Abstract:
Bone plates for engaging bone members are described herein. The bone plates can receive one or more screws to secure the bone plates to an underlying bone member. The one or more screws can be inserted into bone plate holes that can be considered locking or non-locking. The bone plates described herein can have particular combinations of locking and/or non-locking holes. In addition, instruments such as distal and proximal aiming guides can accompany the bone plates to guide one or more screws into the bone plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/874,273, filed Apr. 30, 2013, which is a continuation of U.S. patent application Ser. No. 12/616,772, filed Nov. 11, 2009, now issued as U.S. Pat. No. 8,430,882, which is a continuation-in-part of U.S. patent application Ser. No. 12/210,089, filed on Sep. 12, 2008, now issued as U.S. Pat. No. 8,323,320, which claims priority to U.S. Provisional Patent Application No. 60/972,192, filed on Sep. 13, 2007. All of these references are hereby incorporated by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to devices and methods of spinal surgery. More particularly, the invention relates to systems and methods for creating and repairing a transcorporal access channel through a vertebral body. 
       INCORPORATION BY REFERENCE 
       [0003]    All publications, patents and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference. 
       BACKGROUND 
       [0004]    The performance of cervical discectomy, excision of tissue, and neural element decompression procedures have become standard neurosurgical approaches for the treatment of disorders of the spine and nervous system, as may be caused, for example, by disc degeneration, osteophytes, or tumors. The compressive pathologies impinge onto a neural element, causing a compression of nerve tissue that results in a symptomatic response such as loss of sensation or strength, occurrence of pain, or other related disorders. The majority of these procedures are performed with an anterior approach to the cervical spine. Disc and bone tissue are removed, a neural decompression is achieved, and a spinal repair procedure is performed. 
         [0005]    The current conventional repair procedure includes a vertebral fusion in which a biocompatible implant is inserted and secured between the affected adjacent vertebrae. A bone plate is then is rigidly attached to the two vertebrae adjacent to the implant, immobilizing these vertebral segments and preventing the expulsion of the implant from the intervertebral space. Subsequently, osteogenesis of the vertebrae into the implant occurs, and ultimately the adjacent vertebrae fuse into a single bone mass. The fusion of the vertebral segments, however, can lead to problematic results. For example, the immobility of the fused vertebral joint is commonly associated with the progressive degeneration of the adjacent segments, which, in turn, can lead to degeneration of the intervertebral discs on either side of the fused joint. 
         [0006]    Implantation of an artificial disc device offers an alternate approach to vertebral fusion. The objective of the artificial disc device is to preserve the relative motion of the vertebrae across the joint and to restore normal articulating function to the spinal column. In spite of the benefits that these procedures have brought to patients, both fusion and disc replacement have inherent problems. The surgeries are extensive, recovery time is relatively long, and there is often a loss of function, particularly with the use of fusion implants. The long-term biocompatibility, mechanical stability, and durability of replacement disc devices have not been well established. Further, there is no clinical consensus that the use of a replacement disc reduces the risk of adjacent segment degeneration. 
         [0007]    Methods for surgery on the spine and cervical discs from an anterior approach were first developed in the 1950&#39;s, and a number of variations have been developed since then. Each anterior cervical discectomy procedure, however, has had to face the challenge represented by removing the tissue overlaying the compressing lesion (i.e., the herniated disc material, osteophyte or tumor) after having dissected through the soft tissue anterior to the spine. Early procedures exposed the compressing tissue by first making a cylindrical bone-and-disc defect in the spine centered on the disc space in sagittal and coronal planes, and generally following the plane of the disc itself. Later procedures made use of a rectangular, box-like defect in the disc space centered on the disc space and generally following the plane of the disc. 
         [0008]    Procedures recently developed by Jho (referenced below) were motivated by the concern that procedures like those described above destroyed more of the natural disc tissue than was necessary to remove a laterally-positioned disc herniation or osteophyte (a bone spur). An alternative procedure, an uncovertebrectomy, was therefore developed that involved the removal of only the lateral-most aspect of the disc space, and the vertebral bone above and below it, which together comprise the entire uncovertebral joint. (See Choi et al., “Modified transcorporeal anterior cervical microforaminotomy for cervical radiculopathy: a technical note and early results”,  Eur. Spine J.  2007 Jan. 3; Hong et al., “Comparison between transuncal approach and upper vertebral transcorporeal approach for unilateral cervical radiculopathy—a preliminary report”,  Minim Invasive Spine Surgery,  2006 October; 49 (5):296-301; and Jho et al., “Anterior microforaminotomy for treatment of cervical radiculopathy: part 1: disc-preserving functional cervical disc surgery”,  Neurosurgery  2002 November; 51 (5 Suppl.): S46-53.) This new type of procedure allows much of the disc space to remain untouched. While preserving more of the disc space and disc material than its predecessor procedures, the uncovertebrectomy nevertheless does obliterate the uncovertebral joint, and there is concern in the field regarding the eventual development of spinal instability at that disc level. Further, drilling bone at high speed adjacent to the nearby vertebral artery and sympathetic nerve process increases the concern of a higher risk of vertebral artery, secondary soft tissue injury, and Homer&#39;s Syndrome. 
         [0009]    In another refinement of the uncovertebrectomy procedure, an anterior cervical microforamenotomy, the uncinate process and the lateral disc tissue may be left largely intact as a hole is drilled through the bone adjacent to the disc space near the uncinate process. In both uncovertebrectomy and anterior microforamenotomy, the exposure and decompression of the neural elements generally follow the plane of the disc space. While vertebral artery injury and spinal instability remain concerns with both procedures, the risk associated with anterior microforamenotomy is considered less than that of uncovertebrectomy. 
         [0010]    An additional refinement of both uncovertebrectomy and anterior microforamenotomy is a transcorporeal decompression procedure (also referred to as an upper vertebral transcorporeal foramenotomy or a transcorporeal discectomy) may have advantages. This procedure differs from its disc space-preserving precedent procedures in several ways. First, the axis of the access hole drilled to expose the compressing pathology (e.g., herniated disc fragment) does not parallel the plane of the disc, but instead entirely avoids the disc space plane anteriorly and captures the disc only at its most posterior aspect. Second, while uncovertebrectomy and anterior cervical microforamenotomy are applicable only to lateral pathology, the transcorporeal decompression is potentially applicable to compressing pathology located laterally in the disc space region, bilaterally, or in the midline. Further, the procedure is performed from a substantially medial position on the vertebra assuring maximal distance from the vertebral artery and other sensitive soft tissue and thereby minimizing the risk of accidental injury. 
         [0011]    Multiple technical challenges remain, however, in optimizing the transcorporeal cervical decompression procedure for general surgical use. First, manually orienting and controlling a hand-held cutting tool to make an access channel is a subjective and error-prone procedure. The target pathology is wholly behind and/or within the bony structure of the vertebra and is not visible in any way when approached from a traditional anterior approach to the cervical spine. As the channel is essentially being driven blindly, it can easily fail to capture the targeted pathology being within the range of the posterior opening of the access channel. Consequently the surgeon needs to prolong the procedure, and explore the space by excising tissue until the pathology is found. The exploration typically leads to the access channel becoming larger than necessary and undesirably irregular, thus putting surrounding bone at risk of fracturing during or after the procedure. Given the proximity of many target pathologies to the uncovertebral joint and the vertebral artery, it is likely that exploration of the space will lead to removal of the stabilizing bone and disc tissue. This tissue damage or loss can cause spinal instability, and may further result in accidental perforation of the vertebral artery. 
         [0012]    Second, a manual drilling process increases the risk of over penetration into the spinal canal, with highly undesirable consequences. 
         [0013]    Third, the posterior longitudinal ligament, once exposed in the access channel, can be difficult to open. The objective is to remove the ligament cleanly from the access channel area so as to provide unobstructed visualization of the compressed neural tissue. Current surgical techniques are subjective and time-consuming, often producing a shredding of the ligament within the access channel rather than its removal therefrom, thereby impeding the visualization of the underlying target pathology or dura mater protective layer. 
         [0014]    Fourth, currently available microsurgical instruments are not well-suited for retrieving the herniated disc or bone fragments that may be found deep to the posterior longitudinal ligament. 
         [0015]    Fifth, after the decompression is complete, the present solutions for filling the void remaining in the vertebra are not completely satisfactory. Demineralized bone matrix putties or similar materials can fill the defect but they offer no resistance to the normal compressing or torsional forces until calcification occurs. Such materials may also impose a new source of compression on the exposed neural structures if too much putty is applied or if the vertebra deforms or sustains a compression fracture subsequently because of the absence of an implant that sufficiently resists compressive forces. 
         [0016]    Sixth, after a solid implant plug is placed in the surgically-formed access channel, there is presently no anterior cervical plate suited to preventing its outward migration. Currently available anterior cervical plates are designed to be placed across two or more adjacent vertebrae at or near the midline, not laterally, as would be needed for lateral compressing lesions. Existing plates also are designed as motion-restriction or motion-prevention devices to be placed bridging across a disc space rather than onto a single vertebral body, consequently they are too large and are counterproductive in the application such as that described above where the objective is to preserve the articulation and relative motion of the adjacent vertebrae. 
         [0017]    Accordingly, there is a need for a system and method whereby any compressing spinal pathology may be removed or moved so as to decompress the neural elements involved while desirably also (1) preserving native disc and bone tissue and the natural motion of the spine with natural disc material, (2) minimizing the risk of injury to the vertebral artery, (3) minimizing the risk of structural spinal instability, (4) minimizing the risk of an inadequate decompression, (5) minimizing the risk of injury to the protective dura mater layer, (6) minimizing the risk of post operative bleeding and/or (7) minimizing the risk of a subsequent vertebral body fracture due to an unrepaired defect within it. 
