Abstract:
A method and apparatus for the preparation and implantation of an osteochondral allograft of the intervertebral disc with the adjacent bone segments prepared in a matched fashion to allow for press-fit of the grafts into the recipient vertebral bodies to increase the mechanical fixation of the grafts to the host.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/274,899, filed Aug. 24, 2009. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OR PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     SEQUENCE LISTING 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods of performing surgical bone transplants. More particularly, the present invention relates to techniques by which donor allograft vertebral bones and intervertebral discs may be transplanted into a recipient patient to treat degenerative disc disease of the cervical, thoracic, and/or lumbar spine. 
     2. Background Discussion 
     Osteochondral allografts have a long history of clinical success in the treatment of articular cartilage defects in the knee, shoulder, hip, and ankle The principal advantage of the technique over all other techniques of cartilage restoration is the maintenance of an intact interface between the bone and cartilage of the graft and the preservation of the cartilage architecture; the allograft bone is placed in such a way that it heals to the bone of the recipient. 
     Spinal degenerative disc disease is the second most common cause of disability and a major cause of lost work days in the United States. (Morbidity and Mortality Weekly Report. 2001; 50:94-97) The economic impact of this disease is staggering, accounting for an estimated 149 million days of lost work per year due to low back pain in the United States (H.R. Guo, et al., Am J Public Health, 1999; 89(7): 1029-1035). The estimated cost is between $100 billion and $200 billion per year, mainly due to decreased productivity.(Katz, JN. Bone Joint Surg (Am), 2006; 88 Suppl. 2:21-24). The strategies for the treatment of degenerative disc disease in most cases do not involve surgery. However, should such treatment fail, surgical treatment consisting of nerve decompression and discectomy may be indicated. In more severe cases of disc degeneration or in cases associated with deformity, spinal arthrodesis (fusion) or disc replacement has been advocated. The advantages of fusion are the high rate of clinical success in pain relief and in the correction of deformity. The disadvantage is in the risk of adjacent segment degeneration. 
     Disc replacement has been developed over the past 20 years and has recently been approved by the United States Food and Drug Administration. The long term results of this procedure are unknown. Furthermore, as the procedure is performed through the anterior approach, revision for failure is an exceedingly dangerous procedure. Additionally, the generation of particular wear debris adjacent to the great vessels may bring up some catastrophic complications. 
     Spinal discs are similar to articular cartilage in their composition from collagen, proteoglycans, and water. As such, disc allograft transplants have been performed with some early success in the cervical spine as published by Luk, K.D., et al (Spine, 2003; 28(9): 864-869). The present invention applies principles learned from fresh osteochondral allograft procedures to the treatment of spinal disc degenerative disease. The objective of the procedure is to maintain segmental motion with a fresh or frozen allograft bone-disc composite, taking advantage of the avascular properties of the disc and achieving rigid fixation to the host vertebral bodies on both sides of the allograft. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention includes a method and apparatus for the preparation, transplantation, and fixation of fresh osteochondral allografts of the vertebral bones and the intervertebral discs for the treatment of degenerative disc disease of the cervical, thoracic, or lumbar spine of humans and other mammals. In its most general aspect, the inventive apparatus includes a first and second bone cutting assembly, the first bone cutting assembly employed to prepare a contoured cavity in a recipient spinal segment to receive a bone/disc allograft, the second cutting assembly to prepare the bone/disc combination allograft to tightly fit into the previously prepared contoured cavity. Using the inventive apparatus and methods, a precisely machined allograft hybrid comprising a superior vertebral body, an intervertebral disc, and an inferior vertebral body is prepared while maintaining the allograft disc in its pristine condition without any penetration of its annulus fibrosis. 
     Additionally, the invention includes a method for the preparation of the recipient diseased disc and adjacent vertebral bodies to receive the allograft hybrid tissue. This is facilitated by precisely shaping and sizing the bone segments of the donor and recipient to match so as to facilitate provide for a press fit fixation of the bone and to allow rapid healing between the donor and recipient bone. The intervertebral disc is in many ways an ideal tissue for transplantation due to its limited vascular supply. Furthermore since the transplant is denervated, the inventive method provides an excellent treatment for low back pain caused by degenerative disc disease and one that avoids the complications associated with intervertebral fusion and total disc transplantation. 
