Abstract:
An intervertebral spacer formed of dense cancellous human or animal bone is provided. In one preferred embodiment, the intervertebral spacer includes at least one bore which is dimensioned to receive a plug formed from cortical bone tissue. The cortical bone plug provides increased mechanical strength to the intervertebral spacer. Instrumentation for gauging the size of an intervertebral receiving bed and for grasping and inserting an intervertebral spacer or implant into an intervertebral receiving bed are also provided. These instruments include a spacer trial or set of spacer trials for determining the appropriate size spacer required for a particular surgical procedure, a spacer introducer for grasping and positioning a spacer at least partially within a receiving bed formed in the intervertebral space, and a bone tamp for driving a spacer into the receiving bed. Any one or all of these instruments may be provided in a kit for inserting an implant into the intervertebral space. The kit may also include one or more intervertebral spacers or implants.

Description:
[0001]    This application claims priority from U.S. provisional application Serial No. 60/220,941, filed Jul. 26, 2000, which is incorporated herein by reference. 
     
    
     
       BACKGROUND  
         [0002]    1. Technical Field  
           [0003]    The present disclosure relates generally to spinal implants and to spinal implant insertion instruments, and more particularly, to a spinal implant suitable for insertion into a receiving bed formed in the cervical region of the spine and to spinal implant insertion instruments adapted to facilitate the placement of an implant into a receiving bed formed in an intervertebral space.  
           [0004]    2. Background of Related Art  
           [0005]    Intervertebral implants for fusing together adjacent vertebrae of spinal column are well known in the art. Such implants are formed in a variety of different shapes and sizes and are configured for insertion into receiving beds formed in the various regions of the spine. Such implants are also formed of a variety of different biologically compatible materials including ceramics, polymers, human or animal bone, composites, etc. Intervertebral implants formed of natural bone may be formed of cancellous or cortical bone. Typically, due to its limited mechanical strength, implants constructed entirely from cancellous bone are used in the cervical region of the spine. In contrast, cortical bone has the mechanical strength suitable for use in any region of the spine. Because of its osteoinductive properties, it is more desirable to use a spinal implant constructed from cancellous bone where possible, than a spinal implant formed of cortical bone.  
           [0006]    Instruments for positioning implants in a receiving bed formed between adjacent vertebrae are also well known. Such instruments include instruments for gauging the size of a receiving bed, instruments for grasping an implant and instruments for driving an implant into the receiving bed.  
           [0007]    U.S. Pat. No. 4,566,466 discloses a surgical instrument for sizing a graft for insertion between distracted vertebral bodies. Each instrument includes a template head having a pair of spaced parallel flat surfaces separated by a predetermined distance. A handle is attached to the template head for grasping by a surgeon. A plurality of depth indicating lines are formed on the template head. In use, a surgeon inserts the template head of the instruments into a receiving bed formed between the distracted vertebral bodies to determine the size implant required for a spinal fusion procedure. The size of the required implant is determined when a template head fits snugly within the receiving bed.  
           [0008]    U.S. Pat. No. 6,066,174 discloses an implant insertion device for gripping a surgical implant. The instrument includes a handle, a shaft having a proximal end attached to the handle, a pair of jaws attached to the shaft and a hollow sleeve slidably positioned over the jaws. The jaws are biased apart to a release position. The hollow sleeve is slidable over the jaws to urge the jaws from the release position to an approximated position in which the jaws are approximated to grip an implant. In order to slide the hollow sleeve over the jaws, a surgeon must grasp the handle with one hand and advance the hollow sleeve over the jaws with the other hand. Thereafter, the surgeon must apply constant pressure on the hollow sleeve to prevent the implant from falling from between the jaws.  
           [0009]    Accordingly, a continuing need exists for a spinal implant having improved strength characteristics and osteoinductive properties. A continuing need also exists for implant insertion tools which can be operated by a surgeon using a single hand.  
         SUMMARY  
         [0010]    In accordance with the present disclosure, an intervertebral spacer formed of dense cancellous human or animal bone is provided. The implant may have a rectangular configuration or, in the alternative, may assume any configuration to meet a particular surgical requirement. In one preferred embodiment, the intervertebral spacer includes at least one bore which is dimensioned to receive a plug formed from cortical bone tissue. The cortical bone plug provided increased mechanical strength to the intervertebral spacer.  