       SUMMARY OF THE DISCLOSURE 
       [0018]    The invention relates to a system and method for forming and repairing an access channel through a vertebral body, typically a cervical vertebral body, for the purpose of gaining access to a site in need of a medical intervention. In its formation, the channel originates on the anterior surface of the vertebral body, and it then provides access from the anterior approach. The channel follows a prescribed trajectory to a prescribed exit on the posterior surface of the vertebral body, and provides an opening at the site of sufficient size to address the medical need. The access channel is typically formed in cervical vertebral bodies. The nature of the medical need typically includes the need for a decompression procedure, as may occur as a result of a problematic portion or the whole of a herniated disc, an osteophyte, a thickened ligament, a tumor, a hematoma, a degenerative cyst, or any other compressing pathology. The medical intervention may be as minimal as observing the site, or performing exploration, or it may include a diagnostic procedure, or delivering a therapy, or it may include a surgery. A typical surgery performed through the access channel can include decompressing a neural element, such an individual nerve root, a spinal cord, or a cauda equina. 
         [0019]    The system of the invention may further include an implantable bone repair device having an external geometry complementary to the internal geometry of the access channel, and a method for repairing or healing the channel by implanting such device. Some embodiments of the device include materials that are biocompatible, biologically absorbable, or any material known to be able to substitute for bone, and to be able to be stably and effectively integrated into bone. The device may further include as well as biologically active agents, such as osteogenic agents, that promote healing of the wound represented by the access channel, and fusion of the device such that it integrates into the vertebral body. 
         [0020]    In some embodiments, the implantable bone repair device includes an assembly with a porous body that includes actual bone tissue. Such bone tissue may be provided by the bone removed during the formation of the channel itself, or it may come from another site from the patient as an autologous graft, or it may be provided by a separate donor. 
         [0021]    The system to form and repair an access channel includes a bone cutting tool with a cutting element, a bone plate configured to be secured to the anterior surface of the vertebral body and having an opening sized to receive the cutting element; and a trajectory control sleeve configured to detachably engage the bone plate and having a cylinder configured to receive the cutting element. The bone plate and the trajectory control sleeve, when mutually engaged, are configured to cooperate to guide the cutting element to form the access channel with a prescribed trajectory from the anterior entry to the prescribed posterior opening. 
         [0022]    Embodiments of a method for prescribing of the point of anterior entry and the channel trajectory toward the posterior opening are typically provided by a physician who observes the cervical spine of the patient radiographically. From such observation of patient anatomy and the site of pathological interest, the physician prescribes a trajectory according to a cranio-caudal axis and a medial lateral axis with respect to a point of entry on the anterior surface of vertebral body. Such radiographic observation may occur before the attachment of the bone plate, to be summarized below, and/or after the attachment of the bone plate. 
         [0023]    Returning to summarizing the system for forming the access channel, some embodiments include fixation elements to secure the bone to the anterior surface of the vertebral body. The bone plate may include openings to accommodate fixation elements to secure the bone plate to the anterior surface of the vertebral body. In some embodiments, the bone plate and fixation elements are configured of a biocompatible material. In some embodiments, the bone plate and the fixation elements have a composition and structure of sufficient strength that that the bone plate may be permanently implanted. 
         [0024]    Embodiments of the trajectory control sleeve may be configured to direct the bone cutting tool on a trajectory prescribed by the method above, the prescribed trajectory being an angle according to a cranio-caudal axis and a medial lateral axis with respect to a reference plane tangential to the access channel entry on the anterior surface of vertebral body. 
         [0025]    Embodiments of the bone plate provide a reference plane such that the trajectory control sleeve, when secured to the bone plate, may be configured with a range of angles formed on two axes with respect to the plane of the bone plate, a cranio-caudal axis and a medial lateral axis, the range of the angles varying between about 1 degree and about 30 degrees from an angle perpendicular to the plate. In typical embodiments, the range of the angles varies between about 10 degrees and about 30 degrees from the perpendicular angle. In some embodiments, the system includes a plurality of trajectory control sleeves, the sleeves varying in regard to angles formed with respect to a plane represented by the bone plate when secured thereto, the angles ranging between about 10 degrees and about 30 degrees cranio-caudally from a perpendicular angle. 
         [0026]    In some embodiments, the trajectory control sleeve and the bone plate have mutually-engageable features that orient the engagement of the trajectory control sleeve on the bone plate in a configuration that allows the trajectory control sleeve to guide the cutting tool into the vertebral body with the prescribed trajectory. And in some embodiments, the trajectory control sleeve includes a contact surface for engaging a corresponding surface on the bone cutting tool, the surfaces configured so as to limit the penetration of the cutting tool into the vertebral body to a prescribed depth. 
         [0027]    In some embodiments, the posterior surface of the bone plate includes one or more penetrating elements configured to impinge into the vertebral bone tissue to improve fixation and resist the torsional forces associated with bone cutting procedures. In some embodiments, the bone plate includes an anatomically-orienting feature to establish the position of the bone plate relative to the medial centerline of the vertebral body. In some embodiments, the bone plate includes a biocompatible material. And in some embodiments, at least a posterior surface of the bone plate is of sufficiently porous composition to support in-growth of bone. 
         [0028]    In various embodiments, the bone-cutting tool is any of a drill, a reamer, a burr, or cylindrical cutting tool, such as a core cutter or a trephine. In some of these embodiments, the cutting element of the bone-cutting tool has a cutting diameter of between about 5 mm and about 7 mm. 
         [0029]    As noted above, embodiments of the implantable bone repair device have an external geometry complementary to the internal geometry of the access channel. These bone repair device embodiments may be sized to be insertable through an opening of the bone plate, the opening also being sized to receive the bone cutting element. In some embodiments, the bone repair device includes an abutting surface configured to engage a corresponding surface of the bone plate through which it is implanted, the engagement of these surfaces adapted to prevent the bone repair device from penetrating too deeply into or through the access channel of the vertebral body. In some embodiments, the bone repair device includes receiving features in or on its anterior surface configured to accommodate the attachment of an insertion tool. 
         [0030]    In some of these embodiments, bone repair device and the bone plate have mutually engageable orientation and locking features. In various embodiments, the locking engagement results from the application of an axial force to snap the locking feature into a corresponding retaining feature of the bone plate. In other embodiments, the locking engagement results from the application of a torsional force to engage the locking feature into a corresponding retaining feature in or on the bone plate. 
         [0031]    In some embodiments of the surgical system the bone repair device comprises a porous cage with a porosity sufficient to permit through movement of biological fluids, such as blood, and bone cells. The composition of the porous cage portion of the device may include any of a polymer, a metal, a metallic alloy, or a ceramic. An exemplary polymer may polyetheretherketone (PEEK), which may be present in the form of PEEK-reinforced carbon fiber, or hydroxyapatite-reinforced PEEK. In some embodiments of the bone repair device with a porous cage, the porous cage device includes a closeable opening through which harvested bone material (such a native bone from the access channel site) may be passed. And in some of these embodiments, the porous cage device includes a closeable cap configured to increase pressure on the harvested bone within the cage as the cap is closed. Further, some embodiments include an internal element adapted to enhance compressive force applied to the contents of the porous cage upon application of compressive force to the cage, such force inducing extrusion of harvested bone and blood from within the cage through its porous structure to the external surfaces of the cage. 
         [0032]    Some embodiments of the surgical system include a trajectory and depth visualization device. In some of these embodiments, the trajectory and depth visualization device includes a radio-reflective feature so as to confirm the location of the bone plate device on the appropriate vertebral body and to facilitate the extrapolation of the projected trajectory of the bone cutting tool using a radiographic image. In some embodiments, the trajectory and depth visualization device includes visual markings to indicate the distance from the point of contact with the vertebral body and cutter penetration control feature on the bone cutter guide device. 
         [0033]    A method for performing a procedure through a vertebral body overlaying a site in need of a medical procedure includes attaching the bone plate on the anterior surface of the vertebral body, engaging the trajectory control sleeve to the bone plate, inserting a bone cutting tool through the trajectory control sleeve, and forming an access channel body by removing bone with the bone cutting tool (the channel having a centerline co-incident with the centerline of the trajectory control sleeve through the vertebral), disengaging the trajectory control sleeve from the bone plate, and performing the medical procedure through the open space provided by the access channel and the opening on the posterior surface of the vertebral body. 
         [0034]    The access channel follows a prescribed trajectory from an anterior entry point to a prescribed opening on a posterior surface of the vertebral body in the locale of the site in need of the medical procedure. The prescription for the points of entry and exit and the vectors of the access channel are determined by radiographic observations and measurements, as summarized above. In some embodiments of the method, forming the access channel includes forming the channel with a constant, circular cross-section along a single, straight axis aligned with the trajectory control sleeve. 
         [0035]    Before engaging the trajectory control sleeve to the bone plate, the method may include selecting the sleeve to be used in the procedure such that when the sleeve and the bone plate are engaged, the sleeve has an angular orientation relative to the bone plate that is consistent with the prescribed trajectory of the access channel. Further, before attaching the bone plate to an anterior vertebral surface, the method may include exposing one or more vertebral bodies in a spinal column by anterior incision. Further still, after performing the medical procedure, the method may include leaving the bone plate attached to the vertebral body. 
         [0036]    In some embodiments of the method, after engaging the trajectory control sleeve to the bone plate, the method may include inserting a radiopaque locating device into the trajectory control sleeve device, radiographically observing the locating device and determining therefrom an extrapolated trajectory of the access channel toward the posterior surface of the vertebral body, and verifying that the extrapolated trajectory is consistent with the prescribed trajectory such that the point of exit at the posterior surface is proximal to the targeted site of interest. 
         [0037]    In some embodiments of the method, after engaging the trajectory control sleeve to the bone plate, the method may include inserting a depth-measuring device into the trajectory control sleeve device to establish an optimal depth of penetration of the bone-cutting tool into the vertebral body, the depth being influenced by the disposition of the bone plate against a variable topography of the anterior surface of the vertebral body. 
         [0038]    In some embodiments, after the completing the medical procedure through the access channel, the method further includes repairing the access channel with an implantable bone repair device, the device having an external geometry complementary to the internal geometry of the channel. In typical embodiment of the method, repairing the access channel includes implanting the bone repair device through the bone plate and into the channel. And in some of these embodiments, the method includes securing a proximal portion of the bone repair device to the bone plate. 
         [0039]    In some embodiments of the method, repairing the access channel includes in-growing bone from the vertebral body into at least a portion of the surface of the bone repair device. And in some embodiments, repairing the access channel includes stimulating bone growth within the bone repair device by providing an osteogenic agent within the repair device. 
