US20040098131A1 - Human spinal disc prosthesis - Google Patents

Abstract

The invention relates to a spinal disc endoprosthesis. The endoprosthesis has a resilient body formed of one or more materials which may vary in stiffness from a relatively stiff exterior annular gasket portion to a relatively supple central nucleus portion. Concaval-convex elements at least partly surround that nucleus portion so as to retain the nucleus portion and gasket between adjacent vertebral bodies in a patient's spine. Assemblies of endoprosthetic discs, endoprosthetic vertebral bodies, and endoprosthetic longitudinal ligaments may be constructed. To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient's damaged spine. Thereafter, one or more prosthetic vertebral bodies and disc units are constructed in conformity with that information. Finally, the completed and conformed vertebral body and disc assembly is implanted in the patient's spine.

Description

CROSS-REFERENCE
• This application is a continuation of U.S. patent application Ser. No. 09/776,394 entitled “HUMAN SPINAL DISC PROSTHESIS” filed on Feb. 2, 2001, which is a reissue application of the U.S. Pat. No. 5,865,846 entitled “HUMAN SPINAL DISC PROSTHESIS” filed on May 15, 1997, each of which is hereby incorporated by reference.[0001]
BACKGROUND
• This invention relates generally to human prostheses, and especially to spinal column vertebral disc prostheses. The invention also relates to surgical procedures for preparing the patient to receive a vertebral disc endoprosthesis, and for implanting that endoprosthesis in the patient's spine.[0002]
• The herniation of a spinal disc and the often resultant symptoms of intractable pain, weakness, sensory loss, incontinence and progressive arthritis are among the most common of debilitating processes affecting mankind. If a patient's condition does not improve after conservative treatment, and if clear physical evidence of nerve root or spinal cord compression is apparent, and if correlating radiographic studies (i.e., MRI or CT imaging or myelography) confirm the condition, surgical removal of the herniated disc may be indicated. The process of discectomy—as the name implies—involves the simple removal of the disc without attempt to replace or repair the malfunctioning unit. In the United States in 1985, over 250,000 such operations were performed in the lumbar spine and in the cervical spine.[0003]
• Statistics suggest that present surgical techniques are likely to result in short-term relief, but will not prevent the progressive deterioration of the patient's condition in the long run. Through better pre-operative procedures and diagnostic studies, long-term patient results have improved somewhat. But it has become clear that unless the removed disc is replaced or the spine is otherwise properly supported, further degeneration of the patient's condition will almost certainly occur.[0004]
• In the mid-1950's and 60's, Cloward and Smith & Robinson popularized anterior surgical approaches to the cervical spine for the treatment of cervical degenerative disc disease and related disorders of the vertebrae, spinal cord and nerve root; these surgeries involved disc removal followed by interbody fusion with a bone graft. It was noted by Robinson (Robinson, R. A.: The Results of Anterior Interbody Fusion of the Cervical Spine, J. Bone Joint Surg., 440A: 1569-1586, 1962) that after surgical fusion, osteophyte (bone spur) reabsorption at the fused segment might take place. However, it has become increasingly apparent that unfused vertebral segments at the levels above and below the fused segment degenerate at accelerated rates as a direct result of this fusion. This has led some surgeons to perform discectomy alone, without fusion, by a posterior approach in the neck of some patients. However, as has occurred in surgeries involving the lower back where discectomy without fusion is more common as the initial treatment for disc herniation syndromes, progressive degeneration at the level of disc excision is the rule rather than the exception. Premature degenerative disc disease at the level above and below the excised disc can and does occur.[0005]
• Spine surgery occasionally involves fusion of the spine segments. In addition to the problems created by disc herniation, traumatic, malignant, infectious and degenerative syndromes of the spine can be treated by fusion. Other procedures can include bone grafts and heavy duty metallic rods, hooks, plates and screws being appended to the patient's anatomy; often they are rigidly and internally fixed. None provide for a patient's return to near-normal functioning. Though these procedures may solve a short-term problem, they can cause other, longer term, problems.[0006]
