US20060247633A1 - Inter-cervical facet implant with surface enhancements - Google Patents

Abstract

Systems and method in accordance with the embodiments of the present invention can include an implant for positioning within a cervical facet joint for distracting the cervical spine, thereby increasing the area of the canals and openings through which the spinal cord and nerves must pass, and decreasing pressure on the spinal cord and/or nerve roots. The implant can be inserted laterally or posteriorly.

Description

CLAIM OF PRIORITY
• This application claims priority to all the applications listed below, all of which are incorporated herein by reference. This application claims priority to U.S. Provisional Application, entitled, INTER-CERVICAL FACET IMPLANT AND METHOD filed Dec. 13, 2004, Ser. No. 60/635,453, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT DISTRACTION TOOL filed Apr. 4, 2005, Ser. No. 60/668,053, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT WITH IMPLANTATION TOOL filed May 10, 2005, Ser. No.60/679,377, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT WITH IMPLANTATION TOOL filed May 10, 2005, Ser. No. 60/679,361, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT WITH IMPLANTATION TOOL filed May 10, 2005, Ser. No. 60/679,363, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT WITH MULTIPLE DIRECTION ARTICULATION JOINT AND METHOD FOR IMPLANTING filed Jun. 6, 2005, Ser. No. 60/687,765, and U.S. Provisional Application entitled INTER-CERVICAL FACET IMPLANT WITH SURFACE ENHANCEMENTS filed Sep. 15, 2005, Ser. No. 60/717,369, and claims priority to and is a Continuation-in-Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT AND METHOD filed Feb. 8, 2005, Ser. No. 11/053,399, and is a Continuation-in-Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT AND METHOD filed Feb. 8, 2005, Ser. No. 11/053,624, and is a Continuation-in-Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT AND METHOD filed Feb. 8, 2005, Ser. No. 11/053,735, and is a Continuation in Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT AND METHOD filed Feb. 8, 2005, Ser. No. 11/053,346, and is a Continuation in Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT WITH LOCKING SCREW AND METHOD filed Mar. 30, 2005, Ser. No. 11/093,557, and is a Continuation-in-Part of U.S. Utility patent application entitled INTER-CERVICAL FACET IMPLANT AND METHOD FOR PRESERVING THE TISSUES SURROUNDING THE FACET JOINT filed Mar. 30, 2005, Ser. No.11/093,689, which are all incorporated herein by reference.
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 (September 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 of cervical spine motion on the neuroforaminal dimensions of human 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 herniation and cervical spondylotic 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 inFIG. 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 invention, comprising facet implant, a keel, and screw fixation.
• 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 inFIG. 22A.
• FIG. 23A depicts a posterior view of the embodiment of the implant of the invention shown inFIG. 22A.
• FIG. 23B shows a posterior view of a locking plate of the embodiment of the implant of the invention shown inFIG. 22A.
• FIG. 24A depicts a lateral side view of the embodiment of the implant of the invention shown inFIG. 22A.
• FIG. 24B shows a lateral side view of the keel of the locking plate of the embodiment of the implant of the invention shown inFIG. 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 inFIG. 25A, having a curved, uniformly-thick artificial facet joint 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 perspective view of a further embodiment of the implant of the invention having a locking cam in a second position.
• FIG. 27A shows an anterior perspective view of a further embodiment of the implant of the invention.
• FIG. 27B shows a posterior perspective view of the embodiment of the implant of the invention depicted inFIG. 27A.
• FIG. 27C depicts a side view of the embodiment of the implant of the invention shown inFIGS. 26A and 26B, implanted in the cervical spine.
• FIG. 27D shows a posterior view of the embodiment of the implant of the invention shown inFIGS. 27A, 27B, and27C, implanted in the cervical spine.
• 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 inFIG. 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 inFIG. 29A.
• FIG. 29C depicts a perspective view of an embodiment of the sizing tool of the invention depicted inFIGS. 29A and 29B.
• FIG. 29D depicts a side view of the head of the sizing tool of the invention depicted inFIG. 29A
• FIG. 29E depicts a cross-sectional view of the head of the sizing tool of the invention depicted inFIGS. 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 inFIG. 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 inFIG. 32.
• FIGS. 34A and 34B illustrate a top and bottom plan view of an alternative embodiment of an inter-cervical facet implant in accordance with the present invention.
• FIG. 35 is a partially exploded perspective view of the implant ofFIGS. 34A and 34B.
• FIGS. 36A and 36B illustrate side views of the implant ofFIGS. 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. 38A is a side view of still another embodiment of an implant in accordance with the present invention.
• FIG. 38B is a top view of the implant ofFIG. 38A.
• FIG. 38C is a bottom view of the implant ofFIG. 38A.
• FIG. 38D-F are side views of the implant ofFIG. 38A illustrating the various arrangements of a bone screw associated the implant.
• FIG. 38G is an end view of the implant ofFIG. 38F illustrating the arrangement of the bone screw associated the implant from an alternative viewing angle.
• FIG. 39 is a side view of still another embodiment of an implant in accordance with the present invention.
• FIG. 40 is a flow diagram of an alternative embodiment of a method in accordance with 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. 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 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 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.
• 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 joint1 formed between two adjacent cervical vertebrae. The spinous processes3 are located posteriorly and thevertebral bodies5 are located anteriorly, and anerve root canal7 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 artificial facet joint, described herein.
• FIG. 2 depicts cervical foraminal stenosis. From the drawing, thenerve root canal7 is narrowed relative to thenerve root canal7 depicted inFIG. 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 afirst embodiment100 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-shapedembodiment100 is a wedge-shaped implant that can be positioned in the cervical facet joint101 to distract the joint and reverse narrowing of thenerve root canal107. In thisembodiment100, 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 embodiment100 (FIG. 3B) with the wide portion of the wedge facing anteriorly, to correct for cervical kyphosis or loss of cervical lordosis.
• Referring toFIG. 4, theembodiment200 of the implant has a joint insert orspacer210, also herein referred to as an artificial facet joint, that is positioned in the cervical facet joint101. The joint insert orspacer210 can be wedge-shaped with the narrow part of the wedge facing anteriorly. Alternatively, the joint insert orspacer210 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 joint201. As withembodiment100, one objective of this embodiment is facet joint distraction, and joint mobility after implantation. The joint insert orspacer210 is continuous with aposterior sheath220 bent at an angle from the joint insert orspacer210 to align substantially parallel with the bone. The posterior sheath can lie against the lamina, preferably against the lateral mass. Theposterior sheath220 can have abore230 which can accept abone screw240. Alternatively, thebore230 can accept any other appropriate and/or equivalent fixation device capable of fixing theembodiment200 to the spine. The device is thereby affixed to the vertebra, preferably by fixing to the lateral mass.
• FIG. 5 showsembodiment300, which is the use of twoembodiments200, each fixed to one of two adjacent cervical vertebrae. As withembodiment200, the implanted facet joint is distracted and joint mobility is retained. A joint insert or spacer310 from each of the two implants is inserted and positioned in the cervical facet joint301. In this embodiment, the joint inserts orspacers310 are substantially flat and parallel to each other and are not wedge-shaped. Alternatively, the joint inserts orspacers310 can together define a wedge-shaped insert that is appropriate for the patient. The two joint inserts orspacers310 combined can have, by way of example, the shape of the joint insert orspacer210 inFIG. 4.Embodiment300 then can be fixed to the spine with ascrew340 or any other appropriate fixation device, inserted through abore330 in theposterior sheath320. Theposterior sheath320 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 anembodiment400 which contemplates positioning two implants to correct for this spinal abnormality while retaining facet joint mobility. The joint insert orspacer410 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 inFIG. 3A. Theposterior sheath420 of each implant is bent at an angle from the joint insert orspacer410 to be positioned adjacent to the lateral mass and/or lamina, and has abore430 to accept ascrew440 or other appropriate and/or equivalent fixation means to fix theembodiment400 to the spine, preferably to the lateral mass. The placement of two joint inserts orspacers410 in the cervical facet joint401 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 afurther embodiment500 of the implant of the invention, wherein the joint insert orspacer510 has akeel550 on an underside of the joint insert orspacer510. Thekeel550 can be made of the same material or materials set forth above. The surfaces of thekeel550 can be roughened in order to promote bone ingrowth to stabilize and fix theimplant500. In other embodiments, thekeel550 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 thekeel550.
