Abstract:
The present invention relates to orthopedic implants. More specifically, the present invention is a series of orthopedic implants constructed from biocompatible material, each including a plurality of markers constructed from bioactive glass material, some of which are radio-opaque. In addition to providing recognizable markers for use by the surgeon implanting the device, the bioactive glass markers provide a lattice structure which allows for the in-growth of bone into portions of the implant. The in-growth provides enhanced structural integrity between the implant and the bone structure of the patient and may shorten healing time.

Description:
RELATED APPLICATIONS 
       [0001]    In accordance with 37 C.F.R 1.76, a claim of priority is included in an Application Data Sheet filed concurrently herewith. Accordingly, the present invention claims priority to U.S. Provisional Patent Application No. 61/800,705, entitled “SPINAL IMPLANTS WITH BIO-ACTIVE GLASS MARKERS”, filed Mar. 15, 2013. The contents of the above referenced application are herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention and method of use relate to bone fixation devices. More particularly, the present invention relates to spinal or other medical implants having bioactive glass markers or coatings which aid in positioning of the implant as well as bone fusion. 
       BACKGROUND OF THE INVENTION 
       [0003]    A normal human spine is segmented with seven cervical, twelve thoracic and five lumbar segments. The lumbar portion of the spine resides on the sacrum, which is attached to the pelvis. The pelvis is supported by the hips and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which reside sandwiched between the vertebral bodies and operate as joints, allowing known degrees of flexion, extension, lateral bending and axial rotation. 
         [0004]    The intervertebral disc primarily serves as a mechanical cushion between adjacent vertebral bodies, and permits controlled motions within vertebral segments of the axial skeleton. The disc is a multi-element system, having three basic components: the nucleus pulposus (“nucleus”), the anulus fibrosus (“anulus”) and two vertebral end plates. The end plates are made of thin cartilage overlying a thin layer of hard, cortical bone that attaches to the spongy, richly vascular, cancellous bone of the vertebral body. The plates thereby operate to attach adjacent vertebrae to the disc. In other words, a transitional zone is created by the end plates between the malleable disc and the bony vertebrae. The anulus of the disc forms the disc perimeter, and is a tough, outer fibrous ring that binds adjacent vertebrae together. The fiber layers of the anulus include fifteen to twenty overlapping plies, which are inserted into the superior and inferior vertebral bodies at roughly a 40-degree angle in both directions. This causes bi-directional torsional resistance, as about half of the angulated fibers will tighten when the vertebrae rotate in either direction. It is common practice to remove a spinal disc in cases of spinal disc deterioration, disease or spinal injury. The discs sometimes become diseased or damaged such that the intervertebral separation is reduced. Such events cause the height of the disc nucleus to decrease, which in turn causes the anulus to buckle in areas where the laminated plies are loosely bonded. As the overlapping laminated plies of the anulus begin to buckle and separate, either circumferential or radial anular tears may occur. Such disruption to the natural intervertebral separation produces pain, which can be alleviated by removal of the disc and maintenance of the natural separation distance. In cases of chronic back pain resulting from a degenerated or herniated disc, removal of the disc becomes medically necessary. 
         [0005]    In some cases, the damaged disc may be replaced with a disc prosthesis intended to duplicate the function of the natural spinal disc. In other cases it is desired to fuse the adjacent vertebrae together after removal of the disc, sometimes referred to as “intervertebral fusion” or “interbody fusion.” In this process, spondylodesis or spondylosyndesis is used to join two or more vertebrae to eliminate pain caused by abnormal motion, degradation, fractures or deformities of the vertebrae. 
         [0006]    Spinal plates have become one common approach to attaching one adjacent vertebra to another. A spinal plate generally includes an elongated plate of a metal such as titanium or stainless steel. The plate includes a plurality of apertures positioned to allow a surgeon to attach the plate across at least two vertebras with screws. The combination of the plate and screws serve to hold the adjacent vertebra together while the intervertebral fusion occurs. 
         [0007]    Biomaterials have been used as implants in the field of spine, orthopedics and dentistry including trauma, fracture repair, reconstructive surgery and alveolar ridge reconstruction, for over a century. Although metal implants, such as titanium, have been the predominant implants of choice for these types of load-bearing applications, additional ceramics and non-resorbable polymeric materials have been employed within the last twenty-five years due to their biocompatibility and physical properties. 