• A number of attempts have been made to solve some of the problems described above by providing a patient with spinal disc prostheses, or artificial discs of one sort or another. For example, Steffee, U.S. Pat. No. 5,031,437, describes a spinal disc prosthesis having upper and lower rigid flat plates and a flat elastomeric core sandwiched between the plates. Frey et al., U.S. Pat. Nos. 4,917,704 and 4,955,908, disclose intervertebral prostheses, but the prostheses are described as solid bodies.[0007]
• U.S. Pat. Nos. 4,911,718 and 5,171,281 disclose resilient disc spacers, but no inter-connective or containing planes or like elements are suggested, and sealing the entire unit is not taught.[0008]
• It is the primary aim of the present invention to provide a vertebral disc endoprosthesis which will perform effectively and efficiently within a patient's spine over a long period of time, and which will not encourage degeneration of or cause damage to adjacent natural disc parts.[0009]
• It is another object to provide a vertebral disc endoprosthesis which does not require pins or other common mechanical hinge elements, yet which permits natural motion of the prosthetic parts and the adjacent natural anatomy.[0010]
• It is a related objective to provide a new vertebral disc endoprosthesis surgical procedure which will decrease post-operative recovery time and inhibit post-operative disc, vertebral body and spinal joint degeneration.[0011]
• It is yet another object to provide a method of installing the endoprosthesis so as to accurately mate the endoprosthesis with an adjacent specifically formed bone surface. An associated object is to provide an endoprosthesis which will encourage bone attachment to, and growth upon, adjacent outer surfaces of the endoprosthesis.[0012]
• Yet another object is to provide a vertebral endoprosthesis in which the parts are non-oncogenic.[0013]
• Still another object is to provide a vertebral disc endoprosthesis having a resilient element to accommodate shocks and other forces applied to the spine.[0014]
• Another object is to provide a highly effective vertebral endoprosthesis which includes several disc endoprostheses and one or more prosthetic vertebral bodies. A related object is to provide these elements in a pre-assembled array for implantation in a patient.[0015]
SUMMARY OF THE INVENTION
• To accomplish these objects, the invention comprises a resilient body formed of a material varying in stiffness from a relatively stiff exterior portion to a relatively supple central portion. A concaval-convex means at least partly surrounds that resilient body so as to retain the resilient body between adjacent vertebral bodies of a patient's spine. If medical considerations so indicate, several disc endoprostheses can be combined with one or more endoprosthetic vertebral bodies in an entire assembly.[0016]
• To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient's damaged natural spinal discs. If one or more of the patient's vertebral bodies also require replacement, information about those bodies is also obtained. Thereafter, one or more prosthetic disc units and interposed prosthetic vertebral body units are constructed and preassembled in conformity with that information. Finally, the completed and conformed prosthetic disc and vertebral body assembly is implanted in the patient's spine.[0017]
• Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.[0018]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a fragmentary vertical view of a portion of a human spine in which is installed a novel vertebral disc endoprosthesis embodying the present invention;[0019]
• FIG. 2 is a fragmentary side elevational view similar to FIG. 1 showing the elements of a patient's spine and having a novel vertebral disc endoprosthesis embodying the present invention installed therein;[0020]
• FIG. 3 is a sectional view taken substantially in the plane of line[0021]3-3 in FIG. 1;
• FIG. 4 is an exploded view of the novel vertebral disc endoprosthesis;[0022]
• FIG. 5 is a vertical fragmentary view of a patient's spine similar to FIG. 1, but showing a series of novel disc endoprosthesis units installed in the spine and interconnected to one another;[0023]
