Abstract:
A bone attachment apparatus and implantation system. The attachment device provides a screw with channels formed therein for implantation within a bone aperture. The channels are used as a torque transfer surface during implantation, and cooperate with a thread forming tap to enable screw implantation simultaneously with thread formation within the aperture. The tap can be used to form channels within the bone. A staple is coupled to the screw and the bone, utilizing the respective channels formed therein, to prevent rotation therebetween. The screw can also cooperate with the staple to secure a soft tissue graft.

Description:
FIELD OF THE INVENTION 
     The present invention is generally related to a bone attachment device and, more particularly, to a method and apparatus for implanting a self-tapping resorbable bone screw with locking and soft tissue graft securing features. 
     BACKGROUND OF THE INVENTION 
     Modern medical techniques include suturing soft tissue to bone and repair of bone during, for example, reconstructive surgery. In one form these techniques involve attaching a suture to a bone screw, or anchor, installing the bone screw into the bone and connecting the soft tissue to the bone via the suture. One drawback associated with prior art bone screws is the potential for a bone screw to back out after implantation. To inhibit back out, bone screws have been modified with various thread designs and locking features, with some success. 
     These bone screws can also be used for repair of bone by inserting the screw into a prepared bone aperture. The screw can be used to attach bone to bone or to attach a reconstruction plate or other prosthesis to a bone. Most of these techniques can benefit from the use of a resorbable screw with a self-locking feature. When installing a bone anchor or screw, a surgeon will typically tap a hole, remove the tap and then install the screw into the hole while maintaining the alignment of the bone with another bone or a prosthesis. Therefore, what is needed is an implantation system for a bone screw utilizing a self-tapping resorbable screw with a soft tissue attachment and locking features for repair of bone or soft tissue graft attachment. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a method and apparatus for a self-tapping resorbable bone screw system and locking feature to secure a soft tissue graft is disclosed. In one form, the present invention provides a channeled screw having a generally cylindrical body, a threaded outer surface and a channel defining an interior locking surface and a tap that is configured to fit within the channel such that the channel screw can be threaded into a bone aperture as the tap forms threads within the bone aperture. 
     In another form, the present invention provides a method of installing a bone anchor to a bone wherein a bone screw and tap are threaded into a bone aperture and the tap is removed forming a longitudinal slot within the bone aperture and a staple is inserted into the slot. The staple can then be used to lock the bone screw in place and prevent relative rotation between the bone screw and the bone and also the staple can be used to secure a soft tissue graft. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a bone screw in accordance with the teachings of the present invention; 
         FIG. 2  is a sectional side view of the bone screw of  FIG. 1 ; 
         FIG. 3  is a top view of the bone screw of  FIG. 1 ; 
         FIG. 4  is a bifurcated tap in accordance with the teachings of the present invention; 
         FIG. 5  is a perspective view of the tap of  FIG. 4  installed within the bone screw of  FIG. 1 , forming a screw implantation system aligned with a bone aperture; 
         FIG. 6  is a sectional top view of the screw implantation system of  FIG. 5  taken along the line  6 - 6 ; 
         FIG. 7  is a side sectional view of the screw implantation system of  FIG. 5  illustrating the system inserted within a bone aperture; 
         FIG. 8  is a perspective view of a staple in accordance with the teachings of the present invention; 
         FIG. 9  is a perspective view similar to  FIG. 8 , but taken from a different angle of view than of  FIG. 8 ; 
         FIG. 10  is an alternate embodiment of a staple in accordance with the teachings of the present invention; 
         FIG. 11  is a perspective view of a bone screw in accordance with the teachings of the present invention installed within a bone and having a bone staple attached therein wherein a soft tissue graft is interposed therebetween; 
         FIG. 12  is a top view of the bone screw of  FIG. 11  with the soft tissue graft removed for clarity; 
         FIG. 13  is a side view of the bone screw of  FIG. 12  taken along the line  13 - 13 ; 
         FIG. 14  is a top view of an alternate embodiment of the bone screw of  FIG. 1 , with the anchor locking surface removed for clarity; 
         FIG. 15  is a side view of the bone screw of  FIG. 14 ; 
         FIG. 16  is a top view of a further alternate embodiment of the bone screw of  FIG. 1 ; 
         FIG. 17  is a side view of the bone screw of  FIG. 15 ; 
         FIG. 18  is a top view of an alternate embodiment of the staple of  FIG. 8 ; 
         FIG. 19  is a side view of the staple of  FIG. 18 ; 
         FIG. 20  side view of an alternate embodiment of the bone screw of  FIG. 1 , configured to attach to the staple of  FIG. 18 ; 
         FIG. 21  a perspective view of a further alternate embodiment of the staple of  FIG. 8 ; 
         FIG. 22  side view of an alternate embodiment of the bone screw of  FIG. 1 , configured to attach to the staple of  FIG. 21 ; 
         FIG. 23  is a perspective view of an alternate embodiment of the staple of  FIG. 8 ; and 
         FIG. 24  is a perspective view of a further alternate embodiment of the staple of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the embodiments of a method and apparatus for implantation of a bone screw are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses. Moreover, while the present invention is described in detail with reference to a resorbable polymer bone screw, it will be appreciated by those skilled in the art that the present invention is not limited to a resorbable polymer but the bone screw may also be formed using any other resorbable or biocompatible material, such as allograft, ceramics, ceramic-polymer mixtures, or with non-resorbable materials such as titanium. It should also be appreciated that the staple may be formed of any suitable material that is capable of locking the bone screw and/or securing a bone graft. 