         [0040]    In some embodiments of the method, repairing the access channel includes placing a portion of harvested native bone tissue within a bone repair device that comprises a porous cage. In these embodiments, the method may further include allowing or promoting intimate contact between the bone tissue within the bone repair device and bone tissue of the vertebral body. The method may further include perfusing at least some bone tissue or bone-associated biological fluid from the bone repair device into the vertebral body. Still further, the method may include healing together the harvested native bone tissue within the bone repair device and bone tissue of the vertebral body. 
         [0041]    In some embodiments of the system, the bone plate and the trajectory control sleeve are an integrated or integrally-formed device. In this embodiment, thus the system includes a bone cutting tool with a cutting element and an integrated device comprising a bone plate portion and trajectory control sleeve portion. The bone plate portion is configured to be secured to an anterior surface of the vertebral body and has an opening sized to receive the cutting element. The trajectory control sleeve portion has a cylinder configured to receive the cutting element of the bone cutting tool, and the integrated device is configured to guide the bone cutting tool to form the access channel with a prescribed trajectory from the anterior entry to the prescribed posterior opening. 
         [0042]    A method for performing a procedure through a vertebral body overlaying a site in need of a medical procedure with the integrated device summarized above includes attaching the integrated device on an anterior surface of the vertebral body, inserting a bone cutting tool through the trajectory control sleeve portion of the device, forming an access channel through the vertebral body by removing bone with the bone cutting tool, the access channel prescribed as summarized above, disengaging the integrated device from the bone plate, and performing the medical procedure through the access channel and the opening on the posterior surface of the vertebral body. 
         [0043]    In some embodiments of the system and method, the bone plate or integrally formed bone plate portion does not lie directly over the anterior entry location for the access channel. Rather, the bone plate or bone plate portion is attached to the anterior surface of the vertebral body adjacent to the entry location, and supports a trajectory control sleeve or sleeve portion which may be located adjacent to the entry location. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0044]      FIG. 1  is a view of an implantable bone plate device viewed from an anterior perspective. 
           [0045]      FIG. 2  is a view of an implantable bone plate device viewed from a posterior perspective. 
           [0046]      FIGS. 3A and 3B  provide views of a trajectory control sleeve attachment. 
           [0047]      FIG. 3A  shows a trajectory control sleeve in a side view. 
           [0048]      FIG. 3B  provides a side cross-sectional view of the trajectory control sleeve, showing how the angle of the sleeve relative to its base forms an asymmetrical opening in the base. 
           [0049]      FIG. 3C  shows the trajectory control sleeve from a proximally-directed perspective. 
           [0050]      FIG. 4  is an anterior perspective of the trajectory control sleeve mounted to an implantable bone plate. 
           [0051]      FIG. 5  is a lateral view of the trajectory control sleeve mounted to an implantable bone plate. 
           [0052]      FIG. 6  is a perspective view showing an implanted bone plate screwed a vertebral body and with a trajectory control sleeve mounted thereon. 
           [0053]      FIG. 7  is an anterior view showing an implanted bone plate screwed to a vertebral body and a trajectory control sleeve mounted thereon. 
           [0054]      FIG. 8  is a lateral view showing an implanted bone plate screwed to a vertebral body and with a trajectory control sleeve mounted thereon. 
           [0055]      FIGS. 9A-9B  show various views of a trajectory pin and a drill depth gauge. 
           [0056]      FIG. 9A  is a perspective view of a trajectory pin and a drill depth gauge assembled together 
           [0057]      FIG. 9B  is a perspective view of an embodiment of the depth gauge sub-assembly. 
           [0058]      FIG. 10  is a lateral view of the trajectory pin assembly shown in  FIG. 9A  engaged in a trajectory control sleeve. 
           [0059]      FIG. 11  is a cross sectional view showing a trajectory pin in full engagement with vertebral bone and a trajectory control sleeve. 
           [0060]      FIG. 12  is an anterior perspective view of a trajectory pin and depth gauge engaged within a trajectory control sleeve. 
           [0061]      FIG. 13  is a cross section view showing a bone drill in position relative to a bone plate and trajectory control sleeve prior to cutting bone tissue. 
           [0062]      FIG. 14  is a perspective view of a bone plate after drilling has been completed and the trajectory control sleeve has been disengaged from the implanted bone plate. 
           [0063]      FIG. 15  is a perspective view of a spinal repair implant in the pre-insertion position relative to the implanted bone plate. 
           [0064]      FIG. 16  is a perspective view of a spinal repair implant installed into an access channel through an implanted bone plate. 
           [0065]      FIG. 17  is an anterior perspective view of an alternate embodiment of an implantable bone plate. 
           [0066]      FIGS. 18A and 18B  are views of the trajectory control sleeve mounted on the bone plate embodiment of  FIG. 17 .  FIG. 18A  shows the trajectory control sleeve and bone plate from distally directed perspective. 
           [0067]      FIG. 18B  shows the trajectory control sleeve and bone plate from a side view. 
           [0068]      FIG. 19  shows an implantable bone plate in situ on a vertebral surface. 
           [0069]      FIG. 20  shows a perspective view of an implantable bone plate and trajectory control sleeve in situ on the vertebra surface. 
           [0070]      FIG. 21  shows a drill cutter engaging vertebral bone tissue through the trajectory control sleeve. 
           [0071]      FIG. 22  shows an access channel through an implanted bone plate and into vertebral bone tissue. 
           [0072]      FIGS. 23 and 24  show an intra-vertebral repair device engaging vertebral bone through the bone plate.  FIG. 23  shows the repair device being held by a surgeon immediately prior to inserting into the access channel. 
           [0073]      FIG. 24  shows the surgeon&#39;s finger pressing the repair device through the bone plate and into the access channel. 
           [0074]      FIGS. 25A and 25B  show views of an intravertebral repair device embodiment with a proximal abutting surface orthogonal to the body of the device. 
           [0075]      FIG. 25A  shows the device from a proximally-directed perspective. 
           [0076]      FIG. 25B  shows the device of  FIG. 25A  from a distally-directed perspective. 
           [0077]      FIGS. 26A and 26B  show views of an intravertebral repair device embodiment with a proximal abutting surface canted with respect to main axis of the body of the device.  FIG. 26A  shows the device from a side view. 
           [0078]      FIG. 26B  shows the device of  FIG. 26A  from a proximally-directed perspective. 
           [0079]      FIGS. 27A and 27B  show views of an intravertebral repair device embodiment with a convex external profile, wider in its central portion, narrower at proximal and distal ends.  FIG. 27A  shows the device from a proximally-directed perspective. 
           [0080]      FIG. 27B  shows the device of  FIG. 27A  from a distally-directed perspective. 
           [0081]      FIG. 28  shows the primary components of an exemplary system associated with the creation and repair of the intra-vertebral access channel. 
           [0082]      FIG. 29  shows a typical access channel that may be produced with the inventive systems and methods. 
           [0083]      FIG. 30  shows a cross sectional view of an access channel being formed in a vertebral body with a hollow cutting tool, a trephine, which forms an access channel with a removal bone plug. 
           [0084]      FIG. 31  shows an exploded view of a bone repair device with a porous body configured to hold bone tissue, and to allow compression of the tissue upon closing the porous body. 
           [0085]      FIG. 32  shows a cut away cross sectional view of the bone repair device of  FIG. 31  in assembled form. 
           [0086]      FIG. 33  shows an external view of the assembled bone repair device of  FIG. 33  with bone tissue and associated fluid being extruded under pressure. 
           [0087]      FIG. 34  shows an alternative embodiment of an assembled bone repair device with a porous body and with an internal pressure-amplifying feature. 
           [0088]      FIG. 35  shows a bone repair device with a porous body containing bone tissue poised in a position from where it is about to be implanted in an access channel within a vertebral body. 
           [0089]      FIG. 36  shows the bone repair device of  FIG. 35  implanted in the vertebral body, and locked into a bone plate. 
           [0090]      FIG. 37  shows a lateral cross sectional view of a bone repair device with a porous body containing bone tissue, in situ, within an access channel in a host vertebral body. 
           [0091]      FIGS. 38-40  show various views of a trajectory control tool according to another embodiment. 
           [0092]      FIGS. 41-45  show various views of a repair implant according to another embodiment. 
           [0093]      FIGS. 46-59  show various views of a surgical procedure for creating, using, and repairing a transcorporal access channel using the trajectory control tool of  FIGS. 38-40  and the repair implant of  FIGS. 41-45 . 
           [0094]      FIGS. 60-62  show various views of a repair implant according to yet another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0095]    An inventive surgical system and associated method of use are provided for transcorporeal spinal procedures that create and use an anterior approach to an area in need of surgical intervention, particularly areas at or near a site of neural decompression. Removal or movement of a source of compressing neural pathology is achieved via a surgical access channel created through a single vertebral body instead of through a disc space or through an uncovertebral joint (involving 1 or 2 vertebrae). The access channel has a specifically prescribed trajectory and geometry that places the channel aperture at the posterior aspect of the vertebra in at or immediately adjacent to the targeted compressing pathology, thus allowing the compressing neural pathology to be accessed, and removed or manipulated. The access channel is formed with precise control of its depth and perimeter, and with dimensions and a surface contouring adapted to receive surgical instruments and an implanted bone repair device. 
         [0096]    The channel may be used to access and operate on the compressing pathology, more particularly to remove or to move a portion or the whole of a herniated disc, an osteophyte, a thickened ligament, a tumor, a hematoma, a degenerative cyst, or any other compressing pathology. As a part of the procedure, the posterior longitudinal ligament posterior to the transcorporeal access channel may be opened or removed through the access channel, thereby permitting the visualization or removal of any compressing pathology otherwise obscured by the ligament. 
         [0097]    In some embodiments, the invention preserves native bone and disc tissue that is sacrificed by prior art procedures, and further preserves the natural motion of the vertebral joint. The procedure also preserves at least the anterior half of the vertebral endplate of the vertebral body upon which the cutting occurs. Removal or the movement of the compressing pathology can proceed even when a portion of the compressing pathology resides beyond the limits of the transcorporeal access channel. Further, removal of the compressing pathology may occur without inducing posterior or inward compression on the dura mater protective layer surrounding the spinal cord and exiting nerve roots, or exerting direct pressure on the spinal cord or exiting nerve roots. Also, the compressing pathology removal may occur without lacerating the dura mater protective layer surrounding the spinal cord and exiting nerve roots. 
