US20050283238A1 - Facet arthroplasty devices and methods - Google Patents

Abstract

Devices and surgical methods treat various types of adult spinal pathologies, such as degenerative spondylolisthesis, spinal stenosis, degenerative lumbar scoliosis, and kypho-scoliosis. Various types of spinal joint replacement prostheses, surgical procedures for performing spinal joint replacements, and surgical instruments are used to perform the surgical procedures.

Description

RELATED APPLICATIONS
• This application is a divisional of co-pending application Ser. No. 09/693,272 filed Oct. 20, 2000, which is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/160,891, filed Oct. 22, 1999, and entitled “Facet Arthroplasty Devices and Methods,” which is incorporated herein by reference.
FIELD OF THE INVENTION
• The present invention generally relates to devices and surgical methods for the treatment of various types of spinal pathologies. More specifically, the present invention is directed to several different types of spinal joint replacement prostheses, surgical procedures for performing spinal joint replacements, and surgical instruments which may be used to perform the surgical procedures.
BACKGROUND OF THE INVENTION
• Back pain is a common human ailment. In fact, approximately 50% of persons who are over 60 years old suffer from lower back pain. Although many incidences of back pain are due to sprains or muscle strains which tend to be self-limited, some back pain is the result of more chronic fibromuscular, osteoarthritic, or ankylosing spondolytic processes of the lumbosacral area. Particularly in the population of over 50 year olds, and most commonly in women, degenerative spine diseases such as degenerative spondylolisthesis and spinal stenosis occurs in a high percentage of the population. Iida, et al, 1989.
• Degenerative changes of the adult spine have traditionally been determined to be the result of the interrelationship of the three joint complex; the disk and the two facet joints. Degenerative changes in the disc lead to arthritic changes in the facet joint and vice versa. See Farfan and Sullivan, 1967; see also Farfan, 1969; see also Farfan, 1980.
• One cadaver study of19 cadavers with degenerative spondylolisthesis showed that facet degeneration was more advanced than disc degeneration in all but two cases. Farfan. In mild spondylolisthetic cases, the slip appeared to be primarily the result of predominantly unilateral facet subluxation. Other studies into degenerative changes of the spine have revealed extensive contribution of facet joint degeneration to degenerative spinal pathologies such as degenerative spondylolisthesis, central and lateral stenosis, degenerative scoliosis, and kypho-scoliosis, at all levels of the lumbar spine. See Kirkaldy-Willis et al, 1978; see also Rosenberg, 1975.
• It has been determined that facet joint degeneration particularly contributes to degenerative spinal pathologies in levels of the lumbar spine with sagittally oriented facet joints, i.e. the L4-L5 level.
• When intractable pain or other neurologic involvement results from adult degenerative spine diseases, such as the ones described above, surgical procedures may become necessary. Traditionally, the surgical management of disease such as spinal stenosis consisted of decompressive laminectomy alone. Herkowitz, et al, The Diagnosis and Management of Degenerative Lumber Spondylolisthesis, 1998. Wide decompressive laminectomies remove the entire lamina, and the marginal osteophytes around the facet joint. Because a lot of degenerative spine disease has been demonstrated to be caused by facet joint degeneration or disease, this procedure removes unnecessary bone from the lamina and insufficient bone from the facet joint.
• Furthermore, although patients with one or two levels of spinal stenosis tend to do reasonably well with just a one to two level wide decompressive laminectomy, patients whose spinal stenosis is associated with degenerative spondylolisthesis have not seen good results. Lombardi, 1985. Some studies reported a 65% increase in degree of spondylolisthesis in patients treated with wide decompressive laminectomy. See Johnson et al; see also White and Wiltse. The increase in spinal slippage especially increased in patients treated with three or more levels of decompression, particularly in patients with radical laminectomies where all of the facet joints were removed.
• To reduce the occurrence of increased spondylolisthesis resulting from decompressive laminectomy, surgeons have been combining laminectomies, particularly in patients with three or more levels of decompression, with multi-level arthrodesis. Although patients who undergo concomitant arthrodesis do demonstrate a significantly better outcome with less chance of further vertebral slippage after laminectomy, arthrodesis poses problems of its own. Aside from the occurrence of further spondylolisthesis in some patients, additional effects include non-unions, slow rate of fusion even with autografts, and significant morbidity at the graft donor site. Furthermore, even if the fusion is successful, joint motion is totally eliminated at the fusion site, creating additional stress on healthy segments of the spine which can lead to disc degeneration, herniation, instability spondylolysis, and facet joint arthritis in the healthy segments.
• An alternative to spinal fusion has been the use of an invertebral disc prosthesis. There are at least 56 artificial disc designs which have been patented or identified as being investigated. McMillin C. R. and Steffee A. D., 20th Annual Meeting of the Society for Biomaterials (abstract) (1994). Although different designs achieve different levels of success with patients, disc replacement mainly helps patients with injured or diseased discs; disc replacement does not address spine pathologies such as spondylolisthesis and spinal stenosis caused by facet joint degeneration or disease.
SUMMARY OF THE INVENTION
• There is a need in the field for prostheses and prosthetic systems to replace injured and/or diseased facet joints, which cause, or are a result of, various spinal diseases. There is also a need for surgical methods to install such prostheses. There is also a need for prostheses and prosthetic systems to replace spinal fusion procedures.
• The present invention overcomes the problems and disadvantages associated with current strategies and designs in various treatments for adult spine diseases. The present inventive spinal arthroplastic systems avoid the problems of spine stiffness, increased loads on unfused levels, and predictable failure rates associated with spinal arthrodesis.
• The present invention pertains to spinal prostheses designed to replace facet joints and/or part of the lamina at virtually all spinal levels including L1-L2, L2-L3, L3-L4, L4-L5, L5-S-1, T11-T12, and T12-L1. Various types of joint replacement prostheses are described for treating different types of spinal problems.
• One aspect of the invention provides a facet prosthesis, which suitable for use in virtually all levels of the spine, including all lumbar levels, lower thoracic levels, and the first sacral level. The facet prosthesis may comprise, e.g., a body which attaches to a pedicle and includes a surface defining a facet.
• Another aspect of the invention provides a bilateral facet arthroplasty system. The bilateral facet arthroplasty system may comprise, e.g., an inferior lamina/facet prosthesis that spans the distance from one inferior facet joint to another and replaces both inferior facet segments and any inferior section of a lamina which has been cut. The bilateral facet arthroplasty system may also comprise, e.g., facet prostheses which have replaced the superior facets to form a complete prosthetic facet joint with the inferior facet prosthesis.
• Another aspect of the invention provides a hemi-lamina/facet prosthesis, which may replace parts of a lamina and inferior facet which have been removed in a hemiarthroplasty with or without wide decompressive laminectomy.
• Another aspect of the invention provides surgical procedures for performing replacements of various facets and lamina in the spine, as well as surgical instruments for facilitating performance of the disclosed surgical procedures, including spinal fusion.
• Another aspect of the invention allows sequential replacements of all facet joints from S1 to T11, allowing for motion on all levels.
• Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a lateral view of a spine with degenerative spondylolisthesis at L4-L5;
• FIG. 2 is a front view of a universal facet replacement prosthesis;
• FIGS. 2A, 2B, and2C are view of an alternative embodiment of a universal facet replacement prosthesis;
• FIG. 3 is a lateral view of a spine with a superior universal facet prosthesis installed in a L5 vertebra;
• FIG. 4 is a superior view of a L5 vertebra with an installed superior universal facet prosthesis;
• FIG. 5 is a superior view of a L5 vertebra depicting removal of the prominent bone of the superior articular process;
