickness to
facilitate insertion. The tapered
distal end 1912 meets and is continuous with a proximal mid-section 1916
which, in this preferred
embodiment, has a uniform thickness, and is connected flexibly, preferably
with a hinge 1922, to the lateral
mass plate 1920, as described above. The facet joint spacer (or insert) or
inter-facet joint spacer (or insert)
1910, with its proximal mid-section 1916 and tapered distal end 1912, is
curved downward, causing a
superior surface 1913 of the facet joint spacer or inter-facet joint spacer
1910 to be curved. The curve can
cause the superior surface 1913 to be convex, and the convexity can vary among
different implants 1900 to
suit the anatomical structure of the cervical facet joint(s) of a patient. An
inferior surface 1915 accordingly
can be preferably concave, flat, or convex. The curved shape of the implant
can fit the shape of a cervical
facet joint, which is comprised of an inferior facet of an upper vertebra and
a superior facet of a lower
adjacent vertebra. The convex shape of the superior surface 1913 of the facet
joint spacer or inter-facet
joint spacer 1910 fits with a concave shape of the inferior facet of the upper
cervical vertebrae. The
concave shape of the inferior surface 1915 of the facet joint spacer or inter-
facetjoint spacer 1910 fits with
the convex shape of the superior facet of the cervical vertebrae. The degree
of convexity and concavity of
the facetjoint spacer or inter-facet joint spacer inferior and superior
surfaces can be varied to fit a patient's
anatomy and the particular pairing of adjacent cervical vertebrae to be
treated. For example, a less-curved
facet joint spacer or inter-facet joint spacer 1910 can be used where the
patient's cervical spinal anatomy is
sized (as described below) and found to have less convexity and concavity of
the articular facets.
Generally for the same level the input for the right and left facet joint will
be similarly shaped. It is
expected that the similarity of shape of the facet joint spacer or inter-facet
joint spacer and the smooth,
flush surfaces will allow distraction of the facetjoint without loss of
mobility or damage to the bones of the
cervical spine. Further, and preferably, the width of the mid-section 1916 is
from 1.5 mm to 2.5 mm.
Except as otherwise noted above, the embodiment shown in FIGs. 22A-24B is
similar to the
embodiment shown in FIGs. 25A, 25B. Accordingly the remaining elements on the
1900 series of element
numbers is preferably substantially similar to the described elements in the
1800 series of element
numbers, as set forth above. Thus, by way of example, elements 1923, 1928,
1929 and 1930 are similar,
respective elements 1823, 1828, 1829 and 1830.
FIG. 30 is a flow chart of the method of insertion of an implant of the
invention. The embodiment
1800 or 1900 of the present invention preferably is inserted in the following
manner (only elements of the
embodiment 1800 will be set forth herein, for purposes of the written
description of a method of the
invention). First the facet joint is accessed. A sizing too12200 (see FIGs.
29A-C) can be inserted to select
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the appropriate size of an implant of the invention for positioning in the
cervical facet joint. This step may
be repeated as necessary with, if desired, different sizes of the tool 2200
until the appropriate size is
determined. This sizing step also distracts the facet joint and surrounding
tissue in order to facilitate
insertion of the implant. Then, the natural or artificial facet joint spacer
or inter-facet joint spacer 1810 is
urged between the facets into the facet joint. The facet itself is somewhat
shaped like a ball and socket
joint. Accordingly, in order to accommodate this shape, the spacer 1810 can
have a rounded leading edge
shaped like a wedge or tissue expander to cause distraction of the facet joint
as the facet joint spacer or
inter-facet joint spacer is urged into the facet joint of the spine. The
natural or artificial facet joint spacer
or inter-facet joint spacer 1810 also includes the convex surface 1813 in
order to more fully accommodate
the shape of the facet joint of the spine. However, as set forth above and as
depicted in FIG. 25B, it is
possible in the alternative to have a curve-shaped natural or artificial facet
joint spacer (or insert) or inter-
facet joint spacer (or insert) 1910 with a convex superior surface 1913 and a
concave inferior surface 1915,
the distal end 1912 tapering to facilitate insertion, while the remainder of
the natural or artificial facet joint
spacer or inter-facet joint spacer 1910, (i.e., the proximal section 1916) has
a uniform thickness.
Once the natural or artificial joint spacer 1810 is positioned, the lateral
mass plate 1820 is pivoted
downward about the hinge 1822 adjacent to the vertebrae and preferably to the
lateral mass or to the
lamina. Thus the lateral mass plate 1820 may be disposed at an angle relative
to the natural or artificial
facet joint spacer or inter-facet joint spacer 1810 for a representative spine
configuration. It is to be
understood that as this embodiment is hinged the final position of the lateral
mass plate 1820 relative to the
natural or artificial facet joint spacer or inter-facet joint spacer 1800 will
depend on the actual spine
configuration. It is to be understood that embodiments of the invention can be
made without a hinge, as
long as the connection between the natural or artificial facet joint spacer or
inter-facet joint spacer and the
lateral mass plate is flexible enough to allow the lateral mass plate to be
bent relative to the natural or
artificial facet joint spacer or inter-facet joint spacer in order to fit the
anatomy of the patient. Once the
lateral mass plate 1820 is positioned, or prior to the positioning of the
lateral mass plate 1820, a bore can
be drilled in the bone to accommodate the bone screw 1824. Alternatively the
screw 1824 can be self-
tapping. The screw is then placed through the bore 1830 and secured to the
bone, preferably the lateral
mass or the lamina, thereby holding the natural or artificial facet joint
spacer or inter-facet joint spacer
1800 in place. In order to lock the bone screw 1824 in place and to lock the
position of the natural or
artificial facet joint spacer or inter-facet joint spacer 1800 and the lateral
mass plate 1820 in place, the
locking plate 1824 is positioned over the lateral mass plate 1820. So
positioned, the probe 1826 is
positioned through the bore 1830 and against the head of the bone screw to
keep the bone screw from
moving. The keel 1828, having a sharp chisel-shaped end, preferably can self-
cut a groove in the bone so
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that the kee11828 is locked into the bone as the keel 1828 is aligned by, and
received in, a groove 1831 of
the lateral mass plate 1820. Alternatively, a groove can be pre-cut in the
bone to receive the keel 1828. As
this occurs the bore 1829 of the locking plate 1824 aligns with the threaded
bore 1831 of the lateral mass
plate 1820 and a machine screw can be inserted to lock the locking plate
relative to the lateral mass plate.
This locking prevents the lateral mass plate 1820 and the natural or
artificial facet joint spacer or inter-facet
joint spacer 1810 from rotating and, as previously indicated, prevents the
bone screw 1840 from backing
out from the vertebra. Preferably the implant is between the C5 and C6
vertebrae level, or the C6 and C7
vertebrae level. It is noted that two implants preferably will be implanted at
each level between vertebrae.
That is, an implant 1800 will be placed in a right facet joint and also in a
left facet joint when viewed from
a posterior view point. This procedure can be used to increase or distract the
foraminal area or dimension
of the spine in an extension or in neutral position (without having a
deleterious effect on cervical lordosis)
and reduce the pressure on the nerves and blood vessels. At the same time this
procedure preserves
mobility of the facet joint.
FIGs. 26A-27B show a further embodiment of the implant of the invention, with
the embodiment
2000 implanted in the cervical spine as depicted in FIGs. 27A and 27B. The
implant 2000 comprises a
first natural or artificial facet joint spacer (or insert) or inter-facet
joint spacer (or insert) 2010 and a second
natural or artificial facet joint spacer or inter-facet joint spacer 2010.
Each natural or artificial facet joint
spacer or inter-facet joint spacer can have a distal end 2012 that is tapered
or wedge-shaped in a way that
facilitates insertion into the cervical facetjoints on both sides of two
adjacent cervical vertebrae at the same
level. The natural or artificial facetjoint spacer or inter-facet joint
spacers further can be dome-shaped, or
convex on a superior surface 2013, to approximate the shape of the cervical
facets of the cervical facet
joints.
The first and second natural or artificial facet joint spacers or inter-facet
joint spacers 2010 are
bridged together by a collar 2015. The collar 2015 passes between the spinous
processes of the adjacent
cervical vertebrae. As can be seen in FIG. 26B, the implant can preferably be
"V" shaped or "boomerang"
shaped. The entire implant 2000 or the collar 2015 of the implant can be made
of a flexible material such
as titanium, so that it is possible to bend the collar 2015 so that it
conforms preferably to the shape of the
lateral mass or the lamina of the cervical vertebrae of the patient and
thereby holds the implant in place
with the natural or artificial facet joint spacer or inter-facet joint spacers
2010 inserted in the cervical facet
joints. Bores 2029 are preferably are provided through implant 2000 adjacent
to the natural or artificial
facet joint spacer or inter-facet joint spacer 2010 respectively. These bores
2029 can receive bone screws
to position the implant 2000 against the lateral mass or the lamina as shown
in FIGs. 27A, 27B. The
description of the embodiment 2100, in FIGs. 28A, 28B provide further details
concerning the method of
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affixing the implant 2000 to the vertebrae. The implant 2100 also can be made
of PEEK or other materials
as described herein. Embodiment 2000 (the "boomerang" shape depicted in FIG.
27B) further can have a
locking plate as, for example, the locking plate 1824 in FIG. 22A. The locking
plate for embodiment 2000
(not shown) can have the same features as locking plate 1824, that is: (1) a
probe 1826 that interacts with
the bone screws to prevent the bone screws from backing out of the bone, the
likely consequence of which
would be displacement of the implant 2000; and (2) a keel 1828 with a chisel
end to embed in the bone and
thus to prevent rotational displacement of the implant. However, given the
collar 2015,configuration of
embodiment 2000, a chisel may not serve the same purpose as with the
embodiments set forth above,
which lack a collar stabilized by two bone screws. Therefore, a locking plate
on embodiment 2000 can be
provided without a keel.
FIGs. 28A and 28B depict a further embodiment of the implant of the invention
2100. In this
embodiment 2100, the collar 2115 can be made of a flexible material such as
titanium, of a substantially
inflexible material, or of other materials described herein. Substantial
flexibility can also be derived from
connecting a first natural or artificial facet joint spacer (or insert) or
inter-facet joint spacer (or insert) 2110
with the collar 2115 using a first hinge 2117, and connecting a second natural
or artificial facet joint spacer
or inter-facet joint spacer 2110 with the collar 2115 using a second hinge
2117. Using the first hinge 2117
and the second hinge 2117, the collar 2115 can be pivoted downward to conform
to a particular patient's
cervical spinal anatomy. In other words, the degree of pivoting will vary
among different patients, and the
first hinge 2117 and second hinge 2117 allow the implant 2100 to accommodate
the variance.
In the hinged embodiment 2100, and similar to the embodiment 2000, the collar
2115 can have a
first bore 2129 inferior to the first hinge 2117, and a second bore 2129
inferior to the second hinge 2117.
A first bone screw penetrates the first bore 2130 and into the lateral mass or
the lamina, and the second
bone screw penetrates the second bore 2130 and into the lateral mass or the
lamina, the first and second
bone screws serving to anchor the implant. A bore, preferably in the lateral
mass, can be drilled for the
f irst bone screw and for the second bone screw. Alternatively, the bone
screws can be self-tapping. A first
locking plate similar to the plate 1924 (FIG. 25A) can be secured about the
head of the first bone screw
and a second locking plate can be secured about the head of the second bone
screw to prevent displacement
of the first and second bone screws 2140. The first locking plate can block
the first bone screw with a
probe and the second locking plate can block to the second bone screw with a
probe.