• Thekeel550 can be embedded in the facet bone, to facilitate implant retention. Thekeel550 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 thekeel550 for facilitating retention of theimplant500 in the cervical facet joint501. As noted above, the joint insert orspacer510 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 afurther embodiment600 of the implant of the invention can have both screw fixation and akeel650 for stability and retention of theimplant600. Onembodiment600, the joint insert orspacer610 is continuous with aposterior sheath620 having abore hole630 to accept ascrew640 which passes through thebore630 and into the bone of the vertebrae, preferably into the lateral mass, or the lamina. Thebore630 can be threaded or not threaded where it is to accept a threaded screw or equivalent device. Alternatively, thebore630 need not be threaded to accept a non-threaded equivalent device. Thekeel650 is connected with the joint insert orspacer610 and embeds in the bone of the cervical facet joint601 to promote implant retention.
• A furtheralternative embodiment700 is illustrated inFIG. 10. In thisembodiment700, the joint insert orspacer710 has on a lower side at least onetooth760. It should be clear to one of ordinary skill in the art that a plurality ofteeth760 is preferable. Theteeth760 are able to embed in the bone of the cervical facet joint701 to facilitate retention of theimplant700 in the joint701. Theteeth760 can face in a direction substantially opposite the direction of insertion, for retention of theimplant700. As above, the joint insert orspacer710 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.
• FIG. 11 depicts afurther embodiment800 of the implant of the invention. In thisembodiment800, the joint insert orspacer810 is continuous with aposterior sheath820 having abore830 for accepting afixation device840, as described above. Thefixation device840 can be a screw which fits into a threadedbore830; alternatively, thefixation device830 can be any other compatible and appropriate device. Thisembodiment800 further combines at least onetooth860 on an underside of the joint insert orspacer810 with theposterior sheath820, bore830 andfixation device840 to address fixation of theimplant800 in a cervical facet joint801. It will be recognized by one of ordinary skill in the art that theimplant800 can have a plurality ofteeth860 on the underside of the joint insert orspacer810.
• FIG. 12 shows yet anotherembodiment900 of an implant of the present invention. In thisembodiment900, the joint inserts orspacers910 of twoimplants900 are positioned in a cervical facet joint901. As described above, the joint inserts orspacers910 can be wedge-shaped as needed to restore anatomical curvature of the cervical spine and to distract, or the joint inserts orspacers910 can be of substantially uniform thickness. Theimplants900 each comprise a joint insert orspacer910 with an outer surface970 that interacts with the bone of the cervical facet joint901. On theupper implant900, the surface970 that interacts with the bone is the upper surface970 and on thelower implant900, the surface970 that interacts with the bone is the lower surface970. Each surface970 can comprise a bone ingrowth surface980 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, theimplant900 can have casted porous surfaces970, where the porous surface is integral to theimplant900. As a further alternative, the surfaces970 can be roughened in order to promote bone ingrowth into these defined surfaces of theimplants900. In other embodiments, the surfaces970 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 surfaces970 of theimplant900. These measures facilitate fixation of theimplants900 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 anotherembodiment1000 of the implant of the present invention. In thisembodiment1000, the joint inserts orspacers1010 of twoimplants1000 are positioned inacervical facet joint1001. As described above, the joint inserts orspacers1010 can be wedge-shaped as needed to restore anatomical curvature of the cervical spine and to distract, or the joint inserts orspacers1010 can be of substantially uniform thickness. Theimplants1000 each comprise a joint insert orspacer1010 with an outer surface1070 that interacts with the bone of the cervical facet joint1001. On theupper implant1000, the surface1070 that interacts with the bone is the upper surface and on thelower implant1000, the surface1070 that interacts with the bone is the lower surface. As set forth above, each outer surface1070 can comprise a bone ingrowth surface1080 to create a porous surface and thereby promote bone ingrowth and fixation, without facet joint fusion and loss of mobility. In one preferred embodiment, the bone ingrowth surface1080 can be created with plasma spray titanium, and/or with a coating of sintered beads. In an alternative preferred embodiment, theimplant1000 can have casted porous surfaces1070, where the porous surface is integral to theimplant1000. In a further alternative preferred embodiment, the surfaces1070 can be roughened in order to promote bone ingrowth into these defined surfaces of theimplants1000. In other preferred embodiments, the surfaces1070 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 surfaces1070 of theimplant1000.
• Theimplant1000 can have aposterior alignment guide1090. The posterior alignment guides1090 of eachimplant1000 can be continuous with the joint inserts orspacers1010. The posterior alignment guides substantially conform to the bone of the vertebrae when the joint inserts orspacers1010 are inserted into the cervical facet joint1001. The posterior alignment guides1090 are used to align theimplants1000 so that the joint inserts orspacers1010 contact each other and not the bones of the cervical facet joint1001 when the joint inserts orspacers1010 are positioned in the cervical facet joint1001.
• FIG. 14 depicts afurther embodiment1100 of the implant of the present invention. In thisembodiment1100, the joint inserts orspacers1110 of twoimplants1100 are inserted into the cervical facet joint1101. Each of the joint inserts orspacers1110 is continuous with a cervical facet joint extender or facet-extendingsurface1192. Thebone contacting surfaces1170 of the joint inserts orspacers1110 are continuous with, and at an angle to, thebone contacting surfaces1193 of the cervical facetjoint extenders1192, so that the cervical facetjoint extenders1192 conform to the bones of the vertebrae exterior to the cervical facet joint1101. The conformity of the cervical facetjoint extenders1192 is achieved for example by forming the cervical facetjoint extenders1192 so that when the join inserts1110 are positioned, the cervical facetjoint extenders1192 curve around the bone outsider the cervical facet joint1101.
• The cervical facet joint extenders have asecond surface1184 that is continuous with the jointarticular surfaces1182 of the joint inserts orspacers1110. Thesecond surfaces1184 extend theimplant1100 posteriorly to expand the jointarticular surfaces1182 and there by to increase contact and stability of the spine at least in the region of theimplants1100. It is to be understood that such facetjoint extenders1192 can be added to the other embodiments of the invention described and depicted herein.
• The embodiment depicted inFIG. 15 shows twoimplants1200 positioned in a cervical facet joint1201, having bony ingrowth surfaces as one preferred method of fixation, and using screws as another preferred method of fixation. In this embodiment, each of twoimplants1200 has a joint insert orspacer1210 positioned in a cervical facet joint1201. As described above, the joint inserts orspacers1210 can be wedge-shaped as needed to restore anatomical curvature of the cervical spine and to distract, or the joint inserts orspacers1210 can be of substantially uniform thickness. Theimplants1200 each comprise a joint insert orspacer1210 with an outer surface1270 that interacts with the bone of the cervical facet joint1001. On theupper implant1200, the surface1270 that interacts with the bone is the upper surface and on thelower implant1200, the surface1270 that interacts with the bone is the lower surface. As set forth above, each outer surface1270 can comprise a bone ingrowth surface1280 to create a porous surface and thereby promote bone ingrowth and fixation. In one preferred embodiment, the bone ingrowth surface1280 can be created with plasma spray titanium, and/or with a coating of sintered beads. In an alternative preferred embodiment, theimplant1200 can have casted porous surfaces1270, where the porous surface is integral to theimplant1200. In a further alternative embodiment, the surfaces1270 can be roughened in order to promote bone ingrowth into these defined surfaces of theimplants1200. In other preferred embodiments, the surfaces1270 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 surfaces1270 of theimplant1200.
• Screw fixation or other appropriate fixation also can be used withimplants1200 for fixation in the cervical facet joint1201. The joint insert orspacer1210 is continuous with aposterior sheath1220 bent at an angle from the joint insert orspacer1210 to align substantially parallel with the bone, preferably the lateral mass or lamina. Theposterior sheath1220 can have abore1230 which can accept abone screw1240, preferably into the lateral mass or lamina. Alternatively, thebore1230 can accept any other appropriate and/or equivalent fixation means for fixing theembodiment1200 to the spine.
• FIG. 16 depicts a further preferred embodiment of the present invention. In thisembodiment1300, two joint inserts orspacers1310 are positioned in the cervical facet joint1301. The joint inserts or spacers each have outer surfaces1370 that interact with the bone of the vertebrae forming the cervical facet joint. These outer surfaces1370 of theembodiment1300 can be treated to become bone ingrowth surfaces1380, which bone ingrowth surfaces1380 contribute to stabilizing the two joint inserts orspacers1310 of theimplant1300. In one preferred embodiment, the bone ingrowth surface1380 can be created with plasma spray titanium, and/or with a coating of sintered beads. In an alternative preferred embodiment, theimplant1300 can have casted porous surfaces1370, where the porous surface is integral to theimplant1300. In a further alternative embodiment, the surfaces1370 can be roughened in order to promote bone ingrowth into these defined surfaces of theimplants1300. In other preferred embodiments, the surfaces1370 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 surfaces1370 of theimplant1300. This fixation stabilizes theimplant1300 in the facet joint without fusing the joint, and thus the implant preserves joint mobility, while accomplishing distraction and increasing foraminal dimension.