         [0098]    Embodiments of the system and method also pertain to therapeutic occupation and repair of the vertebral body void created by making such an access channel. This repair is achieved by inserting an implantable vertebral repair device that has a conformation complimentary to the internal geometry of the access channel after the procedure is complete, and by securing the implant in the inserted position by means of a vertebral bone plate. The external surface of the vertebral repair device is in substantial contact with the internal surface of the access channel after insertion is complete, thereby substantially restoring structural and mechanical properties of the vertebrae. Such repair occurs without directly or indirectly inducing compression of underlying dura mater or neural structures. The repair further occurs without the subsequent anterior migration of the vertebral repair device, which could cause injury to soft tissue structures located anterior to the spine. 
         [0099]    In some embodiments, the implanted device has a bioabsorbable composition that allows replacement of the implant device by in-growth of native bone tissue, or which is incorporated into the native bone tissue. As a whole the system increases the objectivity of considerations associated with spinal surgery, reduces patient risk, and contributes to better and more predictable surgical outcomes. 
         [0100]    Various aspects and features of the invention will now be described in the context of specific examples and with the illustrations provided by  FIGS. 1-37 . 
         [0101]    A number of tools and instruments are included in or used within the system and methods described herein.  FIG. 28  shows some of these system elements: an implantable vertebral plate  100 , a cutting tool guide  200 , a confirmation device or depth gauge  300 , a collar  310  for the confirmation device, a cutting tool  400 , an implantable device  500 , and an implant locking device  600 . 
         [0102]    An implantable vertebral plate  100  is adapted to attach to the anterior surface of a vertebra. A trajectory control sleeve  200  is adapted to detachably mount the implanted bone plate  100  to establish the entry point, trajectory, and depth of an access channel created through the vertebral body. A confirmation device  300  is adapted to temporarily engage the cutter tool guide for the purposes of confirming placement of the trajectory control sleeve on the correct vertebra, for visualizing the projected trajectory of the bone cutting device, and for measuring the actual distance between the trajectory control sleeve and the anterior bone surface so as to accurately and predictably penetrate through the vertebra without impinging on the dura-mater or other neural tissue at the posterior aspect of the channel. The pin-shaped confirmation device  300  is typically radio-reflective or radiopaque, thus allowing confirmation of all geometries on a surgical radiograph taken prior to the excision of any tissue. 
         [0103]    A cutting tool  400  is generally adapted to remove bone material and create the vertebral access channel; the tool  400  has the precise cutting geometry necessary to produce the prescribed access channel geometry within the vertebral bone. The access channel provides various forms of advantage for aspects of procedures as described further below. 
         [0104]    A surgical cutting instrument is used to open or partially remove the posterior longitudinal ligament which can obscure a view of the pathology of interest, but becomes observable by way of the access channel. A cutting tool used to remove osteophytes (bone spurs) at or adjacent to the base of the vertebral body can be approached by way of the access channel proximal to the neural elements to be decompressed. An instrument for grasping or moving herniated disc material or other compressing pathology can be provided access to the site located at or near the base of the access channel. 
         [0105]    An implantable bone repair device  500  is adapted repair the vacant vertebral volume created by the formation of the access channel. 
         [0106]    An implant locking device  600  is adapted to retain the implant in the desired position. The locking device is adapted to positively engage the anterior surface of the repair implant and engagably lock it in place with respect to the implanted bone plate device  100 . Fasteners such as elements  600  and  900  (seen in later figures) are applied to retain a bone plate or locking cap (see in other figures) in a desired position. 
         [0107]    Each of these aforementioned system elements and their role in surgical procedures on the spine are described in further detail below. 
         [0108]      FIGS. 1 and 2  show anterior and posterior views, respectively, of an implantable transcorporeal bone plate device  100  with a first or anterior facing surface  101  and a second or posterior facing surface  102 , the posterior facing surface being configured to be proximal or in contact with the anterior surface of a vertebral body after implantation. The device further has one or more holes  103  that form an aperture between surfaces  101  and  102  to accommodate and secure retention screws there to secure the device  100  to vertebral bone. 
         [0109]    Embodiments of implantable bone repair described and depicted herein are may include a multiple number of orifices, as for example, for inserting attachment elements, or for viewing, that have various sizes and typically are circular or ovular in form. These are merely exemplary forms and profiles of openings which may vary depending on particulars of the application of the device, such that size and profile may vary, and for example, by taking the form of any of circular, trapezoidal, multilateral, asymmetrical, or elongated openings. 
         [0110]    The device also has a passage  104  for receiving and detachably-engaging a bone cutting guide device such as a drill or ream. The device  100  further may have one or more engaging features  105  configured to receive and engage a corresponding feature on the trajectory control sleeve in a manner that prevents relative motion of the trajectory control sleeve and its accidental disengagement from the implanted bone plate. The device may have one or more protrusions  106  on the posterior surface ( FIG. 2 ), the protrusions being adapted to impinge into or through the cortical bone so as to increase the stability of the implant on the bone and to allow for temporary placement of the device prior to insertion of the bone screws through the opening  103 . Protrusions  106  further act to stabilize the bone implant and to transfer loads around the vertebral access channel after a surgical procedure is complete, thereby further reducing the risk of bone fractures or repair device expulsion. 
         [0111]      FIGS. 3A-3C  show a side view and perspective view, respectively, of an embodiment of a trajectory control sleeve  200  for a bone cutting tool, a rotary cutting tool, for example, such as a drill, burr, reamer, or trephine.  FIG. 3A  shows a trajectory control sleeve in a side view, while  FIG. 3C  shows the trajectory control sleeve from a proximally-directed perspective. The trajectory control sleeve  200  has an internal cylinder  202  there through to allow passage of a bone-cutting tool, such as a drill or trephine, and to establish and control the angle α of penetration of the drill through a vertebral body. As seen in  FIG. 3B  the angle α refers to the angular difference from a right angle approach with respect to the plane formed by an implantable bone plate  100  to which the trajectory control sleeve is engaged. More specifically, angle α can represent a compound angle according to a cranio-caudal axis and a medial lateral axis with respect to a reference plane tangential (such as would be represented by an implanted bone plate) to the access channel entry on the anterior surface of vertebral body. The angle α is prescribed by a physician by making use of radiographic images of the spine that focus on the target vertebrae and the underlying pathology that are the subject of surgical or diagnostic interest. Such procedures are typically performed prior to surgery, and they may be repeated after the bone plate is attached to the surgical site.  FIG. 3C  provides a cross sectional view of an exemplary control sleeve  200 , which shows the tilt of the annular ring  203  in accordance with angle α, and the consequent off-center opening at the base of the trajectory sleeve, which generally aligns with the base of the bone plate when the two components are engaged. 
         [0112]    In some embodiments of the system and method, a transcorporal access channel is formed using a trephine type device such as those provided by Synthes, Inc (West Chester Pa.), which offers particular advantages. The trephine device produces a cylindrical channel through the vertebral bone while maintaining the core to be removed in an intact state. The core can be removed from the trephine after the tool itself has been removed from the vertebral body, and the bone tissue can be subsequently re-used as graft volume after the surgical procedure is completed. 
         [0113]    Trajectory control sleeve  200  has a surface  201  adapted to be in intimate contact with and be co-planar to an anterior facing surface  101  of a bone plate implant device  100  (after engaging the device, as in  FIG. 4 ) so as to assure that the axial distance d is well established and controlled. The trajectory control sleeve  200  further has an annular abutting surface  203  surrounding the opening of the internal cylinder  202 , the surface being adapted to positively engage a corresponding feature such as a flange or collar of the drill so as to prevent its over-penetration into the vertebral body. This abutment may be internal or external to the guide device as shown in  FIG. 4  and  FIG. 3A  respectively. Trajectory control sleeve  200  also has an engaging and interlocking feature  204  adapted to detachably-engage a corresponding feature  105  (see  FIG. 5 ) on the implantable bone plate  100 . The trajectory control sleeve  200  is further generally adapted to protect surrounding vascular and soft tissue from accidental injury or cutting by providing a solid protective sheath around the sharp edges of the drill while it is operating. 
         [0114]      FIGS. 4 and 5  show a perspective view and side view, respectively, of trajectory control sleeve  200  and an implantable bone plate  100  in their mutually interlocked positions.  FIG. 4  shows the internal cylinder  202  for providing access, guiding and controlling the penetration of a drill into vertebral bone.  FIG. 4  further shows an alternate embodiment of the device that has an abutting surface  203 , in which the abutting surface is internal to the trajectory control sleeve.  FIG. 5  shows the planar engagement of the anterior surface of an implanted bone plate  101  with the corresponding surface  201  of the trajectory control sleeve. This engagement establishes a reference plane  210  from which angle α and distance d are controlled and referenced relative to the vertebral body.  FIG. 5  further shows the engagement of the detachable locking features  205  of the trajectory control sleeve and of the bone plate  105 . 
         [0115]      FIGS. 6-8  relate to the placement of a mutually-engaged bone plate  100  and a trajectory control sleeve  200  to a vertebral body  230 , in preparation for creating an access channel through the vertebral body.  FIG. 6  provides a surface perspective view of bone plate  100  in an implanted position on a vertebral body  230 , the plate secured by a bone screw  900 , and further shows trajectory control sleeve  200  in its engaged position on the bone plate  100 .  FIG. 7  shows an anterior view of a bone plate  100  and trajectory control sleeve  200  mutually engaged and, the engaged assembly in it installed position on vertebral body  230 . A bone screw  900  is inserted at or near the medial centerline  231  of the vertebral body  230 , thus positioning the center point  220  of the trajectory control sleeve cylinder at a prescribed distance l from the centerline. As seen in  FIG. 8 , an angle β is the compliment to angle α shown in  FIG. 5 . After installation of the bone plate implant  100  on a vertebral body  230 , the reference plane  210  may be delineated relative to the vertebral body  230  and as a baseline reference for the angle and depth of drill penetration into the vertebral body. 
