MXPA00002530A - Fusion implant device and method of use - Google Patents

Abstract

An intervertebral prosthesis includes a bone graft implant member dimensioned for insertion within an intervertebral space defined between adjacent vertebrae and having at least first and second longitudinal sections with respective first and second cross-sectional dimensions. The first cross-sectional dimension of the first implant section is greater than the second cross section dimension of the second implant section to define a stepped region having a retaining surface. Consequently, upon insertion of the implant member within a generally correspondingly dimensioned receiving bed formed within the adjacent vertebrae, the retaining surface facilitates securement therewithin by corresponding engagement with surfaces of the receiving bed. A method for fusion of adjacent vertebrae utilizing the prosthesis is also disclosed.

Description

DEVICE FOR IMPLANT WITH FUSION AND METHOD OF USE BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a device for implant with fusion between osteogenic bodies and, more specifically, to an implant of intervertebral bone, unthreaded, having a stepped configuration that facilitates the securing of the implant inside the intervertebral site. 2. Description of the Related Art The spine is a flexible column formed from a series of bones called vertebrae. The vertebrae are hollow and are stacked one on top of the other, forming a hollow, strong column to support the skull and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to each other by means of joint processes and intervertebral, fibrocartilaginous spaces. The intervertebral fibrocartilages are also known as intervertebral discs and are made of a fibrous annulus filled with pulpy material. The discs function as shock absorbers and also cooperate with the synovial joints to facilitate movement and maintain flexibility of the spine. When one or more discs degenerates by accident or disease, the nerves that pass near the affected area can be compressed and consequently irritated. The result can be chronic and / or debilitating back pain. Various methods and devices, both surgical and non-surgical, have been designed to relieve such back pain. One method, intercorporeal fusion includes stretching the spine to a natural position to increase the size of the nerve root canal and eliminate or reduce nerve irritation. The space between vertebrae is maintained by fusing the vertebrae in the affected area at a fixed distance. Numerous prosthetic implants have been suggested to fill the gap between the vertebrae. For example, U.S. Patent No. 4,936,848 discloses a spherical case implant made of metal or ceramic that is inserted between adjacent vertebrae. The box has an interior cavity into which fragments of bone are inserted. These fragments of bone can be autogenous and are proposed to favor the subsequent growth of the bone and the fusion of the vertebrae. Another method for preventing contact of the vertebrae is described in U.S. Patent No. 5,011,484 wherein a rod-shaped insert is inserted longitudinally between two vertebrae and held there by a retainer. U.S. Patent No. 4,309,777 discloses an artificial intervertebral disc having the upper and lower discs that are connected to each other by springs. The artificial disc is held between vertebrae by rays that project from the disc to the vertebrae. U.S. Patent No. 4,743,256 discloses a rigid, porous plug that can be inserted between vertebrae and can be held in place by tips or screws. It is stated that the porous nature of the plug facilitates the internal growth of bone tissue. A bone plug for implant for insertion between vertebrae is also described in U.S. Patent No. 4,878,915 wherein, in one embodiment, the exterior of the plug is provided with external threading which, when the plug is rotated, will advance the plug toward prepared sites between the vertebrae. A portion of the plug is provided with a slot designed to receive the end of a key that is used to rotate the plug. U.S. Patent No. 5,105,255 describes a method for forming a hole between two adjacent vertebrae and inserting the grafted medium, such as cortical bone pieces or finely chopped cancellous bone. U.S. Patent No. 4,961,740 is directed to a substantially open melting box that is inserted between adjacent bone surfaces between vertebrae by screwing the box in place. The box may be filled with pieces of bone or other bone-inducing substances andWhen inserted into the intervertebral space, immediate contact between the bone-inducing substance contained within the box and the native bone occurs through the outer surface of the box. In theory, a graft for fusion should stabilize the intervertebral space and fuse to the adjacent membranes. In addition, during the time the fusion takes, the graft must have sufficient structural integrity to withstand the effort of maintaining the space without substantial degradation or deformation and having sufficient stability to remain safely in place before fusion by internal bone growth. real. Accordingly, a fusion graft must contain some kind of anchor and, in addition, a bone-inducing substance that causes rapid bone growth and rapid fusion of the insert to the adjacent vertebrae. In addition, the material from which the fusion graft is prepared must be biocompatible and closely mimic the natural tissues of the body. All implants described above are proposed to support and maintain an adequate intervertebral space. For example, many of the implants such as those described in U.S. Patent No. 4,936,848 are made of metals and ceramics and, although they are biocompatible, they do not exactly mimic the natural bony tissue of the body. U.S. Patent No. 5,015,255 discloses a graft in the form of pieces of bone that may ultimately give rise to fusion between the vertebrae. If proper fusion of the pieces of bone occurs, the final fused graft can closely mimic the body's natural tissues. However, when the pieces of bone are inserted, they are not confined and may not remain contained between the vertebrae for a sufficient time to adequately fuse with each other and adjacent vertebrae. The bone plug described in U.S. Patent No. 4,878,915 has an external threaded surface to assist in the placement of the implant between adjacent vertebrae. However, external threads compromise the strength of the implant. In addition, the threaded bone implant may have a tendency to withdraw from the prepared hole. Accordingly, there is a need for improved interbody fusion implants that adhere more closely to the ideal of an implant with fusion of the spine.