           [0011]    Instrumentation for gauging the size of an intervertebral receiving bed and for grasping and inserting an intervertebral spacer or implant into an intervertebral receiving bed are also provided. These instruments include a spacer trial or set of spacer trials for determining the appropriate size spacer required for a particular surgical procedure, a spacer introducer for grasping and positioning a spacer at least partially within a receiving bed formed in the intervertebral space, and a bone tamp for driving a spacer into the receiving bed. Any one or all of these instruments may be provided in a kit for inserting an implant into the intervertebral space. The kit may also include one or more intervertebral spacers or implants.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS:  
       [0012]    Preferred embodiments of the presently disclosed intervertebral spacer and insertion instruments are described herein with reference to the drawings, wherein;  
         [0013]    [0013]FIG. 1 is a perspective view of one preferred embodiment of the presently disclosed intervertebral spacer;  
         [0014]    [0014]FIG. 1A is a perspective view of one end of a long bone from which the intervertebral spacer shown in FIG. 1 may be formed;  
         [0015]    [0015]FIG. 1B is a perspective view of cut section taken from the long bone shown in FIG. 1A;  
         [0016]    [0016]FIG. 1C is a perspective view of one of the cut sections shown in FIG. 1B with a pair of intervertebral spacers shown in phantom;  
         [0017]    [0017]FIG. 2A is a top view of one embodiment of the presently disclosed spacer trial;  
         [0018]    [0018]FIG. 2B is a side view of the spacer trial shown in FIG. 2A;  
         [0019]    [0019]FIG. 3A is a side view of one embodiment of the presently disclosed spacer introducer with jaws in an open position;  
         [0020]    [0020]FIG. 3B is a side view of the spacer introducer shown in FIG. 3A with the jaws in an approximated position;  
         [0021]    [0021]FIG. 4A is a top view of one embodiment of the presently disclosed bone tamp;  
         [0022]    [0022]FIG. 4B is a side view of the bone tamp shown in FIG. 4A;  
         [0023]    [0023]FIG. 5 is a top view of the presently disclosed bone tamp positioned to engage the intervertebral spacer shown in FIG. 1;  
         [0024]    [0024]FIG. 5A is a perspective view of an alternate embodiment of the presently disclosed bone tamp;  
         [0025]    [0025]FIG. 5B is a perspective cutaway view of the distal end of the bone tamp shown in FIG. 5A;  
         [0026]    [0026]FIG. 6 is a perspective view with parts separated of another preferred embodiment of the presently disclosed intervertebral spacer;  
         [0027]    [0027]FIG. 7 is a perspective view with parts separated of another preferred embodiment of the presently disclosed intervertebral spacer;  
         [0028]    [0028]FIG. 8A is a perspective view of yet another embodiment of the presently disclosed intervertebral spacer;  
         [0029]    [0029]FIG. 8B is a perspective view of a femoral ring from which the intervertebral spacer shown in FIG. 8A can be formed; and  
         [0030]    [0030]FIG. 8C is a perspective view of the cortical shell of the intervertebral spacer shown in FIG. 8A. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]    Preferred embodiments of the presently disclosed intervertebral spacer and implant insertion instruments will now be described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views.  
         [0032]    Referring to FIG. 1, intervertebral spacer  10  includes a body  12  having a top  14 , a bottom  16  and at least one sidewall  18 . Body  12  is formed from dense cancellous human or animal bone which may be harvested from a bone such as a tibia, humerus, patella, calcaneus or femur. Body  12  may have a rectangular or square configuration and may be further configured to provide lordoses (not shown), i.e., top  14  and/or bottom  16  may be angled or shaped to maintain the natural curvature of the spine upon implantation. Alternately, body  12  may be formed to have other configurations including circular, hexagonal, etc. A trailing end  20  of spacer  10  includes a pair of angled walls  22 .  