• FIG. 6 is a diagram illustrating the trimming of the superior facet to decompress a nerve root prior to reaming;
• FIG. 7 is a superior view of a L5 vertebra depicting the reaming of the facet into the pedicle;
• FIG. 8 is a front view of a facet reamer;
• FIG. 9 is a superior view of a vertebral body depicting broaching an opening into a vertebral body;
• FIG. 10 is a superior view of a vertebral body depicting two universal facet prostheses which have been installed in a vertebral body to form two superior facets;
• FIG. 11 is a posterior view of a spine depicting an installed inferior lamina/facet prosthesis;
• FIG. 12 is a superior view of a vertebral body depicting complete prosthetic facet joints comprising an inferior lamina/facet prosthesis and two superior universal facet prostheses;
• FIG. 13 is a lateral view of an installed complete prosthetic facet joint;
• FIG. 14 is a superior view of a vertebral body depicting sagittally oriented arthritic facets with lateral stenosis;
• FIG. 15 is a superior view of a vertebral body depicting removal of the inferior one eighth of the spinous process;
• FIG. 16 is a superior view of a vertebral body after an inferior lamina/facet resection;
• FIG. 17 is a posterior view of a spine at an L4-L5 showing a spinous process resection line and inferior facet resection line;
• FIG. 18 is a posterior view of an L4-L5 after part of the lamina and inferior facets have been removed, showing an installed universal facet prosthesis;
• FIG. 19 is a posterior view of an L4-L5 after part of the lamina and inferior facets have been removed with an alternative V-type laminal cut, showing an installed universal facet prosthesis;
• FIG. 20 is a posterior view of a L4 vertebra with an alternative shaped inferior lamina/facet prosthesis installed over a V-type laminal cut;
• FIG. 21 is a posterior view of one embodiment of an installed hemi-lamina/facet prosthesis of the present invention;
• FIG. 22 is a front view of one embodiment of a hemi-lamina/facet prosthesis of the present invention;
• FIG. 23 is a posterior view of a spine, at an L4-L5 joint which has undergone hemiarthroplasty with wide decompressive laminectomy, with two base members of a hemi-lamina/facet prosthesis in the process of being installed onto the L4-L5;
• FIG. 24 is a posterior view of one embodiment of an installed hemi-lamina/facet prosthesis of the present invention;
• FIG. 25 is a posterior view of one embodiment of an installed hemi-lamina/facet prosthesis of the present invention;
• FIG. 26 is a posterior view of the L4-L5 depicting various cuts which may be made into the lamina a facets for a hemiarthroplasty with or without wide decompressive laminectomy;
• FIG. 27 is a lateral view of the L4 and L5 vertebrae;
• FIG. 28 is a superior view of the L4 and L5 vertebrae in a separated condition;
• FIG. 29 is a front elevation view of a single-side prosthesis that embodies the feature of the invention;
• FIG. 30 is a side elevation view of the prosthesis shown inFIG. 29;
• FIG. 31 is a lateral view of the L3, L4, and L5 vertebrae, with the prosthesis shown inFIG. 29 secured to the L4 vertebral body;
• FIG. 32 is a lateral view of the L3 and L4 vertebrae, with a link secured to the L4 vertebral body;
• FIG. 33 is a lateral view of the L3 and L4 vertebrae, with a link secured to the L4 vertebral body;
• FIG. 34 is a front elevation view of another single-side facet prosthesis that embodies the feature of the invention;
• FIG. 35 is a lateral view of the L3 and L4 vertebrae, with the prosthesis shown inFIG. 34 secured to the L4 vertebral body;
• FIG. 36 is a front elevation view of a double-side facet joint link assembly that embodies the feature of the invention, being formed of two crisscrossing, mating link bodies;
• FIGS. 37 and 38 are front elevation views of the link bodies forming the joint link assembly shown inFIG. 36, being shown in a mutually separated condition;
• FIG. 39 is a front elevation view of an alternative embodiment of a link body that, when assembled with a mating link body, forms a joint link assembly like that shown inFIG. 36;
• FIG. 40 is a front elevation view of the double-side facet joint link assembly shown inFIG. 36 in relation to its location on a vertebral body;
• FIG. 41 is a side view of a prosthesis, like that shown inFIGS. 29, 34, or36, secured for use on the pedicle of a vertebral body (shown in lateral view); and
• FIG. 42 is a side view of the lower end of the prosthesis shown inFIG. 41, forming the inferior half of a facet joint, the superior half of the facet joint being formed by a superior universal facet prosthesis shown inFIG. 2.
• The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• I. Anatomy of Lumbar Vertebrae
• FIGS. 27 and 28 show the fourth and fifth lumbar vertebrae L4 and L5, respectively, in a lateral view (while in anatomic association) and in a superior view (separately). The lumbar vertebrae (of which there are a total of five) are in the lower back, also called the “small of the back.”
• As is typical with vertebrae, the vertebrae L4 and L5 are separated by anintervertebral disk25. The configuration of the vertebrae L4 and L5 differ somewhat, but each (like vertebrae in general) includes avertebral body10, which is the anterior, massive part of bone that gives strength to the vertebral column and supports body weight. Thevertebral arch12 is posterior to thevertebral body10 and is formed by the right and leftpedicles14 andlamina16. Thepedicles14 are short, stout processes that join thevertebral arch12 to thevertebral body10. Thepedicles14 project posteriorly to meet two broad flat plates of bone, called thelamina16.
• Seven other processes arise from the vertebral arch. Three processes—thespinous process18 and two transverse20 processes—project from thevertebral arch12 and afford attachments for back muscles, forming levers that help the muscles move the vertebrae. The remaining four processes, called articular processes, project superiorly from the vertebral arch (and are thus called the superior articular processes22) and inferiorly from the vertebral arch (and are thus called the inferior articular processes24). The superior and inferior articular processes22 and24 are in opposition with corresponding opposite processes of vertebrae superior and inferior adjacent to them, forming joints, called zygapophysial joints or, in short hand, the facet joints or facets. The facet joints permit gliding movement between the vertebrae L4 and L5. Facet joints are found between adjacent superior and inferior articular processes along the spinal column.
• The facet joints can deteriorate or otherwise become injured or diseased, causing lack of support for the spinal column, pain, and/or difficulty in movement.
• As described in this Specification, a facet joint has a superior half and an inferior half. The superior half of the joint is formed by the vertebral level below the joint, and the inferior half of the joint is formed by the vertebral level above the joint. For example, in the L4-L5 facet joint, the superior half of the joint is formed by structure on the L-5 vertebra, and the inferior half of the joint is formed by structure on the L-4 vertebra.
• II. Superior Universal Facet Prosthsis
• A. Structure
• A superioruniversal facet prosthesis330 is shown inFIG. 1 that embodies features of the invention. Theprosthesis330 is designated “superior” because it creates an artificial facet surface for the superior half of the facet joint. The artificial surface articulates with the inferior half of the facet joint. Theprosthesis330 allows for the replacement of injured, diseased and/or deteriorating components along the superior half of facet joints, to provide improved support for the spinal column.
• Theuniversal facet prosthesis330 may be constructed and configured in various ways. Theuniversal facet prosthesis330 may, e.g., comprise acup member315. Thecup member315 itself may be made of various materials commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, titanium alloys, chrome cobalt, surgical steel, or any other total joint replacement metal and/or ceramic, bony in-growth surface, sintered glass, artificial bone, any uncemented metal or ceramic surface, or a combination thereof. Thecup member315 may also be any appropriate shape including, but not limited to, rectangular, disc shaped, trough shaped, or cup shaped. The cup member may be fixed or anchored directly to a vertebra with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away anchors and/or wires to facilitate any future removal of the prosthesis, or a combination thereof, or any other means known in the art.
• As shown inFIG. 2, thecup member315 is made of any joint materials commonly used in the prosthetic arts, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, bony in-growth surfaces, artificial bone, uncemented surface metals or ceramics, or any combination thereof, preferably covered with a bony in-growth surface.