COMPENDIUM Accordingly, the present invention is directed to an intervertebral prosthesis. The prosthesis includes an implant element (preferably bone) sized for insertion into an intervertebral space defined between adjacent vertebrae and having at least a first and second longitudinal sections with respect to the first and second transverse dimensions. The first transverse dimension of the first section of the implant is larger than the second transverse dimension of the second section of the implant to define a stepped region having a retaining surface. Accordingly, with the insertion of the implant element into a receiving bed generally dimensioned correspondingly within the adjacent vertebrae, the retaining surface facilitates securing therein by corresponding engagement with the surfaces of the receiving bed. The implant element preferably is generally circular cut with the second longitudinal section defining a diameter in the range from about 50% to about 95% of the diameter defined by the first longitudinal section. A one-step or step implant is preferred, however, a multi-step implant is also contemplated. The implant element can also define an interior hollow cavity to accommodate the bone growth inducing material. At least one hole may extend through the external wall of the implant element to allow communication with the bone growth inducing material placed within the hollow cavity to facilitate the fusion process. A method for fusing adjacent vertebrae using the prosthesis is also described.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the description are described herein with reference to the drawings, wherein: FIGURE 1 is a front perspective view of the stepped implant for bone fusion according to the principles in FIG. present description; FIGURE 2 is a rear perspective view of a fusion implant of FIGURE 1; FIGURE 3 is a perspective view of a novel implant cutter for forming the bone fusion implant of FIGURES 1-2; FIGURE 4 is a sectional side view of the implant cutter of FIGURE 3; FIGURE 5 is a view of the implant cutter taken along lines 5-5 of FIGURE 4; FIGURE 6 is a perspective view with portions cut away of an alternative embodiment of the implant cutter of FIGURE 3; FIGURE 7 is a side cut-away view of the implant cutter of FIGURE 6; FIGURE 8 is an axial view of the implant cutter taken along lines 8-8 of FIGURE 7; FIGURE 9 is a perspective view of the distal end portion of a cutting instrument having the implant cutter of FIGURES 3-5 mounted thereon; FIGURE 10 is a side elevational view of the cutting instrument with the cutter for cutting implants illustrating the positioning of the cutter for implants adjacent to the bone mass with the guide of the drill of the instrument penetrating the mass; FIGURE 11 is a view similar to the view of FIGURE 10 illustrating the cylindrical cutting blade of the implant cutter penetrating the bone mass; FIGURE 12 is a side elevational view of a cutting instrument with portions of the cutter for separate implants, illustrating the fully advanced cylindrical cutting blade for forming the stepped fusion implant; FIGURE 13 is a view similar to the view of FIGURE 12 illustrating the separation of the implant cutter with the stepped fusion implant formed from the bone mass; FIGURE 14 is a perspective view of a portion of the spinal column illustrating a recipient bed of the implant formed within adjacent vertebrae for receipt of the stepped fusion implant; FIGURE 15 is a view illustrating a lumbar retractor mounted to the adjacent vertebrae to separate the vertebrae to facilitate insertion of the fusion implant; FIGURE 16 is a view similar to the view of FIGURE 15 illustrating the adjacent vertebrae separated by the lumbar retractor; FIGURE 17 is a view illustrating implant insertion for fusion between separate vertebrae and within the implant recipient bed; FIGURE 18 is a view illustrating the implant for fusion received within the implant recipient bed; FIGURE 19 is a cross-sectional view of the spine illustrating the positioning of a pair of implants for fusion in the spine from a posterior approach; FIGURE 19A is a cross-sectional view of the spine illustrating the positioning of a pair of implants for fusion in the spine through an anterior approach; FIGURES 20-25 are perspective views of alternative embodiments of the fusion implant of FIGURES 1-2; FIGURE 26 is a perspective view of an alternative metal spike fusion implant; FIGURE 27 is a sectional view of the implant for metallic pin fusion taken along lines 27-27 of FIGURE 26; and FIGURES 28-29 are side plan and top plan views of another alternative fusion implant having a wedge-shaped configuration; and FIGURE 30 is a perspective view of the fusion implant of FIGURES 28-29.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The device for interbody, spinal fusion according to the present invention is proposed to be placed between adjacent vertebrae in an attempt to correct a debilitating degeneration of the spinal structure. In humans, the device can be used mainly in the lumbar region of the spine, but it is adjustable for use in the thoracic and cervical regions as well. When placed in place, the device supports and maintains an adequate distance between vertebrae and causes the bone tissue to form and integrate with the device. As a result, the intervertebral space fills with autologous bone tissue and forms a rigid bony connection, integrated between adjacent vertebrae. Now with reference to FIGURES 1-2, the fusion implant of the present invention will be described. The implant 10 includes the elongated body 12 which is made of cortical and / or cancellous bone, the bone can be autologous, allogenic or xenogenic and is preferably recovered from humerus, warmth, femur, etc., as is known in the art. As shown, the elongated body 12 defines a longitudinal axis "a" and has the first and second longitudinal sections 14, 16, respectively. The first and second longitudinal sections 14, 16 preferably have cylindrical configuration and are arranged concentrically about the longitudinal axis?, A.The first longitudinal section 14 has a transverse dimension greater than the transverse dimension of the second longitudinal section, defining by this means a stepped region 18 at the junction of the two sections 14, 16. As will be appreciated from the following description, the stepped region 18 defines a retaining surface 20 that facilitates retention of the implant for fusion between adjacent vertebrae, by example, within a specially prepared bed, created within adjacent vertebrae, thereby ensuring that the implant 10 will not be released during the healing process In a preferred embodiment / the first longitudinal section 14 has a diameter the interval between about 8 and 20 millimeters (mm), more preferably, between about 12 and 16 millimeters others (mine) The second longitudinal section 16 has a diameter that is preferably about 2 mm smaller than the diameter of the first section 14. The length of the elongate body 12 is in the range of about 10-35 mm, preferably about 15- 30 mm. In a preferred embodiment, the second section 16 has a greater density than the first section 14. In this way, the smaller diameter of the second section 16 will not compromise the total resistance of the implant 10. The greater density of the second section 16 is achieved during the harvest and formation of the implant. As will be described in more detail below, when the tibial implant is recovered (i.e., in the case of cancellous plugs), the second section 16 is retrieved from the harder and denser proximal subchondral bone while the first section 14 it recovers from the cancellous bone area. Now with reference to FIGURES 3-5, a novel implant cutter is illustrated for forming the stepped fusion implant 10 of the present invention. The implant cutter 100 can be mounted to a rotary piercing instrument, traditional as will be described. The implant cutter 100 includes the outer hollow piercing portion 102 with cutting teeth 104 and the internal hollow piercing portion 106 with cutting teeth 108. In general, the external piercing portion 102 serves in forming the first longitudinal section 14 of the implant 10, while the internal piercing portion 106 serves in the formation of the second longitudinal section 16. The internal piercing portion 106 is located proximal to the outer piercing portion 102 whereby the teeth 108 of the inner piercing portion extend to the inner wall of the external piercing portion 102 as shown in FIGS. 4-5. As best represented in FIGURE 5, the implant cutter 100 includes a threaded inner portion located proximally 110 that engages the corresponding structure of a piercing instrument for mounting the implant cutter 100 to the instrument. The implant cutter 100 further includes a proximal flange 112 for ease of handling and mounting to the instrument. FIGURES 6-8 illustrate an alternative embodiment of the implant cutter of FIGURES 3-5. The implant cutter 120 of this embodiment is similar to the implant cutter 100, but includes an internal piercing portion 122 having two diametrically opposed axial teeth 124. The diametrical teeth 124 have transverse cutting edges 126 that cut the bone to form the second longitudinal section 16 of the implant. In other aspects, the implant cutter 200 is identical to the cutter of FIGURES 3-5.