It should be noted that embodiments 2000 and 2100 also can be configured for
accommodating
treatment of cervical spinal stenosis and other cervical spine ailments where
only a single cervical facet
joint between adjacent vertebrae requires an implant, i.e., where treatment is
limited to one lateral facet
joint. In that case, the collar 2015, 2115 extends medially without extending
further to join a second
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natural or artificial facet joint spacer or inter-facet joint spacer 2010,
2110. For the hinged embodiment
2100, the implant comprises a single hinge 2117, and the collar 2115 has only
one bore 2129 to accept one
bone screw to secure the implant 2100.
FIGs. 29A-E, depict a sizing and distracting tool 2200 of the invention.
Sizing tool 2200 has a
handle 2203 and a distal head 2210 that is shaped as a natural or artificial
facet joint spacer or inter-facet
joint spacer (e.g., 1810) of an implant of the invention. That is, the head
2210 preferably will have
essentially the same features as the natural or artificial facet joint spacer
or inter-facet joint spacer 1810,
but the dimensions of the head 2210 will vary from one tool 2200 to the next,
in order to be able to use
different versions of the sizing too12200 to determine the dimensions of the
cervical facetjoint that is to be
treated and then to select an appropriately-sized implant. The head 2210
preferably can be used to distract
the facet joint prior to the step of implanting the implant in the facet
joint. In this regard, the head 2210 is
rounded at the most distal point 2212, and can be a tapered to facilitate
insertion into a cervical facet joint.
The head 2210 also can have a slightly convex superior surface 2213, the
degree of convexity varying
among different sizing tools 2200 in order to determine the desired degree of
convexity of an implant to be
implanted in the cervical facet joint. The head 2210 may have a uniform
thickness along a proximal mid-
section 2216. Accordingly, the inferior surface 2215 preferably can be
concave. Alternatively, the
proximal mid-section 2212 may be convex on the superior surface 1813 without
being uniform in
thickness. Thus, the inferior surface 2215 can be flat or planar. The head
also can be curved.
The head 2210 has a stop 2218 to prevent over-insertion of the head 2210 of
the sizing too12200
into the facet joint. The stop 2218 can be a ridge that separates the head
2210 from the handle 2203.
Alternatively, the stop 2218 can be any structure that prevents insertion
beyond the stop 2218, including
pegs, teeth, and the like.
Different sizing tools 2200 covering a range of dimensions of the head 2210
can be inserted
successively into a cervical facet joint to select the appropriate size of an
implant to position in the cervical
spine, with the appropriate convexity and concavity of natural or artificial
facet joint spacer or inter-facet
joint spacer. Each preferably larger head also can be used to distract the
facet joint.
FIG. 31A depicts a posterior view of a further embodiment 2300 of the implant
of the invention.
Embodiment 2300, as well as all of the embodiments herein, can benefit from
some or all of the advantages
described herein with regard to the other embodiments described herein.
Further, FIG. 31A, embodiment
2300 has a natural or artificial facet joint spacer (or insert) or inter-facet
joint spacer (or insert) 2310 that
can have a tapered or thinned distal end 2312 so that the distal end 2312
facilitates insertion of the natural
or artificial facet joint spacer or inter-facet joint spacer 2310 into a
cervical facetjoint. The distal end 2312
can be rounded, as seen in the plan view of FIG. 31 A, in order to conform to
the roundness of the facet
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joint. The natural or artificial facet joint spacer or inter-facet joint
spacer 2310 further can be curved so
that a superior surface 2313 of the natural or artificial facet joint spacer
or inter-facet joint spacer 2310 is
convex, and an inferior surface 2315 is concave, to approximate the natural
shape of the cervical facet joint
that is to receive the implant 2300. The curve can have a uniform thickness,
or it can have a varied
thickness. Further, the lateral edges of the natural or artificial facet joint
spacer or inter-facet joint spacer
2310 are curved or rounded, for distribution of load-bearing stress. As with
other embodiments described
herein, the natural or artificial facet joint spacer or inter-facet joint
spacer 2310 also can be made of a
flexible, biocompatible material, such as PEEK, to maintain joint mobility and
flexibility.
The natural or artificial facet joint spacer or inter-facet joint spacer 2310
is connected flexibly with
a lateral mass plate 2320, the flexible connection preferably being a hinge
2322. As seen in the plan view
of FIG. 31A, the implant 2300 is substantially hour-glass shaped. This shape,
as well as the shape of FIG.
32, will be discussed further below. The hinge 2322 is narrower than the
natural or artificial facet joint
spacer or inter-facet joint spacer 2310, with the hinge 2322 sitting at
substantially the isthmus 2317
between natural or artificial facet joint spacer or inter-facet joint spacer
2310 and the lateral mass plate
2320. The curved edges, or fillets, about the hinge 2322 serve to distribute
more evenly the load-bearing
stress on the implant 2300, and thus prevent concentrating the stress about
the edges.
The hinge 2322 allows the implant 2300 to bend at the hinge 2322, bringing a
lateral mass plate
2320 adjacent to the lateral mass and/or lamina of the patient's spine, and to
conform to a particular
patient's anatomy. The lateral mass plate 2320 is made of a biocompatible
flexible material, preferably
titanium or any other biocompatible flexible material as described herein, for
example PEEK, that will
support the use of bone screws and other hardware, as described below. The
lateral mass plate 2320 bends
downward at the hinge 2322 over a wide range of angles relative to the natural
or artificial facet joint
spacer or inter-facet joint spacer 2310, and preferably at an angle of more
than 90 degrees, and this
flexibility facilitates positioning and insertion of the natural or artificial
facet joint spacer or inter-facet
joint spacer. This flexibility of the lateral mass plate 2320 relative to the
natural or artificial facet joint
spacer or inter-facet joint spacer 2310 further facilitates positioning of the
lateral mass plate relative to the
lateral mass and/or the lamina of the patient's spine. Once the lateral mass
plate 2320 is positioned
adjacent to the bone, preferably the lateral mass of a cervical vertebra, a
first bone screw, such as bone
screw 1840, can be inserted through a first bore 2330 through the lateral mass
plate 2320 and embedded
into the bone of the lateral mass of the cervical vertebra.
The lateral mass plate 2320 further comprises a second bore 2329 which is
preferably positioned
medially, relative to the first bore 2330. Thus, viewing the implant from a
posterior perspective as in FIG.
31 A, the second bore 2329 in the lateral mass plate 2320 can be positioried
either to the left or to the right
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of the first bore 2330. The position of the second bore 2329 will depend upon
whether the implant 2300 is
intended to be inserted into a cervical facet joint on the left or right side
of a patient. Specifically, an
implant 2300 to be inserted into a right-side cervical facet joint (i.e., the
patient's rights side) will have a
second bore 2329 positioned to the left of the first bore 2330 as in FIG. 31A,
when implant 2300 is viewed
from a posterior perspective, while an implant 2300 to be inserted into a left-
side cervical facet joint will
have a second bore 2329 positioned to the right of the first bore 2330, when
implant 2300 is viewed from a
posterior perspective.
The second bore 2329 through the lateral mass plate 2320 is adapted to accept
a second screw
2390 (FIG. 31B), which preferably is a locking screw with a chisel point 2391.
The locking screw 2390 is
received by the second bore 2329 and the chisel point 2391 self-cuts a bore
into the bone. The locking
screw 2390 preferably is inserted through the second bore 2329 and embedded in
the bone, after the bone
screw is embedded in the bone through the first bore 2330. The position of the
second bore 2329, i.e.,
medial to the first bore 2330, positions the locking screw 2390 so that it
embeds in stronger bone tissue
than if the second bore 2329 were located more laterally. The locking screw,
in combination with the bone
screw, prevents rotational and/or backward displacement of the implant 2300.
As the locking screw 2390
is received by the second bore 2329, the head 2392 of the locking screw 2390
aligns with the head of the
first bone screw in the first bore 2330, blocking the head of the first bone
screw to prevent the first bone
screw from backing out of the bone of the vertebra and the first bore 2330.
FIG. 32 depicts a further embodiment 2400 of the implant of the invention,
from a posterior view.
Embodiment 2400 is adapted to be implanted in a manner that preserves the
anatomy of the cervical facet
joint, in particular, the soft tissues around the cervical facet joint,
including the joint capsule.
Implant 2400, like implant 2300 and other implants disclosed above, has a
natural or artificial facet
joint spacer (or inert) or inter-facet joint spacer (or insert) 2410, flexibly
connected, preferably by a hinge
2422, to a lateral mass plate 2420. As can be seen in FIG 32, the implant 2400
including the natural or
artificial facet joint spacer (or insert) or inter-facet joint spacer (or
insert) 2410 and the hinge 2422 is
substantially "P" shaped. As explained below, its "P" shape assists in the
insertion of the implant 2400
into the facet joint with most of the facet capsule and facet capsule ligament
and other soft tissue associated
with the facet joint still left intact. The natural or artificial facet joint
spacer or inter-facet joint spacer, as
above for implant 2300 and the other implants disclosed above, can have a
superior surface 2413 of the
natural or artificial facet joint spacer or inter-facet joint spacer 2410 that
is convex, and an inferior surface
2415 that is concave, or any appropriate shaping to approximate the natural
shape of the cervical facet joint
that is to receive the implant 2400. The thickness of the natural or
artificial facet joint spacer or inter-facet
joint spacer 2410 can be uniform, or varied. The natural or artificial facet
joint spacer or inter-facet joint
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spacer 2410 also can be made of a flexible, biocompatible material, such as
PEEK, to maintain joint
mobility and flexibility. The hinge 2422 can have smooth, rounded edges, for
distribution of load stress, as
disclosed above. Other features and advantages of the other embodiments can
be, if desired, incorporated
into the design of the embodiment of FIG. 32. For example, the natural or
artificial facet joint spacer or
inter-facet joint spacer 2410 further can have a tapered or thinned edge 2412
so that the edge 2412
facilitates insertion of the natural or artificial facet joint spacer or inter-
facet joint spacer 2410 into a
cervical facet joint. The edge 2412 can be curved. In this embodiment 2400,
however, the thinned edge
2412 of the natural or artificial facet joint spacer or inter-facet joint
spacer 2410 preferably is not at the
distal end of the natural or artificial facet joint spacer or inter-facet
joint spacer 2400 as is the thinned edge
2312 of the natural or artificial facet joint spacer or inter-facet joint
spacer 2300; rather, the thinned edge
2412 preferably is positioned laterally, toward the hinge 2422 of the implant
2400. The thinned edge 2412
coincides substantially with a lateral curvature 2440 of the natural or
artificial facet joint spacer or inter-
facet joint spacer 2410, which is pronounced relative to the curvature on the
medial side of the implant
2400, i.e., a "P" shape. In other words, the curved part of the head of the
"P" 2440 corresponds to the
thinned edge 2412, and serves as the leading edge of the implant 2400 to begin
insertion of the natural or
artificial facet joint spacer or inter-facet joint spacer 2410 into a cervical
facet joint, preferably through an
incision in the soft tissue of the facet joint. The "P" shape narrows at
isthmus 2417 where the natural or
artificial facet joint spacer or inter-facet joint spacer 2410 that is joined
by the hinge 2422 with the lateral
mass plate 2420. The smooth or rounded edges or fillets serve to distribute
stresses on the implant 2400.
The above described "P" shape of implant 2400 allows the implant 2400 to be
pivoted into place into a
facet joint as described below. The thinned edge 2412 and leading lateral
curvature 2440 of the natural or
artificial facet joint spacer or inter-facet joint spacer 2410 are adapted to
facilitate urging implant 2400 into
the cervical facet joint, through the incision in the joint capsule. The
implant 2400 then is pivoted into
position so that the lateral mass plate 2420 can be bent downward, relative to
the natural or artificial facet
joint spacer or inter-facet joint spacer 2410, to align with and lie adjacent
to the lateral mass and/or the
lamina. The lateral mass plate 2420 is then fastened to the bone.