• In the illustrated embodiment, thecup member315 is fixed to astem310, e.g., pre-welded, or glued with a biocompatible adhesive, or removably secured using a frictional Morse taper. If desired, thestem310 can incorporate one or more fins or ribs (not shown), extending outward from thestem310, which desirably reduce and/or eliminate rotation of thestem310 once positioned within the targeted bone. In addition, thestem310 can be cannulated, if desired, to allow the use of guide pins during insertion of the stem, as is well known in the art.
• Thestem310 may itself be made of any joint materials commonly used in the prosthetic arts, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, bony in-growth surfaces, artificial bone, uncemented surface metals or ceramics, or a combination thereof. In a preferred embodiment, thestem310 is covered with a bony in-growth surface.
• In the illustrated embodiment, thecup member315 carries a surface member, which is made of a material, e.g. polyethylene, ceramic, or metal, which provides glide and cushioning ability for any potential contacting components, such as the articular head members described below. In one embodiment (seeFIG. 2b), thesurface member325 can be formed in a gently upwardly curving shape, similar in shape to a catcher's mitt. In another embodiment (seeFIG. 2c), thesurface member325 is rectangular in shape with rounded corners. Thecup member315 is sized to be larger than the articulating superior half of the facet joint, to allow for motion of the joint.
• Thesurface member325 may be a separate component that is fixed to thecup member315, e.g., with a biocompatible adhesive, screws, nails, or comprise a formed part of thecup member315. Thesurface member325 may also be held into thecup member315 with compressive forces or friction (e.g., using a Morse taper).
• As shown inFIGS. 2aand2b, thestem310acould alternately comprise a threaded portion, such as in a pedicle screw, with the head orpedestal315aincorporating adepression316asized to accommodate a hexagonal driver or other surgical driving tool well know in the art. In addition, theprosthesis320acould incorporate alower insert321asized to fit into thedepression316ain thehead315a. If desired, theinsert321acould comprise a Morse taper. In this embodiment, thestem310acan be screwed into the bone, with theinsert321apositioned or otherwise secure within thedepression316a. Thestem310acould be placed by tapping without screwing. If revision surgery is required, or some other condition required removal of the prosthesis, theinsert321acan be removed from thestem310a, and thestem310acan subsequently be removed from the bone.
• AsFIG. 2ashows, thestem310acan also include an enlarged projection or collar311aabutting thecup member315a. The collar311aserves to prevent unintended ingress of thestem310afurther into the pedicle, beyond a desired distance.
• FIG. 1 depicts a spondylolisthetic spine with slippage at the L4-L5 joint between the L4 and L5 vertebrae.FIG. 3 andFIG. 4 depict auniversal facet prosthesis330 which has been installed into anL5 vertebra105 to replace theinferior half305 of a facet joint. In one embodiment, thestem310 ofuniversal facet prosthesis330 is fixed into theL5 vertebra105 with poly (methylmethacrylate) bone cement, hydroxyapatite, a ground bone composition, or a combination thereof. In another embodiment, both thestem310 and thecup member315 are fixed to a vertebra with stainless steel wire to provide addition stability.
• The new support provided by auniversal facet prosthesis330 helps correct degenerative spine diseases such as spondylolisthesis, spinal stenosis, or any spine disease. As demonstrated by comparingFIG. 1 showing a spondylolisthetic spine with slippage between theL4 vertebra100 and theL5 vertebra105 withFIG. 3 where the diseasedsuperior half305 of the facet joint has been replaced with a superioruniversal facet prosthesis330 of the present invention, correcting spondylolisthesis at the L4-L5 joint and preventing further spondylolisthesis. Similarly, where correction of scoliosis and/or kypho-scoliosis is desired, the size and/or shape of the prosthesis may be chosen to re-orient the affected level(s) of the spine.
• The superioruniversal facet prosthesis330 described above may be used as a replacement for the superior half of one or more of facet joints at any facet joint at any level of the spine. In the preferred embodiment, theuniversal facet prosthesis330 is used to replace the superior half of one or more facet joints in one or more facet joints. Thesuperior facet prosthesis330 is designed such that it has the appropriate cephalad and caudad directions as well as the appropriate medial/lateral angulation for the given level of the spine where the implant occurs.
• In further embodiments, one or more surfaces of auniversal facet prosthesis330 may be covered with various coatings such as antimicrobial, antithrombotic, and osteoinductive agents, or a combination thereof. See, e.g., U.S. Pat. No. 5,866,113, which is incorporated herein by reference. These agents may further be carried in a biodegradable carrier material with which the pores of the stem and/or cup member of certain embodiments may be impregnated. See, e.g., U.S. Pat. No. 5,947,893, which is also incorporated herein by reference.
• In still further embodiments of the present invention, a universal facet prosthesis may be attached to strengthened or fortified bone. Vertebrae may be strengthened prior to or during fixation of the prostheses using the methods, e.g., described in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening is particularly suggested for osteoporotic patients who wish to have facet replacement.
• B. Surgical Method for Facet Replacement Using the Superior Universal Facet Prosthesis
• A surgical procedure that embodies features of the invention replaces the superior half of a facet joint with the superioruniversal facet prosthesis330 described above. The surgical procedure comprises exposing the spinous process, lamina, and facet joints at a desired level of the spine using any method common to those of skill in the medical arts. Theprominent bone306b(seeFIG. 5) may then be rongeured using any means common in the field. Thesuperior facet305 may also be trimmed, as depicted inFIG. 6, to decompress thenerve root203. Areamer400, or any other instrument that is useful for grinding or scraping bone, may be used to ream thefacet305binto thepedicle304bas depicted inFIG. 7 andFIG. 8.
• In a preferred embodiment (seeFIG. 9), anopening407 is made into thevertebral body107 with abroach405. Theuniversal facet prosthesis330bis installed into theopening407 made by thebroach405, as shown inFIG. 10. Theopening407 may be partly filled with bone cement, hydroxyapatite, or any bone adhesive before installation of theuniversal facet prosthesis330b.
• In an alternative embodiment, thestem310 of the superioruniversal facet prosthesis330 may be constructed in such a way that the superioruniversal facet prosthesis330 can be directly screwed or tapped into thevertebral body107.
• In another arrangement, thecup member315 of theuniversal facet member330 may additionally be fixed to thevertebral body107 with bone cement, hydroxyapatite, or any other biocompatible adhesive. In yet another arrangement, a universal facet prosthesis without astem310 may be attached to the vertebral body with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away anchors to facilitate later removal of the prosthesis, or a combination thereof, or any other means known in the art.
• In a further embodiment of the present invention, theuniversal facet prosthesis330 may be fixed into strengthened or fortified bone. Vertebrae may, be strengthened prior to or during fixation of the prosthesis using the methods described in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening procedure is particularly suggested for osteoporotic patients who wish to have facet replacement surgery.
• III. Inferior Lamina/Facet Prosthesis
• A. Structure
• An inferior lamina/facet prosthesis500 that embodies features of the invention is shown inFIG. 11. Theprosthesis500 is designated “inferior” because it creates an artificial facet surface for the inferior half of a facet joint. The artificial surface articulates with the superior half of the facet joint. Theprosthesis330 allows for the replacement of injured, diseased and/or deteriorating components along the inferior halves of facet joints to provide improved support for the spinal column.
• Theprosthesis330 may span the distance from a region on one side of a vertebra to a region of the other side of the vertebra. It can thus replace both inferior halves of a facet joint.
• FIG. 14 depicts a superior view of a vertebral body depicting sagitally oriented arthritic facets with lateral stenosis, showing how thespinal process631 presses forward onto thenerve roots205 and200. Theprosthesis500 allows for replacement of diseased and deteriorating inferior regions of the vertebra and partial replacement of lamina (seeFIG. 12), which may be pressing on the spinal nerves, to relieve pain. Theprosthesis500 creates artificial facet surfaces for the inferior half of facet joints in the spine, which provide improved support for the spinal column.