         [0033]    Referring to FIGS.  1 A- 1 C, cervical spacer  10  (FIG. 1) may be formed by making horizontal cuts  40  in the metaphysics (subchondral layer) of a proximal tibia  42  (FIG. 1A) to form rings  46  (FIG. 1B). Each ring  46  includes an outer cortical shell  48  and an inner cancellous block plate  50 . Cortical shell  48  can be removed from about cancellous block  50  and block  50  can be cut and/or shaped to form cervical spacer  10  (FIG. 1). By making horizontal cuts across the metaphysics of a long bone, cervical spacer  10  can be formed such that the loading on spacer  10 , after spacer  10  has been implanted between adjacent vertebrae, will be in the same direction as was the anatomical loading on the bone.  
         [0034]    [0034]FIGS. 2A and 2B illustrate the presently disclosed spacer trial shown generally as  100 . Spacer trial  100  includes a head portion  110 , a handle portion  112  and an elongated body portion  114  which interconnects head portion  110  and handle portion  112 . Handle portion  112  includes a recess  116  to facilitate gripping. The flat surface defining the base of recess  116  may also be used for etching indicia, e.g., instrument name and size, manufacturer, etc. Preferably, spacer trial  100  is formed from a surgical grade metal such as stainless steel, e.g., 17-4 stainless steel. Alternately, trial  100  can be formed from any material suitable for surgical use and meeting the requisite strength requirements including plastics, metals, aluminum, etc. Head portion  112  has a predetermined shape and size which, preferably, corresponds to the shape and size of a spacer to be introduced into a receiving bed formed in the intervertebral space. Although only one spacer trial is shown, a set of spacer trials, each having a progressively larger size head portion, are provided. For example, a set of four trials may be provided each having a length of 11 mm and a width of 11 mm. The height of each trial increases by 1 mm from 5 mm to 8 mm. Alternately, nine trials may be provided, each trial having a head portion having a length of 11 mm, a width of 14 mm and a height which increases by 1 mm from 5 mm to 13 mm. Other trial head portion dimensions and set sizes are also envisioned.  
         [0035]    In use, a surgeon will grasp handle portion  112  of a spacer trial  100  from a set of spacer trials (not shown) and position head portion  110  of spacer trial  100  into a receiving bed formed between adjacent vertebrae. The surgeon will repeat this process until the head portion of a spacer trial fits snugly within the receiving bed. Since each spacer trial includes a head portion which corresponds in size to a particular size spacer, the appropriate size spacer is identified when a spacer trial fits snugly within the receiving bed.  
         [0036]    [0036]FIGS. 3A and 3B illustrate the presently disclosed spacer introducer shown generally as  200 . Spacer introducer  200  includes a handle  210 , a stationary arm  212 , and a pivotable arm  214 . Each arm has a proximal end and a distal end having a jaw  216  and  217 , respectively, formed thereon. The proximal end of stationary arm  212  is fastened to handle  210  using any known fastening technique including welding, screw threads, adhesives, etc . . . Each arm  212  and  214  includes a centrally located transverse extension  218  and  219 , respectively, adapted to receive a pivot member  220 . Pivotable arm  214  is pivotably secured to stationary arm  212  about pivot member  220  such that jaws  216  and  217  can be moved between spaced (FIG. 3A) and approximated positions (FIG. 3B). A biasing member (not shown) is positioned between transverse extensions  218  and  219  to urge jaws  216  and  217  to the approximated position. Preferably, introducer  200  is formed from surgical grade steel, although other materials suitable for surgical use may also be used including plastics, metals, etc.  
         [0037]    In use, a surgeon can grasp introducer  200  by handle  210 , which may include a knurled or roughened outer surface  230  to improve gripping. Using his thumb, the surgeon can press on the proximal end of pivotable arm  214  to pivot jaw  217  away from jaw  216  to the spaced position. A spacer or implant can now be positioned between jaws  216  and  217 . The surgeon can now release pivotable arm  214  to allow jaw  217  to be urged towards the approximated position by the biasing member to compress the trailing end of a spacer between the jaws. Each jaw  216  and  217  may include ridges  224  to prevent the spacer from slipping from between the jaws. The surgeon can now maneuver the introducer  200  to position the leading end of a spacer into a receiving bed formed between the adjacent vertebrae.  
         [0038]    [0038]FIGS. 4A and 4B illustrate the presently disclosed bone tamp shown generally as  300 . Bone tamp  300  includes a handle portion  310 , a head portion  312  and an elongated body portion  314  interconnecting head portion  312  and handle portion  310 . Head portion  312  includes a pair of spaced angled extensions  316  defining a recess  318 . Recess  318  is configured to matingly engage trailing end  20  of spacer  10 . A pair of depth limiting stops  322  extend upwardly and downwardly from head portion  312 . Stops  322  are positioned to engage the adjacent vertebrae after a spacer has been driven into a receiving bed formed in the intervertebral space.  