The lateral mass plate 2420 of implant 2400, like the lateral mass plate for
implant 2300, is
flexibly connected, preferably by the smooth-edged hinge 2422, to the natural
or artificial facetjoint spacer
or inter-facet joint spacer 2410 at the narrow lower part of the natural or
artificial facet joint spacer or inter-
facet joint spacer. The lateral mass plate 2420 is made of a biocompatible
flexible material, preferably
titanium or any other biocompatible flexible material such as PEEK that will
support the use of bone
screws and other hardware, as described below.
The lateral mass plate 2420 bends downward at a wide range of angles relative
to the natural or
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artificial facet joint spacer or inter-facet joint spacer 2410, and preferably
at an angle of more than 90
degrees. The flexibility of the lateral mass plate 2420 relative to the
natural or artificial facet joint spacer
or inter-facet joint spacer 2410 further facilitates positioning of the
lateral mass plate 2420 relative to the
lateral mass and/or the lamina of the patient's spine.
Like embodiment 2300, described above, the lateral mass plate 2420 has first
bore 2430, which is
adapted to receive a bone screw 2440, to help anchor implant 2400 in position.
The lateral mass plate
2420 further includes a second bore 2429 adapted to be positioned medially,
relative to the first bore 2430,
as disclosed above for implant 2300. The position of the second bore 2429,
when viewing implant 2400
from a posterior perspective (FIG. 32), will depend upon whether implant 2400
is intended to be implanted
into a left-side or right-side cervical facet joint of a patient. Thus,
implant 2400 with the second bore 2429
positioned to the left of the first bore 2430 is intended to be implanted in a
right-side cervical facet joint of
a patient, as depicted in FIG. 32, while an implant 2400 with a second bore
2429 positioned to the right of
the first bore 2430 is intended to be implanted in a left-side cervical facet
joint of a patient.
The second bore 2429 through the lateral mass plate 2420 is adapted to receive
a second screw
2490 with head 2492, which preferably is a locking screw with a chisel point,
such as screw 2390. The
function and purpose of the bone screw disposed through bore 2430 and the
locking screw disposed
through bore 2429 are as described above with respect to the implant 2300.
The present invention further includes a method of implanting the implant 2400
(FIGS. 33A,
33B). To insert the natural or artificial facet joint spacer or inter-facet
joint spacer 2410, a facet joint is
accessed and an incision or a pair of incisions is made in the capsular
ligament, the joint capsule, and the
synovial membrane so that the thinned edge 2412 of the implant 2400 can be
urged into the cervical facet
joint through these tissues. The capsular ligament and the joint capsule and
other soft tissues around the
cervical facet joint are allowed to remain substantially intact, except for
the small incision, and will be
sutured and allowed to heal around the implant 2400. If desired, the cervical
facet joint can be distracted
prior to urging the curved section 2440 with the thinned edge 2412 of the
natural or artificial facet joint
spacer or inter-facet joint spacer 2410 into the cervical facet joint. Once
the curved section 2440 of the
natural or artificial facet joint spacer or inter-facet joint spacer 2410 with
the thinned edge 2412 is urged
into the cervical facet joint, implant 2400 is pivoted, preferably about 90
degrees, so that the second bore
2429 is placed medially relative to the first bore 2430. This allows the
natural or artificial facet joint spacer
or inter-facet joint spacer 2410 to be positioned in the facet joint. It is
noted that the overall size, including
the isthmus 2417, of the natural or artificial fact joint 2410, as that of
2310, can be somewhat smaller than
in prior embodiments to allow the natural or artificial facet joint spacer or
inter-facet joint spacer to be
positioned within the edges of the facet joint with the joint capsule
substantially intact. The lateral mass
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plate 2420 then can be bent downward about the hinge 2422 into position
adjacent the lateral mass or
lamina of the spine of the patient, which position will depend upon the
anatomy of an individual patient's
cervical spine.
Once the lateral mass plate 2420 is positioned adjacent to the bone,
preferably the lateral mass of a
cervical vertebra, a first bone screw can be inserted through the first bore
2430 through the lateral mass
plate 2420 and become embedded into the bone of the lateral mass of the
cervical vertebra to anchor the
implant 2400. After the bone screw is embedded, a locking screw is inserted
through the second bore 2429
of the lateral mass plate 2420, the second bore 2429 medial to the first bore
2430. The locking screw has a
chisel end that allows the locking screw to dig into the bone without use of a
tool to pre-cut a bore.
Alternatively, a bore can be pre-cut and a locking screw without a chisel end
can be used. As the locking
screw is embedded in the bone, the locking head of the locking screw is
brought into proximity with the
head of the bone screw to block its backward movement so that the implant 2400
remains anchored with
the bone screw, i.e., so that the bone screw cannot back out of the bone. The
embedded locking screw also
serves to prevent rotational displacement of implant 2400, while blocking
backward displacement of the
first bone screw.
Referring to FIGs. 34A through 36B, a still further embodiment of an implant
2500 in accordance
with the present invention can include a natural or artificial facet joint
spacer (or insert) or inter-facet joint
spacer (or insert) 2510 connected with a lateral mass plate (also referred to
herein as an anchoring plate)
2520 by a spheroidal joint arrangement 2538 or otherwise shaped multiple
direction articulation joint
arrangement. The natural or artificial facet joint spacer or inter-facet joint
spacer 2510 has a load bearing
structure sized and shaped to distribute, as desired, a load applied by
opposing surfaces of superior and
inferior facets to one another. As shown, the load bearing structure has a
saucer shape, but as described in
further detail below (and as described in previous embodiments above), in
other embodiments the load
bearing structure can have some other shape so long as a desired load
distribution and separation between
superior and inferior facets is achieved. The natural or artificial facet
joint spacer or inter-facet joint spacer
2510 includes a handle-like structure connected with the load bearing surface,
the handle-like structure
necking at an isthmus 2517 and terminating at a pivot end 2526. In an
embodiment, the pivot end 2526 is
substantially spherical, ovoidal, or similarly rounded in shape. As further
described below, the natural or
artificial facet joint spacer or inter-facet joint spacer 2510 can comprise a
flexible material, for example a
biocompatible polymer such as PEEK, or a more rigid material, for example a
biocompatible metal such as
titanium. As shown, the lateral mass plate 2520 has a generally square shape
with rounded corners;
however, in other embodiments the lateral mass plate 2520 can have any number
of shapes so long as the
lateral mass plate 2520 provides sufficient support for anchoring the implant
2500 in position and so long
as the lateral mass plate 2520 allows a desired range of motion for the
natural or artificial facetjoint spacer
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or inter-facet joint spacer 2510. The lateral mass plate 2520 includes a
cavity 2527 within which the pivot
end 2526 is held. The spheroidal joint arrangement 2538 comprises the pivot
end 2526 and the cavity
2527 and as described below allows the natural or artificial facet joint
spacer or inter-facet joint spacer
2510 to tilt and swivel relative to the lateral mass plate 2520.
FIG. 34A is a posterior view showing a posterior face 2532 of the lateral mass
plate 2520, while
FIG. 34B is an anterior view showing an anterior face 2534 of the lateral mass
plate 2520. The lateral
mass plate 2520 includes an anterior notch 2524 (see FIG. 35) or other
indentation formed along the edge
of the anterior face 2534 and a posterior notch 2522 or other indentation
formed along the posterior face
2532. The posterior and anterior notches 2522,2524 are generally aligned with
one another along the edge
of the lateral mass plate 2520 and are connected with the cavity 2527. The
notches 2522,2524 confine
movement of the natural or artificial facet joint spacer or inter-facet joint
spacer 2510 in the anterior and
posterior directions relative to the lateral mass plate 2520, allowing the
natural or artificial facet joint
spacer or inter-facet joint spacer 2510 to tilt at varying degrees of angle in
an anterior and posterior
direction. Referring to FIG. 35, the anterior notch 2524 can have a narrower
width than the posterior
notch 2522 which is sized to provide the pivot end 2526 of the natural or
artificial facet joint spacer or
inter-facet joint spacer 2510 with access to the cavity 2527 so that the pivot
end 2526 can be inserted into
the cavity 2527. Once the pivot end 2526 is positioned within the cavity 2527
a plug 2528 can be mated
with the lateral mass plate 2520 to lock the pivot end 2526 in place within
the cavity 2527 and to further
limit freedom of movement of the natural or artificial facet joint spacer or
inter-facet joint spacer 2510,
particularly limiting tilting of the natural or artificial facet joint spacer
or inter-facet joint spacer 2510 in a
posterior direction. The plug 2528 can be press fit to the posterior notch
2522 and further welded or
otherwise fixedly fastened with the lateral mass plate 2520. A physician can
select an appropriate and/or
desired natural or artificial facet joint spacer or inter-facet joint spacer
2510, lateral mass plate 2520, and
plug 2528 according to the motion segment targeted for implantation and/or the
particular anatomy of the
patient. Once an appropriate combination of components is identified, the
natural or artificial facet joint
spacer or inter-facet joint spacer 2510 and the lateral mass plate 2520 can be
mated, and the natural or
artificial facet joint spacer or inter-facet joint spacer 2510 can be locked
in place by the plug 2528.
As can further be seen in FIGs. 34A through 35 the lateral mass plate 2520 has
a first bore 2530
therethrough. The first bore 2530 can accept a bone screw 2540 (also referred
to herein as a lateral mass
screw) to secure the lateral mass plate 2520 preferably, to the lateral mass,
lamina, or alternatively to
another part of the spine, and thus to anchor the implant 2500. The lateral
mass screw 2540 preferably has
a head 2542 that can accept a tool chosen for the surgical procedure whether a
wrench, screwdriver, or
other tool. The lateral mass plate 2520 further has a second bore 2529 which
is preferably positioned
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medially, relative to the first bore 2530. Referring to FIG. 34A, the second
bore 2529 in the lateral mass
plate 2520 can be positioned either to the left or to the right of the first
bore 2530. The position of the
second bore 2529 will depend upon whether the implant 2500 is intended to be
inserted into a cervical
facet joint on the left or right side of a patient. Specifically, an implant
2500 to be inserted into a right-side
cervical facet joint (i.e., the patient's rights side) will have a second bore
2529 positioned to the left of the
first bore 2530 as in FIG. 34A, when implant 2500 is viewed from a posterior
perspective, while an
implant 2500 to be inserted into a left-side cervical facet joint will have a
second bore 2529 positioned to
the right of the first bore 2530, when implant 2500 is viewed from a posterior
perspective.
The second bore 2529 through the lateral mass plate 2520 is adapted to accept
a second screw
2590 which preferably is a locking screw having a chisel point 2591. The
locking screw 2590 is received
by the second bore 2529 and the chisel point 2591 self-cuts a bore into the
bone. The locking screw 2590
is preferably inserted through the second bore 2529 and embedded in the bone
after the bone screw 2540 is
embedded in the bone through the first bore 2530. The medial position of the
second bore 2529 relative to
the first bore 2530 positions the locking screw 2590 so that it embeds in
stronger bone tissue than if the
second bore 2529 were located more laterally. The locking screw 2590, in
combination with the bone
screw 2540, prevents rotational and/or backward displacement of the lateral
mass plate 2520. As the
locking screw 2590 is received by the second bore 2529, the head 2592 of the
locking screw 2590 aligns
with the head 2542 of the first bone screw 2540 in the first bore 2530,
blocking the head 2542 of the first
bone screw 2540 to prevent the first bone screw 2540 from backing out of the
bone of the vertebra and the
first bore 2530. The posterior face 2532 can include a recessed portion 2539,
and/or the second bore 2529
can be countersunk, so that the locking screw 2590 does not protrude farther
from the posterior face 2532
than desired.