• AsFIG. 12 shows, a superioruniversal facet prosthesis330, as described above, may also be installed to replace the superior halves of the facet joints and, with the inferior lamina/facet prosthesis500 replacing the inferior halves of the facet joints, forming a total facet replacement system that can result in entire artificial facet joints along a length of the spinal column. Alternatively, just the inferior half one or more facet joints, or just the superior half of one or more facet joints, may be replaced. The inferior and/or superior halves of facet joints may be replaced on one side of a given vertebra (unilateral), on the both sides of a given vertebra (bilateral), or a combination of each along a length of the spinal column.
• The inferior lamina/facet prosthesis500 may be constructed in various ways. As shown inFIG. 11, theprosthesis500 can comprise abase member505. Thebase member505 may be made of any joint materials commonly used in the prosthetic arts, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, bony in-growth surfaces, artificial bone, uncemented surface metals or ceramics, or a combination thereof. Thebase member505 may also be any appropriate shape to give appropriate support to the spine and to appropriately and sturdily attach to the inferior portions of a vertebral body. Thebase member505 may be fixed or anchored directly to the inferior portion of a vertebral body with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away screws to facilitate any future removal of the prosthesis, or a combination thereof, or any other means known in the art.
• In a preferred arrangement, as depicted inFIG. 11,FIG. 12, andFIG. 13, thebase member505 of the inferior lamina/facet prosthesis500 is attached to each pedicle102aand102bwith bilateral pedicle screws520aand520b. Thebase member505 of the inferior lamina/facet prosthesis500 may further be attached to thespinous process630 with a trans-spinous-process screw515 to provide additional stability.
• In another embodiment, the inferior lamina/facet prosthesis500 may have ahead member510 for articulation with thecup member315 of a superioruniversal facet prosthesis330 or with a superior articular process of the adjoining vertebral body. Thehead member510 may be made of various materials commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, tantalum, titanium, chrome cobalt, surgical steel, bony in-growth surfaces, ceramics, artificial bone, or a combination thereof. Thehead member510 may further be any shape which facilitates attachment to the rest of the inferior lamina/facet prosthesis500 and to smooth connection to, and movement in orientation to, auniversal facet prosthesis330 or a superior articular process of an adjoining vertebral body. In one embodiment, ahead member510 is attached to thebase member505 of the inferior facet/lamina prosthesis500 with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, or any other means known in the art. Thehead member510 may also be removably attached by frictional engagement (e.g., using a Morse taper).
• In a preferred embodiment (seeFIGS. 11 and 12), the inferior facet/lamina prosthesis500 comprises twohead members510aand510bformed in the shape of an articular head. Thehead members510aand510bpreferably each have aMorse taper512 at their upper surface to allow them to lock into thebase member505 of the inferior facet/lamina prosthesis500. Of course, either or bothhead members510aand510bcould be formed integrally with theprosthesis500. In the preferred arrangement, a complete prosthetic facet joint560 is provided (seeFIG. 11), in which thehead members510aand510barticulate with thecup member315 of the superioruniversal facet prosthesis330.
• In further embodiments, one or more surfaces of the inferior lamina/facet prosthesis500 may be covered with various coatings such as antimicrobial, antithrombotic, and osteoinductive agents, or a combination thereof. See, e.g., U.S. Pat. No. 5,866,113, which is incorporated herein by reference. These agents may further be carried in a biodegradable carrier material with which the pores of the base member and/or any screws, bolts, or nails of certain embodiments may be impregnated. See, e.g., U.S. Pat. No. 5,947,893, which is incorporated herein by reference.
• In other arrangements, an inferior lamina/facet prosthesis500 may be attached to strengthened or fortified bone. Vertebrae may be strengthened prior to or during fixation of the prosthesis using the methods described, e.g., in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening is particularly suggested for osteoporotic patients who wish to have facet replacement.
• B. Surgical Method for Partial Inferior Lamina/Facet Replacement Using the Inferior Lamina/Facet Prosthesis
• A surgical procedure that embodies features of the invention replaces inferior lamina and articulated processes with the inferior lamina/facet prosthesis500 as described above. The surgical procedure exposes the spinous process, lamina, and facet joints at a desired level of the spine using any method common to those of skill in the medical arts. AsFIG. 15 shows, an inferior one eighth to one half of the spinous process302 may be cut along the spinousprocess resection line610 and removed, if the spinous process appears diseased or damaged. The cutting and removal of the spinois process may be performed using any means common in the field.
• As shown inFIGS. 16 and 17, the inferior half of the facet joint may also be cut at or near the inferiorfacet resection line600. In a preferred embodiment (seeFIGS. 16 and 17), most of thelamina615 is preserved, as is the facetjoint capsule625, which may be opened and folded back. In a preferred embodiment, the facetjoint capsule625 may be cut perpendicular to its direction. Theinferior half621 of the facet joint620 may then be retracted from thesuperior half622. Once the facet joint620 is separated, the cutinferior bone615 of the upper joint (i.e. the cut inferior portion of the L4 vertebra in the L4-L5 joint) may be removed. Alternatively, it may be possible to remove the cutinferior bone615 while simultaneously separating the facet joint620.
• In a preferred embodiment (seeFIGS. 18 and 19), a superioruniversal facet prosthesis330 is then installed as previously described. Alternatively, the superioruniversal facet prosthesis330 may be installed before the inferior bone is removed or even cut.
• An inferior lamina/facet prosthesis500 as described above may be placed onto the facet joints and over the spinous process. The inferior lamina/facet prosthesis500 may be fixed or anchored to the vertebral body with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away screws, or a combination thereof to facilitate any future removal of the prosthesis, or any other means known in the art. In the preferred embodiment (seeFIG. 11,FIG. 12, andFIG. 13), the inferior lamina/facet prosthesis500 is attached to each pedicle102aand102bof the inferior facets with bilateral pedicle screws520aand520band is further attached to thespinous process630 with a trans-spinous-process screw515 to provide additional stability.
• Ahead member510 of an inferior lamina/facet prosthesis500 may articulated into thecup member315 of the superioruniversal facet prosthesis330, or into a inferior half of a facet joint if the inferior half has not been replaced, to create a complete prosthetic facet joint.
• In an alternative embodiment, as depicted byFIG. 19, the inferiorfacet resection line610 may be a V-type cut. If a V-type cut is used, an appropriately shaped inferior lamina/facet prosthesis550 should be used, such as depicted inFIG. 20. The inferior facet resection line may alternatively be cut in other ways, which are apparent to one of skill in the art of orthopedic surgery and will require inferior lamina/facet prostheses of varying shapes to appropriately fit the cut vertebra.
• In a further embodiment of the present invention, a universal facet prosthesis and/or an inferior lamina/facet prosthesis may be fixed into strengthened or fortified bone. Vertebrae may be strengthened prior to or during fixation of the prosthesis using the methods described, e.g., in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening procedure is particularly suggested for osteoporotic patients who wish to have facet replacement surgery.
• IV. Hemi-Lamina/Facet Prosthesis
• A. Structure
• A hemi-lamina/facet prosthesis700 that embodies features of the invention (seeFIG. 21) may be used to replace parts of a lamina and inferior processes, some or all which may have been removed in a primary procedural bone resection, (i.e. with or without wide decompressive laminectomy). The hemi-lamina/facet prosthesis700 may be designed similarly, or even identically, to the inferior lamina/facet prosthesis500 described above, depending on how much of the bone is removed.