• FIG. 6 is a fragmentary sectional view of a patient's spine similar to FIG. 3 and taken along line[0024]6-6 in FIG. 5, but showing a natural upper vertebral body, and upper endoprosthetic disc; an adjacent endoprosthetic vertebral body; a second or lower endoprosthetic disc; and a second or lower natural vertebral body; p FIG. 7 is a sectional view taken substantially in the plane of line7-7 of FIG. 6;
• FIG. 8 is a fragmentary side elevational view of the assembly shown in FIG. 6; and[0025]
• FIG. 9 is a fragment vertical view, similar to FIG. 1, of a portion of a human spine in which is installed a variant form of the novel vertebral disc endoprosthesis the variant form having a prosthetic longitudinal ligament;[0026]
• FIG. 10 is a sectional view taken substantially in the plane of line[0027]10-10 in FIG. 9;
• FIG. 11 is a top view of a retainer means for use with a vertebral disc endoprosthesis;[0028]
• FIG. 12 is a sectional view taken substantially in the plane of line[0029]12-12 of FIG. 11;
• FIG. 13 is a side view of a vertebral disc endoprosthesis having a groove for receiving the retainer means; and[0030]
• FIG. 14 is a cross-sectional view of the retainer means in use.[0031]
DETAILED DESCRIPTION
• While the invention will be described in connection with a preferred embodiment and procedure, it will be understood that it is not intended to limit the invention to this embodiment or procedure. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.[0032]
• Turning more specifically to FIGS.[0033]1-3, a portion of ahuman spine10 is shown. The illustratedspine10 has been subjected to a discectomy surgical process. To discourage degeneration of or damage to the naturalvertebral bodies12 and14 and their respective facet joints, in accordance with the invention, avertebral disc endoprosthesis18 is affixed between the adjacent naturalvertebral bodies12 and14. Here thisvertebral disc endoprosthesis18 comprises aresilient disc body20 having a relatively stiff annulargasket exterior portion22 and a relatively supple nuclearcentral portion24. Theannular gasket22 can be formed from a suitable biocompatible elastomer of approximately90 durometer hardness and the nuclearcentral portion24 can be formed from a softer biocompatible elastomeric polymer of approximately30 durometer hardness.
• Concaval-[0034]convex means30 surround theresilient body20 to retain theresilient body20 between the adjacent naturalvertebral bodies12,14 in a patient'sspine10. To this end, as shown in FIG. 3, the concaval-convex means30 comprise two generally L-shapedsupports32 and34. The supports32,34 each have confronting first concaval-convex legs42,44, each leg being of relatively constant cross-sectional thickness. Eachleg42,44 has an outerconvex surface52,54 for engaging the adjacent bone of the naturalvertebral bodies12,14. Corresponding innerconcave surfaces62,64 in confronting array retain theresilient body20 in its illustrated compressive force shock-absorbing position. These supports32 and34 can undergo principle movement away from one another, but only limited secondary translational, rotational and distractional motion will occur. Eachsupport32,34 has a second wing orleg72,74 extending generally perpendicularly to thefirst legs42,44 respectively, and adapted for affixation to the adjacent bone structure. To carry out aspects of the invention described below, this affixation is effectively accomplished by cannulatedscrew devices82,84 which may be of a biodegradable type manufactured by Zimmer of Largo, Fla. Eachdevice82,84 comprises ascrew92,94; and ascrew anchor102,104 adapted to threadably receive the screw extends radially into and seats within thebone structure12,14 as especially shown in FIG. 3.
• To discourage and prohibit migration of fluids between the[0035]endoprosthesis18 and adjacent parts of the anatomy, aseal member110 is attached to thesupports32,34 so as to surround theresilient body20 comprised of thegasket22 andnucleus24, in accordance with another aspect of the invention. Here, thisseal member110 comprises a flexible sheet material having a multiplicity of pores. Preferably, the pores are from about5 microns to about60 microns in size. A flexible, strong polymer sheet material from which this seal is formed can be a Kevlar-like material, or it can be Goretex-like material, or other appropriate biocompatible material, such as polyether, polyurethane, or polycarbonate urethane membranes, can be used. Kevlar material is offered by the E.I. DuPont de Nemours Company of Wilmington, Del. and Goretex material is offered by the W.T. Gore Company of Flagstaff and Phoenix, Ariz. Known sealing material can be applied to the flexible sheet material so as to render the flexible sheet material substantially impervious to the passage of any fluid. A watertight seal is perfected when theseal110 is glued or otherwise affixed to thelegs42,44 and mediate portions of thelegs72,74 as suggested in FIGS.1-3.