         [0008]    Polyetheretherketone (PEEK) is a biomaterial often used in medical implants. For example, PEEK can be molded into preselected shapes that possess desirable load-bearing properties. PEEK is a thermoplastic with excellent mechanical properties, including a Young&#39;s modulus of about 3.6 GPa and a tensile strength of about 100 MPa. PEEK is semi-crystalline, melts at about 340.degree. C., and is resistant to thermal degradation. Such thermoplastic materials, however, are not, osteoproductive, or osteoconductive. 
         [0009]    Therefore, there is a need for a series of orthopedic implants which combine a biocompatible material or polymer such as, but not limited to, titanium or PEEK with a glass. The combination should provide the surgeon with radio opaque markers for use in positioning the implant. The radio opaque markers should be constructed of glass of various particle sizes, and have the appropriate structural and mechanical properties to withstand the stresses necessary for use in spinal and orthopedic implants. In addition, the bioactive glass should provide a lattice for bone in-growth into a portion of the implant to integrate the implant into the bone of the patient. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention relates to orthopedic implants. More specifically, the present invention is a series of orthopedic implants constructed from biocompatible material, each including a plurality of markers constructed from bio-active glass material, some of which are radio-opaque. In addition to providing recognizable markers for use by the surgeon implanting the device, the glass markers provide a lattice structure which allows for the in-growth of bone into portions of the implant. The in-growth provides enhanced structural integrity between the implant and the bone structure of the patient and may shorten healing time. In an alternative embodiment, glass is coated or impregnated into the outer surface of the implant to provide a lattice structure which allows for the in-growth of bone into portions of the implant. 
         [0011]    Accordingly, it is an objective of the present invention to provide a series of orthopedic implants constructed of a biocompatible material having bioactive glass markers which aid in the implants insertion. 
         [0012]    It is another objective of the present invention to provide a series of orthopedic implants constructed of a biocompatible material having bioactive glass markers wherein the markers aid in providing bone in-growth into and around the implant. 
         [0013]    It is yet another objective of the present invention to provide a radio opaque marker constructed from bioactive glass for orthopedic implants. 
         [0014]    It is still another objective of the present invention to provide a plurality of methods of securing a bioactive glass marker to an orthopedic implant. 
         [0015]    It is still yet a further objective of the present invention to provide an interbody spinal implant having bioactive glass markers. 
         [0016]    Yet another objective of the present invention is to provide a spinal plate having bioactive glass markers. 
         [0017]    Still yet another objective of the present invention is to provide an orthopedic implant having an outer surface coated or impregnated with glass particles, some of which may be radio opaque. 
         [0018]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0019]      FIG. 1  is a top view of a pivotable interbody spacer, according to one exemplary embodiment; 
           [0020]      FIG. 2  is a side view of the embodiment illustrated in  FIG. 1 ; 
           [0021]      FIG. 3  is an end view of the embodiment illustrated in  FIG. 1 ; 
           [0022]      FIG. 4  is a section view taken along lines  4 - 4  of  FIG. 1 ; 
           [0023]      FIG. 5  is a section view taken along lines  5 - 5  of  FIG. 4 ; 
           [0024]      FIG. 6  is a section view taken along lines  6 - 6  of  FIG. 2 ; 
           [0025]      FIG. 7  is a top view of an alternative embodiment of the interbody spacer having an angled profile for correction of spinal deformities; 
           [0026]      FIG. 8  is a side view of the embodiment illustrated in  FIG. 7 ; 
           [0027]      FIG. 9  is an end view of the embodiment illustrated in  FIG. 7 ; 
           [0028]      FIG. 10  is a section view taken along lines  10 - 10  of  FIG. 7 ; 
           [0029]      FIG. 11  is a section view taken along lines  11 - 11  of  FIG. 10 ; 
           [0030]      FIG. 12  is a section view taken along lines  12 - 12  of  FIG. 8 ; 
           [0031]      FIG. 13  is a perspective view of a spinal section, illustrated with an interbody spacer in the disc space; 
           [0032]      FIG. 14  is a section view taken along lines  14 - 14  of  FIG. 13 ; 
           [0033]      FIG. 15  is a perspective view of a spinal plate according to one embodiment of the present invention; 
           [0034]      FIG. 16  is a partial section view taken along lines  16 - 16  of  FIG. 15  illustrating in-growth pockets containing bio-active glass markers; 
           [0035]      FIG. 17  is a partial section view taken along lines  17 - 17  of  FIG. 15  illustrating in-growth pockets containing bio-active glass markers; 
           [0036]      FIG. 18  is a side view of the embodiment illustrated in  FIG. 15 ; 