         [0116]      FIGS. 9A and 9B  show a pin or plug type confirmation device  300  used for confirming vertebral position prior to excision of bone or other tissue and a collar  310  into which the confirmation device is inserted. A standard procedure in spinal surgery is to insert a radiographically reflective screw or pin into the vertebral body and to take an x-ray of the cervical spine prior to beginning any procedure so as to assure that the procedure is being performed at the correct vertebral level. In the embodiment described the confirmation device  300  is slidably inserted within the internal diameter of the control sleeve  200  and progressed axially therethrough until the proximal end of the device  300  is in contact with the anterior surface of the vertebral body. A radiographic image is taken inter-operatively and reviewed prior to the excision of any vertebral bone tissue. The examination includes an extrapolation of the trajectory through the vertebral body so as to confirm that the actual point of exit at the posterior surface of the vertebra is at the surgically prescribed location. Further, the axial distance from the both the anterior and/or posterior surfaces of the vertebra are measured and used as references to control the depth of bone cutting necessary to produce the access channel and to prevent over penetration into the dura mater or neural tissue. In some instances the device  300  may be used during the bone cutting procedure as a checking device to determine the actual progression of the channel across the vertebra. 
         [0117]      FIG. 9B  shows a trajectory confirmation pin  300  and a collar  310  that slidably-engages the external diameter of the pin by way of features  320  that engage complementary features  321  on the internal diameter of the collar. In this exemplary embodiment, the trajectory pin features  320  are convexities that are complementary to concave collar feature  321 . Collar  310  can slide axially along the length of the pin diameter  320  and frictionally-engage the pin diameter in a manner that requires an axial force to be applied to the collar to induce axial movement. Collar  310  has a surface of engagement feature  330  that is adapted to make intimate contact with the annular surface  203  of the trajectory control sleeve when the pin is inserted into the trajectory control sleeve. Once surfaces  203  and  330  are engaged, insertion force F ( FIG. 9A ) applied by a surgeon causes pin  300  to travel axially through the internal diameter of collar  340 , increasing the distance L 2  between point  350  on the tip of the pin and the control surface  330  of the collar  310 . 
         [0118]      FIGS. 10-12  relate to the use of a trajectory confirmation pin  300 , a collar  310 , and trajectory control sleeve  200  in the context of a bone plate  100  in place, as implanted in a vertebral body  230 . An embodiment of a pin device  300  is temporarily inserted into the internal cylinder of the trajectory control sleeve  200  and an x-ray is taken. The x-ray confirms the location of the vertebral body  230  and an anterior-to-posterior extrapolation along the centerline of the device through the image of vertebral body indicates the trajectory of the drill or cutting tool and the projected point of exit at or near the posterior longitudinal ligament. Angular and distance measurements may be made using the radiograph, and if adjustments are required, the surgeon disengages the trajectory control sleeve and installs another device with the desired geometry. 
         [0119]      FIG. 11  shows the confirmation pin  300  at its maximum depth of penetration through the transparently rendered trajectory control sleeve  200  and bone plate implant  100 . In this position, tip  350  of the pin device is in intimate contact with the surface of the vertebral bone  230 . Because of the mechanical engagement of the collar  310  on the external surface, the collar remains in position relative the bone-contacting tip of the pin  350 . Upon removal of the pin, distance L 2  (see  FIG. 9A ), as measured between the collar surface  330  and the pin contact tip  350 , provides a reference dimension with which the penetrating depth of the bone drill can be controlled by setting a mechanical stop that engages the annular surface  203  of the trajectory control sleeve. For ease of use, the surface of the confirmation pin  300  may have linear graduations. 
         [0120]      FIG. 13  shows a bone cutting tool  400 , such as a drill, burr, or reamer, inserted through the trajectory control sleeve  200  and the bone plate implant  100  with the tip of the cutting tool  420  at the initial point of contact on the vertebral body. Cutting tool  400  has a mechanical stop  450 . The distance D 4  from the drill tip  420  to the lower surface  430  of the drill stop  450 , is a prescribed dimension equivalent to the measured distance L 2  (see  FIG. 9A ) plus the desired depth of penetration into the vertebral body, such depth being established by the surgeon through radiographic analysis. 
         [0121]      FIG. 14  shows a surgical access channel  470  in a vertebral body  230 , as viewed through the bone plate implant  100  after drilling has been completed and the trajectory control sleeve has been removed from the plate. After removal of the trajectory control sleeve, a neural decompression or other surgical procedure is performed through the access channel. On completion of the procedure, an intra-vertebral bone implant  500  is inserted ( FIGS. 15 and 16 ) into access channel  470  to fill an close it, restore mechanical strength and stability to the host vertebral body  230 , and to provide a medium within the vertebral body suitable for osteogenesis. 
         [0122]    In some embodiments of the invention, the intra-vertebral access channel  470  ( FIG. 14 ) of an implantable bone plate has a diameter of about 5 mm to about 8 mm. This size creates a surgical field that is sufficiently open enough for typical procedures, and is sufficiently large enough to minimize the possibility that the access channel will not intersect the area of neural compression. In some embodiments, the angle of entry a provided by the access channel is about 10-30 degrees, with the center of the point of entry being generally at mid-point on the cranio-caudal length of the vertebra. While these dimensions are typical, alternative embodiments of bone plate implants may have varying widths and geometries so as to accommodate wide anatomical variations. In various alternative embodiments, trajectory control sleeve devices also may include a wide range of angles and depths for the same reason. 
         [0123]    With a combination of the angle of entry, the point of entry into the vertebral body, and the size of drill used to create the access channel  470 , some embodiments may result in a penetration of the posterior disc space in the posterior 20%-30% of the disc volume  480 , leaving the vertebral end plate  490  and the native disc tissue  495  substantially intact.  FIG. 29  illustrates a typical access channel  470  that may be formed using a 6 mm drill diameter, about a 10 degree angle of entry, with an entry point on the cranio-caudal centerline of the vertebral body. 
         [0124]      FIG. 15  shows an intra-vertebral implantable bone repair device  500  positioned for implantation within the vertebra  230  through the bone plate implant  100 . Various embodiments and features of a bone repair device are described in U.S. Provisional Patent Application No. 60/990,587 of Lowry et al. (filed on Nov. 27, 2007, entitled “Methods and systems for repairing an intervertebral disk using a transcorporal approach”), which is incorporated herein in its entirety by this reference. In the embodiment shown, implant  500  has an abutting surface  520  adapted to engage with a corresponding surface of the bone plate implant. This arrangement prevents excess penetration of the implant through the access channel and prevents the implant from compressively engaging neural elements.  FIG. 16  shows the implantable device  500  in the final installed position relative to the bone plate  100 . The device  500  has a locking mechanism  510 , such as a conventional bayonet mount, for engaging the bone plate in order to prevent migration of the implant within or out of the access channel. 
         [0125]      FIG. 17  shows an alternative embodiment  620  of an implantable bone plate as previously described and shown in  FIGS. 1 and 2 . In this present embodiment, bone plate  620  has a larger lateral dimension to accommodate particular anatomies that may be encountered, including those of patients, for example, with small stature, degenerative bone conditions, or osteophytes or other abnormalities that may require alternate fixations. To assure accurate location of the device relative to the medial centerline of the vertebra, implant device  620  may include a viewing port  650  or some other positioning indicator.  FIGS. 18A and 18B  show anterior perspective and side views, respectively, of the engagement of a trajectory control sleeve  200 , as previously described, with the alternative bone implant device embodiment  620 . 
         [0126]    In another alternate embodiment, an implantable bone plate and bone cutting device may be formed as a unitary device and temporarily fixed to the vertebral body. In this embodiment an intra-vertebral access channel is created using the temporarily implanted device; subsequently, the device is removed, the surgical procedure performed, and the access channel repaired using the intra-vertebral implant as previously described. In this embodiment, a bone cutting device may have a least two cutting diameters or widths, the first being that necessary to produce the access channel, the second being a larger diameter configured to remove an annulus of bone on the anterior vertebral surface so as to provide an abutting surface against which the implant would rest in order to prevent over-penetration of the intra-vertebral repair implant within the vertebra. 
         [0127]      FIGS. 19-24  show exemplary devices being put to exemplary use to evaluate the practical viability, fit, and the functionality of methods for their use.  FIG. 19  shows an implantable bone plate  100  in situ on a vertebral surface  230 .  FIG. 20  shows a perspective view of the implantable bone plate and trajectory control sleeve  200  in situ on the vertebral surface.  FIGS. 21-24  include a view of surgeon&#39;s finger to show scale and feasibility of manual manipulation of elements of the inventive system.  FIG. 21  shows a bone cutting tool  400  engaging vertebral bone tissue through the trajectory control sleeve  200 .  FIG. 22  shows an access channel  470  through the implanted bone plate and into vertebral bone tissue.  FIG. 23  shows an intra-vertebral repair device  500  being readied for engaging vertebral bone through the bone plate  100 . 
         [0128]      FIGS. 25A-27B  show embodiments of alternative external geometries of the intra-vertebral implantable devices  500  as may appropriate for particular patients or procedures.  FIGS. 25A and 25B  show views of what may be considered a default embodiment of an intravertebral repair device with a proximal abutting surface orthogonal to the body of the device.  FIG. 25A  shows the device from a proximally-directed perspective, while  FIG. 25B  shows it from a distally-directed perspective. 
         [0129]      FIGS. 26A and 26B  show and embodiment wherein abutting surface  520  is canted at an angle not orthogonal to the central axis of the device  500 .  FIGS. 27 a    and  27   b  show an intra-vertebral implant device  500  with a convex external profile where dimension D 4  is nominally larger than the internal diameter of the access channel so as to compressively engage the cancellous bone tissue. Such a compressive engagement can improve the interference fit of the device therein and to inter-diffuse cancellous bone tissue within the implant volume to improve osteogenesis. 
         [0130]      FIG. 28  shows an assemblage of some of these system elements, and was described at the outset of the detailed description; shown is an implantable vertebral plate  100 , a cutting tool guide  200 , a confirmation device or depth gauge  300 , a collar  310  for the confirmation device, a cutting tool  400 , an implantable device  500 , and an implant locking device  600 .  FIG. 29  provides an exemplary embodiment of the invention that was discussed earlier in the context of the formation of an access channel, in conjunction with associated description of  FIGS. 14-16 . 