     With specific reference to  FIGS. 1-3 , an implant, or bone screw,  10  is illustrated generally to be a channeled screw including a top surface  12 , a bottom portion  14 , a contoured portion  16  and screw channels  18  that define anchor locking surfaces  20 . Top surface  12  includes a graft holding face  26  with spikes  28  extending therefrom. Graft holding face  26  and spikes  28  bindingly engages a material such as a soft tissue graft and will be discussed later in more detail. Contoured portion  16  is illustrated to define a threaded surface intersecting channels  18  to define threaded end surfaces  30 . Channels  18  are formed within bone screw  10  to provide a torque surface  32  for implantation of bone screw  10 , as discussed hereinafter. Anchor locking surfaces  20  include a series of resilient, downwardly facing surfaces  34 . 
     Referring now briefly to  FIG. 4 , a tap or driver  40  is illustrated to include a shaft  42 , driving portions  44  defining linearly spaced cutting, or thread forming, portions  46  and alignment ends  48 . Driving portions  44  are bifurcated with respect to shaft  42 . Tap  40  is formed of titanium or of any suitable material for forming threads in a working surface, such as a bone, as described below. Thread forming portions  46  are illustrated to include a plurality of linearly spaced extensions configured to cut a predetermined surface within a work material, as detailed herein. 
       FIGS. 5-7  illustrate a screw implantation system  60  comprising the bone screw  10  and the tap or driver  40 . Driving portions  44  of tap  40  are interposed within screw channels  18  of bone screw  10  such that thread forming portions  46  and threaded end surfaces  30  are generally aligned. 
     With specific reference to  FIG. 7 , screw implantation system  60  is illustrated with a work material such as a bone  70  to provide an environmental reference. Bone  70  includes a pre-drilled aperture  72  having a generally cylindrical interior surface  74 . 
     With continued reference to  FIG. 7 , the implantation of bone screw  10  will be described. When a self tapping fastening system is desired, a surgeon prepares a bone  70  by drilling or otherwise forming an aperture  72  therein. Tap  40  with bone screw  10  engaged therein is inserted into aperture  72  until alignment ends  48  are in contact with bone  70 . Rotation of shaft  42  of tap  40  causes thread forming portions  46  to engage interior surface  74  of bone  70  thereby forming an implant engaging surface  76  within bone  70 . As implant engaging surface  76  is formed by tap  40 , contoured portion  16  of bone screw  10  engages implant engaging surface  76 . Further rotation of tap  40  causes bone screw  10  to fully engage within implant engaging surface  76  such that bone screw  10  is further threaded into aperture  72 . Thus provided, tap  40  drives bone screw  10  into aperture  72  while simultaneously forming implant engaging surface  76 . Contoured portion  16  mates with implant engaging surface  76  to retain implant  10  in bone  70 . It would be appreciated that, while contoured portion  16  is illustrated as having a threaded surface, contoured portion  16  can be provided with any surface that engages with an implant engaging surface formed within bone  70 . When bone screw  10  has been inserted into aperture  72  to a desired engagement or depth, tap  40  is pulled out of aperture  72  in a direction that is parallel to the axis of bone screw  10 . As tap  40  is pulled, a slot  80  (as best seen in  FIG. 13 ) is formed by each driving portion  44 . 
     Referring now to  FIGS. 8-9 , a staple  90  is illustrated to include a top portion  92  defining a contoured, or graft holding surface,  94 , legs  96  defining upward locking surfaces  98  and a bottom portion  100 . Graft holding surface  94  is illustrated to include spikes  102  that are configured to bindingly engage a graft as described herein. Staple  90  may be constructed of titanium or stainless steel, or other biocompatible material. 