• In an alternative embodiment, the watertight seal between the[0036]endoprosthesis18 and adjacent parts of the anatomy can be provided by developing agroove402 completely encircling the periphery of each of thelegs42,44. Only one of the grooves is shown in FIG. 13. In this embodiment, theseal member410 is provided with abeaded edge412 for each groove. Additionally, a retainingband415 is provided for each groove to retain theseal member410 ingrooves402. The retainingbands415 can be in the form of a biocompatible monofilament wire of, for example, stainless steel or titanium, a synthetic polymer cable or a braided wire cable. As shown in FIG. 11, each retaining band is crimped anteriorly by a crimpingsleeve420. Of course, more than one crimping sleeve may be used, if necessary. Although one sealing arrangement consisting of the groove, beaded edge and retaining band is shown in FIG. 14, it should be understood that the sealing arrangement on the concaval-convex leg of the other support is identical in design and function.
• In use, the[0037]seal member410 is placed about the concaval-convex means30. The retainingbands415 are then placed adjacent to therespective groove402 and crimped anteriorly, thereby fitting the bands into the grooves. Eachbeaded edge412 prevents the slipping of the seal member underneath the retaining band. Thus, the retaining band, the groove and the beaded edge all cooperate to provide a water-tight seal to prevent the migration of fluids between theendoprosthesis18 and adjacent parts of the anatomy. Glue can also be used to affix the seal member to the concaval-convex means30 as a supplemental means for perfecting the seal.
• In accordance with another aspect of the invention, the[0038]supports32,34 are formed of a biocompatible metal which may contain chromium cobalt or titanium. Surface roughening ortitanium beading112,114 on the exterior surfaces52,54 oflegs42,44 encourages positive bonding between the adjacent bone and theconvex surfaces52,54.
• As suggested in FIGS. 9 and 10, a prosthetic[0039]longitudinal ligament250 can be connected between thescrews92,94 to limit motions between elements of thespine10 in the area where theendoprosthesis18 is implanted. Thisstrap250 may be made of the Kevlar-like material or the Goretex-like material described above, or it may be made of any other strong biocompatible material.
• In accordance with another aspect of the invention, multiple endoprosthetic disc units can be placed in series with a straddling interlock appendage providing stability and fixation as shown in FIG. 5. Entire portions of a patient's spine can be replaced by a series of interconnected endoprosthetic vertebral bodies and endoprosthetic disc units. FIGS.[0040]6-8 show an upper naturalvertebral body unit312 to which an upperendoprosthetic body308 has been attached. A lower naturalvertebral body314 has attached, at its upper end, anendoprosthetic disc unit318. Between theseendoprosthetic disc units308 and318 is an endoprostheticvertebral body320. As suggested by FIG. 7, the endoprostheticvertebral body320 need not be irregularly shaped in cross sectional aspect; rather, manufacturing processes may suggest that it have a circular cross-sectional shape. As show in FIGS. 6 and 8, this endoprostheticvertebral body320 comprises atitanium element321, to which are attached the preformed upper and lower endoprosthetic vertebral body upper and lower concaval-convex elements322,324. Each concaval-convex element322,324 is attached to the prostheticvertebral body320, as shown in FIG. 7, by extending setscrews330 through the titaniumvertebral body321 into a stem-like projection331 extending from each of the concaval-convex elements322,324. Ahole360 in thebody320 accommodates the stem-like projections331 of the concaval-convex elements322 and324. The stem-like projection331 of the concaval-convex elements322 and324 is used only in conjunction with a prosthetic vertebralbody implant construction320.