         [0131]    Implantation of the patient&#39;s own bone tissue (an autologous graft) is a generally advantageous approach to repairing bone, as autologous grafting typically yields high success rates and a low rate of surgical complications. Accordingly, some embodiments of the invention include using core bone tissue harvested from the fanning of the access channel, and implanting the plug, intact, in the form of bone repair graft. An advantage to recovering and making use of bone derived from the channel includes the absence of a need to harvest bone from a second site. Embodiments of the invention, however, do include harvesting bone from secondary sites on the patient, such as the iliac crest, as may be appropriate in the practice of the invention under some circumstances. In some embodiments, for example, it may be advantageous to supplement bone derived from the access channel with bone from other sites. In still other embodiments, under various clinical circumstances, it may be appropriate to make use of bone from donor individuals. Bone from other autologous sites or other donor individuals may be used as a repair device in the form of an appropriately formed plug, or bone may be fragmented or morselized, and packaged as a solid plug, or bone may be included as a preparation provided in a porous cage, as described further below. 
         [0132]    Some embodiments of methods provided make use of a trephine type bone cutting system, as noted above. With a trephine bone cutting system, the external diameter of the bone tissue core is about equal to the internal diameter of the trephine device, while the internal diameter of the access channel is about equal to the external diameter of the device. Thus, a trephine-derived bone plug from forming the access channel provides an appropriately-sized piece to be inserted into the channel for repair and healing, but does not necessarily make intimate contact with the inside surface of the channel due to the width of the kerf created by the trephine. 
         [0133]    Optimal healing and recovery from implantation of bone material into an access channel occurs when there is an intimate or compressive engagement of the graft material with the vertebral bone tissue (substantially cancellous bone), as this intimate association provides for rapid blood profusion and bone healing while providing mechanical support during healing. Accordingly, an embodiment of the bone repair device provided herein includes a device with bone tissue inside a porous cage, as described in detail below. 
         [0134]    The porosity of the cage is a particularly advantageous feature for allowing cell to cell contact through the boundary of the device. To some degree, it may also allow cell migration, however the most advantageous factor in promoting rapid healing is cell to cell contact that initiates sites of tissue unification, which can then spread, stabilize a healing zone around the graft or bone repair device, and ultimately lead to effective fusion and integration of the graft within the host vertebral body. 
         [0135]    A porous cage, as provided by aspects of this invention, also has a compressibility, such that when the contents of the cage are subject to a compressive force, however transient and minimal, blood or plasma and bone cells that are present in the harvested cancellous bone are forced outward into the environment within and around the access channel site. Extrusion of biological fluid in this manner, advantageously packs bone tissue closer together within the cage, and bathes the periphery of the graft and the host-graft intersectional zone with a medium that is optimal for exchange of dissolved gas and nutrients that are critical in the initial stages of healing. Some embodiments of the invention include bathing the bone tissue preparation in a supportive liquid medium before implantation. Such bathing may occur prior to placing the bone tissue preparation in the porous cage and/or after placing the preparation in the cage. The liquid medium may be any appropriate cell culture medium, and may be further supplemented with biological agents, such as osteogenic agents or other growth factors. 
         [0136]    Embodiments of the implantable porous cage bone repair device, as provided herein, encapsulate the bone tissue contained therein, and provide mechanical stability to the access channel during healing. These embodiments compensate for the volumetric loss associated with the bone cutting process of the trephine and promote contact between the bone volume within the device and the surrounding vertebral bone tissue. The device, as a whole, and like other bone repair embodiments provided, cooperates with the implanted bone plate so that the orientation and penetration depth of the implant device within the access channel may be controlled. These forms of control assure that the device does not over-penetrate through the channel, thereby compressing the dura mater or neural elements within the vertebra, and assuring that the implanted device cannot migrate in an anterior direction out of the access channel. 
         [0137]    Exemplary embodiments of the porous cage device and associated method of use will now be described in further detail, and in the context of  FIGS. 30-37 . 
         [0138]      FIG. 30  provides a cross-sectional view of a vertebral body  809  with a bone plate  801  attached to the anterior bone surface  810 . Mounted on the bone plate is a trajectory control sleeve  802  cooperating with the bone plate  801  to establish and control the trajectory of a bone cutting tool  804  with a cutting surface  808  through the vertebral body to direct the trajectory of the formed access channel to a prescribed point of exit at the posterior surface of the vertebra  820 , in the locale of a site of medical interest. 
         [0139]    The depicted exemplary bone cutting tool  804  is a hollow bone cutting tool, a trephine, with an external diameter  805  selected to be complementary to the internal diameter of the trajectory control sleeve  802 , and to cooperate therewith so as to assure that the centerlines of the bone cutting tool and the trajectory control sleeve are substantially co-incident during the bone cutting process. The trephine  804  progresses through the vertebral body  820  from an anterior to posterior direction until the cutting surface  808  penetrates the cortical bone at the posterior surface of the vertebra proximal to the spinal cord  850 . Upon removal of the trephine from within the vertebral body, a core of bone tissue within the interior of the trephine is extracted from the wound opening, thus creating or exposing an open access channel from the anterior surface of the vertebral body to the neural elements and the prescribed site of medical interest immediately behind the posterior wall of the same vertebral body. 
         [0140]      FIG. 31  shows components of an exemplary bone repair device in a linearly exploded view from an external perspective. At the top, a cap  950  is above a vertebral bone core  860 ; the bone core is positioned for placement in a porous cage  900 .  FIG. 32  is a cross-sectional view of the fully assembled device  905 . According to aspects of the inventive method, the vertebral bone core  860  is placed within an implantable intravertebral bone repair device  900  with a porous wall, and encapsulated by a cap or closing element  950 . In this exemplary embodiment the cap has a screw thread  951  disposed to engage a mating thread  901  on the body  900  of the implantable device; the cap further has a compression element  952  disposed to exert a compressive force F on the bone graft core  860  when the cap is being closed on the body  900  of the repair device, and consequently inducing extrusion of native tissue within the device, through open pores  902  contained within the perimeter wall of the implant device. As described above, the bone tissue placed within the body of the repair device is not necessarily an integral bone plug intact from the trephine used to form the channel; the bone tissue may be a fragmented or morselized preparation, it may include bone from another site on the patient, and it may include bone from another donor. 
         [0141]      FIG. 33  provides an external perspective view of an assembled bone repair device  905 . This view captures a moment shortly after the cap  950  has been closed, and by such closing has increased the pressure on the bone tissue contained within the device. By virtue of this elevated pressure within the porous walled body  900 , bone core graft tissue and associated biological fluid are extruding through the porous perimeter wall. In some embodiments of the method, the cap  950  is closed on the porous body  900  of the repair device immediately prior to insertion of the assembled device  905  into the access channel within the host vertebral body, and in some embodiments of the method, the cap is closed after insertion of the porous body  900 , thereby forming the complete assembly  905  in situ. 
         [0142]      FIG. 34  shows a cross sectional view of an alternate embodiment of the porous body portion  900 ′ of an assembled repair device  905 ′ that includes an internal tissue expander feature  920  disposed to induce radial extrusion of the bone core tissue through the orifices. 
         [0143]      FIGS. 35 and 36  show similar views of the porous cage device embodiment  905  as were provided earlier by  FIGS. 15 and 16  for solid bone repair device  500  embodiments.  FIG. 37  shows a cross sectional view of the implanted device  905  within an intravertebral access channel  470 . Upon completion of the surgical procedure through the access channel, the bone repair implant assembly  905  (containing the harvested bone graft core  860 ) is introduced into the transcorporal access channel through the aperture  830  in the implanted bone plate device  100 . In one exemplary embodiment, the bone repair assembly  905  has an abutting surface disposed to cooperate with a mating surface of engagement  871  on the bone plate implant. The completed mating of the bone repair assembly  905  with the bone plate  100  prevents the distal tip  890  of the implant assembly from penetrating into the spinal cord volume posterior to the vertebral body. 
         [0144]    The implantable repair device assembly  905  further has an orientation and locking feature  951  disposed to engage a mating feature  950  on the implantable bone plate  100  so as to control the radial orientation of the implant with respect to the bone plate and to lockably engage the bone repair implant device with the bone plate implant so as to prevent migration or expulsion of the bone repair implant assembly  905  out of the access channel. Such radial orientation of the implant relative to the access channel may be particularly advantageous when the bottom or distal end of the repair device body  900  is formed at an angle (not shown) to completely fill the access channel. 
         [0145]    As a consequence of the implantation of the bone repair assembly  905  within the access channel, the general mechanical integrity of the vertebral body has been restored, the internal void of the access channel has been filled in a manner such that native disc material  980  cannot migrate into the channel, bone tissue (typically autologous) has been re-implanted in a manner that establishes intimate contact between the bone graft and the cancellous bone of the vertebra thereby promoting blood profusion and rapid bone healing. 
         [0146]      FIGS. 38-59  show another embodiment of transcorporal spinal decompression and repair system and method of use. As in the previously described embodiments, the system and method of this exemplary embodiment involve the use of a trajectory control sleeve to form an access channel with a prescribed trajectory through a vertebral body, from an anterior surface entry to a prescribed posterior surface opening on the vertebral body. The access channel may then be used to perform a surgical procedure. For example, instruments may be inserted through the access channel for decompressing a neural element, such as an individual nerve root, a spinal cord, a cauda equine, or a combination thereof. The channel may be used to access a portion or the whole of a herniated disc, an osteophyte, a thickened ligament, a tumor, a hematoma, a degenerative cyst, or any other compressing pathology. This embodiment also includes an implant for repairing the access channel after use. In this exemplary embodiment, the trajectory control sleeve is separate from the repair implant. A common mounting hole formed in the vertebral body may be used to first secure the trajectory control sleeve, and then secure the repair implant to the vertebral body. In this embodiment, the repair implant comprises a bone cage integrally formed with a mounting plate that secures the implant to the anterior surface of the vertebral body. 