Referring now to FIGURE 9, an implant cutter 100 of FIGURES 3-5 mounted on the distal end of a conventional cannulated surgical piercing instrument 1000 is illustrated. The implant cutter 100 shown incorporated with a mounting unit 200 serves in the assembly of the implant cutter 100 to the piercing instrument 1000. This particular assembly unit contemplated is disclosed in co-assigned US Patent Application Serial No. 08 / 404,255, filed on March 15, 1995, the contents of which incorporated herein as a reference. The assembly or cutting unit 20 described in the application '255 includes the mounting element 202, the support shaft 204 (FIGURE 10) and the threaded fittings 206. The mounting element 202 has a proximal end configured for mounting to a tool holder of the piercing instrument 1000 and a threaded distal rod 208 which is threadably coupled to the internal thread 110 of the implant cutter 100 as shown in FIGURE 10 for mounting the cutter 100. The support shaft 204 traverses an axial hole located within the mounting element 202 and extends proximally through an associated hole in the instrument (as shown in dotted lines in FIGURE 10) and distally through the implant cutter 100. The support shaft 204 has a drill guide 210 mounted at its distal end, which forms a pilot hole to help guide the implant cutter 100 towards the bone mass. The threaded fitting 206 extends through the mounting element 202 and serves to selectively secure the support shaft 204 in the desired longitudinal positions relative to the mounting element 202. Further details of the mounting unit 200 can be investigated by making reference to the request '255.