• Also shown inFIG. 16 are articularinner surfaces1382 of theimplants1300. 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. Theembodiment1300 ofFIG. 16 can be made in at least two configurations. The first configuration includes aflexible spacer1382 made, by way of example, using polyethylene or other suitable, flexible implant material. Theflexible spacer1382 can be permanently affixed to the upper and lower joint insert orspacer1310. Thespacer1382 can be flat or wedge-shaped or have any other shape that would correct the curvature of the spine. In other configurations, thespacer1382 can be affixed to only theupper insert1310 or to only thelower insert1310. Alternatively, aspacer1382 can be affixed to each of anupper insert1310 and alower insert1310 with theupper insert1310 and thelower insert1310 being separate units.
• FIG. 17 shows a further preferred embodiment of the implant of the present invention. In thisembodiment1400, the implant has aroller1496 mounted on a joint insert orspacer1410, the roller being a further means of preserving joint mobility while accomplishing distraction. Both theroller1496 and the joint insert orspacer1410 are positioned in the cervical facet joint1401. The joint insert orspacer1410 as in other embodiments has a bone-facingsurface1470 and jointarticular surface1482. The bone-facingsurface1470 can interact with the lower bone of the cervical facet joint1401. Alternatively, the bone-facing surface can interact with the upper bone of the cervical facet joint1401. Between the bone-facingsurface1470 and the jointarticular surface1482 is an axis about which theroller1496 can rotate. Theroller1496 rotates in a cavity in the joint insert orspacer1410, and interacts with the top bone of the cervical facet joint1401. Alternatively, where the bone-facingsurface1470 of the joint insert orspacer1410 interacts with the top bone of the cervical facet joint1401, theroller1496 rotates in a cavity in the joint insert orspacer1410 and interacts with the lower bone of the cervical facet joint1401. The rotation of theroller1496 allows flexion and extension of the cervical spine. Alternatively, a roller such asroller1496 can be secured to an upper and a lower insert such asinserts410 inFIG. 7. As depicted inFIG. 18, a plurality ofrollers1496 also is possible.
• FIG. 19 depicts a further embodiment of the implant of the present invention. In this embodiment, twoimplants1500 are implanted in the cervical facet joint1501. Screw fixation or other appropriate fixation is used withimplants1500 for fixation in the cervical facet joint1501. The joint insert orspacer1510 is continuous with aposterior sheath1520 bent at an angle from the joint insert orspacer1510 to align substantially parallel with the bone, preferably the lateral mass or lamina. Theposterior sheath1520 of eachimplant1500 can have abore1530 which can accept abone screw1540, preferably into the lateral mass or lamina. Alternatively, thebore1530 can accept any other appropriate and/or equivalent fixation means for fixing theembodiment1500 to the spine. The head of thescrew1540 in eachposterior sheath1520 of eachimplant1500 has agroove1598 or other mechanism for retaining anelastic band1597. Theelastic band1597 is looped around each of the twoscrews1540 to restrain movement of the cervical spine without eliminating facet joint mobility. Theband1597 preferably can restrain flexion and lateral movement. Theelastic band1597 can be made of a biocompatible, flexible material.
• FIG. 20 shows an alternative to use of an elastic band as inFIG. 19. In the embodiment inFIG. 20, the elastic band is replaced with aspring restraint1699, which extends between the heads of twoscrews1640, one screw fixing each of twoimplants1600 in the cervical facet joint1601.
• FIG. 21 shows another alternative to using an elastic band and/or a spring as in FIGS.19 or20. InFIG. 21,magnets1795 is used for restraint between the twoscrews1740. Themagnet1795 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 twoscrews1740 is magnetized, and the head of theother screw1740 is magnetized with either the same or opposite field. If themagnets1795 have the same polarity, themagnets1795 repel each other and thus limit extension. If themagnets1795 have opposite polarities, themagnets1795 attract each other and thus limit flexion and lateral movement.
• FIGS. 22A-24B, depict afurther embodiment1800 of the implant of the present invention. In this embodiment, a natural or artificial 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 ahinge1822. Thehinge1822 allows thelateral mass plate1820 to bend at a wide range of angles relative to the artificial facet joint and preferably at an angle of more than 90 degrees, and this flexibility facilitates positioning and insertion of the facet joint spacer (or insert)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. Thehinge1822 further facilitates customizing the anchoring of the implant, i.e., the positioning of a fixation device. The hinge enables positioning of thelateral mass plate1820 to conform to a patient's cervical spinal anatomy, and thelateral mass plate1820 accepts a fixation device to penetrate the bone. The facet joint spacer (or insert)1810 can be curved or rounded at a distal end1812 (FIG. 23A), and convex or dome-shaped on asuperior surface1813 to approximate the shape of the bone inside the facet joint. Theinferior surface1815 can be flat or planar. Alternatively, theinferior surface1815 can be concave. As another alternative, theinferior surface1815 can be convex.
• Thelateral mass plate1820, when implanted in the spine, is positioned outside the facet joint, preferably against the lateral mass or against the lamina. Thelateral mass plate1820 has abore1830 therethrough. Thebore1830 can accept abone screw1840, also referred to as a lateral mass screw, to secure thelateral mass plate1820 preferably to the lateral mass or alternatively to another part of the spine, and thus to anchor the implant. Thelateral mass screw1840 preferably has a hexagonal head to accept an appropriately-shaped wrench. As described below, the head accepts acompatible probe1826 from alocking plate1824.
• Thelocking plate1824 includes akeel1828 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 thelateral mass plate1820 and thelocking plate1824. Thekeel1828 aligns with a groove1823 through an edge of thelateral mass plate1820 to guide and align thekeel1828 as thekeel1828 cuts into a vertebra.
• As noted above, thelocking plate1824 includes aprobe1826 that fits against the head of thelateral mass screw1840. The locking plate further includes abore1831 that can accept a machine screw (not shown) which passes through to an alignedbore1829 in thelateral mass plate1820 to hold thelocking plate1824 and thelateral mass plate1820 together without rotational displacement relative to each other. Thelocking plate1824 thus serves at least two functions: (1) maintaining the position of thelateral mass screw1840 with theprobe1826, so that thescrew1840 does not back out; and (2) preventing rotation of the implant with thekeel1828 and machine screw relative to the cervical vertebra or other vertebrae.
• It is to be understood that other mechanisms can be used to lock thelocking plate1824 to thelateral mass plate1820. 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 inFIGS. 25A, 25B, thelateral mass plate1920 includes a recessedarea1922 for receiving thelocking plate1924 so that thelocking plate1924 is flush with theupper surface1925 of thelateral mass plate1920 when theprobe1926 is urged against thelateral mass screw1940 and thekeel1928 is inserted into the lateral mass or the lamina of the vertebra. In the preferred embodiment depicted inFIGS. 25A, 25B, the shape and contours of the facet joint spacer (or insert)1910 can facilitate insertion of the facet joint spacer (or insert)1910 into the cervical facet joint. In this embodiment, the facetjoint spacer1910 has a roundeddistal end1912. Thedistal end1912 is tapered in thickness to facilitate insertion. The tapereddistal end1912 meets and is continuous with aproximal mid-section1916 which, in this preferred embodiment, has a uniform thickness, and is connected flexibly, preferably with ahinge1922, to thelateral mass plate1920, as described above. The facetjoint spacer1910, with itsproximal mid-section1916 and tapereddistal end1912, is curved downward, causing asuperior surface1913 of the facetjoint spacer1910 to be curved. The curve can cause thesuperior surface1913 to be convex, and the convexity can vary amongdifferent implants1900 to suit the anatomical structure of the cervical facet joint(s) of a patient. Aninferior surface1915 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 thesuperior surface1913 of the facetjoint spacer1910 fits with a concave shape of the inferior facet of the upper cervical vertebrae. The concave shape of theinferior surface1915 of the facetjoint spacer1910 fits with the convex shape of the superior facet of the cervical vertebrae. The degree of convexity and concavity of the 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 facetjoint spacer1910 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 and the smooth, flush surfaces will allow distraction of the facet joint without loss of mobility or damage to the bones of the cervical spine. Further, and preferably, the width of the mid-section1916 is from 1.5 mm to 2.5 mm.
• In still other embodiments, some other structure can be employed to resist movement of the seated bone screw within the first bore. Referring toFIGS. 26A and 26B, in some embodiments acam3824 can be rotatably associated with thelateral mass plate3820 so that thefirst bore3830 can be selectably obstructed or unobstructed, thereby allowing abone screw3840 to be received within thefirst bore3830, or resisting movement of thebone screw3840 seated within thefirst bore3830. As shown inFIG. 26A, thecam3824 can have a shape such that at a first position thesurface3828 of the cam is approximately flush with thefirst bore3830, thereby allowing abone screw3840 to pass through thefirst bore3830. Rotated to a second position (FIG. 26B), a protrudingportion3826 of the surface of thecam3824 can extend across at least a portion of thefirst bore3830, thereby blocking abone screw3840 seated within thefirst bore3830 and preventing thebone screw3840 from backing out of thefirst bore3830. Thecam3824 can include features3831 (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, thecam3824 is positioned within a slot of thelateral mass plate3820 so that the cam does not protrude undesirably from the surface of thelateral mass plate3820.