In a preferred embodiment (as shown in FIGs. 34A-37), the spheroidal joint
arrangement 2538
includes a spherical pivot end 2526 and a cavity 2527 having a shape
approximately conforming to the
spherical pivot end 2526 so that the spheroidal joint arrangement 2538 is a
ball-in-socket arrangement.
The ball-in-socket arrangement 2538 allows the natural or artificial facet
joint spacer or inter-facet joint
spacer 2510 to move freely relative to the lateral mass plate 2520 where the
natural or artificial facet joint
spacer or inter-facet joint spacer 2510 is unobstructed by the lateral mass
plate 2520. For example, as
shown in FIG. 36A the natural or artificial facet joint spacer or inter-facet
joint spacer 2510 can tilt in an
anterior direction (to position 1, for example) and can tilt in a posterior
direction (to position 2, for
example). As the natural or artificial facet joint spacer or inter-facet joint
spacer 2510 tilts in an anterior
direction, the isthmus 2517 moves within the anterior notch 2524 so that the
natural or artificial facet joint
spacer or inter-facet joint spacer 2510 can continue tilting without
obstruction. Conversely, as the natural
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or artificial facet joint spacer or inter-facet joint spacer 2510 tilts in a
posterior direction (to position 2, for
example), the isthmus 2517 contacts the plug 2528, limiting the amount of tilt
of the natural or artificial
facet joint spacer or inter-facet joint spacer 2510 in a posterior direction.
Referring to FIG. 36B, the ball-and-socket arrangement allows the natural or
artificial facet joint
spacer or inter-facet joint spacer 2510 to swivel (to position 3, for example)
relative to the lateral mass
plate 2520, potentially providing a more conformal arrangement of the natural
or artificial facet joint spacer
or inter-facet joint spacer 2510 with the surfaces of the superior and
inferior facets. Further, the ability of
the natural or artificial facet joint spacer or inter-facet joint spacer 2510
to swivel can increase options for
lateral mass plate 2520 anchor positions. A physician can anchor the lateral
mass plate 2520 in a more
conformal or advantageous orientation and/or position along the lateral mass,
for example, by altering the
arrangement of the lateral mass plate 2520 relative to the natural or
artificial facet joint spacer or inter-facet
joint spacer 2510. The amount of swiveling accommodated (and the degree of
freedom of movement
accommodated in general) depends on the geometries of the components. For
example, where the isthmus
2517 is sufficiently narrow and long in length, a greater degree of swiveling
in combination with tilt can be
achieved, or for example where the plug 2528 extends over a portion of the
natural or artificial facet joint
spacer or inter-facet joint spacer 2510, as shown in FIGs. 36A and 36B, the
amount of tilt possible in the
posterior direction can be limited. One of ordinary skill in the art will
appreciate that the freedom of
movement of the natural or artificial facet joint spacer or inter-facet joint
spacer 2510 relative to the lateral
mass plate 2520 is limited substantially or wholly by the geometries of the
components, and therefore can
be substantially altered to achieve a desired range of movement. The ball-and-
socket arrangement need not
include a ball that extends from the natural or artificial facet joint spacer
or inter-facet joint spacer and a
socket that is formed in the lateral mass plate. For example, the ball of such
a joint can extend from a
locking or anchoring plate and the socket can be included in the natural or
artificial facet joint spacer or
inter-facet joint spacer. Further, while the preferred embodiment has been
described as a ball-and-socket
arrangement, other arrangements can be employed with varied results. It should
not be inferred that
embodiments in accordance with the present invention need include a spheroidal
shaped end mated with a
rounded cavity. The scope of the present invention is not intended to be
limited to ball-and-socket
arrangements, but rather is intended to encompass all such arrangements that
provide a plurality of degrees
of freedom of movement and substitutability of components.
Referring again to FIGs. 36A and 36B, the load bearing structure of the
natural or artificial facet
joint spacer or inter-facet joint spacer 2510 includes a superior surface 2513
having a generally convex
shape and an inferior surface 2514 having a slightly concave shape. The shape
of the load bearing
structure is intended to approximate a shape of opposing surfaces of the
superior and inferior facets. The
shape of the superior and inferior surfaces 2513,2514 can vary between motion
segments and between
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patients. For example, as shown in FIG. 37, where the cervical vertebra
includes an inferior facet having a
substantially convex natural surface, a physician may select a natural or
artificial facet joint spacer (or
insert) or inter-facet joint spacer (or insert) 2610 including a load bearing
structure with an inferior surface
2614 having a more concave shape combined with a lateral mass plate 2620
having a bone screw 2640
more appropriately sized for the particular lateral mass to which it will be
fixed. (As shown the bone screw
2640 has a shorter length and wider diameter.) A physician can be provided
with a natural or artificial
facet joint spacer or inter-facet joint spacers having a multiplicity of load
bearing structure shapes. As
mentioned above, the ability to match different natural or artificial facet
joint spacer or inter-facet joint
spacers with different lateral mass plates can improve a physician's ability
to provide appropriate treatment
for a patient, and can further provide the physician flexibility to
reconfigure an implant once a surgical site
has been exposed and the physician makes a determination that a different
combination of components is
appropriate.
In yet another embodiment, the spheroidal joint arrangement 2538 of FIGs. 34A-
37 can be applied
to collar structures, for example as shown in FIGs. 26A-27B so that the
natural or artificial facet joint
spacer or inter-facet j oint spacers at each end of the collar structure
include an increased range of motion to
improve surface matching between the natural or artificial facet joint spacer
or inter-facet joint spacers and
the surfaces of the superior and inferior facets (i.e., increasing the amount
of facet surface area contacting
the natural or artificial facet joint spacer or inter-facet joint spacers).
FIG. 38 is a flow chart of an embodiment of a method in accordance with the
present invention for
implanting an implant as described in FIGs. 34A through 37. An incision must
first be made to expose the
surgical site and access the targeted facet joint (Step 2500). Once the facet
joint is made accessible, the
facet joint can be sized and distracted (Step 2502). A sizing too12200 (for
example, see FIGs. 29A-C) can
be inserted to select the appropriate size of an implant 2500 of the invention
for positioning in the cervical
facet joint. This step may be repeated as necessary with, if desired,
different sizes of the tool 2200 until the
appropriate size is determined. This sizing step also distracts the facet
joint and surrounding tissue in
order to facilitate insertion of the implant 2500. Once the appropriate size
is determine, the physician can
select an appropriate natural or artificial facet joint spacer (or insert) or
inter-facet joint spacer (or insert)
2510 with the lateral mass plate 2520 (Step 2504). The natural or artificial
facet joint spacer or inter-facet
joint spacer 2510 can then be urged between the facets into the facet joint
(Step 2510). The facet itself is
somewhat shaped like a ball and socket joint. Accordingly, in order to
accommodate this shape, the natural
or artificial joint 2510 can have a rounded leading edge shaped like a wedge
or tissue expander to cause
distraction of the facet joint as the natural or artificial facet joint spacer
or inter-facet joint spacer is urged
into the facet joint of the spine. The natural or artificial facet joint
spacer or inter-facet joint spacer 2510
also includes the convex superior surface 2513 in order to more fully
accommodate the shape of the facet
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joint of the spine. However, as set forth above and as depicted in FIG. 37, it
is possible in the alternative
to have a curve-shaped natural or artificial facet joint spacer or inter-facet
joint spacer 26.10 with a convex
superior surface 2613 and a concave inferior surface 2614, the distal end of
the natural or artificial facet
joint spacer or inter-facet joint spacer 2610 tapering to facilitate
insertion, while the remainder of the
natural or artificial facet joint spacer or inter-facet joint spacer 2610 has
a uniform thickness.
Once the natural or artificial joint 2510 is positioned, the lateral mass
plate 2520 is tilted and/or
swiveled so that the lateral mass plate 2520 is adjacent to the vertebrae and
preferably to the lateral mass or
to the lamina (Step 2512). Thus the lateral mass plate 2520 may be disposed at
an angle relative to the
natural or artificial facet joint spacer or inter-facet joint spacer 2510 for
a representative spine
configuration. It is to be understood that the final position of the lateral
mass plate 2520 relative to the
natural or artificial facet joint spacer or inter-facet joint spacer 2510 will
depend on the actual spine
configuration. Once the lateral mass plate 2520 is positioned, or prior to the
positioning of the lateral mass
plate 2520, a bore can be drilled in the bone to accommodate the bone screw
2540. Alternatively the screw
2540 can be self-tapping. The screw 2540 is then placed through the first bore
2530 and secured to the
bone, preferably the lateral mass or the lamina, thereby holding the natural
or artificial facet joint spacer or
inter-facet joint spacer 2510 in place (Step 2514). In order to lock the bone
screw 2540 in place and to
lock the position of the natural or artificial facet joint spacer or inter-
facet joint spacer 2510 and the lateral
mass plate 2520 in place, a self-tapping locking screw 2590 is positioned
within a second bore 2529 of the
lateral mass plate 2520 and secured to the bone, thereby resisting undesirable
movement of the lateral mass
plate 2520 (Step 2516). A head 2592 of the locking screw 2590 can further
block movement of the bone
screw 2540 by trapping the bone screw head 2542 between the locking screw head
2592 and the first bore
2530. The locking screw 2590 therefore prevents the lateral mass plate 2520
and the natural or artificial
facet joint spacer or inter-facet joint spacer 2510 from rotating and, as
previously indicated, prevents the
bone screw 2540 from backing out from the vertebra. Preferably the implant is
between the C5 and C6
vertebrae level, or the C6 and C7 vertebrae level. It is noted that two
implants preferably will be implanted
at each level between vertebrae. That is, an implant will be placed in a right
facet joint and also in a left
facet joint when viewed from a posterior view point. This procedure can be
used to increase or distract the
foraminal area or dimension of the spine in an extension or in neutral
position (without having a deleterious
effect on cervical lordosis) and reduce the pressure on the nerves and blood
vessels. At the same time this
procedure preserves mobility of the facet joint.
FIG. 39A depicts a posterior view of another embodiment 2600 of the implant of
the invention.
Embodiment 2600, as well as all of the embodiments herein, can benefit from
some or all of the features
and advantages with regard to the other embodiments described herein. As
shown, embodiment 2600 has a
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natural or artificial facet joint spacer (or insert) or inter-facet joint
spacer (or insert) 2610 that can have a
tapered or thinned distal end 2612. The natural or artificial facet joint
spacer or inter-facet joint spacer
2610 further can be curved so that a superior surface 2613 of the natural or
artificial facet joint spacer or
inter-facet joint spacer 2610 is convex, and an inferior surface 2615 is
concave, to approximate the natural
shape of the cervical facet joint that is to receive the implant 2600. In one
embodiment, the inferior surface
2615 is substantially flat whereby the superior surface 2613 is convex (FIG.
39B). As shown in FIG.
39B, the convex superior surface 2613 tapers downward at an increased angle
toward the inferior surface
2615 at the distal end 2612. This contour of the superior surface 2513 aids in
smooth insertion of the
natural or artificial facet joint spacer or inter-facet joint spacer 2610 into
the facet joint. As with other
embodiments described above, the natural or artificial facet joint spacer or
inter-facet joint spacer 2610 also
can be made of a flexible, biocompatible material, such as PEEK, to maintain
joint mobility and flexibility.
The natural or artificial facet joint spacer or inter-facet joint spacer 2610
is connected flexibly with
the lateral mass plate 2620, preferably with a hinge 2622. The hinge 2622
allows the natural or artificial
facet joint spacer or inter-facet joint spacer 2610 and the lateral mass plate
2620 of the implant 2600 to
bend with respect to one another between an extended position and a bent or
folded position as discussed
above. Once the lateral mass plate 2620 is positioned adjacent to the bone,
preferably the lateral mass of a
cervical vertebra, a first bone screw, such as bone screw 1840, can be
inserted through a first bore 2630
through the lateral mass plate 2620 and embedded into the bone of the lateral
mass of the cervical vertebra.