FORMATION OF THE BONE IMPLANT The formation of the bone implant 10 using the implant cutter 100, together with the mounting unit 200 and the cannulated piercing instrument 1000 will now be described. Referring to FIGS. 10-13, a preferred method for forming the bone fusion implant 10 of FIGURES 1-3 is illustrated in sequence. With initial reference to FIGURE 9, the implant cutter 100 is mounted by the mounting unit 200 to the piercing instrument 1000 as already described above. Now with reference to FIGURE 10, with the threaded fitting 206 of the mounting unit engaged against the support shaft 204, the guide of the perforator 210 is directed towards the bone mass "b" to form a pilot hole as shown. Bone mass "b" can represent the tibia or the iliac crest. The piercing instrument 1000 is then actuated to impart rotational movement to the implant cutter 100. The implant cutter 100 is advanced towards the bony one so that the cutting edge 104 of the outer piercing portion 102 penetrates the bone mass "b". With the penetration of the cutting edge 104 towards the bone mass "b" as shown in FIGURE 11), the piercing instrument 1000 is stopped. The threaded fitting 206 is rotated to a release position (FIGURE 11) to release the shaft. of support 204 thereby allowing the support shaft 204 to slide proximally as the implant 100 is formed, i.e., as the implant cutter 100 is advanced toward the bone mass "b". Referring now to FIGURE 12, the piercing instrument 1000 is actuated once more and the advancing movement of the implant cutter 100 is continued towards the bone mass 100"b". During this advancing movement, the cutting teeth 104 of the outer piercing portion 102 cut the bone mass "b" to form the first longitudinal section 14 of the implant. Another advancing movement of the implant cutter 100 causes the cutting teeth 108 of the internal piercing portion 108 [sic] to cut the received bone material into the implant cutter 100 to form the second longitudinal section 16 of the implant. The implant cutter 100 advances towards the bone mass "b" until the flange of the implant cutter 100 abuts the bone mass "b". When drilling in the tibia for the lowest implant 10, the blunt external portion 102 removes the core of the underlying cancellous bone to form the first less dense longitudinal section 14 of the implant while the blunt internal portion 108 removes the denser sub-dome core to form the denser second longitudinal section 16 of the implant 10. With the bone implant 10 completely formed, the piercing instrument 1000 is stopped. The threaded fitting 206 is once again pressed against the support shaft 204 and the implant cutter 100 with the formed implant located therein is removed from the implant. bone mass wb "as shown in FIGURE 13. The bone implant 10 is then separated from the implant cutter 100 by releasing the thread of the accessory 206 and advancing the support shaft 204 distally to remove the implant 10 from the implant cutter 100. In In some cases, the implant of bones may not be separated inside the implant cutter 100. In this case it would be separated by cutting laterally using a serrated, oscillating, normal blade or other cutting device.