         [0039]    Referring to FIG. 5, after a spacer has been partially positioned within a receiving bed, recess  318  of head portion  312  is positioned in engagement with trailing end  20  of spacer  10 . Thereafter, an abutment end  324  of handle portion  310  can be tapped with a mallet to drive the spacer into the receiving bed. Insertion is complete when stops  322  engage the adjacent vertebrae. In an alternate embodiment shown in FIGS. 5A and 5B, head portion  312 ′ of bone tamp  300 ′ does not include stops.  
         [0040]    [0040]FIG. 6 illustrates an alternate embodiment of the presently disclosed intervertebral spacer which is shown generally as  400 . Spacer  400  is similar to spacer  10 , but also includes a plug or pillar  412  formed of cortical bone tissue. Pillar  412  is positioned within a bore  414  extending between top and bottom surfaces  416  and  418  of body  410 . Although illustrated as being cylindrical in shape, pillar  112  may assume other configurations, e.g., rectangular, hexagonal, square, etc. Alternately, intervertebral spacer may be formed having plurality of spaced pillars. For example, intervertebral spacer  500 , shown in FIG. 7 includes four cortical pillars supported within bores  514  extending between top and bottom surfaces  516  and  518  of cancellous body  510 . By providing cortical posts in a cancellous body, the spacer has improved strength while maintaining its osteoinductive properties.  
         [0041]    [0041]FIG. 8A illustrates another embodiment of the presently disclosed intervertebral spacer shown generally as  600 . Spacer  600  has a substantially rectangular shape and includes a U-shaped body portion  610  and a central body portion  612 . U-shaped body portion  610  is formed of cortical bone and includes a base  614  and first and second legs  616  and  618 . Central body  612  is formed of cancellous bone which is positioned between first and second legs  616  and  618  of U-shaped body portion  610 . A retaining pin  620  may be positioned to extend between legs  616  and  618  through body portion  612  to prevent body portion  612  from separating from body portion  610 . Retaining pin  620  may be formed of cancellous or cortical bone, or alternately, from any bio-compatible material having the requisite strength requirements including metals, plastics, composites, etc . . .  
         [0042]    Referring to FIGS. 8B and 8C, cervical spacer  600  can be formed by cutting U-shaped portion  610  from a cortical ring  650  which may be cut from a long bone, e.g., femur, tibia, fibula, ulna or radius. Body portion  610  (FIG. 8A) which is formed from dense cancellous bone, can be inserted thereafter and pinned therein if necessary.  
         [0043]    Each of intervertebral spacers  10 ,  400 ,  500  and  600  may be formed from partially or fully demineralized bone. The bone may be partially demineralized, e.g., surface demineralized, to provide a degree of flexibility to the spacer or to improve the osteoinductive characteristics of the spacer. Alternately, the spacer may be formed of fully demineralized bone for the same reasons. In one preferred embodiment, the cancellous body of the spacer is formed of partially or fully demineralized bone while the cortical pillars are formed of mineralized bone. By demineralizing the cancellous body an osteoconductive matrix is provided about the cortical pillars to maintain the pillars in their designated spatial relationship. Alternately, any portion of implants  10 ,  400 ,  500  and  600  may be partial or fully demineralized to provide the improved characteristics discussed above.  
         [0044]    It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the number of cortical pillars may be varied to suit a particular surgical procedure. Moreover, the cortical bone may be replaced with other bio-compatible materials having the requisite strength requirements including ceramics, polymers, composites, etc. BMP&#39;s may be added to the material used to construct the intervertebral spacer to promote osteoinductivity. Furthermore, the spacers are not limited to use in the cervical spine, but rather may be suitable for use in the lumbar and/or thoracic spine. Additionally, the intervertebral spacer is not limited to the shape illustrated but rather may be configured to suit a particular procedure, i.e., the spacer may be circular, rectangular, square, etc. The shape of the recess in the bone tamp may also be varied accordingly. Therefor, the above description should not be constructed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.