In addition, once the lateral mass plate 2620 is secured with the first bone
screw, a second bone screw can
be inserted through a second bore 2629 in the lateral mass plate 2620, whereby
the second bone screw
would be embedded into the bone of the lateral mass of the cervical vertebra.
Details of the first and
second bores are discussed above.
The lateral mass plate 2620 is made of a biocompatible flexible material,
preferably titanium or
any other biocompatible flexible material as described herein, for example
PEEK, that will support the use
of bone screws and other hardware, as described below. The lateral mass plate
2620 bends downward
about the hinge 2622 over a wide range of angles relative to the natural or
artificial facet joint spacer or
inter-facet joint spacer 2610. In another embodiment, any other type of
interface between the natural or
artificial facet joint spacer or inter-facet joint spacer 2620 and the lateral
mass plate 2610 is contemplated
(e.g. ball and socket joint). This flexibility facilitates positioning and
insertion of the natural or artificial
facet joint spacer or inter-facet joint spacer 2610.
FIG. 39B depicts a side view of the natural or artificial facet joint spacer
or inter-facet joint spacer
and lateral mass plate in accordance with one embodiment. As shown in FIG.
39B, the natural or artificial
facet joint spacer (or insert) or inter-facetjoint spacer (or insert) 2610
includes an hyper-extension tab 2622
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in one embodiment. The hyper-extension tab 2622 prevents the natural or
artificial facet joint spacer or
inter-facet joint spacer 2610 as well as the lateral mass plate 2620 from
moving in a direction beyond the
extended position which is shown in FIGS. 39A and 39B. The lateral mass plate
2620 preferably includes
a recess 2611 at the interface between the lateral mass plate 2620 and the
natural or artificial facet joint
spacer or inter-facet joint spacer 2610 which seats the tab 2622 in the
extended position which is shown in
FIG. 39A. When the natural or artificial facet joint spacer or inter-facet
joint spacer 2610 is bent at an
angle, the tab 2622 is not in contact with the recess 2611. However, the tab
2622 comes into contact with
the recess 2611 when in the extended position, as shown in FIG. 39A. In
addition, the tab 2622, when
seated in the recess 2611, prevents the natural or artificial facet joint
spacer or inter-facet joint spacer 2610
and lateral mass plate 2620 from moving beyond the extended position. This
features aids in placing the
implant into the facet joint as the implant is prevented from bendng back
beyond the extended position
shown in FIG. 39B. This arrangement, however, allows the lateral mass plate
2620 to bend down to meet
the spine when the natural or artificial facet joint 2610 is implanted in the
facet joint.
As shown in FIG. 39A, the lateral mass plate 2620 preferably includes a third
bore 2602 located
near a rear edge, whereby the third bore 2602 preferably receives an engaging
rod 2716 (FIG. 40B) of an
implantation tool 2600 described below. The third bore 2602 preferably extends
through the superior and
inferior surfaces of the lateral mass plate, although not necessarily.
Although the third bore 2602 is
circular in shape, any other shape is contemplated which engages a
correspondingly shaped engaging rod
2716 (FIG. 40B). The rear edge 2604 of the lateral mass plate 2620 can be
engaged by the engagement
head 2706 (FIG. 40B) of the implantation tool 2700 as described below.
In addition, the lateral mass plate 2620 preferably includes one or more
winged protrusions, such
as tabs, winglets or ears, 2608 which protrude from the side edges of the
lateral mass plate 2620. FIG.
39A illustrates the implant 2600 having two winged protrusions 2608. The
protrusions 2608 serve as
guides to successfully couple the implant 2600 to the implantation tool 2700.
In addition, the protrusions
act as an engaging mechanism which secures the implant 2600 to the tool 2700.
It should be noted that the
winged protrusions 2608 are preferred and the implant 2600 can be configured
in any other appropriate
design to ensure that the implant 2600 is able to be effectively guided and
secured to the implantation tool
2700.
FIG. 40A depicts an implantation tool in accordance with one embodiment of the
present
invention. As shown in FIG. 40A, the tool 2700 preferably includes a handle
2702 having a proximal end
and a distal end. The tool 2700 includes an actuating switch 2708 as well as a
shaft 2704 extending from
the distal end of the handle 2702. As shown in FIG. 40A, the shaft 2704
preferably extends axially with
the handle 2702, although the shaft 2704 may be at an angle with respect to
the handle 2702. Extending
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from the shaft 2704 is an engagement head 2706, whereby the engagement head is
preferably oriented at an
angle with respect to the shaft 2704 and/or the handle 2702. The angle of the
head 2706 relative to the
shaft 2704 aids the surgeon in the process of implanting the implant 2600 in
the spine. This angle allows
the surgeon to slip the natural or artificial facet joint spacer or inter-
facet joint spacer 2620 into the facet
joint with the tool 2700 preferably about a right angle to the spine.
Preferably the head is at an angle
between 45 and 90 degrees relative to the handle 2704. However, other angles
are contemplated.
Referring to FIG. 40B, the engagement head 2706 preferably has a forked
configuration and
includes a pair of side walls 2710, an engagement seat 2712 as well as a
receiving space 2718 which is
defined as the area between the side walls 2710 and the seat 2712. The
engagement head 2706 preferably
includes a retractable engaging rod 2716 which extends partially into the
receiving space 2618. The side
walls 2610 each have an inner side which includes a slot 2712 whereby the
slots 2712 face the receiving
space 2718. The slots 2712 are dimensioned to slidably receive the wing
protrusions 2608 of the lateral
mass plate 2620 as well as secure the lateral mass plate 2620 to the
engagement head 2706. The
engagement seat 2712 receives the rear edge 2604 of the lateral mass plate
2620.
In one embodiment, the engagement head 2706 preferably includes the engaging
rod 2716, as
shown in FIG. 40B. The engaging rod 2716 is dimensioned to fit within the
third bore 2602 in the lateral
mass plate 2620. The engaging rod 2716 is coupled the switch 2708 on the
handle 2702, whereby
actuation of the switch 2708 causes the engaging rod 2716 to retract. Upon
being retracted, the engaging
rod 2716 disengages the third bore 2602 and allows the implant 2600 to be
disengaged from the
engagement head 2706. It is preferred that the tool 2700 includes a spring or
other urging means to urge
the engaging rod 2716 to the extended position, as shown in FIG. 40B. In
another embodiment, the
engaging rod 2716 is freely moveable between the extended and retracted
positions without a biasing force
applied thereto.
It should be noted that the engaging rod 2716 is shown as being a circular
cylinder in FIGS. 40A
and 40B. However, it is contemplated that the engaging rod 2716 can have any
other shape which
conforms to the shape of the third bore 2602 in the lateral mass plate 2620.
In another embodiment, the
engagement head 2706 does not include an engaging rod 2716 but some other
mechanism to secure the
implant 2600 to the tool 2700. In yet another embodiment, the slots 2712 in
the side walls 2710 can be
used to retain the implant 2600 in the head 2706 without the use of an
engaging mechanism.
In preferred operation, to engage the implant 2600 with the tool 2700, the
implant 2700 is oriented
to be right side up such that the rear surface 2604 of the implant 2600 will
conform and mate with the
engagement seat 2714. The implant 2600 is aligned with the forked portion of
the engagement head 2706,
whereby the winged protrusions 2608 of the implant 2600 are inserted into the
slot openings 2712. Upon
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registering the winged protrusions 2608 into the corresponding slots 2712, the
lateral mass plate 2620 is
guided into engagement by the slots 2712 until the rear edge 2604 mates with
the engagement seat 2714.
Preferably the engaging rod 2716 is then inserted into the third bore 2602,
thereby securing the lateral mass
plate 2620 to the engagement head 2706. In one embodiment, the user manually
actuates the switch 2708
to retract the engaging rod 2716 to allow the lateral mass plate 2620 to be
inserted completely in the
receiving space. The switch 2708 is then manually released when the bore 2602
and engaging rod 2716
are aligned such that the engaging rod 2716 then extends and engages the third
bore 2602. In another
embodiment, contact between the superior surface of the lateral mass plate
2620 and the engaging rod
2716 causes the engaging rod 2716 to slightly retract while the plate 2620 is
moved into the engagement
seat 2714. Once the lateral mass plate 2620 is seated, the third bore 2602
preferably registers with the
engaging rod 2716, whereby the urging force causes the engaging rod 2716 to
automatically engage the
third bore 2602.
During the surgical procedure, the natural or artificial facet joint spacer or
inter-facet joint spacer
2610 is inserted into the distracted facet joint as described in detail above.
Upon the natural or artificial
facet joint spacer or inter-facet joint spacer 2610 being satisfactorily
inserted in the facet joint, the user
preferably actuates the switch 2708 to disengage the engaging rod 2716 from
the third bore 2602. The
surgeon then draws the tool 2700 away from the facet joint, whereby the
lateral mass plate 2620 slides out
of the received area and is guided by the slots 2712. The lateral mass plate
2620 is then anchored into the
vertebral body as discussed above.
In still other embodiments, some other structure can be employed to resist
movement of the seated
bone screw within the first bore. Referring to FIGs. 41A and 41B, in some
embodiments a cam 2824 can
be rotatably associated with the lateral mass plate 2820 so that the first
bore 2830 can be selectably
obstructed or unobstructed, thereby allowing a bone screw 2840 to be received
within the first bore 2830,
or resisting movement of the bone screw 2840 seated within the first bore
2830. As shown in FIG. 41A,
the cam 2824 can have a shape such that at a first position the surface 2828
of the cam is approximately
flush with the first bore 2830, thereby allowing a bone screw 2840 to pass
through the first bore 2830.
Rotated to a second position (FIG. 41B), a protruding portion 2826 of the
surface of the cam 2824 can
extend across at least a portion of the first bore 2830, thereby blocking a
bone screw 2840 seated within the
first bore 2830 and preventing the bone screw 2840 from backing out of the
first bore 2830. The cam 2824
can include features 2831 (e.g., indentations) that can allow the cam to be
grasped with a tool (not shown),
and thus rotated to the desired position. As shown, the cam 2824 is positioned
within a slot of the lateral
mass plate 2820 so that the cam does not protrude undesirably from the surface
of the lateral mass plate
2820.
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Except as otherwise noted above, the embodiment shown in FIGs. 22A-24B is
similar to the
embodiment shown in FIGs. 41 A-41 B.
A further embodiment of an implant 2900 in accordance with the present
invention is shown in
FIGs. 42A-42G. The implant 2900 resembles implants as shown in FIGs. 22A-25A
in that the natural or
artificial facet joint spacer (or insert) or inter-facet joint spacer (or
insert) 2910 has limited freedom of
movement relative to the lateral mass plate 2920. As can be seen, a hinge 2922
connects the natural or
artificial facet joint spacer or inter-facet joint spacer 2910 with the
lateral mass plate 2920, allowing the
natural or artificial facet joint spacer or inter-facet joint spacer to pivot
up and down relative to a plane of
the lateral mass plate 2920. However, in other embodiments the natural or
artificial facet joint spacer or
inter-facet joint spacer 2910 can be connected with the lateral mass plate
2920 by way of a spheroidal joint
arrangement (as described above) or by way of some other structure. An
inferior surface 2915 of the
natural or artificial facet joint spacer or inter-facet joint spacer 2910
includes a plurality of cleats (also
referred to herein as protrusions) 2986 extending from the inferior surface
2915. In one example as seen
in Fig 42A the cleats point in a direction that is opposed to the direction of
insertion of the natural or
artificial joint in the facet joint in order to ease the insertion step and to
aid in preventing the natural or
artificial facet joint spacer or inter-facet joint spacer from backing out of
the facet joint. Additionally the
cleats or protrusions have, in one embodiment, a thickness that is less that
the thickness of the natural or
artificial facet joint spacer or inter-facet joint spacer defined between a
superior surface of the natural or
artificial facet joint spacer or inter-facet joint spacer and an inferior
surface of a natural or artificial facet
joint spacer or inter-facet joint spacer. The plurality of cleats 2986 can
penetrate or grip a superior facet if
a kiwer vertebre of the targeted facet joint, thereby reducing slippage of the
natural or artificial facet joint
spacer or inter-facet joint spacer 2910 relative to the superior facet. The
cleats 2986 do not directly restrict
the inferior facet of an upper vertebre of the targeted facet joint from
moving along the superior surface
2913 of the natural or artificial facet joint spacer or inter-facet joint
spacer 2910. The cleats 2986 can
further promote bone growth by roughing the surface, which can provide
beneficial results where an
increase in surface contact resulting in a reduction of slippage is desired.