         [0147]    Referring to  FIGS. 38-40 , a trajectory control tool  700  is shown. In this exemplary embodiment, trajectory control tool  700  includes a base plate  702 , a trajectory control sleeve  704  rigidly attached to the base plate  702 , and a handle  706  rigidly attached to control sleeve  704 . Control sleeve  704  includes a straight lumen  707  that extends from the proximal end of sleeve  704  through base plate  702  at the distal end of sleeve  704 . Base plate  702  includes a fastening portion  708  configured to detachably secure tool  700  to the anterior surface of the vertebral body, as will subsequently be described in more detail. In this exemplary embodiment, fastening portion  708  includes a bore  710  through base plate  702 , and a fastener sheath  712  rigidly attached to base plate  702  and coaxially aligned with bore  710 . Sheath  712  may be configured with an inside diameter larger than the diameter of bore  710 , thereby providing a shoulder at the bottom of sheath  712  where it joins plate  702 . 
         [0148]    As shown in  FIGS. 39 and 40 , bore  710  and fastener sheath  712  are configured to removably receive the distal end of an elongated fastening device  714 . The distal end  716  of fastening device  714  is threaded for engaging with a vertebral body. In some embodiments, distal end  716  is configured to be self-drilling and/or self-tapping. The proximal end  718  of fastening device  714  may be provided with a keyed head as shown for attaching to a handle or other driver device (not shown). A proximal or mid-portion of fastening device  714  may be knurled and/or provided with other gripping features to allow a surgeon to at least partially tighten fastening device  714  by hand. In some embodiments, a lever or handle (not shown) may be formed at the distal end of the fastening device. Fastening device  714  may be provided with a flexible shaft so that the proximal end  718  may be angled away from trajectory control sheath  704  when being turned. 
         [0149]    As best seen in  FIG. 39 , the bottom or posterior surface of base plate  702  may be curved to match the mediolateral curvature of the anterior surface of a vertebral body. Since the curvature of a vertebral body may vary from patient to patient, a series of two or more alternate trajectory control tools may be provided to a surgeon, each with a different curvature on its base plate. In some embodiments, three different sizes of a trajectory control tool are provided, each having a different radius of curvature on its base plate ranging from 15 to 30 mm. If only a single, universal trajectory control tool  700  is provided, the radius of the posterior side of the base plate  702  may be configured to match the smallest vertebral body it is expected to be attached to. With this arrangement, the lateral edges of base plate  702  will still contact the anterior surface of the vertebral body, regardless of its size, thereby preventing trajectory control tool  700  from rocking when attached to the vertebral body. 
         [0150]    As best seen in  FIGS. 39 and 40 , the posterior side of base plate  702  may be provided with one or more sharp projections  720 . Projections  720  are configured to bite into the vertebral bone to prevent trajectory control tool  900  from shifting once placed on a vertebral body. Projections  720  may be particularly useful when fastening device  714  is being tightened, to prevent base plate  702  from rotating with device  714  relative to the vertebral body. 
         [0151]    As best seen in  FIG. 39 , trajectory control sleeve  704  may be angled in a mediolateral direction. In some embodiments, the mediolateral angle 0 of sleeve  704  is about 10 degrees from vertical or being perpendicular to base plate  702 , with sleeve  704  projecting downwardly and laterally outward (away from a medial plane when mounted on a vertebral body, as will be later described.) Sleeve  704  may alternatively or also be angled in the craniocaudal direction, as seen in  FIG. 40 . In some embodiments, the craniocaudal angle of sleeve  704  is about 10 degrees from vertical or perpendicular. This can be either in the cranial direction or the caudal direction, depending on which side handle  706  is facing when trajectory control tool  700  is mounted on a vertebral body. Left and right versions of tool  700  may be provided such that the surgeon can specify both the direction of the access channel and the orientation of handle  706 . In light of the above, it can be appreciated that trajectory control sleeve  704  forms a compound angle with base plate  702  in this exemplary embodiment. In this embodiment, the axis of fastening portion  708  is vertical or perpendicular to base plate  702  in both the mediolateral and craniocaudal directions. 
         [0152]    As also shown in  FIG. 39 , fastening portion  708  may be laterally spaced apart from trajectory control sleeve  704  by a predetermined distance D, as measured between the axes of these two features where they exit the posterior side of base plate  702  and cross the anterior surface of a vertebral body. 
         [0153]    As seen in  FIG. 40 , base plate  702  may be formed with a dog-bone shape having recesses  722  and/or other marking indicia (not shown) provided on opposite longitudinal sides. Recesses  722  and/or other marking indicia can assist the surgeon in aligning trajectory control tool  700  on the medial centerline of a vertebral body before attaching tool  700  to the vertebral body. 
         [0154]    Referring to  FIGS. 41-45 , an exemplary repair implant  730  is shown. Implant  730  may be used to repair an access channel formed by previously described trajectory control tool  700 , as will later be described in more detail. Implant  730  may include a central housing  732  and a plug portion  734 . In some embodiments, plug portion  734  is rigidly attached to housing  732  and may be integrally formed therewith. Plug portion  734  may be configured to have an outside diameter that is nominally the same as the inside diameter of previously described lumen  707  of trajectory control sleeve  704 . Plug portion  734  may be provided with a rounded distal tip  736  for ease of insertion into an access channel though a vertebral body. 
         [0155]    As best seen in  FIG. 43 , repair implant housing  732  may be configured with a curved posterior surface  738 . The curvature of posterior surface  738  may be selected in manner similar to that of the radius of curvature of the posterior surface of tool  700  as previously described. In some embodiments, a series of two or more implants may be provided, each with a different radius of curvature. With this arrangement, a closely fitting implant may be selected to match a particular patient&#39;s anatomy. The anterior surface  740  of implant housing  732  may also be curved as shown. All exposed edges and corners may be rounded as shown to avoid interfering with surrounding tissue when implanted. 
         [0156]    As shown in  FIG. 43 , plug portion  734  may be angled in the mediolateral direction. In this exemplary embodiment, plug portion  734  is angled about 10 degrees laterally outward to match the angle of previously described trajectory control sleeve  704 . Similarly, plug portion  734  may be angled in the craniocaudal direction, as best seen in  FIG. 45 . In this embodiment, plug portion  734  has an angle of about 10 degrees in the craniocaudal direction to match the craniocaudal angle of sleeve  704 . 
         [0157]    Implant housing  732  may also comprise a fastening portion  742 . In some embodiments, fastening portion  742  includes a bore  744  vertically through housing  732 , as shown in  FIG. 41 . The anterior end of bore  744  may be provided with a countersunk portion  746  for mating with the head of a bone screw. An exemplary bone screw  748  is shown in  FIGS. 43-45  inserted through the bore. In some embodiments, screw  748  is a variable angle screw. As shown in  FIG. 43 , the axis of fastening portion  742  may be offset from the axis of plug portion  734  where it passes through the posterior surface  738  of housing  732  and into the anterior surface of a vertebral body. In some embodiments, this offset distance D, shown in  FIG. 43 , is configured to be the same as the predetermined distance D of tool  700 , shown in  FIG. 39 . In the current embodiment shown in  FIGS. 38-59 , the compound angle and diameter of plug portion  734  matches the compound angle and diameter of an access channel formed by tool  700  in a vertebral body. With this configuration, plug portion  734  may be inserted into the access channel, and implant screw  748  may be threaded into the same screw hole formed in the vertebral body to temporarily receive the previously described distal end  716  of fastening device  714 , as will be more fully described below. 
         [0158]    As best seen in  FIG. 44 , one or more sharp protrusions  750  may be provided on the posterior surface  738  of implant  730 . In this exemplary embodiment, the locations of protrusions  750  are chosen to match the relative locations of protrusions  720  of tool  700 , so as to use the same indentions in the vertebral body formed by protrusions  720 . Such an arrangement can help align implant  730  when it is being placed on the vertebral body. Protrusions  750  of implant  730  may be made larger than the protrusions  720  of tool  700  to ensure that they fully engage the vertebral body. Implant housing  732  may be provided with recesses  752  on opposite longitudinal sides, similar to previously described recesses  722  of tool  700 . Recesses  752  can aid the surgeon in gripping and aligning implant  730 . 
         [0159]    In some embodiments, the plug portion of repair implant  730  is solid. The outer diameter of the plug portion may be slightly tapered as shown to assume a compressive fit in the bone defect. As best seen in  FIG. 41 , plug portion  734  may include a hollow cavity  754  that extends toward the distal end  736  of plug portion  734  and is open at the proximal end. A removable cap  756  may also be provided for closing the hollow cavity  754 . External threads may be provided on cap  756  for engaging with internal threads in implant housing  732  as shown. In other embodiments, a bayonet, cam or other connection may be provided to couple the cap to implant housing  732 . A keyed socket  758  may be provided in cap  756  for receiving a mating driver tip for tightening cap  756  on housing  732 . Cap  756  may include a downwardly projecting protrusion  760 . A similar upwardly projecting protrusion (not shown) may be provided at the bottom of hollow cavity  754 . In some embodiments, plug portion  734  may be formed of a porous material. In the embodiment shown, holes  762  are provided between hollow cavity  754  and the outer surface of plug portion  734 . 
         [0160]    As with the bone cages of previously described embodiments, autologous, allogeneic, or synthetic bone fragments and/or other osteogenic or therapeutic material may be placed into hollow cavity  754 . In some embodiments, this material is compressed when cap  756  is placed on implant housing  732  and tightened. In some embodiments, downwardly projecting protrusion  760  and/or a similar upwardly projecting protrusion assist in moving the compressed material radially outward through holes  762 . Holes  762  allow intimate contact between the material in cavity  754  and the surrounding bone tissue of the vertebral body. 
         [0161]    A retainer may be provided to lock cap  756  in place. In some embodiments, the retainer is movable between an unlocked position and a locked position, with the retainer covering at least a portion of cap  756  when in the locked position. In some embodiments, a similar retainer may be provided for preventing bone screw  748  from backing out of the bone. In the embodiment shown, a single retainer  764  is used to secure both cap  756  and bone screw  748 . In this embodiment, retainer  764  comprises an element that is rotatably attached to implant housing  732  in a recess within the anterior surface of housing  732 . Retainer  764  has a keyed socket  766  within its anterior face for receiving a driver tip to rotate the retainer. Retainer  764  may be rotated between an unlocked position, as shown in  FIG. 41 , and a locked position, as shown in  FIG. 59 . When in the unlocked position, curved cutouts  768  in the periphery of retainer  764  line up with the bores that receive cap  756  and screw  748 . Once cap  756  and screw  748  are in place, retainer  764  may be rotated about 90 degrees such that solid portions of its periphery cover a portion of both cap  756  and screw  748 , thereby preventing their removal until such time that retainer  764  may be unlocked. 