           [0037]      FIG. 19A  is a side view illustrating a pedicle screw according to one embodiment of the present invention; 
           [0038]      FIG. 19B  is an exploded view of the embodiment illustrated in  FIG. 19A ; 
           [0039]      FIG. 20  is a side view of the embodiment illustrated in  FIG. 19A ; 
           [0040]      FIG. 21  is a side view of the embodiment illustrated in  FIG. 19A ; 
           [0041]      FIG. 22  is a perspective view of the embodiment illustrated in  FIG. 19A ; 
           [0042]      FIG. 23  is a perspective view illustrating an intervertebral implant according to one embodiment of the present invention; 
           [0043]      FIG. 24  is a top view of the intervertebral implant illustrated in  FIG. 23 ; 
           [0044]      FIG. 25  is a side view of the intervertebral implant illustrated in  FIG. 23 ; 
           [0045]      FIG. 26  is a perspective view illustrating an intervertebral implant according to one embodiment of the present invention; 
           [0046]      FIG. 27  is a perspective view of the intervertebral implant illustrated in  FIG. 26 ; 
           [0047]      FIG. 28  is a side view of the intervertebral implant illustrated in  FIG. 26 ; 
           [0048]      FIG. 29  is a top view of the intervertebral implant illustrated in  FIG. 26 ; 
           [0049]      FIG. 30  is a side view of the intervertebral implant illustrated in  FIG. 26 ; 
           [0050]      FIG. 31  is a perspective view illustrating an intervertebral implant according to one embodiment of the present invention; 
           [0051]      FIG. 32  is a top view of the intervertebral implant illustrated in  FIG. 31 ; 
           [0052]      FIG. 33  is a side view of the intervertebral implant illustrated in  FIG. 31 ; 
           [0053]      FIG. 34  is a perspective view illustrating an intervertebral implant according to one embodiment of the present invention; 
           [0054]      FIG. 35  is a top view of the intervertebral implant illustrated in  FIG. 34 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred, albeit not limiting, embodiment with the understanding that the present disclosure is to be considered an exemplification of the present invention and is not intended to limit the invention to the specific embodiments illustrated. 
         [0056]    Referring to  FIGS. 1-6 , which are now referenced, one embodiment of the interbody spacer  100  is illustrated. As illustrated, the present exemplary interbody spacer is designed for use as an intervertebral spacer in spinal fusion surgery, where portions of an affected disc are removed from between two adjacent vertebrae  102  and replaced with an interbody spacer  100  that provides segmental stability, may correct a deformity, and allows for bone to grow between the two vertebrae to bridge the gap created by disk removal ( FIG. 13 ). 
         [0057]    As shown, the present exemplary interbody spacer  100  has a generally rectangular shape comprised of a pair of side rails  104 , a pair of cross supports  106 ,  107  and a transverse spindle  108  to facilitate the insertion of the interbody spacer through a narrow approach window into the disk space. As illustrated, the side rails  104  and cross supports  106 ,  107  are constructed to include bio-active glass markers  119  held within pockets  118 . The markers and pockets are arranged to provide a visual indicator to a surgeon inserting the device, indicating the orientation of the interbody spacer  100 . In the preferred embodiment, the markers are cylindrical in shape to fit within the pockets  118 . The markers may be sized for a press fit, or alternatively a biocompatible adhesive may be utilized to retain the markers within the pockets. In alternative embodiments, locking tapers or mechanical mechanisms including biocompatible shrink wrap (not shown) may be utilized to retain the markers in place for insertion. While the basic preferred embodiment of the interbody spacer  100  is preferably constructed from biocompatible material such as polyetheretherketone (PEEK), polyaryletherketone (PEAK), stainless steel, titanium or the like, the markers are preferably constructed from a bioactive glass having a composition such as that found in 45S5 and 13-93 glasses made by Mo-Sci Corporation of Rolla, Mo. It should be noted that in some embodiments these compositions are constructed and arranged to be radio opaque bioactive glass. It should also be noted that other bioactive glass materials may be utilized without departing from the scope of the invention; such bioactive glass compositions may include, but should not be limited to, 55SF, S53P4, Trubone and Osteofelt also produced by Mo-Sci Corporation of Rolla, Mo. These glasses may be produced to include micro-spheres, powders, chopped or continuous glass fibers. The glass may include enhanced bone growth properties or antibacterial properties which includes antimicrobial and single cell organisms. It should also be noted that while the markers of the preferred embodiment include a length and diameter that would position a top surface of the marker below the top surface of the pocket  118  as illustrated in  FIGS. 1-6 , the marker may include a length that would cause the marker to extend beyond the distal edges of the implant as illustrated in  FIGS. 7-12  without departing from the scope of the invention. 