     The novel features characteristic of the invention, as to structure, composition, organization, and method of operation, together with further objects and advantages thereof will be better understood from the following description, considered in connection with the accompanying drawings, in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the invention. The various features of novelty that characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. Those skilled in the art will appreciate that the conception, upon which this disclosure is based may readily be used as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. The claims should be understood to include such equivalent constructions as far as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
         FIG. 1A  is a lower front exploded perspective view of the cutting jig and disc measurement stylus of the present invention; 
         FIG. 1B  is a lower rear perspective view of the assembled cutting jig and disc measurement stylus of  FIG. 1A , showing the stylus inserted into the cutting jig; 
         FIG. 2A  is a side view in elevation showing a recipient lumbar spine with the cutting jig and disc measurement stylus of  FIGS. 1A-1B  poised for insertion and placement; 
         FIG. 2B  is a side view in elevation of the recipient lumbar spine with the cutting jig and disc measurement stylus inserted in the intervertebral disc and the cutting jig screwed in place at the superior vertebral body of the diseased disc segment; the saw blade is shown poised for insertion in the jig to commence cutting; 
         FIG. 2C  is a side view in elevation showing how the disc measurement stylus is removed after cutting has commenced; 
         FIG. 2D  shows the cutting jig removed from the superior vertebral body after cutting is completed, inverted, and then poised for placement on the inferior vertebral body; 
         FIG. 2E  shows placement of the cutting jig and disc measurement stylus on the inferior vertebral body with the saw poised to commence cutting; 
         FIG. 2F  shows removal of the disc measurement stylus after cutting of the inferior vertebral body of the diseased segment has commenced; 
         FIG. 3A  is an upper perspective view showing the recipient lumbar spine after performance of saw cuts; 
         FIG. 3B  is an upper perspective view showing the recipient lumbar spine after removal of the cutting jig, and the bone cuts from both the superior and inferior vertebral bodies, as well as the intervening disc; 
         FIG. 4  is an upper rear perspective view of a donor alignment guide with a central peg installed for the positioning and placement of vertebral bodies and intervertebral discs into a recipient; 
         FIG. 5  is an upper front perspective view of the alignment guide of  FIG. 4  showing the guide with a cutting jig installed over the central peg; 
         FIG. 6A  is a side view in elevation showing the donor alignment guide of  FIGS. 4-5  poised for placement on the superior vertebral body of a donor two level bone-disc-bone hybrid allograft; 
         FIG. 6B  is a side view in elevation showing the donor alignment guide placed on the donor allograft, which is typically positioned using visual or fluoroscopic guidance; 
         FIG. 6C  is a side view in elevation showing the removal of the donor allograft alignment guide as cutting is commenced; 
         FIG. 6D  is a side view in elevation showing the donor alignment guide inverted from its position in  FIGS. 6A-6B  for placement on the inferior vertebral body of the two level bone-disc-bone hybrid allograft; 
         FIG. 6E  shows placement of the donor alignment guide on the inferior vertebral body of the donor allograft; 
         FIG. 6F  shows removal of the alignment guide as cutting is commenced on the inferior vertebral body; 
         FIG. 7A  is an upper rear perspective view showing the two level bone-disc-bone donor allograft after performance of saw cuts; 
         FIG. 7B  is an upper rear perspective view showing the donor lumbar spine after removal of the bone cuts from both the superior and inferior vertebral bodies, as well as the intervening disc; 
         FIG. 8A  is an upper rear perspective view showing the donor bone-disc-bone allograft poised for placement in the recipient patient spine; 
         FIG. 8B  is an upper rear perspective view showing the recipient spine after placement of the donor allograft; 
         FIGS. 9A through 14B  are top plan views showing six different pairs of donor and recipient cutting jigs with alternative cutting jig cut patterns, varied according to the specific anatomical location and biomechanical requirements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIGS. 1A and 1B , there is shown in perspective view a first bone cutting assembly  70  of the present invention. This assembly is adapted for use in preparing a contoured cavity in a recipient spinal segment for transplantation of a combination bone/disc allograft harvested from a donor spinal segment. These views show that the first cutting assembly includes a cutting guide (or jig)  10 , which has a front side  12 , a rear side  14 , a generally planar bottom side  16 , an arcuate upper side  18 , and cutting slots  20  to guide the exact path of a cutting device, such as a saw blade or cutting burr. In a preferred embodiment of the invention, the cutting slots include an initial short vertical segment  22  which opens to and through the bottom side of the jig. This “opening slot” is followed by a longer centrally directed first horizontal segment  24 , followed by an oblique segment  26  directed away from center, and finally a centrally directed second horizontal segment  28 . In this way, a precise dovetail pattern is cut into both the donor and recipient vertebral bodies. 