In a preferred embodiment the
natural or artificial facet joint spacer or inter-facet joint spacer 2910 can
include a inferior surface 2915
connected with the hinge 2922 and formed of a light-weight, bio-compatible
material having a desired
strength, such as titanium, titanium alloys, aluminum, aluminum alloys,
medical grade stainless steel, etc.
Such a structure is also referred to herein as an inferior shim 2980. As
shown, a substantial portion of the
natural or artificial facet joint spacer or inter-facet joint spacer 2910
including the superior surface 2913
can be formed of a biocompatible polymer, such as described below. Such a
substantial portion is also
referred to herein as a superior shim 2982. Such a material is radiolucent,
and can have a desired
smoothness and reduced compressive strength relative to the inferior surface
2915 such that the superior
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surface 2913 of the natural or artificial facet joint spacer or inter-facet
joint spacer 2910 allows for a
desired slippage relative to the inferior facet of the facet joint. A superior
surface 2913 having a reduced
compressive strength and an increased elasticity relative to a bony structure
of the spine. The superior shim
2982 can be molded onto the inferior shim 2980 to form the natural or
artificial facet joint spacer or inter-
facet joint spacer 2910, or the superior shim 2982 can be adhesively fastened
to the inferior shim 2980,
interference fit with optional protuberances of the inferior shim 2980, etc.
One of ordinary skill in the art
will appreciate the different techniques for fixedly connecting a superior
shim 2982 with the inferior shim
2980.
It is also to be understood that the inferior shim can be comprised of a rigid
material while the
superior shim can be comprised of a more compliant and/or compressible
material. Thus the inferior shim
can carry the load experienced in the facet joint while the superior shim can
be more compliant. The
natural or artificial facet joint spacer or inter-facet joint spacer can, for
example, be comprised of one
material that has been formed to have a gradient of stiffness from more stiff
in the area of the inferior shim
to less stiff and more compliant I the area of the superior shim. For example
a PEEK polymer material as
described below can be formed in the area of the inferior shim with fillers
that increase the stiffness and
strength of the material while the PEEK polymer in the area of the superior
shim does not have such fillers
and is thus more compliant.
In a preferred embodiment, the cleats 2986 of the implant 2900 can extend from
the inferior
surface 2915 to have a sawtooth shape and arrangement to resist movement in a
generally posterior
direction away from the facet joint (i.e., toward the lateral mass plate 2920
as shown) and further to resist
movement in a lateral direction relative to the facet joint. However, the
cleats 2986 need not necessarily
be sawtooth in shape and arrangement. For example, the cleats 2986 can have a
conical shape, a pyramid
shape, a curved shape, etc. Further, as shown particularly in FIG. 42C four
cleats 2986 extend from the
inferior surface 2915. In other embodiments, any number of cleats 2986 can be
provided, the cleats 2986
being similarly sized and shaped, or varying in size and shape. In reflection
on the teachings contained
herein, one of ordinary skill in the art will appreciate the myriad different
shapes with which the cleats
2986 can be formed. The cleats 2986 can vary in performance and technique for
implantation with shape
and number; however, the present invention is meant to encompass all such
variations.
The implant 2900 can further optionally include plate cleats 2988 extending
from a surface of the
lateral mass plate 2920 substantially contacting the bony structures of the
spine (e.g., the lateral mass). The
plate cleats 2988 can help anchor the lateral mass plate 2920 in position
either to assist in resisting shifting
as a bone screw 2940 is associated with the bony structure, or as an adjunct
to the bone screw 2940.
Surface roughening caused by the plate cleats 2988 can further promote bone
growth near and/or integrally
with the lateral mass plate 2920. As shown particularly in FIG. 42C there are
four plate cleats 2988, each
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plate cleat 2988 having a conical structure. However, as above the plate
cleats 2988 can vary in size,
number and shape. For example, the plate cleats 2988 can have a saw-tooth
shape, a pyramid shape, a
curved shape, etc.
Referring to FIGs. 42D through 42G, a bone screw 2940 of the implant 2900 can
be arranged in a
bore 2930 so that the bone screw 2940 and bore 2930 permit a relative degree
of freedom of movement
resembling a ball-in-socket joint. Such an arrangement can allow for
flexibility in fastening the implant
2900 to a bony structure, thereby allowing a surgeon to avoid diseased or
fragile bony structures, fastening
the implant 2900 to more durable, healthy bony structures. The bone screw 2940
can swivel within the
bore 2930 toward or away from the natural or artificial facet joint spacer or
inter-facet joint spacer 2910
and/or from side-to-side relative to the natural or artificial facet joint
spacer or inter-facet joint spacer 2910.
When the bone screw 2940 is arranged as desired a retaining plate 2924 (FIG.
42B) can be attached to the
lateral mass plate 2920 to resist backing out of the bone screw 2940, similar
to the functioning of features
as shown in previous embodiments. As can be seen in FIG. 42B, retaining plates
2924 can have a
projection 2925 that fits in a recess 2927 of the lateral mass plate 2920 in
order to prevent rotation of the
retaining plate 2924 once bone screw 2940 is tightened against retaining plate
2924.
Referring to FIG. 43, in still further embodiments, implants in accordance
with the present
invention can have both an inferior surface 3015 and a superior surface 3013
having cleats 3086 extending
therefore. Such embodiments can be employed, for example, to fuse the facet
joint. The cleats 3086 can
resist relative movement of the inferior and superior facets, and can further
promote bone growth through
roughening of the facet surface, thereby promoting fusion of the facet joint.
The natural or artificial facet
joint spacer (or insert) or inter-facet joint spacer (or insert) 3010 can be
formed from a light-weight, high
strength, biocompatible material such as titanium, titanium alloys, aluminum,
aluminum alloys, medical
grade stainless steel, etc. Alternatively, the natural or artificial facet
joint spacer or inter-facet joint spacer
3010 can be formed from a biocompatible polymer, as described below, or the
natural or artificial facet
joint spacer or inter-facet joint spacer 3010 can comprise inferior and
superior shims (not shown) fixedly
connected and formed of the same or different materials. Upon reflection of
the teachings herein, one of
ordinary skill in the art will appreciate the different ways in which the
natural or artificial facetjoint spacer
or inter-facet joint spacer 3010 can be formed.
As described above in reference to FIGs. 42A-G, the cleats 3086 are saw-tooth
in shape and
arrangement, but alternatively can have some other shape and/or arrangement.
For example, the cleats
3086 can have a pyramidal shape, a curved shape, a conical shape, etc.
Further, the shape, size and
arrangement for cleats 3086 of the inferior surface 3015 can be different or
the same from cleats 3086 of
the superior surface 3013. The shape, size, and arrangement of the cleats 3086
can be chosen based on the
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location of implantation, the preferences of the surgeon, the physical
condition of the target facet joint, etc.
FIG. 40 is a flow chart of an embodiment of a method in accordance with the
present invention for
implanting an implant as described in FIGs. 34A through 39.
FIG. 44 illustrates a side view of a distractor tool in accordance with one
embodiment of the
present invention. As shown in FIG. 44, the distractor tool 203 preferably
includes a handle portion 202,
an arm portion 204, and a distractor head portion 206. In particular, the
handle portion 202 preferably
includes a first handle 202A and a second handle 202B. The proximal ends of
each handle 202A, 202B
preferably include finger loops 212A and 212B, respectively. The handles 202A
and 202B are coupled to
one another at a pin 208. In a preferred embodiment, the first handle 202A is
moveable whereas the
second handle 202B is stationary with respect to the first handle 202A. In
another embodiment, the second
handle 202B is able to be pivotably rotated with respect to first handle 202A
about pin 208. Alternatively,
both handles are movable with respect to one another about pin 208.
As shown in the embodiment in FIG. 44, the arm portion 204 has a first arm
204A and a second
arm 204B. The arms 204 are oriented longitudinally along the X-axis. The upper
arm 204B is preferably
attached to the second handle 202B. However, the second arm 204B can
alternatively be attached to the
first handle 202A. In the embodiment in FIG. 44, the first arm 204A and the
second handle 202B are of
one formed piece. Alternatively, the first arm 204A and the second handle 202B
are two separate pieces
which are coupled together.
As stated above, the first handle 202A is rotatable about pin 208, whereby the
pin 208 is preferably
located between the midpoint and a distal end of the handle 202A. In one
embodiment shown in FIG. 3A
and 3B, a proximal end of the first arm 204A is coupled to the distal end of
the first handle 202A at pin
210. In another embodiment, the distal end of the handle 202A is coupled to an
intermediate link which
couples the handle 202A to the first arm 204A.
The first handle 202A is preferably moveable about pin 208 between an non-
distracted position, as
shown in FIG. 44, and a distracted position as shown in FIG. 45. As shown in
FIG. 44, the first handle
202A is oriented at angle a with respect to the X-axis. In addition, the
second handle 202B is oriented at
angle 0 with respect to the X-axis. In FIG. 44, the angle a of the first
handle 202A in the non-distracted
position is greater than the angle 0 of the first handle 202A in the
distracted position. It is preferred that, as
the handles 202A, 202B are squeezed together, the tool 203 actuates from an
non-distracted position to a
distracted position.
When the handles 202A, 202B of the tool 203 are squeezed together, the
clockwise rotational
movement of the handle 202A about the pin 208 causes the distal end of the
handle 202A to move the first
arm 204A longitudinally along the positive X-axis (FIG. 45). In contrast, when
the handle 202 is released
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or when manually actuated to the non-distracted position, the counter-
clockwise rotational movement of the
handle 202A causes the distal end of the handle 202A to move the first arm
204A in the opposite direction,
along the negative X-axis (FIG 44). The longitudinal movement of the first arm
204A along the X-axis
causes the distraction head 206 to actuate and thus separate adjacent facets
apart to allow implantation of
the implant.
The distal ends of the first and second arms 204A, 204B are coupled to the
distraction head 206 as
shown in FIGs. 44 and 45. The distraction head 206 preferably includes a first
distraction head component
206A and a second distraction head component 206B. In one embodiment, the
distal end of the first arm
204A is coupled to the first distraction head component 206A and the first
distal end of the second arm
204B is coupled to the second distraction head component 206B. In another
embodiment, the distal end of
the first arm 204A is coupled to the second distraction head 206B and the
distal end of the second arm
204B is coupled to the first distraction head 206B. Since the first arm 204A
is attached to the first
distraction head component 206A, the movement of the first arm 204A along the
X-axis preferably causes
the first distraction head component 206A to also move along the X-axis. The
second head component
206B is preferably fixed to the second arm 204B. Therefore, the movement of
the arm 204along the
positive X-axis causes the first head component 206A to move preferably away
from the second head
component 206B. The first head component 206A and the second head component
206B preferably
separate the adjacent facets apart between 1.5 and 2.5 mm to accommodate the
thickness of the natural or
artificial joint facet or inter-facet joint spacer of the implant. However,
other distances are contemplated
and are not limited to that described above.