• Except as otherwise noted above, the embodiment shown inFIGS. 22A-24B is similar to the embodiment shown inFIGS. 25A-26B. Accordingly the remaining elements on the1900 series of element numbers is preferably substantially similar to the described elements in the1800 series of element numbers, as set forth above. Thus, by way of example,elements1923,1928,1929 and1930 are similar,respective elements1823,1828,1829 and1830.
• FIG. 30 is a flow chart of the method of insertion of an implant of the invention. Theembodiment1800 or1900 of the present invention preferably is inserted in the following manner (only elements of theembodiment1800 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 tool2200 (see FIGS.29A-C) can be inserted to select 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 thetool2200 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 facet joint spacer (or insert)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 facetjoint spacer1810 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 is urged into the facet joint of the spine. The facetjoint spacer1810 also includes theconvex surface1813 in order to more fully accommodate the shape of the facet joint of the spine. However, as set forth above and as depicted inFIG. 25B, it is possible in the alternative to have a curve-shaped facetjoint spacer1910 with a convexsuperior surface1913 and a concaveinferior surface1915, thedistal end1912 tapering to facilitate insertion, while the remainder of the facetjoint spacer1910, (i.e., the proximal section1916) has a uniform thickness.
• Once the facet joint spacer (or insert)1810 is positioned, thelateral mass plate1820 is pivoted downward about thehinge1822 adjacent to the vertebrae and preferably to the lateral mass or to the lamina. Thus thelateral mass plate1820 may be disposed at an angle relative to the facetjoint spacer1810 for a representative spine configuration. It is to be understood that as this embodiment is hinged the final position of thelateral mass plate1820 relative to the facetjoint spacer1800 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 facet joint spacer and the lateral mass plate is flexible enough to allow the lateral mass plate to be bent relative to the facet joint spacer in order to fit the anatomy of the patient. Once thelateral mass plate1820 is positioned, or prior to the positioning of thelateral mass plate1820, a bore can be drilled in the bone to accommodate thebone screw1824. Alternatively thescrew1824 can be self-tapping. The screw is then placed through thebore1830 and secured to the bone, preferably the lateral mass or the lamina, thereby holding the facetjoint spacer1800 in place. In order to lock thebone screw1824 in place and to lock the position of the facetjoint spacer1800 and thelateral mass plate1820 in place, thelocking plate1824 is positioned over thelateral mass plate1820. So positioned, theprobe1826 is positioned through thebore1830 and against the head of the bone screw to keep the bone screw from moving. Thekeel1828, having a sharp chisel-shaped end, preferably can self-cut a groove in the bone so that thekeel1828 is locked into the bone as thekeel1828 is aligned by, and received in, agroove1831 of thelateral mass plate1820. Alternatively, a groove can be pre-cut in the bone to receive thekeel1828. As this occurs thebore1829 of thelocking plate1824 aligns with the threadedbore1831 of thelateral mass plate1820 and a machine screw can be inserted to lock the locking plate relative to the lateral mass plate. This locking prevents thelateral mass plate1820 and the facetjoint spacer1810 from rotating and, as previously indicated, prevents thebone screw1840 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, animplant1800 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. 27A-27D show a further embodiment of the implant of the invention, with theembodiment2000 implanted in the cervical spine as depicted inFIGS. 27C and 27D. Theimplant2000 comprises a first facet joint spacer (or insert)2010 and a second facet joint spacer (or insert)2010. Each facet joint spacer (or insert) can have adistal end2012 that is tapered or wedge-shaped in a way that facilitates insertion into the cervical facet joints on both sides of two adjacent cervical vertebrae at the same level. The facet joint spacers further can be dome-shaped, or convex on asuperior surface2013, to approximate the shape of the cervical facets of the cervical facet joints.
• The first and second facet joint spacers (or insert)2010 are bridged together by acollar2015. Thecollar2015 passes between the spinous processes of the adjacent cervical vertebrae. As can be seen inFIG. 27B, the implant can preferably be “V” shaped or “boomerang” shaped. Theentire implant2000 or thecollar2015 of the implant can be made of a flexible material such as titanium, so that it is possible to bend thecollar2015 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 facetjoint spacers2010 inserted in the cervical facet joints.Bores2029 are preferably are provided throughimplant2000 adjacent to the facetjoint spacer2010 respectively. Thesebores2029 can receive bone screws to position theimplant2000 against the lateral mass or the lamina as shown inFIGS. 27C, 27D. The description of theembodiment2100, inFIGS. 28A, 28B provide further details concerning the method of affixing theimplant2000 to the vertebrae. Theimplant2100 also can be made of PEEK or other materials as described herein. Embodiment2000 (the “boomerang” shape depicted inFIG. 27D) further can have a locking plate as, for example, thelocking plate1824 inFIG. 22A. The locking plate for embodiment2000 (not shown) can have the same features as lockingplate1824, that is: (1) aprobe1826 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 theimplant2000; and (2) akeel1828 with a chisel end to embed in the bone and thus to prevent rotational displacement of the implant. However, given thecollar2015 configuration ofembodiment2000, 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 onembodiment2000 can be provided without a keel.
• FIGS. 28A and 28B depict a further embodiment of the implant of theinvention2100. In thisembodiment2100, thecollar2115 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 facet joint spacer (or insert)2110 with thecollar2115 using afirst hinge2117, and connecting a second facet joint spacer (or insert)2110 with thecollar2115 using asecond hinge2117. Using thefirst hinge2117 and thesecond hinge2117, thecollar2115 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 thefirst hinge2117 andsecond hinge2117 allow theimplant2100 to accommodate the variance.
• In the hingedembodiment2100, and similar to theembodiment2000, thecollar2115 can have afirst bore2129 inferior to thefirst hinge2117, and asecond bore2129 inferior to thesecond hinge2117. A first bone screw penetrates the first bore2130 and into the lateral mass or the lamina, and the second bone screw penetrates the second bore2130 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 first bone screw and for the second bone screw. Alternatively, the bone screws can be self-tapping. A first locking plate similar to the plate1924 (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 screws2140. 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 thatembodiments2000 and2100 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, thecollar2015,2115 extends medially without extending further to join a second facetjoint spacer2010,2110. For the hingedembodiment2100, the implant comprises asingle hinge2117, and thecollar2115 has only onebore2129 to accept one bone screw to secure theimplant2100.
• FIGS.29A-E, depict a sizing anddistracting tool2200 of the invention.Sizing tool2200 has ahandle2203 and adistal head2210 that is shaped as a facet joint spacer (e.g.,1810) of an implant of the invention. That is, thehead2210 preferably will have essentially the same features as the facet joint spacer (or insert)1810, but the dimensions of thehead2210 will vary from onetool2200 to the next, in order to be able to use different versions of thesizing tool2200 to determine the dimensions of the cervical facet joint that is to be treated and then to select an appropriately-sized implant. Thehead2210 preferably can be used to distract the facet joint prior to the step of implanting the implant in the facet joint. In this regard, thehead2210 is rounded at the mostdistal point2212, and can be a tapered to facilitate insertion into a cervical facet joint. Thehead2210 also can have a slightly convexsuperior surface2213, the degree of convexity varying amongdifferent sizing tools2200 in order to determine the desired degree of convexity of an implant to be implanted in the cervical facet joint. Thehead2210 may have a uniform thickness along aproximal mid-section2216. Accordingly, theinferior surface2215 preferably can be concave. Alternatively, theproximal mid-section2212 may be convex on thesuperior surface1813 without being uniform in thickness. Thus, theinferior surface2215 can be flat or planar. The head also can be curved.
• Thehead2210 has astop2218 to prevent over-insertion of thehead2210 of thesizing tool2200 into the facet joint. Thestop2218 can be a ridge that separates thehead2210 from thehandle2203. Alternatively, thestop2218 can be any structure that prevents insertion beyond thestop2218, including pegs, teeth, and the like.
• Different sizing tools2200 covering a range of dimensions of thehead2210 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 facet joint spacer. Each preferably larger head also can be used to distract the facet joint.
• FIG. 31A depicts a posterior view of afurther embodiment2300 of the implant of the invention.Embodiment2300, 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,embodiment2300 has a facet joint spacer (or insert)2310 that can have a tapered or thinneddistal end2312 so that thedistal end2312 facilitates insertion of the facetjoint spacer2310 into a cervical facet joint. Thedistal end2312 can be rounded, as seen in the plan view ofFIG. 31A, in order to conform to the roundness of the facet joint. The facet joint spacer (or insert)2310 further can be curved so that asuperior surface2313 of the facetjoint spacer2310 is convex, and aninferior surface2315 is concave, to approximate the natural shape of the cervical facet joint that is to receive theimplant2300. The curve can have a uniform thickness, or it can have a varied thickness. Further, the lateral edges of the facetjoint spacer2310 are curved or rounded, for distribution of load-bearing stress. As with other embodiments described herein, the facetjoint spacer2310 also can be made of a flexible, biocompatible material, such as PEEK, to maintain joint mobility and flexibility.