         [0058]    Still referring to  FIGS. 1-6 , the interbody spacer  100  includes a proximal end  112  that will be closest to a surgeon during use, and a distal end  114  that will likely be the leading edge of insertion during use. In general, the proximal end  112  is constructed and arranged for connection to an insertion tool that allows the interbody spacer to be grasped or locked into a specific orientation with respect to the insertion tool. In a most preferred embodiment, the insertion tool is constructed and arranged to include a grasping mode which allows rotation of the implant about a spindle axis, and a locking mode that allows the implant to be locked into the desired orientation once the implant is positioned in the desired orientation. This engagement is sufficiently rigid to allow the surgeon to strike the insertion tool when necessary without disturbing the orientation yet allows the surgeon to reposition the interbody spacer as many times as desired without completely releasing the implant by utilizing the grasping mode. In the illustrated embodiment, the distal end  114  of the interbody spacer  100  has a double elliptical leading edge for ease of insertion through the overlying tissues and into the intervertebral space. 
         [0059]    The central portion of the interbody spacer  100  may have a variety of apertures, bores and/or cavities  110  designed to facilitate and support bone growth. The apertures are particularly useful for containing bone growth enhancement materials such as, but not limited to, glass, bone chips or fragments, bone morphogenic protein (BMP), bone cement or the like. In this manner, the bone growth enhancement materials may be delivered directly to the disc space. According to one embodiment, the side rails and cross supports of the interbody spacer are hollowed out to increase cavity volume while maintaining surface area in contact with the bone to prevent the interbody spacer from impacting into the bone. Consequently, the present exemplary interbody spacer  100  employs geometry that provides for a compact interbody spacer with relatively large surface area and internal cavity  110 . Other cavities and geometries may be included in the interbody spacer structure, such as a hollow transverse spindle  108 . 
         [0060]    According to one exemplary embodiment, the interbody spacer  100  has an upper face  124  and an opposing lower face  126 . A series of ridges  128  traverse the upper and lower faces  124 ,  126 . Pockets  118  are dispersed throughout the ridges and troughs for containing the bioactive glass material. The ridges  128  are configured to facilitate the insertion of the interbody spacer  100  by preventing retrograde motion and slippage during the insertion process. After the surgery is complete, the bioactive glass markers  119  positioned between the ridges  128  also may provide increased surface area, encourage bone growth, and/or prevent dislocation of the interbody spacer  100 . In a most preferred embodiment, each ridge  128  includes a substantially vertical face  129  and an angled face  130  wherein the pockets  118  are positioned along the angled face. This construction allows the interbody spacer to be easily pushed or tamped into position while resisting rearward migration. In a preferred embodiment, two markers are positioned relative to the transverse spindle  108 , three markers relative to the center cross support  106  and two relative to the leading cross support  107 . 
         [0061]    Referring to  FIGS. 7-12 , an alternative embodiment of the interbody spacer  300  is illustrated. This embodiment is similar to the embodiment illustrated in  FIGS. 1-6  with the exception that the upper and lower faces  124 ,  126  are arranged to include a face angle  116  with respect to each other so that one side rail  104  is taller than the other. This construction allows the surgeon to correct spinal deformities such as lordosis, scoliosis or the like. It should also be noted that this embodiment illustrates the bioactive glass markers  119  extending beyond the outer surface of the pocket  118 . 