• An[0041]ear340 is affixed, as byweldments341, to aleg342 extending from a concaval-convex element322 as illustrated in FIGS. 6 and 8. Ananchor352 can be threaded into the endoprostheticvertebral body320, and ascrew362 can be turned into theanchor352 so as to rigidly assemble theleg342 to aleg354 extending from the lowerendoprosthetic disc unit318.
• The[0042]upper disc endoprosthesis308, the endoprostheticvertebral body320, and thelower disc endoprosthesis318 can all be assembled and interconnected as a unit before implantation in a patient's body when indicated.
• As also suggested in FIG. 6, the[0043]annular corners372,374 of naturalvertebral bodies312,314 each can extend irregularly radially outwardly of theadjacent disc endoprosthesis308,318. However, the corners382B,384B of the prostheticvertebral body320 do not generally extend significantly outside thosedisc units308,318, thus discouraging vertebral body engagement with and consequent abrasion or other damage to adjacent portions of the patient's natural anatomy. Preferably the endoprostheticvertebral body320 is not exactly right cylindrical in shape, but is rather slightly biconical; that is, the endoprostheticvertebral body320 has awaist390 of minimum radius R at an axial medial point as suggested in FIG. 6.
• According to yet another aspect of the invention, novel surgical procedures permit effective and permanent installation of the endoprosthetic[0044]vertebral body320 and associated parts. First, a surgeon or medical technician develops information about the size, shape and nature of a patient's damaged vertebral body or bodies from radiographs, CT and/or MRI scans, noting specifically the anterior-posterior and lateral dimensions of the end plate of each involved vertebral body and the vertical height of the anterior aspect of each involved vertebral and/or proximate vertebral body and vertical height of the mid portion of involved and proximate relatively normal intervertebral disc spaces. This information is transmitted by telephone, computer datalink or documentary transport to a specialized laboratory. That laboratory constructs one or more prosthetic assemblies of the sort shown in FIG. 6 in conformity with the received information and this disclosure. Each of the assemblies can include a prostheticvertebral body321, and at each body end is aprosthetic disc308,318. Each prosthetic disc unit comprises, in turn, the concaval-convex elements30; theresilient body20 interposed between the concaval-convex elements; and theseal unit110 secured around the interior legs and resilient body. Thereafter, the completed and conformed assembly is implanted in the patient'sspine10.
• When the unit or units have been received and the patient properly prepared, the damaged natural spinal disc or discs and vertebral body or bodies are removed and the adjacent spinal bone surfaces are milled or otherwise formed to provide concave surfaces to receive the confronting[0045]convex surfaces52,54. Thereafter, the disc units and vertebral body are installed in the patient's spine.
• To accurately locate the concaval-convex surfaces in the patient's spine, holes[0046]382A,384A (FIG. 3) are precisely located and then formed in the bone structure using a measuring instrument centered in the evacuated natural intravertebral disc space. These holes are then tapped to form female threads therein. When the threads have been formed, theanchors102,104 are implanted in the respective tapped holes, thereby creating reference points located precisely with respect to the patient's spine. After the holes have been formed and theanchors102,104 implanted, a bone surface milling jig (not shown) is affixed to theanchors102,104 and the desired concave surfaces of predetermined shape are formed on the inferior and superior surfaces of the opposing vertebral bodies using one of a selection of predetermined milling head or bit sizes. Thereafter, the bone milling jig is removed and the concaval-convex elements52,54 identical in shape to the milledsurfaces112,114 are inserted between the distracted milledvertebral bodies12,14. The distraction device is then moved. The concaval-convex structures are then attached by thesame anchors102,104 to the bone, thus insuring a precise and stable mate between the bone surfaces and theconvex surfaces52,54.
• If necessary, a damaged implanted nucleus and/or[0047]gasket24 can be removed and replaced. This can be accomplished by slitting theseal110; removing theannular gasket24 and damagednucleus22, and replacing them with new, undamaged elements. Thereafter, theseal110 can be re-established by suturing or gluing closed the slit seal.