SPINAL FUSION PROCEDURE The insertion of the fusion implant in conjunction with a posterior focus for lumbar discectomy and spinal fusion will be described. It will be appreciated that it is possible to use other surgical methods, for example, anterior, posterolateral, etc. to perform the discectomy and insert the implant 100 as well. Initially, the spine is accessed by a posterior focus with the use of retractors suitable to retract adjacent muscle tissue, blood vessels and / or nerve tissue. Then, at least a portion of the degenerative disk is separated with a suitable rongeur clamp or cutting implements. Now with reference to FIGURE 14, a receiver bed "r" corresponding generally in shape to the fusion implant 10 is formed on the opposite faces of adjacent vertebrae Vi, V2. The receiving bed "r" can be prepared by drilling or chiseling. These techniques are well known. Preferably prepared sites are sized to encompass soft, central cancellous bone and include the hard cortical bone of the adjacent vertebrae i, V. Now with reference to FIGURE 15, a retractor "c" is mounted to the posterior phases of the vertebrae i, V2. A retractor "c" suitable for this purpose is the Cloward Lumbar Lamina Spreader manufactured by Codman. The retractor c "includes a pair of retractor arms that can be mounted to the vertebral posterior faces by screws as shown.With the retractor" c "properly mounted, the arms of the retractor are separated to separate the adjacent vertebrae as depicted in FIG. FIGURE 16 to provide adequate space for the insertion of the fusion implant 100 into the receiving bed "r." The fusion implant 100 is then inserted into the separate space with adequate fastening instrumentation (not shown) where it is received into the receiving bed "r" as shown in FIGURE 17. Once the fusion implant 10 is properly located within the receiving bed "r" the retractor "c" is removed to return the adjacent vertebrae, Vi, V2 to their normal positions. As shown in FIGURE 18, the fusion implant 10 forms a strut supporting and holding the adjacent vertebrae Vi, V2 in the desired separate relationship. In practice, the optimum dimensions for the fusion implant 100 are determined, in part, by the dimensions of the receptor bed "r" between the adjacent vertebrae. The stepped region 18 defined at the junction of the first and second longitudinal sections 14, 16 prevents the inserted implant from "separating" (retro-ejection) or loosening due to engagement of the retaining surface 20 with the vertebral surfaces "s" defined. through the receiving bed. In this way, the fusion implant 10 is permanently fixed within the intervertebral space. As shown, the second smaller diameter section 16 of the implant 10 allows interposition between the vertebral endplates. As already indicated, the second section of the implant 16 is relatively dense thereby providing adequate rigidity to support the vertebrae. Over a period of time, the adjacent vertebral bodies grow in and diffuse with the implant 10 to form a solid fusion. FIGURE 19 illustrates two implants for fusion 10 placed within the intervertebral space. FIGURE 19A illustrates two fusion implants 10 located within the intervertebral space through a conventional anterior approach. It should be appreciated that a previous approach can be easily used for the position of the implants 10.