         [0062]    Referring to  FIGS. 13 and 14 , the interbody spacer  100  is illustrated in position between a pair of vertebrae  102 . While the present interbody spacer may be utilized anywhere along the spine, the axis of rotation along the centerline of the transverse spindle  108  makes the device particularly suited for use in the lower spine, most particularly between the L-2 and S-1 disc spaces.  FIG. 14  is a partial perspective view of  FIG. 13  illustrated with the upper vertebrae removed for clarity, further illustrating the positioning and the cooperation between the upper and lower faces  124 ,  126  with the bone. 
         [0063]    The present exemplary device and unique method provide for a pivotable interbody spacer that provides a user with the ability to insert the interbody spacer in a non-linear path. The insertion instrument can lock onto the interbody spacer at multiple angles to allow for the interbody spacer to be pivoted in increments if the instrument rotation is restricted such that the instrument can only be rotated less than the total rotation required to position the interbody spacer. This additional surgical flexibility can allow insertion of the interbody spacer with the removal of less tissue and bone which results in less invasive surgery, fewer post operative complications, and quicker patient recovery time. 
         [0064]    Referring to  FIGS. 15-18 , a spinal plate assembly  30  including bio-active glass markers  119  is illustrated. The spine plate assembly  30  generally includes a spine plate  32 , a locking member  34 , a plurality of bone screws  36  and a plurality of markers  119 . The spine plate  32  is preferably constructed from a biocompatible material such as titanium, and includes a bottom surface  38 , a top surface  40 , a pair of side surfaces  42  and a pair of end surfaces  44 . At least two bores  46  extend through the top and bottom surfaces  38 ,  40 , each of the bores are sized for passage of a bone screw  36 . In addition, each bore  46  includes a counterbore  48  extending downwardly from the top surface  40 . The counterbore is sized and shaped to substantially contain a head portion  50  of the bone screw. The counterbore may be of any shape desirable to match with the bone screw. For example, the counter bore may be spherical, square, truncated or any suitable combination thereof. A segmented T-slot  52  extends between the pair of end surfaces  44  and substantially parallel to the top surface  40 . A first leg  54  of the T-slot extends through the top surface  40  while portions of the second and third legs  56 ,  58  extend into each counterbore  48 . The segments of the T-slot  52  are separated by sight windows  60  extending between the top and bottom surfaces. The sight windows  60  aid the surgeon in placement of the spinal plate  32  by allowing the surgeon to view anatomical features through the plate. The spinal plate also preferably includes at least one, and more preferably two anchor pockets  62 . The anchor pockets are generally constructed and arranged to cooperate with a portion of the locking member  34  to secure the locking member to the spinal plate. The anchor pockets  62  extend downward from the top surface  40  to about the same depth as the second and third legs  56 ,  58  of the T-slot  52  and are wider than the T-slot  52  when viewed from an end surface  44  of the spinal plate  32 . The anchor pockets  62  include side surfaces  64  and end surfaces  66  which cooperate with the locking member  34 . The spinal plate  32  may additionally include tool apertures  68  which aid in the placement of the plate. The tool apertures  68  are preferably sized for cooperation with a gripping tool or K-wire, whereby the plate may be more easily maneuvered into position within the anatomy of a human or animal in vivo. The tool aperture may additionally function as windows for the surgeon once the plate has been maneuvered into position. 
         [0065]    As illustrated, the bottom surface  38  is constructed to include bioactive glass markers  119  held within pockets  118 . The markers and pockets are arranged to provide a visual indicator to a surgeon inserting the device, indicating the orientation of the interbody body spacer  100 . In the preferred embodiment, the markers are cylindrical in shape to fit within the pockets  118 . The markers may be sized for a press fit, or alternatively a biocompatible adhesive may be utilized to retain the markers within the pockets. In alternative embodiments, locking tapers or mechanical mechanisms including biocompatible shrink wrap (not shown) may be utilized to retain the markers in place for insertion. While the basic preferred embodiment of the plate assembly  30  is preferably constructed from biocompatible material such as titanium, stainless steel, shape memory alloy or the like, the markers are preferably constructed from a bioactive glass having a composition of 45S5 and 13-93 glasses made by Mo-Sci Corporation of Rolla, Mo. It should be noted that some embodiments of these compositions are constructed and arranged to be radio opaque bioactive glass. It should also be noted that other bioactive glass materials may be utilized without departing from the scope of the invention; such bioactive glass compositions may include, but should not be limited to 55SF, S53P4, Trubone and Osteofelt also produced by Mo-Sci Corporation of Rolla, Mo. These glasses may be produced to include micro-spheres, powders, chopped or continuous glass fibers. It should also be noted that while the markers of the preferred embodiment include a length and diameter that would position a top surface of the marker below the top surface of the pocket  118  as illustrated in  FIGS. 1-6 , the marker may include a length that would cause the marker to extend beyond the distal edges of the implant as illustrated in  FIGS. 16-18  without departing from the scope of the invention. It should also be noted that the top surface of the bioactive marker may include a rounded, pointed, truncated or other suitable shape that is constructed and arranged to cooperate with the underlying bone of the patient. In this manner, the markers may serve to hold the implant in position prior to the insertion of fasteners. 