         [0162]    In some embodiments, some or all of the components of implant  730  are made from a polymer, a metal, metallic alloy, or a ceramic. Suitable polymeric materials include polyetheretherketone (PEEK), PEEK-reinforced carbon fiber, and hydroxyapatite-reinforced PEEK. Suitable metals include titanium. Constructing the implant from a polymer may allow for easy monitoring of in-growth into the implant after the procedure. Using a polymer also may also make the implant easily cuttable and/or removable. In some embodiments, components made be constructed of bioabsorbable material(s). In some embodiments, the distal tip  736  of the plug portion  734  may include a tantalum pin for ease of imaging the depth of the implant into the vertebral body. 
         [0163]    Referring to  FIGS. 46-59 , an inventive surgical procedure for creating, using, and repairing a transcorporal access channel using previously described trajectory control tool  700  and implant  730  will now be described. This exemplary procedure may be used, for example, to create an access channel with a prescribed trajectory through a cervical vertebral body, from an anterior surface entry to a prescribed posterior surface opening on the vertebral body. In some embodiments, removing vertebral bone material to create the posterior surface opening may be the ultimate objective of the procedure. In other embodiments, the access channel may then be used to perform a surgical procedure adjacent the posterior surface opening of the vertebral body. For example, instruments may be inserted through the access channel for decompressing a neural element, such as an individual nerve root, a spinal cord, a cauda equine, or a combination thereof. The channel may be used to access a portion or the whole of a herniated disc, an osteophyte, a thickened ligament, a tumor, a hematoma, a degenerative cyst, or any other compressing pathology. 
         [0164]    In this exemplary embodiment, an incision is first made adjacent to the anterior surface of a vertebral body  770  through which an access channel is to be created. Retractors may be used to move soft tissue to further expose the anterior surface of vertebral body  770 . Tool  700  may then be placed on the anterior surface as shown in  FIG. 46 , and may be centered mediolaterally and craniocaudally on the anterior surface. A fastening screw hole may be prepared by inserting a drill and/or a tap (not shown) into fastener sheath  712  of tool  700 . In some embodiments, these screw hole preparation steps may be omitted. Fastening tool  714  may then be aligned with fastener sheath  712 , as shown in  FIG. 46 . The distal end  716  of fastening tool  714  may be inserted through fastener sheath  712  and threaded into vertebral body  770 , as shown in  FIG. 47 . As previously described, fastening tool  714  may have a flexible mid or proximal portion to allow a driver or handle to be attached and operated. The proximal ends of both the fastening tool  714  and trajectory control sleeve  704  may extend outside of the patient for increased accessibility. In some embodiments, fastening tool  714  may be permanently coupled to trajectory control tool  700 , or may be inserted into fastener sheath  712  prior to tool  700  being inserted into the surgical site. The above steps temporarily attach trajectory control tool  700  to vertebral body  770 . 
         [0165]    As shown in  FIGS. 48 and 49 , a bone cutting tool  772  may be aligned with trajectory control sleeve  704  for inserting therein. Tool  772  may have a handle as shown, or be motor driven. Although a drill bit is shown, a mill, burr, trephine, reamer, saw and/or other bone cutting tool may be inserted into sleeve  704  to create an access channel through vertebral body  770 . An accurately controlled end stop surface  774  may be provided on bone cutting tool  772  for engaging the proximal surface  776  of trajectory control sleeve  704 , as shown in  FIG. 50 , to control the depth of the access channel being created in the vertebral body  770 . In some embodiments, the position of end stop surface  774  is adjustable. 
         [0166]    In some embodiments, a series of drills are provided. Each drill has the same diameter shank to match the nominal inside diameter of trajectory control sleeve  704 . However, each drill has a different cutting diameter at its distal end, ranging from 2 to 7 mm. Drills of the same cutting diameter may also be provided with different cutting depths. In some embodiments, one or more drills are provided that each has more than one cutting diameter. With this arrangement, a stepped access channel may be created having a smaller diameter at its distal end (adjacent the posterior side of the vertebral body), and a larger diameter at its proximal end (adjacent the anterior side of the vertebral body). This allows more room at the proximal end for angling tools through the access channel, and allowing for a larger repair implant to reside in the proximal end of the channel. It also prevents excess material from being removed from the posterior side of the vertebral body which might excessively weaken it and/or require additional healing time. In some embodiments, an implant with a stepped diameter is provided to fill the entire access channel. A series of different repair implants may be provided with any of the above drill sets to allow a surgeon to select a particular approach depending on the anatomy and pathology of each patient. 
         [0167]      FIG. 51  shows bone cutting tool  772  being removed from trajectory control sleeve  704 . Tool  772  and sleeve  704  may be configured to cooperate to retain for harvesting the bone tissue  778  that is removed when creating the access channel. In some embodiments, bone tissue  778  is removed from the flutes of cutting tool  772  by tapping tool  772  over a collection tray, or by picking the tissue  778  from the flutes. A positive rake angle may be provided on the bone cutting tool  772  to enhance bone tissue harvesting. 
         [0168]      FIGS. 52-54  show various views of the access channel  780  created through vertebral body  770  by trajectory control tool  700  and bone cutting tool  772  after the tools have been removed. Tool  700  is removed from vertebral body  770  by unscrewing fastening tool  714  in the reverse manner in which it was tightened. As previously described, access channel  780  is created with a prescribed trajectory through vertebral body  770 , from an anterior surface entry to a prescribed posterior surface opening on the vertebral body. In some embodiments, tools  700  and  772  are used to create an access channel that stops just short of the posterior surface, and then the posterior opening of the channel is created by manually picking, chipping or otherwise removing the final bone tissue at the end of the channel. In some embodiments, this can create a desirable flared out channel opening on the posterior surface of vertebral body  770 , thereby providing increased access to adjacent target pathology. 
         [0169]    As previously described, a decompression or other surgical procedure may now be performed through access channel  780 . In some embodiments one or more kerrisons, rongeurs, curettes, nerve hooks and/or other elongated instruments are placed through access channel  780  to perform the procedure. 
         [0170]    Referring to  FIGS. 55-59 , exemplary steps for repairing access channel  780  are shown. Prior to inserting plug portion  734  of repair implant  730  into access channel  780 , osteogenic and/or other therapeutic material may be placed into plug portion  734 , in any manner previously described in relation to bone repair device  905  or plug portion  734 . 
         [0171]    As shown in  FIG. 55 , repair implant is introduced to the anterior surface  782  of vertebral body  770  by aligning plug portion  734  over access channel  780  and aligning bore  744  of fastening portion  742  over the screw hole  784  in vertebral body  770 . Screw hole  784  was formed when the distal end  716  of fastening tool  714  was inserted into vertebral body  770  to temporarily attach trajectory control tool  700 . In some embodiments, screw hole  784  may not have been previously formed, and may be formed at this time. 
         [0172]    As shown in  FIG. 56 , plug portion  734  of implant  730  may be introduced into access channel  780  until its distal end  736  is adjacent to the opening  786  in the posterior surface  788  of vertebral body  770 . 
         [0173]    Referring to  FIG. 57 , implant is shown in its permanent position on the anterior surface  782  of vertebral body  770 . 
         [0174]    Referring to  FIG. 58 , bone screw  748  is shown being inserted into bore  744  of repair implant  730 . At this point retainer  764  is in an unlocked position. 
         [0175]    Referring to  FIG. 59 , repair implant  730  is shown secured to the anterior surface  782  of vertebral body  770  by screw  748 . Once implant  730  is in place, cap  756  may be further tightened to force osteogenic material from within implant  730  into intimate contact with the walls of the access channel to promote rapid more rapid bone ingrowth and healing. Retainer  764  may be rotated into the locked position as shown to cover a portion of screw  748  and cap  756  and thereby prevent them from backing out. With the installation of implant  730  complete, the access incision may then be closed. 
         [0176]    Referring to  FIGS. 60-62 , another embodiment of repair implant is shown. Repair implant  790  is constructed and functions in a similar manner to previously described repair implant  730 . Implant  790  includes a central graft slot  792  extending transversely through the plug portion of the implant. In this exemplary embodiment, graft slot  792  has openings in the cephalad and caudal directions. Transverse holes  793  may be provided in the medial and lateral directions as shown, connecting a mid-portion of graft slot  792  with the exterior surface of the plug portion. Transverse hole  794  may be provided across the bottom of the plug portion for receiving a tantalum pin (not shown.) Such a pin may aid in imaging to confirm the depth of the plug portion in the access channel. 
         [0177]    As best seen in  FIG. 62 , repair implant  790  in this exemplary embodiment does not include an opening or a removable cap over the plug portion, as any osteogenic material is loaded from the side of the plug portion directly into central graft slot  792 . A recess  795  may be provided in the top of implant  790  for rotatably receiving a screw retaining member such as previously described retainer  764  shown in  FIG. 59 . Two detent slots  796  may be provided in the bottom of recess  795  for alternately receiving a mating protrusion (not shown) on the underside of retainer  764  for holding the retainer in either the locked or unlocked position. As previously described, when retainer  764  is in the locked position, it covers a portion of a screw installed in bore  744  to keep it from backing out of the bone. 
         [0178]    As best seen in  FIG. 61 , blunt projections  797  may be provided on the underside of the implant housing for assisting in securing implant  790  to a vertebral body. Blunt protrusions can allow easier positioning of the implant relative to the bone before tightening the securing screw. 
         [0179]    In some situations, repair implant  790  provides greater ease of use in the operating room. Graft material may be packed into a single large open slot  792  instead of being packed through a circular opening on top of the implant. Additionally, no securing cap is needed to retain the graft material, which can eliminate secondary assembly in the operating room. Furthermore, there is no cap to potentially come lose in the wound post-operatively. Additional advantages include ease of manufacture, since there are fewer parts to manufacture and no high tolerance threads to form. The large openings of slot  792  provide large graft contact areas, which promote faster and more complete bone ingrowth during the post-operative healing process.