ALTERNATIVE MODALITIES FIGURES 20-25 illustrate alternative embodiments of the stepped fusion implant of the present invention. The fusion implant 40 of FIGURE 20 is a multi-step configuration defined by a plurality of alternating sections 42, 44 of different transverse dimensions. In particular, the section of the implant 42 has a first diameter that is smaller than the diameter of the second section of the implant 44. The joints of the first and second implant sections 42, 44 define stepped regions with retaining surfaces 46 that engage the corresponding structure defined by the recipient bed within the adjacent vertebrae. FIGURE 21 illustrates another multi-stage implant 50 where the sections of the implant 52, 54, 56, 58 increase sequentially in the transverse dimension from one end of the implant to the other end to define a multitude of retaining surfaces 53, 55, 57. FIGURE 22 depicts a one-step fusion implant 60 similar to the implant of FIGURES 1-3. However, according to this embodiment, it is contemplated that the smaller implant section 62 will be the leading end, i.e., during insertion into adjacent vertebrae V, V2, the implant section with smallest or smallest diameter first. progresses within the intervertebral space followed by the larger implant section 64. The implant sections 62, 64 define the retaining surface 66. FIGURE 23 represents another embodiment where the implant 70 has multiple steps with the implant sections 72, 74 , 76 arranged eccentrically in relation to the "a" axis of the implant body. FIGURES 24-25 illustrate yet another embodiment of the fusion implant of the present invention. This implant 80 is similar to the implant of FIGURES 1-3, but includes an internal hole or cavity 82 for accommodating the bone-inducing substances "s" therein. The outer wall of the implant 80 includes a plurality of orifices 84 communicating with the inner bone 82. When inserted into the intervertebral space, the bone crosses over the external surface of the box toward the internal cavity 82 and makes contact with the substances. inducing "s" bone in it. Bone-inducing substances can be recovered from the iliac crest as is conventional in the art. One form of bone inducing substances incorporable with the fusion implant of the present invention is disclosed in commonly assigned US Patent Application Serial No. 08 / 191,624, filed on February 4, 1994, the content of which is incorporated herein by reference. the present as a reference. The bone inducing substances described in the "624" application includes a fluid composition having an osteogenic bone powder dimensioned into a fluid biocompatible carrier. Referring now to FIGS. 26-27, another embodiment of the present disclosure is illustrated. The implant 90 is made of a metallic material that includes titanium, its alloy or surgical steel. Otherwise, the implant 90 may be formed of ceramic or a suitable rigid polymer material or, in another alternative, bone as already described. The implant 90 is similar in configuration to the implant 10 of FIGURES 1-2, but also includes a plurality of alternate annular grooves and flanges 92, 94 with the stepped region 95. The slits and flanges 92, 94 facilitate retention within the space intervertebral increase to the surface area of contact of the external surface of the implant 90 with the vertebral bodies. FIGURES 28-29 illustrate in side and plan views, respectively, another alternative embodiment of the fusion implant. FIGURE 30 is a perspective view of the alternative embodiment. The implant 96 is generally wedge-shaped as shown and includes the first and second sections 97, 98 and stepped regions 99 defined at the junction of the longitudinal sections. The stepped regions 99 are preferably formed by separating opposite peripheral portions 99a (shown in broken line) of the second section 98. It is also understood that only a stepped region 99 can be formed in place of the two regions that are show The implant 96 is inserted into the dimensioned hole defined in correspondence in the adjacent vertebrae whereby the stepped regions 99 are coupled to the vertebral surface defined by the receiving bed performed in a manner similar to that described in connection with the embodiment of FIGURES 1-2. It will be understood that various modifications may be made to the embodiments of the present invention described herein without departing from the spirit thereof. The above description should not be considered as limiting the invention but simply as exemplifications of the preferred embodiments thereof. Those skilled in the art consider other modifications within the scope and spirit of the present invention as defined by the clauses appended hereto.

Claims (26)

1. An intervertebral prosthesis consisting of an implant element dimensioned for insertion into an intervertebral space defined between adjacent vertebrae, the implant element defining a longitudinal axis and having at least a first and second longitudinal sections with the respective first and second transverse dimensions, the first transversal dimension being greater than the second transversal dimension to define a retention surface of the implant element, wherein the insertion of the implant element between the vertebrae, the retention surface facilitates the assurance between these by the corresponding coupling with the surfaces of the vertebrae adjacent.

2. The intervertebral prosthesis according to claim 1, wherein the implant element is generally of circular cut.

3. The intervertebral prosthesis according to claim 2, wherein the second longitudinal section defines a diameter in the range from about 50% to about 95% of the diameter defined by the first longitudinal section.

4. The intervertebral prosthesis according to claim 1, wherein the implant element is generally wedge-shaped.

The intervertebral prosthesis according to claim 1, wherein the implant element defines a one-step region.