         [0066]    Referring to  FIGS. 19A-22 , an alternative embodiment employing the teachings of the present invention is illustrated herein as a polyaxial pedicle screw  200 . The pedicle screw  200  includes a shaft portion  202  having a spherical head portion  204  which cooperates with a tulip portion  206  to allow polyaxial movement therebetween, as is known in the art. In this embodiment, the shaft portion  202  includes a plurality of cross drilled apertures or pockets  208  sized to accept bioactive glass markers  119 . The markers and pockets are arranged to provide a visual indicator to a surgeon inserting the device, indicating the orientation of the interbody body spacer  100 . In the preferred embodiment, the markers are cylindrical in shape to fit within the pockets  118 . The markers  119  may be sized for a press fit, or alternatively a biocompatible adhesive may utilized to retain the markers within the pockets. In alternative embodiments, locking tapers or mechanical mechanisms including biocompatible shrink wrap (not shown) may be utilized to retain the markers in place for insertion. While the basic preferred embodiment of the pedicle screw  200  is preferably constructed from biocompatible material such as stainless steel, titanium or the like, the markers are preferably constructed from a bioactive glass having a composition such as that found in 45S5 and 13-93 glasses made by Mo-Sci Corporation of Rolla, Mo. It should be noted that some embodiments of these compositions are constructed and arranged to be radio opaque bioactive glass. It should also be noted that other bioactive glass materials may be utilized without departing from the scope of the invention; such bioactive glass compositions may include, but should not be limited to 55SF, S53P4, Trubone and Osteofelt also produced by Mo-Sci Corporation of Rolla, Mo. These glasses may be produced to include micro-spheres, powders, chopped or continuous glass fibers. It should also be noted that while the markers of the preferred embodiment include a length and diameter that would position a top surface of the marker below the top surface of the pocket  208  as illustrated in  FIGS. 19A-20 , the marker may include a length that would cause the marker to extend beyond the distal edges of the shaft as illustrated in  FIG. 21  without departing from the scope of the invention. It should also be noted that while the markers are the preferred embodiment, portions of the outer surface of the shaft or tulip portions may be coated or impregnated with glass particles or fibers without departing from the scope of the invention. The glass may be adhered or otherwise impregnated into the outer surface by any means known in the art for coating materials. 
         [0067]    Referring to  FIGS. 23-25 , an alternative embodiment of an intervertebral spacer  300  is illustrated. The intervertebral spacer has a generally rectangular shape comprised of a pair of side rails  304 , a pair of cross supports  306  and a threaded bore  308  to facilitate the insertion of the intervertebral spacer through a narrow approach window into the disk space. As illustrated, the side rails  304  and cross supports  306  are constructed to include bioactive glass markers  119  held within pockets  118 . The markers and pockets are arranged to provide a visual indicator to a surgeon inserting the device, indicating the orientation of the intervertebral spacer  300 . In the preferred embodiment, the markers are cylindrical in shape to fit within the pockets  118 . The markers may be sized for a press fit, or alternatively a biocompatible adhesive may utilized to retain the markers within the pockets. In alternative embodiments, locking tapers or mechanical mechanisms including biocompatible shrink wrap (not shown) may be utilized to retain the markers in place for insertion. While the basic preferred embodiment of the intervertebral spacer  300  is preferably constructed from biocompatible material such as polyetheretherketone (PEEK), polyaryletherketone (PEAK), stainless steel, titanium or the like, the markers are preferably constructed from a bioactive glass having a composition such as that found in 45S5 and 13-93 glasses made by Mo-Sci Corporation of Rolla, Mo. It should be noted that some embodiments of these compositions are constructed and arranged to be radio opaque bioactive glass. It should also be noted that other bioactive glass materials may be utilized without departing from the scope of the invention; such bioactive glass compositions may include, but should not be limited to 55SF, S53P4, Trubone and Osteofelt also produced by Mo-Sci Corporation of Rolla, Mo. These glasses may be produced to include micro-spheres, powders, chopped or continuous glass fibers. It should also be noted that while the markers of the preferred embodiment include a length and diameter that would position a top surface of the marker below the top surface of the pocket  118  as illustrated in  FIGS. 23-24 , the marker may include a length that would cause the marker to extend beyond the distal edges of the implant as illustrated in  FIG. 25  without departing from the scope of the invention. It should also be noted that while the glass markers are the preferred embodiment, portions of the outer surface of the intervertebral spacer may be coated or impregnated with glass particles or fibers without departing from the scope of the invention. The glass may be adhered or otherwise impregnated into the outer surface by any means known in the art for coating materials. 