• The hemi-lamina/facet prosthesis700 may be constructed in various ways. In one embodiment, hemi-lamina/facet prosthesis700 may, e.g., comprise abase member705. Thebase member705 may be made of any joint materials commonly used in the prosthetic arts, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, bony in-growth surfaces, artificial bone, uncemented surface metals or ceramics, or a combination thereof. Thebase member705 may be any shape which gives appropriate support to the spine and can be appropriately attached to the bone of the remaining lamina. Thebase member705 may be fixed or anchored directly to the inferior portion of a vertebral body with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away screws to facilitate any future removal of the prosthesis, a combination thereof, or any other means known in the art.
• In a preferred embodiment (seeFIG. 21) of a prosthesis for hemiarthroplasty (depicted ascut line800 and further described below) without decompressive laminectomy, thebase member705 of the hemi-lamina/facet prosthesis700 is attached tosuperior pedicle102bwith apedicle screw720. In another preferred embodiment, thebase member705 of the hemi-lamina/facet prosthesis700 may further be attached to thespinous process630 with a trans-spinous-process screw715 to provide additional stability.
• In a preferred embodiment (seeFIGS. 24 and 25) of a prosthesis for hemiarthroplasty with wide decompressive laminectomy, the hemi-lamina/facet prosthesis700 comprises at least onebase member705. Thebase member705 may further comprise apedicle attachment hole725 through which apedicle screw720, or a nail, anchor, break-away anchor, bolt, or any other fastening means, may be installed to help secure the hemi-lamina/facet prosthesis700 to the inferior pedicle. In the preferred embodiment, thebase member705 may also have at least one lamina attachment hole, with two lamina attachment holes741 and742 pictured inFIG. 22, to further secure the hemi-lamina/facet prosthesis700 to the remaining laminal bone with screws, nails, anchors, break-away anchors, bolts, or any other fastening means. Parts of the hemi-lamina/facet prosthesis700 which overlap bone may be additionally fixed with bone cement, or any biocompatible adhesive.
• A hemi-lamina/facet prosthesis700 may further comprise a connection plate, similar to theconnection plate750 depicted inFIG. 24, to connect two base members, i.e.705aand705b, together. Theconnection plate750 may be fixed to eachbase member705aand705bwith a biocompatible adhesive, screws, nails, bolts, compressive force, a combination thereof, or any other means common to those of skill in the art. Alternatively, a hemi-lamina/facet prosthesis700 may further comprise at least one stabilization bar, similar to the stabilization bars761 and762 depicted inFIG. 25. A stabilization bar or bars may be fixed to eachbase member705aand705bwith a biocompatible adhesive, screws, nails, bolts, compressive force, a combination thereof, or any other means common to those of skill in the art. A hemi-lamina/facet prosthesis700 may have any type of bridging or stabilizing members, or no bridging members at all, and may be comprised of any number of base members to provide appropriate stability to the spine. The bridging members may be made of any joint materials commonly used in the prosthetic arts, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, bony in-growth surfaces, artificial bone, uncemented surface metals or ceramics, or a combination thereof.
• In another embodiment, a hemi-lamina/facet prosthesis700 may have ahead member710 for articulation with thecup member315 of a superioruniversal facet prosthesis330 or with the superior articular process of an adjoining superior pedicle. Thehead member710 may be made of various materials commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, chrome cobalt, surgical steel, bony in-growth sintering, sintered glass, artificial bone, or a combination thereof. Thehead member710 may further be any shape which allows it to attach to the rest of the hemi-lamina/facet prosthesis700 and to smoothly connect to, and move in orientation to, theuniversal facet prosthesis330 or superior articular facet of the adjoining superior pedicle. In one embodiment, thehead member710 is attached to the rest of the hemi-lamina/facet prosthesis with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, a combination thereof, or any other means known in the art. Thehead member710 may be removably attached, using, e.g., a Morse taper.
• In a preferred embodiment, hemi-lamina/facet prosthesis700 comprises ahead member710 made in the shape of an articular head. Thehead member710 preferably has a Morse Taper at its upper surface to allow it to lock into hemi-lamina/facet prosthesis700.
• In further embodiments, one or more surfaces of a hemi-lamina/facet prosthesis700 may be covered with various coatings such as antimicrobial, antithrombotic, and osteoinductive agents, or a combination thereof. See, e.g., U.S. Pat. No. 5,866,113, which is incorporated herein by reference. These agents may further be carried in a biodegradable carrier material with which the pores of the base member and/or any screws, bolts, or nails of certain embodiments may be impregnated. See, e.g., U.S. Pat. No. 5,947,893, which is incorporated herein by reference.
• In still further embodiments of the present invention, a hemi-lamina/facet prosthesis700 may be attached to strengthened or fortified bone. Vertebrae may be strengthened prior to or during fixation of the prosthesis using the methods described, e.g., in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening is particularly suggested for osteoporotic patients who wish to have facet replacement.
• B. Hemiarthroplasty With or Without Wide Decompressive Laminectomy Using the Hemi-Lamina/Facet Prosthesis
• A surgical procedure that embodies features of the invention removes at least part of a lamina and at least one superior portion of a facet joint and replacing it with a hemi-lamina/facet prosthesis700 as described above. The general surgical procedure is generally similar to the inferior lamina/facet replacement previously described, with the main difference being the types of cuts made into the laminal bone, and that two separate prostheses are used to replace the superior portions of two facet joints (left and right) of a given vertebra.
• One embodiment of the surgical procedure comprises exposing the spinous process, lamina, and facet joints at a desired level of the spine using any method common to those of skill in the medical arts. The inferior facet joint and part of the lamina may be cut with ahemiarthroplasty resection line800 as depicted inFIG. 26 for a hemiarthroplasty. The lamina may additionally be cut for a wide decompressive laminectomy along thedecompression resection line810 as depicted inFIG. 26. The inferior facet joint may be cut on one side or both sides of the lamina. Likewise, the lamina may be cut along a decompression resection line on one side or both sides.
• In a preferred embodiment of a hemiarthroplasty without a wide decompressive laminectomy, leaving the cutinferior facet bone300 in place, the facetjoint capsule625 may be opened and folded back. In the preferred embodiment, the facetjoint capsule625 may be cut perpendicular to its direction. Theinferior half621 of the facet joint620 may then be retracted from thesuperior half622. Once the facet joint620 is separated, the cut inferior facet bone825 may be removed. Alternatively, it may be possible to remove the cut inferior facet bone825 while simultaneously separating the facet joint620.
• In a preferred embodiment of a hemiarthroplasty with a wide decompressive laminectomy, a superioruniversal facet prosthesis330 is then installed as previously described, and depicted inFIG. 18.
• Abase member705 of hemi-lamina/facet prosthesis700 as described in any of the embodiments above may be placed onto at least one facet joint and at least one pedicle as depicted inFIG. 23, and over the spinous process if it has not been removed for hemiarthroplasty without decompressive laminectomy as depicted inFIG. 21. The hemi-lamina/facet prosthesis700 may be fixed or anchored to the vertebral body with poly(methylmethacrylate) bone cement, hydroxyapatite, screws, nails, bolts, anchors, break-away screws to facilitate any possible future removal of the prosthesis, a combination thereof, or any other means known in the art. In the preferred embodiment, as depicted inFIG. 21,FIG. 24, andFIG. 25, the hemi-lamina/facet prosthesis500 is attached to each pedicle with bilateral pedicle screws720.
• A hemi-lamina/facet prosthesis700 that may be used in hemiathroplasty without wide decompressive laminectomy, depicted inFIG. 21, may further be attached to thespinous process630 with a trans-spinous-process screw715 to provide additional stability. A hemi-lamina prosthesis700 that may be used in hemiathroplasty with wide decompressive laminectomy, as depicted inFIGS. 23, 24, and25, may further be attached to remaining laminal bone with screws, bolts, nails, anchors, or breakaway anchors through at least onelamina attachment hole741 to provide additional stability.