In the preferred embodiment, the distal portion of the distraction head
extends substantially
perpendicular to the arms 204A, 204B, as shown in FIGs. 44 and 45. In another
embodiment, the superior
and inferior surfaces of the distraction head extend at an angle other than 90
degrees from the arms 204A
and 204B. In the preferred embodiment shown in FIGs. 44 and 45, the head
components 206A, 206B of
the distraction head 206 are oriented such that the leading edge 230 extends
in the negative Y direction.
Alternatively, the distraction head 206 is oriented such that the leading edge
faces the positive Y direction.
However, it is contemplated that the distraction head 206 can be oriented to
extend from the arm 202 such
that the leading edge faces the Z direction, as shown in FIGs. 48A and 48B. It
is contemplated that the
leading edge 230 of the distraction head 206 of the present invention can face
any direction with respect to
the arms 204 and the handles 202 including the negative Z direction.
The tool 203 of the present invention is preferably made from a medical grade
metal. For example,
the tool 203 can be made of titanium, stainless steel, an alloy or any other
material which provides the tool
203 with a sufficient amount of strength to distract the adjacent facets apart
during the implantation
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process. In one embodiment, the distraction head 206 is removable from the
distal ends of arms, such that
different sized distraction heads can be used with the same tool. This feature
would allow the surgeon to
replace the distraction head with one of a different size for a different
inter-cervical facet joint without
having to use a different tool. In another embodiment, the distraction head
206 is mounted to the arms 204
of the tool 203, whereby the upper head component 206A is welded to the lower
arm 204A and the lower
head component 206B is welded to the upper arm 204B or vice versa. Any other
appropriate method of
attaching the distraction head 206 to the arms 204 is contemplated.
It is preferred that the tool 203 includes a movement limitation mechanism.
The mechanism
preferably limits the amount of distraction between the first and second head
components 206A, 206B
when the handles 202 are actuated. As shown in FIGs. 44 and 45, the proximal
end of the first arm 204A
preferably has a wedge-shaped portion 216. In addition, the second arm 204B
includes a correspondingly
shaped slot 218 which receives the wedged portion 216 during movement of the
wedged portion 216 in the
positive X direction. The slot 218 limits longitudinal movement of the first
arm 204A along the X-axis
when the handles 202 are squeezed. This, in effect, limits the distance that
the head components 206A,
206B separate in distracting the facets apart from one another during the
implantation procedure.
Alternatively, any other mechanism is contemplated to limit movement of the
distraction head 206 and is
not limited to the wedged portion 216 and corresponding slot 218 of the
present tool. It should be noted
that the movement limitation mechanism is alternatively not incorporated in
the tool of the present
invention.
FIG. 46A illustrates a perspective view of the distraction head 206 in a
distracted position in
accordance with one embodiment. FIG. 46B illustrates a perspective view of the
distraction head 206 in
FIG. 46A in a non-distracted position. As shown in FIGs. 46A and 46B, the
distraction head 206
preferably includes the first head component 206A having a proximal portion
and a distal portion as well
as the second head component 206B having a proximal portion and a distal
portion. As shown in FIGs.
46A and 46B, the first head component 206A includes an engagement slot 222A at
the proximal end. In
addition, the second head component 206B includes a pass-through slot 222B
which is aligned with the
engagement slot 222A. The engagement slot 222A of the first head component
206A preferably receives
and mounts to the distal end of the first arm 204A. The first arm 204A
preferably extends through the
pass-through slot 222B in the second head component 206B to allow the arm 204A
to freely move the first
head component 206A without interfering with the second head component 206B.
The proximal portion
of the second distraction head 206B is attached to the distal end of the
second arm 204B. The second arm
204B is preferably mounted to the underside 240 of the second head component
206B, whereby the second
arm 204B is located adjacent to the first arm 204A. It should be noted that
the above description of the
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head components is preferred and can have any other appropriate configuration
to allow distraction in
accordance with the present invention.
The distal portion of both first and second distraction heads 206A, 206B
includes leading edges,
shown as 230A and 230B, which are used to penetrate the facet joint to insert
the distraction head 206
therein. The distal portion of the first and second head components, as shown
in FIG. 46A, include
several fingers which are shown alternately arranged. In particular, the first
distraction head 206A is
shown to have two fingers 224A whereas the second distraction head 206B is
shown to have three fingers
224B. In another embodiment, the upper and lower distraction heads 206A, 206B
have a greater or fewer
number of fingers than that shown in FIG. 46A, including only one finger each.
The fingers 224A, 224B
together form an overall rounded leading edge 230 of the distraction head 206
as shown in FIG. 46B. In
another embodiment, the leading edges 230 of the fingers do not form a rounded
leading edge, but can
form any other shape.
As shown in FIGs. 46A and 46B, the second head component 206B includes finger
slots 232
which receive the fingers 224A of the first head component 206A when the
distraction head 206 is in the
non-distracted position (FIG. 46B). In the non-distracted position, as shown
in FIG. 46B, the first head
component 206A and the second head component 206B are co-planar, whereby the
fingers 224A and 224B
are preferably inter-digitated. The co-planar head components provide a height
dimension or thickness
which allows the distraction head 206 to be easily inserted into the facet
joint. Upon the handles 202 being
squeezed, the first head component 206A is forced away from the second head
component 206B, thereby
causing the first set of fingers 224A from sliding out of the finger slots 232
of the second head component
206B. The first head component 206A thus moves apart from the second head
component 206B until the
desired distance between the head components is achieved. As shown in FIG.
46A, the fingers 224A of
the first head component 206A are separated from the fingers 224B of the
second head component 206B
and is no longer co-planar in the distracted position.
As shown in FIG. 46A, the fingers 224A, 224B each have a superior surface
226A, 226B, as well
as an inferior surface 228A, 228B. In one embodiment, the leading edge 231A,
231B of the fingers 224A,
224B are rounded or curved, as shown in FIGs. 46A and 46B. In another
embodiment, the leading edges
of the fingers 224A, 224B are sharpened.
In one embodiment, the superior surfaces 226A, 226B of the distraction head
components 206A,
206B mate with the inferior facet of the vertebral body when the distraction
head 206 is inserted into the
facet joint. Additionally, in one embodiment, the inferior surfaces 228A, 228B
of the distraction heads
206A, 206B mate with the superior facet of the vertebral body. However, it is
contemplated that the tool
203 can be oriented upside down such that the superior surface of the head 206
mates with the superior
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facet and the inferior surface of the head 206 mates with the inferior facet
of the vertebral bodies.
As shown in FIGs. 46A and 46B, the distal portion of the distraction head 206
is relatively flat
such that the superior and inferior surfaces 226, 228 of the head components
206A, 206B are generally
parallel with one another and have a uniform thickness. In another embodiment,
the inferior and superior
surfaces taper toward each other at the leading edge 231A, 231B. The head
components 306A, 306B can
alternatively be shaped to contour the shapes of the facets. The facet itself
is somewhat shaped like a ball
and socket joint. Accordingly, as depicted in FIGs. 47A and 47B, the
distraction head 306 can have a
convex superior surface 326 and a concave inferior surface 328. The curved
superior and inferior surfaces
preferably taper toward each other at the leading edge 322A, 322B to
facilitate insertion, while the
remainder of the distraction head has a uniform thickness.
In addition, as shown in FIG. 47B, the individual head components each can
have a concave
and/or convex shape. In another embodiment, one of the superior and inferior
surfaces 326A, 326B, 328A,
328B have a convex or concave shape, whereas the other surface is planar and
does not have a curved
shape. The superior and inferior surfaces of the distraction head 306 thus
preferably contour the respective
facets of the joint. The contour of the superior and/or inferior surfaces of
the head 306 allows the upper
and lower head components to apply a relatively constant force to the superior
and inferior facets while the
tool is actuated to the distracted position. In addition, the contoured shaped
of the distraction head 306
along with its fingers allow the head components to obtain a better grip with
their respective facets during
the distraction procedure.
FIGs. 48A and 48B illustrate another embodiment of the tool having the
distraction head in an
alternative orientation than that shown in FIGs. 44 and 45. As shown in FIG.
48A, the too1403 includes
the handle portion 402, the arm section 404 and the distraction head 406. As
shown in FIG. 48A, the arm
portion 404 is oriented along the X-axis. However, unlike the too1203
described in FIGs. 44 and 45, the
distraction head 406 extends from the arm portion 404 such that the leading
edge 430 faces in the positive
Z direction. In the embodiment shown in FIG. 48A, the distraction head 406
extends from the arm portion
along the positive Z direction at approximately a 90 degree angle with respect
to the arm 404. However,
the distraction head 406 can be oriented to extend from the arm 404 along the
negative Z direction or at
any other angle besides 90 degrees.
In operation, actuation of the handle 402A causes the arm 404A to move along
the X axis to
actuate the distraction head 406 as shown in FIG. 48B. As shown in FIG. 48B,
the leading edges 430A
and 430B of the first and second head components 406A, 406B are preferably
tapered. The orientation of
the leading edge 230 in the Z direction allows the tool 403 to be oriented in
a different manner than the tool
203 in FIGs. 44 and 45 during the implantation procedure. This alternative
orientation of the tool 403 may
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be advantageous to distract facets along different portions of the spine which
require the tool 403 to be
oriented at a different angle. Additionally, the individual tastes of each
physician may prefer the alternative
orientation of the tool 403 over the orientation of the head 206 in the
embodiment in FIGs. 44 and 45.
FIGs. 49A - 49C illustrate one method of distracting adjacent facets in
accordance with the tool of
the present invention. FIG. 49D illustrates a flow chart of the method of
implantation in accordance with
one embodiment of the invention. The facet joint 60 is initially accessed as
in step 602, as shown in FIG.
49A. A sizing tool can be inserted into the facet joint 60 to select the
appropriate size of implant to be
inserted as in step 604. In one embodiment, the sizing tool is a unit separate
from the tool 203 of the
present invention. In another embodiment, the tool 203 of the present
invention has a sizing gauge to allow
the surgeon to determine what size of implant is to be inserted into the facet
joint as discussed in relation to
FIG. 49. As shown in FIG. 49A, the leading edge 231 of the tool 203 is then
inserted into the entrance of
the facet joint 60. The leading edge 231 of the tool 203 is then urged into
the facet joint 60 until the
distraction head 206 is sufficiently displaced within the facet joint 60 and
between the superior and inferior
facets 56, 58, as in FIG. 49B. In FIGs. 49A - 49C, the tool 203 accesses the
joint from a superior
approach (i.e. upside down). However, it should be noted that the tool 203 can
alternatively access the
facet joint from an inferior (e.g. right side up) or lateral (e.g. sideways)
approach.
Once the distraction head 206 is inserted, the physician squeezes the handles
202A, 202B together,
whereby the distraction head components 206A and 206B separate from one
another and distract the facet
joint and surrounding tissue in order to facilitate insertion of the implant,
as in step 604 (FIG. 49C). Once
the adjacent facets are distracted apart the'desired distance, the tool 203 is
then removed from the joint,
thereby leaving the adjacent facets apart from one another. The distracted
tissue surrounding the facets
slowly contract, thereby leaving time for the physician to urge the natural or
artificial facet joint spacer or
inter-facet joint spacer 104 of the implant between the facets into the facet
joint, as in step 606.