Claims (20)

We claim:

1. A method of surgery comprising:

forming concave surfaces in endplates of confronting vertebral bodies; and

inserting between the formed concave surfaces an intervertebral disc endoprosthesis wherein the intervertebral disc endoprosthesis comprises:

L-shaped supports wherein each of the L-shaped support comprises an exterior convex surface adapted to mate with one of the formed concave surfaces; and

a resilient body interposed between the L-shaped supports.

2. The method ofclaim 1, further comprising affixing the L-shaped supports to the confronting vertebral bodies.

3. The method ofclaim 1, further comprising implanting at least one anchor in at least one of the confronting vertebral bodies.

4. The method ofclaim 3, wherein the implanting is located in an anterior surface of the at least one of the confronting vertebral bodies.

5. The method ofclaim 4, further comprising affixing a bone surface milling mechanism to the at least one anchor.

6. The method ofclaim 1 wherein the resilient body comprises a relative stiff portion and a relative supple portion.

7. A method of surgery comprising:

implanting at least one anchor in an anterior surface of at least one of confronting vertebral bodies;

forming concave surfaces in the endplates of the confronting vertebral bodies; and

inserting between the formed concave surfaces an intervertebral disc endoprosthesis comprising:

confronting supports, each support having an exterior convex surface adapted to mate with one of the formed concave surfaces; and

a resilient body interposed between the supports.

8. The method ofclaim 7, further comprising affixing a bone surface milling mechanism to the at least one anchor.

9. The method ofclaim 7, further comprising removing damaged disc material.

10. The method ofclaim 7 wherein the resilient body comprises a relative stiff portion and a relative supple portion.

11. A method of spinal surgery comprising:

forming mounting holes in one or more vertebral bodies of a patient's spine;

implanting at least one anchor into one of the mounting holes;

utilizing the at least one anchor to mount a bone mill on the patient's spine;

milling confronting bone surfaces on and in the patient's spine to a predetermined surface shape;

removing the bone mill; and

mounting an intervertebral disc endoprosthesis having a predetermined outer surface shape so that outer surfaces of the intervertebral disc endoprosthesis mate with the previously milled bone surfaces and are capable of motion relative to each other.

12. A method of endoprosthetic discectomy surgery comprising:

receiving information about the size, shape, and nature of a patient's involved natural spinal vertebral bodies and natural spinal vertebral discs from imaging devices;

removing at least the involved and damaged natural spinal disc material from the patient's spine;

implanting at least one anchor into a hole having a predetermined position in an anterior surface of at least one adjacent vertebral body;

forming concave surfaces in the adjacent vertebral bodies; and

implanting into the patient's spine, an intervertebral disc endoprosthesis comprising a resilient disc body and concaval-convex elements that at least partly surround and are capable of movement relative to the resilient disc body in the patient's spine.

13. The method ofclaim 12, further comprising affixing a bone surface milling mechanism to the at least one anchor.

14. The method ofclaim 12 wherein the concaval-convex elements are adjacent to the resilient body.

15. The method ofclaim 12 wherein the concaval-convex elements are in contact with the resilient body.

16. A method of surgery comprising:

implanting at least one anchor into a hole having a predetermined position in an anterior surface of at least one adjacent vertebral body;

affixing a bone surface milling mechanism to the at least one anchor;

forming concave surfaces in the endplates of the adjacent vertebral bodies; and

inserting between the formed concave surfaces an intervertebral disc endoprosthesis, comprising:

confronting concaval-convex supports, each support having an exterior convex surface adapted to mate with one of the formed concave surfaces; and

a resilient body between the concaval-convex supports.

17. The method ofclaim 14 wherein the concaval-convex supports are adjacent to the resilient body.

18. The method ofclaim 14 wherein the concaval-convex supports are in contact with the resilient body.

19. The method ofclaim 14 wherein the resilient body comprises a gasket portion and a nucleus portion.

20. A method of inserting a prosthesis in a disc space between two adjacent vertebral bodies, comprising:

implanting at least one anchor into a hole having a predetermined position in an anterior surface of at least one adjacent vertebral body;

affixing a bone surface milling mechanism to the at least one anchor;

forming at least a portion of a hemispherical cavity in an endplate of one of the vertebral bodies, the endplate have a remaining surface surrounding the cavity; and

inserting an endoprosthesis into the disc space and the cavity, the endoprosthesis including at least one support having an exterior convex surface adapted to mate with the cavity, and a body interposed between the at least one support and the second vertebral body, wherein the at least one support is movable relative to the body.

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