• In embodiments where a hemi-lamina/facet prosthesis700 with more than onebase member705 is installed, a connection plate, depicted asconnection plate750 inFIG. 24, at least one stabilization bar, depicted as stabilization bars761 and762 inFIG. 25, or any other connecting or stabilizing means known in the art, may be installed with the base members to provide additional stability to the spine.
• At least one head member, depicted ashead member710 inFIGS. 21, 23,24, and25, of a hemi-lamina/facet prosthesis700 may be articulated into a cup member of a superioruniversal facet prosthesis330 to create a prosthetic facet joint capsule.
• The embodiments may be used to replace one or more facet joints for the entire length of the spine from S1 to T11, on one side of a given vertebra, or both sides of a given vertebra, or a combination thereof along a length of the spine. If only one facet joint at a given level is to be replaced, the unilateral arthroplasty prosthesis for the inferior half of the joint may be fixed to the superior ipso-lateral pedicle and include a box fitted over the spinous process, combined with screw fixation. The spinous process box is similar to the spinous process box in the bilateral total facet arthroplasty embodiment previously discussed.
• In a further embodiment of the present invention, auniversal facet prosthesis330 and/or a hemi-lamina/facet prosthesis700 may be fixed into strengthened or fortified bone. The vertebrae may be strengthened prior to or during fixation of the prosthesis using the methods described, e.g., in U.S. Pat. No. 5,827,289, which is incorporated herein by reference. This type of bone strengthening procedure is particularly suggested for osteoporotic patients who wish to have facet replacement surgery.
• V. Other Facet Prosthesis
• A. Single Side
• FIGS. 29 and 30 show aninferior prosthesis26 that embodies features of the invention. Theprosthesis26 is designated “inferior” because it creates an artificial facet surface in the inferior half of a facet joint. The artificial surface articulates with the superior half of the facet joint. Theprosthesis26 is particularly well suited to single-sided procedures and/or for procedures involving vertebral bodies which are not symmetrical.
• When the processes on one side of a vertebral body are differently spaced from those on the other side of the same body, the prostheses on each side would desirably be of differing sizes as well. Moreover, it is often difficult and/or impossible for a surgeon to determine the precise size and/or shape necessary for a prosthesis until the surgical site has actually been prepared for receiving the prosthesis. In such a case, the surgeon typically needs a family of prostheses possessing differing sizes and/or shapes immediately available during the surgery. The surgeon cannot wait for a custom-fitted device to be created during the surgery, so a number of prostheses of varying sizes and/or shapes must be available for each procedure.
• Theprosthesis26 can be conveniently formed in different sizes and shapes, to offer an array ofprostheses26 from which the surgeon can pick and choose as surgery proceeds. This allows a surgeon to create a “custom” implant during the surgical procedure.
• In the illustrated embodiment (seeFIGS. 29 and 30), theprosthesis26 comprises abody28 sized and shaped to span the distance between apedicle14 and an inferiorarticular process24 on the same side of a vertebral body (seeFIG. 31). Thebody28 may be formed of a material commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, chrome cobalt, surgical steel, bony in-growth sintering, sintered glass, artificial bone, or a combination thereof.
• The upper section of thebody28 desirably includes anopening32. Theopening32 accommodates a pedicle screw34 (seeFIG. 41), which secures the upper end of thebody28 into thepedicle14 of the vertebral body. Theopening32 could be elongated, to allow for varying orientations and/or sizes of thepedicle screw34. The remainder of thelink body28 can be secured to the exterior of the vertebra using, e.g., biocompatible adhesive.
• The lower section of thebody28 is oriented to serve as the superior half of a facet joint. The lower section of thebody28 desirably incorporates ahead30. Thehead30 can be permanently affixed to thebody28, using, e.g., adhesive. Alternatively, the head can be frictionally secured, e.g., using a Morse taper, for removal and replacement (asFIG. 41 shows). Like thebody28, thehead30 can be formed of a material commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, chrome cobalt, surgical steel, bony in-growth sintering, sintered glass, artificial bone, or a combination thereof. Thehead30 possesses a curvilinear shape that desirably curves along a gradual arc (asFIG. 42 shows), or can present a “button” shape.
• If desired, the lower section of thejoint link body28 could be angled, to more naturally mimic the orientation of a non-diseased facet joint. In one alternative embodiment, the lower section of thejoint link body28 could rotate relative to the upper section, and could be rotationally secured in a desired position by a surgeon using a locking screw or other locking means known in the art. Such an embodiment would allow the surgeon to alter the orientation of the lower section to fit the particular needs of a patient during the actual surgical procedure.
• In use (seeFIG. 31), thehead30 articulates with the superior half of the facet joint. Thesuperior facet22 can comprise the natural superior articular process itself (asFIG. 31 shows),. or it can comprise a superior prosthetic facet created, e.g., by the previously described universal facet prosthesis330 (asFIG. 42 shows). Thesurface member320 of theuniversal facet prosthesis330 can comprise a metal material made of, e.g., titanium, cobalt, chrome, etc., or a plastic material such as, e.g., polyethylene, or a ceramic material. Thus the surgeon can select the same or different materials to form the joint interface between thehead30 andfacet prosthesis330.
• FIGS. 34 and 35 show another embodiment of an inferioruniversal prosthesis36 that embodies features of the invention. Theprosthesis36, like theprosthesis26, is designated “inferior” because it creates an artificial facet surface in the inferior half of the facet joint. The artificial surface articulates with the superior half of the facet joint. Like theprosthesis26, theprosthesis36 is particularly well suited to single-sided procedures and/or for procedures involving vertebral bodies which are not symmetrical.
• Theprosthesis36 comprises abody38 sized and shaped to span the distance between apedicle14 and an inferior articular process24 (seeFIG. 35). Thebody38 may be formed of the same types of material as thelink body28. Like thelink body28, the upper section of thejoint link body38 desirably includes anopening42, to accommodate a pedicle screw34 (seeFIG. 35), which secures the upper end of thebody38 into thepedicle14 of the vertebral body, in similar fashion as generally shown inFIG. 41. As before described with reference to thelink26, theopening42 in thelink body38 could be elongated, to allow for varying orientations and/or sizes of thepedicle screw34. The remainder of thelink body28 can be secured to the exterior of the vertebra using, e.g., biocompatible adhesive.
• Unlike thelink body28, thelink body38 includes anintermediate opening44. In use (seeFIG. 35), the spinous process18 (if present) can extend through theopening44, to stabilize thelink body38 on the vertebral body. Desirably, a trans-spinous-process screw45 can be used to provide additional stability.
• The lower section of thejoint link body38 is oriented to serve as the inferior half of a facet joint. The lower section of thejoint link body38 desirably incorporates ahead40, which can be constructed in the same fashion as thehead30 of thelink26. Like thehead30, thefacet head40 can be permanently affixed to thebody38 or can be secured in with a frictional fit (e.g., using a Morse taper) for removal and replacement. Like thehead30, thehead40 can be formed of a material commonly used in the prosthetic arts.
• In use (seeFIG. 35); thehead40 articulates with the superior half of the facet joint with the next adjacent vertebra level. As before explained for thelink26, thesuperior facet22 can comprise the natural superiorarticular facet22 itself, or it can comprise a prosthetic facet created, e.g., by the previously describeduniversal facet prosthesis330.
• FIG. 32 shows a superiorprosthetic link26′ that also embodies features of the invention. Theprosthetic link26′ is designated “superior” because it creates an artificial facet surface in the superior half of a facet joint. The artificial surface articulates with the inferior half of the facet joint. Thesuperior prosthesis link26′, like theprosthesis26, is particularly well suited to single-sided procedures and/or for procedures involving vertebral bodies which are not symmetrical.