Once the natural or artificial joint is inserted, the lateral mass plate of
the implant is pivoted
downward about the hinge toward the lateral mass or to the lamina, as in step
608. Once the lateral mass
plate is positioned, or prior to the positioning of the lateral mass plate, a
bore can be drilled into the bone to
accommodate the bone screw. The screw is then placed through the bore and
secured to the bone to anchor
the natural or artificial facet joint spacer or inter-facet joint spacer in
place as in step 610. In order to lock
the bone screw and position of the natural or artificial facet joint spacer or
inter-facet joint spacer and
lateral mass plate in place, the locking plate is positioned over the lateral
mass plate, as in step 612. The
keel located adjacent to the locking plate can preferably self-cut a groove
into the bone to lock the keel and
anchor the implant, as in step 614. The locking plate is then fastened to the
lateral mass plate with the
screw through the bore, as in step 616. This method is then repeated for any
other facet joints in the spine,
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as in step 618.
FIG. 50A and 50B illustrate another embodiment of the tool of the present
invention. The
embodiment shown in FIGs. 50A and 50B includes a distraction head 806 which is
configured to distract
adjacent facets of the vertebral bodies and simultaneously allow insertion of
the implant into the facet joint.
The tool 803 shown in FIGs. 50A and 50B includes the handle portion 802, the
arm portion 804 as well
as the distraction head 806.
As shown in FIGs. 50A and 50B, the fingers of the distraction head 806 are
offset and adjacent to
the arms 804A and 804B of the tool 803. As shown in FIGs. 50A and 50B, the
distraction head 806
includes a leading edge 808 which is shown facing the negative Y direction as
well as insertion edges
811A, 811B which face the positive Y direction. The insertion edges 811A, 811B
are preferably located
on the opposite end of the head 806 from the leading edge 808. The leading
edge 808 is configured to be
inserted into the facet joint to distract the adjacent facets apart as stated
above. The insertion end 811A,
811B, upon distraction, allows the implant to be inserted into the facet joint
while the tool 203 is
simultaneously distracting the facets apart. The insertion edges 811A, 811B of
the head components
806A, 806B, respectively, move apart as the head components 806A, 806B are
distracted. This creates an
insertion conduit 824 between (FIG. 50B) the first and second head components
806A, 806B. The
insertion conduit 812 has a height distance, D, which provides adequate
clearance between the inferior
surface 822 of the first head component 806A and the superior surface 824 of
the second head component
804B to allow the implant to be inserted therethrough. As stated above, the
distraction head 806 is offset
and located adjacent to the arms 804 and handle 802 of the too1803, whereby
the location of the head 806
provide ample room to insert the implant therethrough.
In operation, upon the distraction head 806 being inserted into the facet
joint, the handles 802 are
squeezed together to cause the distraction head components 806 to separate,
thereby distracting the facets
until the insertion conduit 812 is at the desired height dimension D. The
desired height dimension, D, will
depend on several factors, such as size of the natural or artificial inter-
facet joint or inter-facet joint spacer,
the thickness of the fingers of the head components, and the location of the
facet joint (e.g. cervical,
thoracic, lumbar). It is preferred that the height dimension D be between 1.5
and 2.5 mm, although other
dimensions are contemplated. The height dimension D can be measured by a
distraction gauge, as stated
below, to achieve the desired height dimension.
Upon achieving the desired height dimension, D, the natural or artificial
insertion joint of the
implant is inserted into the insertion conduit 812 via the insertion ends
811A, 811B. Considering that the
insertion conduit 812 is in communication with the facet joint of the spine,
the implant is able to slide
through the conduit 812 into the facet joint. Upon the natural or artificial
inter-facet joint or inter-facet
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joint spacer being secured in the facet joint, the distraction head 806 can
then be removed from the facet
joint, thereby leaving the implant inserted therein. The implant can then be
anchored as discussed above.
This embodiment allows the physician to maintain the distraction distance
between the facets while
inserting the implant. This embodiment, including the sizing gauge discussed
below, can allow the
physician to- size, distract, and insert the implant using one tool. It should
be noted that although the
embodiment in FIG. 49A has the lead and insertion edges of the distraction
head facing in the Y direction,
the lead and insertion edges can face the Z direction or any other direction.
In one embodiment shown in FIG. 51, the distraction too1903 can include a
sizing mechanism in
accordance with one embodiment of the present invention. As shown in FIG 51,
the distraction gauge 950
is coupled to one of the handles 902A and 902B. The other handle can include a
flag 952 or pointer for
indicating a distraction height measurement on the distraction gauge 950.
Thus, as the handle 902A is
urged toward the distraction position, the distraction gauge 950 slides past
the flag 952, along with indicia
indicating the increasing distraction height, D, between the distraction head
components 906A and 906B.
In one embodiment, the distraction gauge 950 is configured to provide the
amount of distance between the
inferior surface of the first head component 906A and the superior surface of
the second head component
906B (i.e. the insertion conduit). In another embodiment, the distraction
gauge 950 can be configured to
include the thickness of the first and second head components and thereby
indicate the total distraction
distance between adjacent facets.
In one embodiment, the too1903 includes a spring mechanism to urge the handles
902A, 902B
apart toward the non-distracted position. For example, a leaf spring 912 can
be configured along the inner
surfaces of the handles 902A, 902B to provide an outward bias against the
handles 902A, 902B. In
another example, a spring can be positioned between the interior wall of the
slot 918 and the wedge portion
916 of the arm 904A to urge the wedged portion 916 and thus the handle 902A
toward the.non-distracted
position.
Additionally, or alternatively, the tool 903 can include a locking mechanism
to lock the tool 903 in
a desired position. For example, the locking mechanism can include a threaded
rod 914 which is coupled
to one of the handles 902A, 902B at a pivot point 916, whereby the rod 914
freely passes through a
through-hole in the other of the first and second handles 902A, 902B. The rod
914 includes a turning bolt
922 on the outer surface of the handle 904A which limits movement of the
handles 902 which is caused by
the force of the spring 910. As the handle 902A is urged closed, the threaded
rod 914 passes through the
through-hole and pivots to follow the arcing travel of the handle 902A. A
distraction stop 920 can be
positioned along the threaded rod 914 and sized such that the distraction stop
920 blocks the free travel of
the threaded rod 914, thereby preventing further movement of the handle 902
and limiting the distraction
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height. In one embodiment, the distraction stop 920 is fixed in position along
the threaded rod 914,
however, in other embodiments the distraction stop 920 can be adjustably
positionable along the threaded
rod 914 to allow the maximum distraction height to be adjusted.
MATERIALS FOR USE IN IMPLANTS OF THE PRESENT INVENTION
As alluded to above, and as described in further detail as follows, in some
embodiments, the
implant, and components of the implant (i.e., a lateral mass plate, a bone
screw, a locking screw, etc.) can
be fabricated from medical grade metals such as titanium, stainless steel,
cobalt chrome, and alloys thereof,
or other suitable implant material having similar high strength and
biocompatible properties. Additionally,
the implant can be at least partially fabricated from a shape memory metal,
for example Nitinol, which is a
combination of titanium and nickel. Such materials are typically radiopaque,
and appear during x-ray
imaging, and other types of imaging. Implants in accordance with the present
invention, and/or portions
thereof (in particular a natural or artificial facet joint spacer or inter-
facet joint spacer) can also be
fabricated from somewhat flexible and/or deflectable material. In these
embodiments, the implant and/or
portions thereof can be fabricated in whole or in part from medical grade
biocompatible polymers,
copolymers, blends, and composites of polymers. A copolymer is a polymer
derived from more than one
species of monomer. A polymer composite is a heterogeneous combination of two
or more materials,
wherein the constituents are not miscible, and therefore exhibit an interface
between one another. A
polymer blend is a macroscopically homogeneous mixture of two or more
different species of polymer.
Many polymers, copolymers, blends, and composites of polymers are radiolucent
and do not appear during
x-ray or other types of imaging. Implants comprising such materials can
provide a physician with a less
obstructed view of the spine under imaging, than with an implant comprising
radiopaque materials entirely.
However, the implant need not comprise any radiolucent materials.
One group of biocompatible polymers is the polyaryletherketone group which has
several members
including polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). PEEK
is proven as a durable
material for implants, and meets the criterion of biocompatibility. Medical
grade PEEK is available from
Victrex Corporation of Lancashire, Great Britain under the product name PEEK-
OPTIMA. Medical grade
PEKK is available from Oxford Performance Materials under the name OXPEKK, and
also from CoorsTek
under the name BioPEKK. These medical grade materials are also available as
reinforced polymer resins,
such reinforced resins displaying even greater material strength. In an
embodiment, the implant can be
fabricated from PEEK 450G, which is an unfilled PEEK approved for medical
implantation available from
Victrex. Other sources of this material include Gharda located in Panoli,
India. PEEK 450G has the
following approximate properties:
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Property Value
Density 1.3 g/cc
Rockwell M 99
Rockwell R 126
Tensile Strength97 MPa
Modulus of Elasticity 3.5 GPa
Flexural Modulus 4.1 GPa
PEEK 450G has appropriate physical and mechanical properties and is suitable
for carrying and spreading
a physical load between the adjacent spinous processes. The implant and/or
portions thereof can be formed
by extrusion, injection, compression molding and/or machining techniques.
It should be noted that the material selected can also be filled. Fillers can
be added to a polymer,
copolymer, polymer blend, or polymer composite to reinforce a polymeric
material. Fillers are added to
modify properties such as mechanical, optical, and thermal properties. For
example, carbon fibers can be
added to reinforce polymers mechanically to enhance strength for certain uses,
such as for load bearing
devices. In some embodiments, other grades of PEEK are available and
contemplated for use in implants
in accordance with the present invention, such as 30% glass-filled or 30%
carbon-filled grades, provided
such materials are cleared for use in implantable devices by the FDA, or other
regulatory body.
Glass-filled PEEK reduces the expansion rate and increases the flexural
modulus of PEEK relative to
unfilled PEEK. The resulting product is known to be ideal for improved
strength, stiffness, or stability.
Carbon-filled PEEK is known to have enhanced compressive strength and
stiffness, and a lower expansion
rate relative to unfilled PEEK. Carbon-filled PEEK also offers wear resistance
and load carrying
capability.
As will be appreciated, other suitable similarly biocompatible thermoplastic
or thermoplastic
polycondensate materials that resist fatigue, have good memory, are flexible,
and/or deflectable, have very
low moisture absorption, and good wear and/or abrasion resistance, can be used
without departing from the
scope of the invention. As mentioned, the implant can be comprised of
polyetherketoneketone (PEKK).
Other material that can be used include polyetherketone (PEK),
polyetherketoneetherketoneketone
(PEKEKK), polyetheretherketoneketone (PEEKK), and generally a
polyaryletheretherketone. Further,
other polyketones can be used as well as other thermoplastics. Reference to
appropriate polymers that can
be used in the implant can be made to the following documents, all of which
are incorporated herein by
reference. These documents include: PCT Publication WO 02/02158 Al, dated
January 10, 2002, entitled
"Bio-Compatible Polymeric Materials;" PCT Publication WO 02/00275 Al, dated
January 3, 2002,
entitled "Bio-Compatible Polymeric Materials;" and, PCT Publication WO
02/00270 Al, dated January 3,
CA 02590049 2007-06-07
WO 2006/065774 PCT/US2005/044979
-49-
2002, entitled "Bio-Compatible Polymeric Materials." Other materials such as
Bionate7, polycarbonate
urethane, available from the Polymer Technology Group, Berkeley, California,
may also be appropriate
because of the good oxidative stability, biocompatibility, mechanical strength
and abrasion resistance.
Other thermoplastic materials and other high molecular weight polymers can be
used.
The foregoing description of the present invention has been presented for
purposes of illustration
and description. It is not intended to be exhaustive or to limit the invention
to the precise forms disclosed.
Many modifications and variations will be apparent to practitioners skilled in
this art. The embodiments
were chosen and described in order to explain the principles of the invention
and its practical application,
thereby enabling others skilled in the art to understand the invention for
various embodiments and with
various modifications as are suited to the particular use contemplated. It is
intended that the scope of the
invention be defined by the following claims and their equivalents.