• The facetjoint spacer2310 is connected flexibly with alateral mass plate2320, the flexible connection preferably being ahinge2322. As seen in the plan view ofFIG. 31A, theimplant2300 is substantially hour-glass shaped. This shape, as well as the shape ofFIG. 32, will be discussed further below. Thehinge2322 is narrower than the facetjoint spacer2310, with thehinge2322 sitting at substantially theisthmus2317 between facetjoint spacer2310 and thelateral mass plate2320. The curved edges, or fillets, about thehinge2322 serve to distribute more evenly the load-bearing stress on theimplant2300, and thus prevent concentrating the stress about the edges.
• Thehinge2322 allows theimplant2300 to bend at thehinge2322, bringing alateral mass plate2320 adjacent to the lateral mass and/or lamina of the patient's spine, and to conform to a particular patient's anatomy. Thelateral mass plate2320 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. Thelateral mass plate2320 bends downward at thehinge2322 over a wide range of angles relative to the facetjoint spacer2310, and preferably at an angle of more than 90 degrees, and this flexibility facilitates positioning and insertion of the facet joint spacer. This flexibility of thelateral mass plate2320 relative to the facetjoint spacer2310 further facilitates positioning of the lateral mass plate relative to the lateral mass and/or the lamina of the patient's spine. Once thelateral mass plate2320 is positioned adjacent to the bone, preferably the lateral mass of a cervical vertebra, a first bone screw, such asbone screw1840, can be inserted through afirst bore2330 through thelateral mass plate2320 and embedded into the bone of the lateral mass of the cervical vertebra.
• Thelateral mass plate2320 further comprises asecond bore2329 which is preferably positioned medially, relative to thefirst bore2330. Thus, viewing the implant from a posterior perspective as inFIG. 31A, thesecond bore2329 in thelateral mass plate2320 can be positioned either to the left or to the right of thefirst bore2330. The position of thesecond bore2329 will depend upon whether theimplant2300 is intended to be inserted into a cervical facet joint on the left or right side of a patient. Specifically, animplant2300 to be inserted into a right-side cervical facet joint (i.e., the patient's rights side) will have asecond bore2329 positioned to the left of thefirst bore2330 as inFIG. 31 A, whenimplant2300 is viewed from a posterior perspective, while animplant2300 to be inserted into a left-side cervical facet joint will have asecond bore2329 positioned to the right of thefirst bore2330, whenimplant2300 is viewed from a posterior perspective.
• Thesecond bore2329 through thelateral mass plate2320 is adapted to accept a second screw2390 (FIG. 31B), which preferably is a locking screw with achisel point2391. The lockingscrew2390 is received by thesecond bore2329 and thechisel point2391 self-cuts a bore into the bone. The lockingscrew2390 preferably is inserted through thesecond bore2329 and embedded in the bone, after the bone screw is embedded in the bone through thefirst bore2330. The position of thesecond bore2329, i.e., medial to thefirst bore2330, positions thelocking screw2390 so that it embeds in stronger bone tissue than if thesecond bore2329 were located more laterally. The locking screw, in combination with the bone screw, prevents rotational and/or backward displacement of theimplant2300. As thelocking screw2390 is received by thesecond bore2329, thehead2392 of thelocking screw2390 aligns with the head of the first bone screw in thefirst bore2330, blocking the head of the first bone screw to prevent the first bone screw from backing out of the bone of the vertebra and thefirst bore2330.
• FIG. 32 depicts afurther embodiment2400 of the implant of the invention, from a posterior view.Embodiment2400 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.
• Implant2400, likeimplant2300 and other implants disclosed above, has a facetjoint spacer2410, flexibly connected, preferably by ahinge2422, to alateral mass plate2420. As can be seen inFIG. 32, theimplant2400 including the facet joint spacer (or insert)2410 and thehinge2422 is substantially “P” shaped. As explained below, its “P” shape assists in the insertion of theimplant2400 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 facet joint spacer, as above forimplant2300 and the other implants disclosed above, can have asuperior surface2413 of the facetjoint spacer2410 that is convex, and aninferior surface2415 that is concave, or any appropriate shaping to approximate the natural shape of the cervical facet joint that is to receive theimplant2400. The thickness of the facetjoint spacer2410 can be uniform, or varied. The facetjoint spacer2410 also can be made of a flexible, biocompatible material, such as PEEK, to maintain joint mobility and flexibility. Thehinge2422 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 ofFIG. 32. For example, the facetjoint spacer2410 further can have a tapered or thinned edge2412 so that the edge2412 facilitates insertion of the facetjoint spacer2410 into a cervical facet joint. The edge2412 can be curved. In thisembodiment2400, however, the thinned edge2412 of the facetjoint spacer2410 preferably is not at the distal end of the facetjoint spacer2400 as is the thinnededge2312 of the facetjoint spacer2300; rather, the thinned edge2412 preferably is positioned laterally, toward thehinge2422 of theimplant2400. The thinned edge2412 coincides substantially with alateral curvature2440 of the facetjoint spacer2410, which is pronounced relative to the curvature on the medial side of theimplant2400, i.e., a “P” shape. In other words, the curved part of the head of the “P”2440 corresponds to the thinned edge2412, and serves as the leading edge of theimplant2400 to begin insertion of the facetjoint spacer2410 into a cervical facet joint, preferably through an incision in the soft tissue of the facet joint. The “P” shape narrows atisthmus2417 where the facetjoint spacer2410 that is joined by thehinge2422 with thelateral mass plate2420. The smooth or rounded edges or fillets serve to distribute stresses on theimplant2400. The above described “P” shape ofimplant2400 allows theimplant2400 to be pivoted into place into a facet joint as described below. The thinned edge2412 and leadinglateral curvature2440 of the facetjoint spacer2410 are adapted to facilitate urgingimplant2400 into the cervical facet joint, through the incision in the joint capsule. Theimplant2400 then is pivoted into position so that thelateral mass plate2420 can be bent downward, relative to the facetjoint spacer2410, to align with and lie adjacent to the lateral mass and/or the lamina. Thelateral mass plate2420 is then fastened to the bone.
• Thelateral mass plate2420 ofimplant2400, like the lateral mass plate forimplant2300, is flexibly connected, preferably by the smooth-edgedhinge2422, to the facetjoint spacer2410 at the narrow lower part of the facet joint spacer. Thelateral mass plate2420 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.
• Thelateral mass plate2420 bends downward at a wide range of angles relative to the facetjoint spacer2410, and preferably at an angle of more than 90 degrees. The flexibility of thelateral mass plate2420 relative to the facetjoint spacer2410 further facilitates positioning of thelateral mass plate2420 relative to the lateral mass and/or the lamina of the patient's spine.
• Likeembodiment2300, described above, thelateral mass plate2420 hasfirst bore2430, which is adapted to receive abone screw2440, to help anchorimplant2400 in position. Thelateral mass plate2420 further includes asecond bore2429 adapted to be positioned medially, relative to thefirst bore2430, as disclosed above forimplant2300. The position of thesecond bore2429, when viewingimplant2400 from a posterior perspective (FIG. 32), will depend upon whetherimplant2400 is intended to be implanted into a left-side or right-side cervical facet joint of a patient. Thus,implant2400 with thesecond bore2429 positioned to the left of thefirst bore2430 is intended to be implanted in a right-side cervical facet joint of a patient, as depicted inFIG. 32, while animplant2400 with asecond bore2429 positioned to the right of thefirst bore2430 is intended to be implanted in a left-side cervical facet joint of a patient.
• Thesecond bore2429 through thelateral mass plate2420 is adapted to receive asecond screw2490 withhead2492, which preferably is a locking screw with a chisel point, such asscrew2390. The function and purpose of the bone screw disposed throughbore2430 and the locking screw disposed throughbore2429 are as described above with respect to theimplant2300.
• The present invention further includes a method of implanting the implant2400 (FIGS. 33A, 33B). To insert the facet joint spacer (or insert)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 edge2412 of theimplant2400 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 theimplant2400. If desired, the cervical facet joint can be distracted prior to urging thecurved section2440 with the thinned edge2412 of the facetjoint spacer2410 into the cervical facet joint. Once thecurved section2440 of the facetjoint spacer2410 with the thinned edge2412 is urged into the cervical facet joint,implant2400 is pivoted, preferably about 90 degrees, so that thesecond bore2429 is placed medially relative to thefirst bore2430. This allows the facetjoint spacer2410 to be positioned in the facet joint. It is noted that the overall size, including theisthmus2417, of the artificial fact joint2410, as that of2310, can be somewhat smaller than in prior embodiments to allow the facet joint spacer to be positioned within the edges of the facet joint with the joint capsule substantially intact. Thelateral mass plate2420 then can be bent downward about thehinge2422 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 thelateral mass plate2420 is positioned adjacent to the bone, preferably the lateral mass of a cervical vertebra, a first bone screw can be inserted through thefirst bore2430 through thelateral mass plate2420 and become embedded into the bone of the lateral mass of the cervical vertebra to anchor theimplant2400. After the bone screw is embedded, a locking screw is inserted through thesecond bore2429 of thelateral mass plate2420, thesecond bore2429 medial to thefirst bore2430. 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 theimplant2400 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 ofimplant2400, while blocking backward displacement of the first bone screw.