• Astem37 extends out from the upper end of thelink26′. Thestem37 is inserted (by screwing or tapping) into the pedicle, to thereby secure thelink26′ to the vertebral body.
• AsFIG. 32 shows, the upper end of thelink26′ is shaped to form acup36, which articulates with the inferior half of the facet joint.
• The inferior half of the facet joint can comprise the natural inferiorarticular process24 itself (asFIG. 32 shows), or it can comprise thehead30 of aninferior prosthesis26 or link26′ attached to the next adjacent upper vertebra level (asFIG. 33 shows).
• The lower end of thelink26′ can also carry ahead30 for articulation with the superior half of a facet joint with the next adjacent lower vertebra. The superior half of the facet joint can comprise the natural superiorarticular process22 itself, or it can comprise the cup of alink26′ attached to the next adjacent lower vertebra level.
• It can thus be appreciated that thelink26′ is well suited for use in procedures requiring replacement of multiple levels of facet joints, and can be interlinked in superior and inferior pairs, like a structure formed out of interlinking tinker-toy pieces. Thelink26′ also allow subsequent surgeries to build upon already replaced levels, rather than requiring the removal and replacement of an existing implant to accommodate replacement of failing facet joints in an adjacent level. It should be appreciated that the upper end of theprosthesis36 can also be shaped to form a cup to articulate with the superior half of the facet joint with the next adjacent upper vertebra level.
• Theprosthesis26,36, or link26′ are well suited for use in a single side of the vertebral body, such as where the facet joints need only be replaced on a single side of the vertebral body. Theprosthesis26,36, or link26′ are also well suited for use in a dual-sided procedure where the vertebral body is either symmetrical or non-symmetrical. In this arrangement,other prostheses26,36, orlinks26′ can be secured on the opposite side of the vertebral body, allowing both sides of the vertebral body to be treated. Because the surgeon can pickprostheses26,36, and links26′ of varying sizes, depending upon the size of the vertebral site, and can individually position eachprosthesis26 or link26′ relative to the vertebral body, the surgeon can tailor the linked implant system to the individual's needs.
• B. Multiple Level, Sequential Link Assemblies
• FIG. 36 shows a universal prostheticjoint link assembly56 that embodies features of the invention. Thejoint link assembly56 is particularly well suited to double-sided procedures and for sequential, multiple level procedures.
• In the illustrated embodiment (seeFIG. 36), thejoint link assembly56 comprises two criss-crossing link bodies58 and60. Eachbody58 and60 (shown mutually separated inFIGS. 37 and 38, respectively) may be formed of a material commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, chrome cobalt, surgical steel, bony in-growth sintering, sintered glass, artificial bone, or a combination thereof.
• AsFIG. 36 shows, thelink bodies58 and60 are desirably locked together for use at an intermediate key-way62, to form the x-shaped, criss-crossingassembly56. The key-way62 is formed by a shapedopening68 in one body60 (seeFIG. 37) and a mating shaped key70 in the other body58 (seeFIG. 38). The key70 nests within the opening60 (asFIG. 36 shows), to frictionally hold thebodies58 and60 together and resist relative rotation between thebodies58 and60.
• Of course, the shape of theopening68 and key70 can vary. InFIGS. 36, 37, and38, theopening68 and key70 are generally square or rectilinear in shape. InFIG. 39, analternative link body58 is shown, which possesses a key70′ that is generally octagonal in shape, sized to nest within a corresponding octagonal opening in the other link (not shown). In this arrangement, the twolink bodies58 and60 can be mutually assembled in different arcuately spaced orientations, allowing for variations in facet joint size and positioning. If desired, the key-way62 could alternately be formed in a tooth and gear arrangement, which would desirably allow a multiplicity of potential arcuately spaced orientations for the twolink bodies58 and60 forming theassembly56.
• The key70 desirable peripherally defines an opening72 (seeFIG. 38), through which thespinous process18 can (if present) project during use. This is generally shown in phantom lines byFIG. 41.
• Alternatively, thelink bodies58 and60 could be formed in a criss-crossing shape as a single, unitary body.
• The upper section of eachlink body58 and60 desirably includes acup64. Thecups64 form the left and right superior halves of a facet joint and, in use, articulate with the left and right inferior halves of the facet joint.
• Astem65 extends out from the upper end of eachlink body58 and60. The stem67 is inserted (by screwing or tapping) into the pedicle, to thereby secure thelink bodies58 and60 to the vertebral body. In use, the stems67 secure the upper end of thebodies58 and60 into anopposite pedicle14 of a vertebral body.
• AsFIG. 40 best shows, thebodies58 and60 are each sized, shaped and mutually oriented to span the distance between apedicle14 on one side of the vertebral body and the region of the inferior articular process on the opposite side of the vertebral body. The remainder of thelink bodies58 and60 can be secured to the exterior of the vertebra using, e.g., biocompatible adhesive. A trans-spinous-process screw63 can also be used to provide additional stability.
• The lower section of eachlink body58 and60 is oriented to serve as the inferior half of a facet joint. AsFIG. 40 shows, thelink body58, secured to the right pedicle, is positioned to serve as the inferior half of the facet joint on the left side of the vertebra. Thelink body60, secured to the left pedicle, is positioned to serve as the inferior half of the facet joint on the right side of the vertebra. For this purpose, the lower section of eachlink body58 and60 desirably incorporates ahead66. As before explained, thehead66 can be permanently affixed to eachbody58 and60 or it can be secured in a frictional way using, e.g., a Morse taper for removal and replacement. Like thebodies58 and60, thehead66 can be formed of a material commonly used in the prosthetic arts including, but not limited to, polyethylene, rubber, titanium, chrome cobalt, surgical steel, bony in-growth sintering, sintered glass, artificial bone, or a combination thereof.
• In use, theheads66 articulate with the superior halves of the left and right facet joints with the next adjacent vertebra level. As earlier described with reference to the single link structures, the superior halves of the facet joints can comprise the natural superiorarticular process22 itself, or it can comprise a prosthetic facet created, e.g., by thecups64 of anotherlink assembly56 secured to the next adjacent lower vertebra.
• The interlocking of the crisscrossinglink bodies58 and56 increases the strength of theoverall link assembly56. Thelink assembly56 distributes forces to both of the pedicles (and the spinous process, if desired), rather than relying upon fixation to a single pedicle.
• Like thelink26′, thelink assembly56 is well suited for implantation in procedures requiring replacement of multiple levels of facet joints, and can be interlinked in superior and inferior pairs, like a structure formed out of interlinking tinker-toy pieces. Like thelink26′, thelink assembly56 also allows subsequent surgeries to build upon already replaced levels, rather than requiring the removal and replacement of an existing implant to accommodate replacement of failing facet joints in an adjacent level.
• The size and shape of any prosthesis disclosed herein are desirably selected by the physician, taking into account the morphology and geometry of the site to be treated. The shape of the joint, the bones and soft tissues involved, and the local structures that could be harmed if move inappropriately, are generally understood by medical professionals using textbooks of human anatomy along with their knowledge of the site and its disease and/or injury. The physician is also desirably able to select the desired shape and size of the prosthesis and its placement in and/or around the joint based upon prior analysis of the morphology of the targeted joint using, for example, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning. The shape, size and placement are desirably selected to optimize the strength and ultimate bonding of the prosthesis to the surrounding bone and/or tissue of the joint.
• Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All documents referenced herein are specifically and entirely incorporated by reference. The specification and examples should be considered exemplary only with the true scope and spirit of the invention indicated by the following claims. As will be easily understood by those of ordinary skill in the art, variations and modifications of each of the disclosed embodiments can be easily made within the scope of this invention as defined by the following claims.