     Two screw holes  30  are disposed on the superior aspect of the top side of the jig for passing screws  32  to secure the jig to the vertebral body during the preparation process. In the central portion  34  of the jig, a cylindrical hole  36  is provided for insertion of an indexing element of a disc measurement stylus, such as a cylindrical indexing peg. 
     The disc measurement stylus  40  of the present invention. The stylus consists of two spaced apart and generally parallel horizontal blades  42  that slide into the annulus fibrosis of the diseased disc on the surface of the bone end plate and establish the depth of bone removal from the vertebral bodies such that the neural elements are protected posteriorly. The blades each include a leading edge  44 , an outer spine  46 , an inner edge  48 , an upper surface  50 , a lower surface  52 , a heel portion  54 , and a bolster  56 . The bolsters are connected with upwardly angling elements  58  of equal length which converge at a vertex to form a central cylindrical peg  60 , which fits within the cylindrical hole  36  of the cutting jig. 
       FIG. 1B  is a lower rear perspective view showing the cutting jig with the attached disc measurement stylus with its blades  42  and its central cylindrical peg  60  placed within the cylindrical indexing hole  36  of the cutting jig  10 . These two elements—the cutting jig and attached disc measurement stylus—comprise the apparatus adapted for performing the first phase of the osteochondral allograft procedure of the present invention, namely, preparation of the transplant site in the recipient patient spinal segment. For simplification these assembled bone and disc cutting elements are variously referred to herein as either the first cutting assembly or “the recipient bone cutting assembly”  70 . 
       FIG. 2A , is a side view in elevation showing a recipient spinal segment RS with the cutting jig  10  and disc measurement stylus  40  of  FIGS. 1A-1B  poised for placement on the anterior aspect of the recipient spine. In this instance, the spinal segment is a portion of the lumbar spine. From this position the first of two recipient bone cutting processes will be carried out to define and create the space for placement of a donor osteochondral allograft. The cutting assembly is placed first at the superior vertebral body SVBr and the diseased intervertebral disc segment IDr. This view also shows the screws  32  positioned for insertion in the screw holes disposed on the superior portion of the top side of the cutting jig. The inferior vertebral body IVBr is not involved in the first cutting process. 
       FIG. 2B  is a side view in elevation showing the first (recipient) cutting assembly  70  affixed to the recipient spine RS superior vertebral body SVBr with screws  32  threadably inserted into the superior end plate SEPr of the vertebral body and the disc measurement stylus  40  with its horizontally disposed blades  42  placed within the annulus fibrosis of the recipient&#39;s diseased disc in such a way as to protect the posterior neural elements. Once the cutting jig is secured by screws, the disc measurement stylus may be removed (see  FIG. 2C ). A cutting device, such as a cutting burr or saw blade  62 , is then inserted into the cutting slots  20 . 
       FIG. 2C  shows how the disc measurement stylus  40  is removed from the annulus fibrosis when the cutting process commences. 
     After passage of the cutting device using the cutting slots of the cutting jig, the screws are unscrewed and the jig is removed from the superior vertebral body. The cut portion of the superior end plate may be removed at this time. Preferably, however, this removal may be deferred until completion of the second cutting process of the inferior vertebral body. The residual screw holes SHr remain (see  FIGS. 3A-3B ), as does the new contoured cavity defined within the superior vertebral body that is in continuity with the diseased disc space. 