• Referring toFIGS. 34A through 36B, a still further embodiment of animplant2500 in accordance with the present invention can include a facet joint spacer (or insert)2510 connected with a lateral mass plate (also referred to herein as an anchoring plate)2520 by a spheroidaljoint arrangement2538 or otherwise shaped multiple direction articulation joint arrangement. The facetjoint spacer2510 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 facetjoint spacer2510 includes a handle-like structure connected with the load bearing surface, the handle-like structure necking at anisthmus2517 and terminating at apivot end2526. In an embodiment, thepivot end2526 is substantially spherical, ovoidal, or similarly rounded in shape. As further described below, the facetjoint spacer2510 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, thelateral mass plate2520 has a generally square shape with rounded corners; however, in other embodiments thelateral mass plate2520 can have any number of shapes so long as thelateral mass plate2520 provides sufficient support for anchoring theimplant2500 in position and so long as thelateral mass plate2520 allows a desired range of motion for the facetjoint spacer2510. Thelateral mass plate2520 includes acavity2527 within which thepivot end2526 is held. The spheroidaljoint arrangement2538 comprises thepivot end2526 and thecavity2527 and as described below allows the facetjoint spacer2510 to tilt and swivel relative to thelateral mass plate2520.
• FIG. 34A is a posterior view showing aposterior face2532 of thelateral mass plate2520, whileFIG. 34B is an anterior view showing ananterior face2534 of thelateral mass plate2520. Thelateral mass plate2520 includes an anterior notch2524 (seeFIG. 35) or other indentation formed along the edge of theanterior face2534 and aposterior notch2522 or other indentation formed along theposterior face2532. The posterior andanterior notches2522,2524 are generally aligned with one another along the edge of thelateral mass plate2520 and are connected with thecavity2527. Thenotches2522,2524 confine movement of the facetjoint spacer2510 in the anterior and posterior directions relative to thelateral mass plate2520, allowing the facetjoint spacer2510 to tilt at varying degrees of angle in an anterior and posterior direction. Referring toFIG. 35, theanterior notch2524 can have a narrower width than theposterior notch2522 which is sized to provide thepivot end2526 of the facet joint spacer (or insert)2510 with access to thecavity2527 so that thepivot end2526 can be inserted into thecavity2527. Once thepivot end2526 is positioned within the cavity2527 aplug2528 can be mated with thelateral mass plate2520 to lock thepivot end2526 in place within thecavity2527 and to further limit freedom of movement of the facetjoint spacer2510, particularly limiting tilting of the facetjoint spacer2510 in a posterior direction. Theplug2528 can be press fit to theposterior notch2522 and further welded or otherwise fixedly fastened with thelateral mass plate2520. A physician can select an appropriate and/or desired facetjoint spacer2510,lateral mass plate2520, and plug2528 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 facetjoint spacer2510 and thelateral mass plate2520 can be mated, and the facetjoint spacer2510 can be locked in place by theplug2528.
• As can further be seen inFIGS. 34A through 35 thelateral mass plate2520 has afirst bore2530 therethrough. Thefirst bore2530 can accept a bone screw2540 (also referred to herein as a lateral mass screw) to secure thelateral mass plate2520 preferably to the lateral mass, lamina, or alternatively to another part of the spine, and thus to anchor theimplant2500. Thelateral mass screw2540 preferably has ahead2542 that can accept a tool chosen for the surgical procedure whether a wrench, screwdriver, or other tool. Thelateral mass plate2520 further has asecond bore2529 which is preferably positioned medially, relative to thefirst bore2530. Referring toFIG. 34A, thesecond bore2529 in thelateral mass plate2520 can be positioned either to the left or to the right of thefirst bore2530. The position of thesecond bore2529 will depend upon whether theimplant2500 is intended to be inserted into a cervical facet joint on the left or right side of a patient. Specifically, animplant2500 to be inserted into a right-side cervical facet joint (i.e., the patient's rights side) will have asecond bore2529 positioned to the left of thefirst bore2530 as inFIG. 34A, whenimplant2500 is viewed from a posterior perspective, while animplant2500 to be inserted into a left-side cervical facet joint will have asecond bore2529 positioned to the right of thefirst bore2530, whenimplant2500 is viewed from a posterior perspective.
• Thesecond bore2529 through thelateral mass plate2520 is adapted to accept asecond screw2590 which preferably is a locking screw having achisel point2591. The lockingscrew2590 is received by thesecond bore2529 and thechisel point2591 self-cuts a bore into the bone. The lockingscrew2590 is preferably inserted through thesecond bore2529 and embedded in the bone after thebone screw2540 is embedded in the bone through thefirst bore2530. The medial position of thesecond bore2529 relative to thefirst bore2530 positions thelocking screw2590 so that it embeds in stronger bone tissue than if thesecond bore2529 were located more laterally. The lockingscrew2590, in combination with thebone screw2540, prevents rotational and/or backward displacement of thelateral mass plate2520. As thelocking screw2590 is received by thesecond bore2529, thehead2592 of thelocking screw2590 aligns with thehead2542 of thefirst bone screw2540 in thefirst bore2530, blocking thehead2542 of thefirst bone screw2540 to prevent thefirst bone screw2540 from backing out of the bone of the vertebra and thefirst bore2530. Theposterior face2532 can include a recessedportion2539, and/or thesecond bore2529 can be countersunk, so that the lockingscrew2590 does not protrude farther from theposterior face2532 than desired.
• In a preferred embodiment (as shown inFIGS. 34A-37), the spheroidaljoint arrangement2538 includes aspherical pivot end2526 and acavity2527 having a shape approximately conforming to thespherical pivot end2526 so that the spheroidaljoint arrangement2538 is a ball-in-socket arrangement. The ball-in-socket arrangement2538 allows the facet joint spacer (or insert)2510 to move freely relative to thelateral mass plate2520 where the facetjoint spacer2510 is unobstructed by thelateral mass plate2520. For example, as shown inFIG. 36A, the facet joint spacer (or insert)2510 can tilt in an anterior direction (toposition1, for example) and can tilt in a posterior direction (toposition2, for example). As the facetjoint spacer2510 tilts in an anterior direction, theisthmus2517 moves within theanterior notch2524 so that the facetjoint spacer2510 can continue tilting without obstruction. Conversely, as the facetjoint spacer2510 tilts in a posterior direction (toposition2, for example), theisthmus2517 contacts theplug2528, limiting the amount of tilt of the facetjoint spacer2510 in a posterior direction.
• Referring toFIG. 36B, the ball-and-socket arrangement allows the facet joint spacer (or insert)2510 to swivel (toposition3, for example) relative to thelateral mass plate2520, potentially providing a more conformal arrangement of the facetjoint spacer2510 with the surfaces of the superior and inferior facets. Further, the ability of the facetjoint spacer2510 to swivel can increase options forlateral mass plate2520 anchor positions. A physician can anchor thelateral mass plate2520 in a more conformal or advantageous orientation and/or position along the lateral mass, for example, by altering the arrangement of thelateral mass plate2520 relative to the facetjoint spacer2510. 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 theisthmus2517 is sufficiently narrow and long in length, a greater degree of swiveling in combination with tilt can be achieved, or for example where theplug2528 extends over a portion of the facetjoint spacer2510, as shown inFIGS. 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 facetjoint spacer2510 relative to thelateral mass plate2520 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 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 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 toFIGS. 36A and 36B, the load bearing structure of the facetjoint spacer2510 includes asuperior surface2513 having a generally convex shape and aninferior surface2514 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 andinferior surfaces2513,2514 can vary between motion segments and between patients. For example, as shown inFIG. 37, where the cervical vertebra includes an inferior facet having a substantially convex natural surface, a physician may select a facet joint spacer (or insert)2610 including a load bearing structure with aninferior surface2614 having a more concave shape combined with alateral mass plate2620 having abone screw2640 more appropriately sized for the particular lateral mass to which it will be fixed. (As shown thebone screw2640 has a shorter length and wider diameter.) A physician can be provided with facet joint spacers having a multiplicity of load bearing structure shapes. As mentioned above, the ability to match different 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 spheroidaljoint arrangement2538 ofFIGS. 34A-37, can be applied to collar structures, for example, as shown inFIGS. 26A-27B, so that the facet joint spacers at each end of the collar structure include an increased range of motion to improve surface matching between the facet joint spacers and the surfaces of the superior and inferior facets (i.e., increasing the amount of facet surface area contacting the facet joint spacers).