         [0068]    Referring to  FIGS. 26-30 , an alternative embodiment of the interbody spacer  400  is illustrated. In this embodiment the glass markers are replaced with elongated glass rods. The glass rods are preferably positioned along the longitudinal length of the intervertebral implant  400  so that the outer diameter of the elongated rod is below the top surface of the teeth  404  but above the root of the teeth  406  to expose the side portion of the elongated rod(s). 
         [0069]    Referring to  FIGS. 31-33 , an alternative embodiment of the interbody spacer  500  is illustrated. The interbody spacer  500  has a generally rectangular shape comprised of a pair of side rails  504 , a pair of cross supports  506  and an aperture  508  combined with a keyslot  510  and a pair of apertures  512  to facilitate the insertion of the interbody spacer into the disk space. As illustrated, the side rails  504  and cross supports  506  are constructed to include glass markers  119  held within pockets  118 . The markers and pockets are arranged to provide a visual indicator to a surgeon inserting the device, indicating the orientation of the interbody body spacer  500 . In the preferred embodiment, the markers are cylindrical in shape to fit within the pockets  118 . The markers may be sized for a press fit, or alternatively a biocompatible adhesive may utilized to retain the markers within the pockets. In alternative embodiments, locking tapers or mechanical mechanisms including biocompatible shrink wrap (not shown) may be utilized to retain the markers in place for insertion. While the basic preferred embodiment of the interbody spacer  100  is preferably constructed from biocompatible material such as polyetheretherketone (PEEK), polyaryletherketone (PEAK), stainless steel, titanium or the like, the markers are preferably constructed from a bioactive glass having a composition such as that found in 45S5 and 13-93 glasses made by Mo-Sci Corporation of Rolla, Mo. It should be noted that some embodiments of these compositions are constructed and arranged to be radio opaque bioactive glass. It should also be noted that other bioactive glass materials may be utilized without departing from the scope of the invention; such bioactive glass compositions may include, but should not be limited to 55SF, S53P4, Trubone and Osteofelt also produced by Mo-Sci Corporation of Rolla, Mo. These glasses may be produced to include micro-spheres, powders, chopped or continuous glass fibers. It should also be noted that while the markers of the preferred embodiment include a length and diameter that would position a top surface of the marker below the top surface of the pocket  118  as illustrated in  FIGS. 31-32 , the marker may include a length that would cause the marker to extend beyond the distal edges of the implant as illustrated in  FIG. 33  without departing from the scope of the invention. It should also be noted that while the glass markers are the preferred embodiment, portions of the outer surface of the intervertebral spacer may be coated or impregnated with glass particles or fibers without departing from the scope of the invention. The glass may be adhered or otherwise impregnated into the outer surface by any means known in the art for coating materials. 
         [0070]    Referring to  FIGS. 34-35 , an alternative embodiment of the interbody spacer  600  is illustrated. In this embodiment the glass markers are replaced with elongated glass rods  602 . The glass rods are preferably positioned along the longitudinal length of the intervertebral implant  600  so that the outer diameter of the elongated rod is below the top surface of the teeth  604  but above the root of the teeth  606  to expose the side portion of the elongated rod(s). 
         [0071]    All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
         [0072]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
         [0073]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.