       FIG. 2D  shows the first cutting assembly  70  inverted from its upright orientation in  FIGS. 2A-2C  and positioned for placement on the recipient lower vertebral body immediately under the intervertebral disc. In placing the cutting assembly for the second cutting process, and to effect the proper cavity contour, the edges of the opening slot in the bottom side of the cutting jig are aligned with the corresponding cut edges on the superior vertebral body end plate. 
       FIGS. 2E-2F  show how the cutting process shown in  FIGS. 2A-2C  is repeated in a mirror fashion on the inferior vertebral body to complete the second cutting process. Again, the cutting assembly is fixed to the inferior vertebral body with screws and the disc measurement stylus with its horizontally disposed blades are placed within the inferior annulus fibrosis of the diseased disc. After passage of the cutting device through the slots of the cutting jig, the screws and the cutting jig are removed. 
     At this point the inferior end plate may be removed, as may the superior end plate, if not already removed.  FIGS. 3A-3B  show that when the cut portion BDr is removed after completion of the first and second (upper and lower) cutting process, the residual screw holes SHr in the inferior vertebral body remain as does the new contoured cavity CCr placed within the superior and inferior vertebral bodies and the intervertebral disc. (While the various bone tissues are not distinguished in the drawings, it should be understood that the tissue removed from the recipient may include compact bone, cancellous bone, and marrow.) Furthermore, the bone BDr can be removed en bloc after the cutting or in a piecemeal fashion using instruments well known to those skilled in the art. In particular in the posterior aspect of the vertebral body, great care is required to avoid inadvertent injury to the dural sac and thus manual preparation of the posterior most segment of CCr is required using instruments such as Kerrison rongeurs and pituitary rongeurs. At the end of this segment the CCr should extend all the way from the anterior to the posterior aspect of the vertebral body with the profile contoured to the cutting jig. 
       FIGS. 4 and 5  show the second bone cutting assembly employed in the present invention, this assembly including an alignment guide  80  employed for mounting a cutting jig  10   b  that matches the earlier described jig to create and harvest a combined bone/disc allograft from a donor which perfectly matches the contoured cavity of the recipient. The donor alignment guide includes an annulus  81  with a plurality of bosses  82  with screw holes  83  for affixing the guide to a donor spinal segment DS (see  FIG. 6A  et seq.) with suitable screws  84 . A central cylindrical indexing peg  85  is disposed slightly above the upper surface  86  of the annulus so that a portion of the bottom side  16   b  of the cutting jig can be placed flush with that upper surface  86 . Preferably, the indexing peg  85  is supported by either a vertical support or two angled supports  87 , which generally match the supports  58  of the disc measurement stylus. As will be appreciated, the donor alignment guide is sized with an interior diameter  88  sufficiently large to permit placement over a donor spine segment DS after removal of both the spinous processes SPd and transverse processes TPd. The assembly comprising the donor alignment guide and the cutting jig may be referred to variously as either “the harvesting assembly” or simply the second cutting assembly. 
     As will be appreciated, in both the first and second cutting assemblies, the jig is described as including a hole or receptacle for insertion of an indexing element. However, the transposition of these elements will produce the same indexing function so as to ensure accurate placement of the jig on the stylus or on the alignment guide. Accordingly, the disc measurement stylus of the first cutting assembly may include an indexing hole and the jig an indexing peg; likewise, the donor alignment guide may include an indexing hole corresponding to an indexing peg disposed on the second cutting assembly jig body. 