The intervertebral prosthesis according to claim 1, wherein the implant element includes regions of multiple steps.

7. The intervertebral prosthesis according to claim 1, wherein the implant element is a bone graft implant.

The intervertebral prosthesis according to claim 1, wherein the implant element consists of cancellous bone or cortical bone.

The intervertebral prosthesis according to claim 1, wherein the implant element consists of a material selected from the group consisting of titanium, titanium alloys, surgical steel, polymeric material and ceramic material.

The intervertebral prosthesis according to claim 1, wherein the implant element defines an interior hollow cavity for accommodating the bone growth inducing material.

11. The intervertebral prosthesis according to claim 10, includes bone growth inducing material located in the inner hollow cavity, the bone growth inducing material includes bone growth factors, glycerol, demineralized bone matrix (dbm), bone marrow. , morphogenic bone protein (BMP-4).

The intervertebral prosthesis according to claim 10, wherein the implant element includes at least one hole extending through an external surface in communication with the bone growth inducing material located within the hollow cavity.

13. An intervertebral prosthesis consisting of an implant element of biocompatible material and being dimensioned to be positioned between the adjacent vertebrae, the implant element including the first and second generally cylindrical sections, the first cylindrical section defining a diameter greater than a diameter defined by the second section cylindrical, the union of the first and second cylindrical sections defining a retention flange so that with the insertion of the implant element between adjacent vertebrae in a shape to prevent movement relative to the vertebrae thereby facilitating retention therein.

The intervertebral prosthesis according to claim 13, wherein the first and second cylindrical sections are arranged concentrically about a longitudinal axis of the implant element.

15. The intervertebral prosthesis according to claim 13, wherein the implant member has an unthreaded outer surface.

The intervertebral prosthesis according to claim 13, wherein the implant member includes a plurality of annular slits formed on an outer surface portion thereof.

17. The intervertebral prosthesis according to claim 14, wherein the implant element defines anterior and posterior ends, the first cylindrical section located adjacent to the anterior end.

18. The intervertebral prosthesis according to claim 13, wherein the implant element consists of cortical bone.

19. The intervertebral prosthesis according to claim 13, wherein the implant element consists of cancellous bone.

20. A device for interbody vertebral fusion comprises a bone graft implant element dimensioned to encompass an intervertebral space between adjacent vertebrae, the implant element having an unthreaded external surface and first and second longitudinal sections, with the respective first and second transverse dimensions , the union of the first and second longitudinal section defining a retaining surface, the retaining surface facilitating the retention of the implant element within the intervertebral space through the cooperative coupling with corresponding surfaces of the adjacent vertebrae.

21. A method for fusing adjacent vertebrae, comprises the steps of: accessing a defined intervertebral space between adjacent vertebrae; prepare a recipient bed in the intervertebral space; providing a bone graft implant element in the recipient bed, the implant element including an elongate body having the first and second longitudinal sections with the respec first and second transverse dimensions, the first transverse dimension being greater than the second transverse dimension for defining a region stepped of the implant element; and positioning the implant element within the receiving bed whereby the stepped region is coupled to a vertebral retention surface defined by the receiving bed to prevent the implant element from being pushed back from the receiving bed.

22. The method according to claim 21, wherein the access step includes accessing the intervertebral space from a posterior location.

The method according to claim 21, wherein the step of providing includes providing an implant element with an unthreaded outer surface.

The method according to claim 21, wherein the step of providing includes providing an implant element with multiple stepped regions.

25. An instrument for forming a bone graft implant device from a bed of bone material, consisting of an elongate bore having an outer drilling portion defining a cavity therein and an internal drilling machine located within the outer drilling portion.

26. A method for forming a device for implanting bone graft from a bed of bone material comprises the steps of: providing an elongated piercer having an outer hollow piercing portion defining a cavity therein and an internal piercer concentrically mounted within the body. external drilling portion; and advancing the elongated bore towards the bed of the bone material a first distance so that the external piercing portion pulls the core out of a first cylindrical section of the bone material; and advancing the elongated bore a second distance so that the inner bore dries the core of the bone material into the outer bore to form a second cylindrical section of the bone material.