• A further embodiment of animplant2600 in accordance with the present invention is shown inFIGS. 38A-38G. Theimplant2600 resembles implants as shown inFIGS. 22A-25A in that the facet joint spacer (or insert)2610 has limited freedom of movement relative to thelateral mass plate2620. As can be seen, ahinge2622 connects the facetjoint spacer2610 with thelateral mass plate2620, allowing the facet joint spacer to pivot up and down relative to a plane of thelateral mass plate2620. However, in other embodiments the facetjoint spacer2610 can be connected with thelateral mass plate2620 by way of a spheroidal joint arrangement (as described above) or by way of some other structure. Aninferior surface2615 of the facetjoint spacer2610 includes a plurality of cleats (also referred to herein as protrusions)2686 extending from theinferior surface2615. In one example as seen inFIG. 38A the cleats point in a direction that is opposed to the direction of insertion of the facet joint spacer in the facet joint in order to ease the insertion step and to aid in preventing the 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 facet joint spacer defined between a superior surface of the facet joint spacer and an inferior surface vertebra of a facet joint spacer. The plurality ofcleats2686 can penetrate or grip a superior facet of a lower vertebra of the targeted facet joint, thereby reducing slippage of the facetjoint spacer2610 relative to the superior facet. Thecleats2686 do not directly restrict the inferior facet of an upper vertebra of the targeted facet joint from moving along thesuperior surface2613 of the facetjoint spacer2610. Thecleats2686 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 facetjoint spacer2610 can include ainferior surface2615 connected with thehinge2622 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 aninferior shim2680. As shown, a substantial portion of the facetjoint spacer2610 including thesuperior surface2613 can be formed of a biocompatible polymer, such as described below. Such a substantial portion is also referred to herein as asuperior shim2682. Such a material is radiolucent, and can have a desired smoothness and reduced compressive strength relative to theinferior surface2615 such that thesuperior surface2613 of the facetjoint spacer2610 allows for a desired slippage relative to the inferior facet of the facet joint. Asuperior surface2613 having a reduced compressive strength and an increased elasticity relative to a bony structure of the spine. Thesuperior shim2682 can be molded onto theinferior shim2680 to form the facetjoint spacer2610, or thesuperior shim2682 can be adhesively fastened to theinferior shim2680, interference fit with optional protuberances of theinferior shim2680, etc. One of ordinary skill in the art will appreciate the different techniques for fixedly connecting asuperior shim2682 with theinferior shim2680. Thelateral mass plate2620 can be made of any of the materials described herein. Preferably thelateral mass plate2620 can be comprised of a biocompatible polymer as described herein.
• 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 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 in 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, thecleats2686 of theimplant2600 can extend from theinferior surface2615 to have a sawtooth shape and arrangement to resist movement in a generally posterior direction away from the facet joint (i.e., toward thelateral mass plate2620 as shown) and further to resist movement in a lateral direction relative to the facet joint. However, thecleats2686 need not necessarily be sawtooth in shape and arrangement. For example, thecleats2686 can have a conical shape, a pyramid shape, a curved shape, etc. Further, as shown particularly inFIG. 38C fourcleats2686 extend from theinferior surface2615. In other embodiments, any number ofcleats2686 can be provided, thecleats2686 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 thecleats2686 can be formed. Thecleats2686 can vary in performance and technique for implantation with shape and number; however, the present invention is meant to encompass all such variations.
• Theimplant2600 can further optionally includeplate cleats2688 extending from a surface of thelateral mass plate2620 substantially contacting the bony structures of the spine (e.g., the lateral mass). Theplate cleats2688 can help anchor thelateral mass plate2620 in position either to assist in resisting shifting as abone screw2640 is associated with the bony structure, or as an adjunct to thebone screw2640. Surface roughening caused by theplate cleats2688 can further promote bone growth near and/or integrally with thelateral mass plate2620. As shown particularly inFIG. 38C there are fourplate cleats2688, eachplate cleat2688 having a conical structure. However, as above theplate cleats2688 can vary in size, number and shape. For example, theplate cleats2688 can have a saw-tooth shape, a pyramid shape, a curved shape, etc.
• Referring toFIGS. 38D through 38G, abone screw2640 of theimplant2600 can be arranged in abore2630 so that thebone screw2640 and bore2630 permit a relative degree of freedom of movement resembling a ball-in-socket joint. Such an arrangement can allow for flexibility in fastening theimplant2600 to a bony structure, thereby allowing a surgeon to avoid diseased or fragile bony structures, fastening theimplant2600 to more durable, healthy bony structures. Thebone screw2640 can swivel within thebore2630 toward or away from the facet joint spacer (or insert)2610 and/or from side-to-side relative to the facetjoint spacer2610. When thebone screw2640 is arranged as desired a retaining plate2624 (FIG. 38B) can be attached to thelateral mass plate2620 to resist backing out of thebone screw2640, similar to the functioning of features as shown in previous embodiments. As can be seen inFIG. 38B, retainingplates2624 can have a projection2625 that fits in a recess2627 of thelateral mass plate2620 in order to prevent rotation of the retainingplate2624 oncescrew2640 is tightened against retainingplate2624.
• Referring toFIG. 39, in still further embodiments, implants in accordance with the present invention can have both aninferior surface2715 and asuperior surface2713 havingcleats2786 extending therefore. Such embodiments can be employed, for example, to fuse the facet joint. Thecleats2786 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 facet joint spacer (or insert)2710 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 facetjoint spacer2710 can be formed from a biocompatible polymer, as described below, or the facetjoint spacer2710 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 facetjoint spacer2710 can be formed.
• As described above in reference to FIGS.38A-G, thecleats2786 are saw-tooth in shape and arrangement, but alternatively can have some other shape and/or arrangement. For example, thecleats2786 can have a pyramidal shape, a curved shape, a conical shape, etc. Further, the shape, size and arrangement forcleats2786 of theinferior surface2715 can be different or the same fromcleats2786 of thesuperior surface2713. The shape, size, and arrangement of thecleats2786 can be chosen based on the 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 inFIGS. 34A through 39. An incision must first be made to expose the surgical site and access the targeted facet joint (Step2500). Once the facet joint is made accessible, the facet joint can be sized and distracted (Step2502). A sizing tool2200 (for example, see FIGS.29A-C) can be inserted to select the appropriate size of animplant2500 of the invention for positioning in the cervical facet joint. This step may be repeated as necessary with, if desired, different sizes of thetool2200 until the appropriate size is determined. This sizing step also distracts the facet joint and surrounding tissue in order to facilitate insertion of theimplant2500. Once the appropriate size is determine, the physician can select an appropriate facet joint spacer (or insert)2510 with the lateral mass plate2520 (Step2504). The facetjoint spacer2510 can then be urged between the facets into the facet joint (Step2510). The facet itself is somewhat shaped like a ball and socket joint. Accordingly, in order to accommodate this shape, the facetjoint spacer2510 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 is urged into the facet joint of the spine. The facetjoint spacer2510 also includes the convexsuperior surface2513 in order to more fully accommodate the shape of the facet joint of the spine. However, as set forth above and as depicted inFIG. 37, it is possible in the alternative to have a curve-shaped facet joint spacer (or insert)2610 with a convexsuperior surface2613 and a concaveinferior surface2614, the distal end of the facetjoint spacer2610 tapering to facilitate insertion, while the remainder of the facetjoint spacer2610 has a uniform thickness.
• Once the facetjoint spacer2510 is positioned, thelateral mass plate2520 is tilted and/or swiveled so that thelateral mass plate2520 is adjacent to the vertebrae and preferably to the lateral mass or to the lamina (Step2512). Thus thelateral mass plate2520 maybe disposed at an angle relative to the facetjoint spacer2510 for a representative spine configuration. It is to be understood that the final position of thelateral mass plate2520 relative to the facetjoint spacer2510 will depend on the actual spine configuration. Once thelateral mass plate2520 is positioned, or prior to the positioning of thelateral mass plate2520, a bore can be drilled in the bone to accommodate thebone screw2540. Alternatively thescrew2540 can be self-tapping. Thescrew2540 is then placed through thefirst bore2530 and secured to the bone, preferably the lateral mass or the lamina, thereby holding the facetjoint spacer2510 in place (Step2514). In order to lock thebone screw2540 in place and to lock the position of the facetjoint spacer2510 and thelateral mass plate2520 in place, a self-tappinglocking screw2590 is positioned within asecond bore2529 of thelateral mass plate2520 and secured to the bone, thereby resisting undesirable movement of the lateral mass plate2520 (Step2516). Ahead2592 of thelocking screw2590 can further block movement of thebone screw2540 by trapping thebone screw head2542 between the lockingscrew head2592 and thefirst bore2530. The lockingscrew2590 therefore prevents thelateral mass plate2520 and the facetjoint spacer2510 from rotating and, as previously indicated, prevents thebone screw2540 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.
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 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:

  	Property	Value

  	Density	1.3	g/cc
  	Rockwell M	99
  	Rockwell R	126
  	Tensile Strength	97	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 A1, dated Jan. 10, 2002, entitled “Bio-Compatible Polymeric Materials;” PCT Publication WO 02/00275 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials;” and, PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials.” Other materials such as Bionate®, polycarbonate urethane, available from the Polymer Technology Group, Berkeley, Calif., 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.

Claims (20)

1. A facet joint implant that can treat ailments of the spine, the implant comprising:

a facet joint spacer adapted to be inserted into a facet joint;

an anchoring plate extending from the facet joint spacer and adapted to be attached to the spine; and

said facet joint spacer including an inferior shim and a superior shim, wherein said inferior shim is stiffer and less compliant that the superior shim.

2. The implant ofclaim 1 wherein said facet joint spacer is secured to the anchoring plate with an articulation joint.

3. The implant ofclaim 1 wherein said superior shim is molded onto said inferior shim.

4. The implant ofclaim 1 wherein said inferior shim is comprised of a metal and said superior shim is comprised of a polymer.

5. The implant ofclaim 1 wherein said inferior shim consists of one of titanium and stainless steel and the superior shim consists of polyaryletherketone.

6. The implant ofclaim 1 wherein said inferior shim defines an inferior surface of the facet joint spacer and at last one protrusion extends from said inferior surface.

7. The implant ofclaim 1 wherein said inferior shim defines an inferior surface of the facet joint spacer and at least one protrusion extends from said inferior surface which said protrusion is comprised of a metal.

8. The implant ofclaim 1 wherein said artificial facet shim provides a continuum from a stiffer inferior shim to a more compliant superior shim.

9. The implant ofclaim 5 wherein said inferior shim defines an inferior surface of the facet joint spacer and at least one protrusion extends from said inferior surface which said protrusion is comprised of the same material that the inferior shim is comprised of.

10. The implant ofclaim 1 wherein said superior shim is secured to the inferior shim.

11. A facet joint implant that can treat ailments of the spine, the implant comprising:

a facet joint spacer adapted to be inserted into a facet joint;

an anchoring plate extending from the facet joint spacer and adapted to be attached to the spine; and

said facet joint spacer including an inferior shim and a superior shim, wherein said inferior shim is comprised of a different material than the superior shim.

12. The implant ofclaim 1 wherein said facet joint spacer is secured to the anchoring plate.

13. The implant ofclaim 1 wherein said superior shim is molded onto said inferior shim.

14. The implant ofclaim 1, wherein said inferior shim is comprised of a metal and said superior shim is comprised of a polymer.

15. The implant ofclaim 1, wherein said inferior shim consists of one of titanium and stainless steel and the superior shim consists of polyaryletherketone.

16. The implant ofclaim 1 wherein said inferior shim defines an inferior surface of the artificial facet joint and at least one protrusion extends from said inferior surface.

17. The implant ofclaim 4 wherein said inferior shim defines an inferior surface of the facet joint spacer and at least one protrusion extends from said inferior surface which said protrusion is comprised of a metal.

18. The implant ofclaim 1 wherein said artificial facet shim provides a continuum from a stiffer inferior shim to a more compliant superior shim.

19. The implant ofclaim 5 wherein said inferior shim defines an inferior surface of the facet joint spacer and at least one protrusion extends from said inferior surface which said protrusion is comprised of the same material that the inferior shim is comprised of.

20. The implant ofclaim 1 wherein said inferior shim is secured to the inferior shim.

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