Claims (31)

1. A prosthesis to replace a cephalad portion of a left natural facet joint on a vertebral body and a cephalad portion of a right natural facet joint on the vertebral body, the prosthesis comprising

an integrated base member including left and right side regions and a mid-region joining the side regions without fixation of the mid-region to bone, to form the integrated base member,

a fixation area on at least one of the left and right side regions to accommodate fixation of the integrated base member to the vertebral body,

an artificial left facet joint structure on the left side region adapted and configured to replace a cephalad portion of the left natural facet joint, and

an artificial right facet joint structure on the right side region adapted and configured to replace a cephalad portion of the right natural facet joint.

2. A prosthesis according toclaim 1

wherein the fixation area is located superior to the artificial facet joint structure to accommodate fixation of the integrated base member to the vertebral body at or near a pedicle.

3. A prosthesis according toclaim 1

wherein the fixation area is located superior to the artificial facet joint structure to accommodate fixation of the integrated base member to a pedicle of the vertebral body.

4. A prosthesis according toclaim 1

further including an auxiliary fixation area on the mid-region to accommodate fixation of the integrated base member to the vertebral body at or near a spinous process.

5. A prosthesis according toclaim 1

further including an auxiliary fixation area on the mid-region to accommodate fixation of the integrated base member to a spinous process of the vertebral body.

6. A prosthesis according toclaim 1

wherein at least one of the left and right artificial facet joint structures includes means for replacing a cephalad portion of a respective one of the left and right natural facet joints after removal of the cephalad portion of the respective natural facet joint from the vertebral body.

7. A prosthesis according toclaim 1

wherein the left and right artificial facet joint structures include means for replacing a cephalad portion of the left and right natural facet joints after removal of the cephalad portion of the left and right natural facet joints from the vertebral body.

8. A prosthesis according toclaim 1

further including a third artificial facet joint structure on one of the left and right side regions superior to the respective artificial left or right facet joint structure adapted and configured to replace a caudal portion of a natural facet joint formed by a vertebral body.

9. A prosthesis according toclaim 8

wherein the third artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of the caudal portion of the natural facet joint from the vertebral body.

10. A prosthesis according toclaim 1

wherein at least one of the left and right artificial facet joint structures includes means for replacing a cephalad portion of at least one of the left and right natural facet joints after removal of at least one inferior articular process and at least a portion of a lamina from the vertebral body.

11. A prosthesis according toclaim 1

wherein the left and right artificial facet joint structures include means for replacing a cephalad portion of the left and right natural facet joints after removal of left and right inferior articular processes and at least a portion of a lamina from the vertebral body.

12. A prosthesis according toclaim 8

wherein the third artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of at least a portion of a mamillary process, or an accessory process, or part of a transverse process, or part of a pedicle from the vertebral body.

13. A method of replacing, on a vertebral body, a cephalad portion of a left natural facet joint and a cephalad portion of a right natural facet joint using the prosthesis as defined inclaim 1 to provide improved support for the spinal column, the method comprising the steps of

(i) removing the cephalad portions of the left and right natural facet joints from the vertebral body, and

(ii) after step (i), fixing the prosthesis as defined inclaim 1 to the vertebral body to replace both removed cephalad portions of the first and second natural facet joints with the first and second artificial facet joint structures.

14. A method according toclaim 13

wherein the removing step includes removing left and right inferior articular processes and at least a portion of a lamina from the vertebral body.

15. A prosthesis to replace a cephalad portion of a natural facet joint on a vertebral body comprising

a base member,

a fixation area on the base member to accommodate fixation of the base member to the vertebral body, and

an artificial facet joint structure on the base member including means for replacing a cephalad portion of a natural facet joint after removal of at least a portion of an inferior articular processes and at least a portion of a lamina from the vertebral body.

16. A prosthesis according toclaim 15

wherein the fixation area is located superior to the artificial facet joint structure to accommodate fixation of the base member to the vertebral body at or near a pedicle.

17. A prosthesis according toclaim 15

wherein the fixation area is located superior to the artificial facet joint structure to accommodate fixation of the base member to a pedicle of the vertebral body.

18. A prosthesis according toclaim 15

further including an other artificial facet joint structure on the base member superior to the first defined artificial facet joint structure adapted and configured to replace a caudal portion of a natural facet joint on the vertebral body.

19. A prosthesis according toclaim 18

wherein the other artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of at least a portion of the caudal portion of the natural facet joint from the vertebral body.

20. A prosthesis according toclaim 18

wherein the other artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of at least a portion of a mamillary process, or an accessory process, or part of a transverse process, or part of a pedicle from the vertebral body.

21. A method of replacing on a vertebral body, a cephalad portion of a natural facet joint using the prosthesis as defined inclaim 15 to provide improved support for the spinal column, the method comprising the steps of

(i) removing the cephalad portion of the natural facet joint from the vertebral body, including removal of an inferior articular process and at least a portion of a lamina from the vertebral body, and

(ii) after step (i), fixing the prosthesis as defined inclaim 15 to the vertebral body to replace the removed cephalad portion of the natural facet joint with the artificial facet joint structure.

22. A prosthesis to replace a caudal portion of a natural facet joint on a vertebral body comprising

a stem member including a fixation area to accommodate fixation of the stem member to the vertebral body at or near a pedicle, and

an artificial facet joint structure carried by the stem member adapted and configured to replace a caudal portion of a natural facet joint.

23. A prosthesis according toclaim 22

wherein the fixation area accommodates fixation of the stem member to the vertebral body without fixation of the stem member to a lamina of the vertebral body.

24. A prosthesis to replace a caudal portion of a natural facet joint on a vertebral body comprising

a screw member including a fixation area to accommodate fixation of the screw member to the vertebral body at or near a pedicle, and

an artificial facet joint structure carried by the screw member adapted and configured to replace a caudal portion of a natural facet joint.

25. A prosthesis according toclaim 24

wherein the fixation area accommodates fixation of the screw member to the vertebral body without fixation of the screw member to a lamina of the vertebral body.

26. A prosthesis according toclaim 22 or24

wherein the artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of at least a portion of the caudal portion of the natural facet joint from the vertebral body.

27. A prosthesis according toclaim 22 or24

wherein the artificial facet joint structure includes means for replacing a caudal portion of a natural facet joint after removal of at least a portion of a mamillary process, or an accessory process, or part of a transverse process, or part of a pedicle from the vertebral body.

28. A method of replacing, on a vertebral body, a caudal portion of a natural facet joint using the prosthesis as defined inclaim 22 or24 to provide improved support for the spinal column, the method comprising the steps of

(i) removing the caudal portion of the natural facet joint from the vertebral body, and

(ii) after step (i), fixing the prosthesis as defined inclaim 22 or24 to the vertebral body to replace the removed caudal portion of the natural facet joint with the artificial facet joint structure.

29. A method according toclaim 25

wherein the removing step includes removing at least a portion of a mamillary process, or an accessory process, or part of a transverse process, or part of a pedicle from the vertebral body.

30. A prosthesis system to replace a cephalad portion and a caudal portion of a natural facet joint on a vertebral body comprising

a first prosthesis as defined inclaim 15 to replace a cephalad portion of the natural facet joint,

a second prosthesis as defined inclaim 22 or24 to replace a caudal portion of the natural facet joint, and

the artificial facet joint structure of the first prosthesis being adapted and configured to articulate with the artificial facet joint structure of the second prosthesis to replace the cephalad and caudal portions of the natural facet joint.

31. A prosthesis according toclaim 1

wherein the fixation area accommodates fixation of the integrated base member to the vertebral body without fixation of the integrated base member to a lamina of the vertebral body.

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