       FIGS. 6A-7B  illustrate the process of creating and harvesting the combined bone/disc allograft from a donor spine segment using the harvesting assembly. These views show that the donor spine segment is prepared by removing the spine segment from the donor and then removing all or a portion of the spinous processes SPd and transverse processes TPd from the superior vertebral body SVBd and the inferior vertebral body IVBd, preferably with cuts through the pedicle close to the dorsal aspect of each of the vertebral bodies. The annulus of the donor alignment guide is then placed over the superior vertebral body using fluoroscopic or visual landmarks and is affixed with screws. A cutting device is then inserted through the cutting slots of the jig and employed to make cuts that defines an outer contour of the combined bone/disc allograft that corresponds precisely with the interior edges and walls of the contoured cavity of the recipient. When the first cutting process on the superior vertebral body is completed, the donor alignment guide is removed and inverted for placement on the inferior vertebral body, and the process is then repeated in mirror fashion on the inferior vertebral body. 
       FIGS. 7A-7B  show how the healthy combined bone/disc allograft BDA is removed after the cutting processes are completed. The combined bone/disc allograft includes the cut portion of the superior vertebral body SVBd′, the intervening healthy intervertebral allograft disc IDd, and the cut portion of the inferior vertebral body IVBd′. 
       FIG. 8A  shows the prepared portions of the recipient spine segment RS. As noted previously, the residual screw holes SHr and the contoured cavity CCr remain.  FIG. 8B  shows the recipient spinal segment after implantation of the allograft in the contoured cavities of the superior and inferior vertebral body of the recipient spine. The prepared portion of the superior vertebral body of the graft is placed in the contoured cavity in the recipient&#39;s superior vertebral body; the prepared portion of the inferior vertebral body of the graft is placed in the contoured cavity in the inferior vertebral body of the recipient; the healthy allograft intervertebral disc remains attached to the bone of the superior and inferior allograft end plates throughout this process. As will be appreciated, the shape of this exemplary donor allograft and the contoured cavity of the recipient resemble the joining method employed by dovetail tails and pins in woodworking. The principles for cutting, sizing, and fitting the elements are essentially identical. 
       FIGS. 9A-12B  show four different matched pairs of cutting jigs, respectively  9 A- 9 B,  10 A- 10 B,  11 A- 11 B, and  12 A- 12 B. These show that several suitable slot patterns may be employed for preparing the contoured cavity and the allograft, including, without limitation, an angled Z pattern,  9 A- 9 B; a rectangular sled pattern  10 A- 10 B; an L-shaped pattern  11 A- 11 B; a rectangular/oval configuration  12 A- 12 B, an oblique/horizontal configuration  13 A- 13 B; and an oval configuration  14 A- 14 B. As will be appreciated, such patterns may take a virtually unlimited number of practicable shapes, and all be used with both the disc measurement stylus and the allograft donor disc measurement ring to prepare the donor and recipient bone to matching size configurations for maximal contact and stability. As will be appreciated, in each pair of cutting jigs, the donor cutting jigs,  90  in  FIG. 9A ,  100  in  FIG. 10A ,  110  in  FIG. 11A ,  120  in  FIG. 12A ,  130  in  FIG. 13A , and  140  in  FIG. 14A , each have slots  92 ,  102 ,  112 ,  122 ,  132 ,  142 , respectively, with an interior edge  94 ,  104 ,  114 ,  124 ,  134 ,  144 , respectively, that trace or match the dimensions of the corresponding outer edge  96 ,  106 ,  116 ,  126 ,  136 , and  146 , respectively, of the cutting slot  98 ,  108 ,  118 ,  128 ,  138 ,  148 , of the paired recipient cutting jig  90 ′,  100 ′,  110 ′,  120 ′,  130 ′,  140 ′. In this way, the edges, angles, corners, and overall shape of the allograft is sized to match the prepared contoured cavity in the recipient spine. 
     While in general it is desirable that the slot patterns create both a contoured cavity and a matching allograft that are substantially bilaterally symmetrical along any medial line of symmetry (i.e., have reflection symmetry), other geometries, perhaps less than perfectly regular or symmetrical, are possible. Accordingly, the bilaterally symmetrical geometries described and shown herein shall not be considered as limiting. 
     The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention. The description also provides the best mode of practicing the invention presently contemplated by the inventor. However, while there is provided herein a full and complete disclosure of the preferred embodiments of this invention, the written description and the drawings do not limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. 
     Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined instead by the appended claims.