     With reference now to  FIGS. 11-13 , additional features of bone screw  10  will now be described in detail. As best seen in  FIGS. 12 and 13 , bone screw  10  is implanted, or driven, into aperture  72  of bone  70 . Slots  80  are formed within bone  70  as discussed above, and provide a pair of rectangular channels  110  that align with screw channels  18  of bone screw  10 . Staple  90  is inserted into screw channels  18  and rectangular channels  110  until downwardly facing surfaces  34  engage with upward locking surfaces  98 . Thus provided, staple  90  is locked within screw channels  18  and rectangular channels  110  such that bone screw  10  is inhibited from rotation relative to bone  70 . Staple  90  can be further inserted into screw channels  18  and rectangular channels  110  to provide greater engagement depth and/or clearance. 
     An additional feature of bone screw  10  is illustrated in  FIG. 11  wherein a soft tissue graft  120  is interposed between staple  90  and bone screw  10 . In the embodiment shown, bottom portions  100  of staple  90  are inserted into screw channels  18  and rectangular channels  110  until upward locking surfaces  98  engage downwardly facing surfaces  34  and graft holding surface  94  bindingly secures graft  120  to graft holding face  26 . 
       FIG. 10  illustrates an alternate embodiment of staple  90  in accordance with the teachings of the present invention as a staple  90 ′. Staple  90 ′ includes a top portion  92 ′ defining a surface  94 ′, legs  96 ′ defining upward locking surfaces  98 ′ and a bottom portion  100 . In the embodiment shown, staple  90 ′ does not include spikes, and is intended for use as a screw locking member that couples to a bone screw  10  that does not include spikes  28 . In this manner, staple  90 ′ provides a low profile locking feature for bone screw  10 . 
       FIGS. 14-17  illustrate an alternate embodiment of the implant of the present invention wherein the implant is intended to be axially, or linerally, driven into a bone.  FIGS. 14 and 15  illustrate an implant  210  having a top surface  212 , a bottom portion  214 , a contoured portion  216  and screw channels  218 . The top surface  212  is illustrated to include a torque surface  220 . While contoured portion  216  is illustrated in  FIG. 15  as a series of annular protrusions  222 , contoured portion  216  may also comprise a helical screw surface.  FIGS. 16 and 17  illustrate an implant  310  having a top surface  312 , a bottom portion  314 , a contoured portion  316  and screw channels  318 . The top surface  312  is illustrated to include a torque surface  320 . While contoured portion  316  is illustrated in  FIG. 17  as a series of annular protrusions  322 , contoured portion  316  may also comprise a helical screw surface. 
     During implantation, the implant  210 ,  310  is attached to an impact driver. Implant  210 ,  310  is then driven or impacted into a bone, thereby forming a pair of slots within the bone as contoured surface  216  displaces a portion of the bone. The bone may be prepared with an aperture that is about of equivalent diameter to the bottom portion  214 ,  314  of implant  210 ,  310 . As presently preferred, the implants  210  and  310  are constructed of a material that is capable of being driven into a bone without damage to the implant  210 ,  310 . Implant  210 ,  310  is then rotated about 90 degrees to lock implant  210 ,  310  into the bone as contoured portion  216 ,  316  forms an implant engaging surface within the bone. Implant  210 ,  310  may be rotated by a tool attached to torque surface  220 ,  320 . In a manner similar to implant  10 , a staple may be inserted into the pair of slots formed into the bone to prevent rotation of implants  210 ,  310  to thereby lock the implant  210 ,  310  in place. 
       FIGS. 18-20  illustrate an alternate embodiment of the implant  10  and staple  90  of  FIG. 13 . As best seen in  FIGS. 18 and 19 , staple  590  includes graft apertures  604 .  FIG. 20  illustrates implant  510  to include graft pins  528 . Graft pins  528  are configured to secure a graft between implant  510  and staple  590 . Graft pins  528  are further configured to interpose within graft apertures  604  as staple  590  is attached to staple  510 , thereby preventing the graft from detaching from graft pins  528 . 
       FIGS. 21-22  illustrate a further alternate embodiment of the implant  10  and staple  90  of  FIG. 13 . As best seen in  FIG. 21 , staple  690  includes graft pins  702 .  FIG. 22  illustrates implant  610  to include graft apertures  704 . Graft pins  702  are configured to secure a graft between implant  610  and staple  590 . Graft pins  702  are further configured to interpose within graft apertures  704  as staple  690  is attached to staple  610 , thereby preventing the graft from detaching from graft pins  702 . 
       FIGS. 23 and 24  illustrate a further alternate embodiment of the staple of  FIG. 8  wherein suture apertures are included to provide a suture attachment location for attachment of grafts to bone.  FIG. 23  illustrates a staple  790  to include a suture aperture  799 .  FIG. 24  illustrates a staple  890  to include an alignment aperture  897  and a suture aperture  899 . Alignment aperture  897  may be used with a guide wire to ensure proper alignment of staple  890  during installation onto an implant  10 . Alignment aperture  897  may also be used as a suture aperture  899 . 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.