Abstract:
Methods and apparatus for modifying the bone portion of a graft, such as that used in the reconstruction of a damaged anterior cruciate ligament. Embodiments of the present invention comprise a driving member for threaded engagement with a housing member and a cutting member engaged with the driving member. The housing member is capable of receiving and supporting the bone graft without damaging a ligament attached thereto. Upon rotation of the driving member, the cutting member will engage the bone portion of the graft and modify it to have a generally circular cross section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. provisional application Ser. No. 60/595,557, filed Jul. 14, 2005, and entitled “Bone and Ligament Graft Modification System,” which is incorporated by reference in its entirety 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND INFORMATION  
       [0003]     Embodiments of the present invention are directed toward methods and apparatus for modifying a bone graft to have a generally circular cross section. Embodiments of the present invention are particularly directed towards methods and apparatus for modifying the bone section of a bone and ligament graft used in the reconstruction of a damaged ligament, such as the anterior cruciate ligament (ACL). Although the procedure and associated problems of ACL reconstructive surgery are described below, embodiments of the present invention may be used in other procedures where it is desired to produce bone grafts that have a generally circular cross section and are generally cylindrical in shape.  
         [0004]     In a typical ACL reconstructive surgery, a graft is harvested from each of the patellar and tibial bones. As harvested, these patellar and tibial bone grafts are connected by a tendinous attachment, which will be used to reconstruct the damaged ACL ligament. When harvested, the bone grafts are typically not cylindrical in shape and do not have a circular cross section. However, as part of the reconstruction/replacement of the ACL, the grafts will be inserted into generally circular holes drilled into the femur and tibia. Therefore, the grafts need to be re-shaped to conform to the recipient holes and provide a proper fit between the graft and the hole. A surgeon typically shapes the bone graft with a rongeur by removing a small amount of material and then checking the graft against a gauge or other sizing device.  
         [0005]     The surgeon uses trial and error to shape the bone graft to conform to the gauge, which is approximately the same size as the hole that will be drilled in the recipient bone. This trial and error process can require considerable time and extend the length of the operation, increasing both the cost of surgery and the potential risks to the patient. The surgeon must also take care not to remove too much material from the graft, which would result in a loose fit between the graft and recipient bone. A loose fit between the graft and recipient bone increases the likelihood that the graft will not properly heal and could result in the graft being pulled out of the recipient bone completely. The use of a rongeur also requires extensive handling of the graft, which increases the risk of bacterial infection or possibly even dropping the graft.  
         [0006]     Some prior art devices, such as that disclosed in U.S. Pat. No. 6,776,938 (incorporated herein by reference), have attempted to address the issues described above. However, such prior art devices potentially create other issues by generating potentially damaging compressive and shear forces on the bone graft.  
         [0007]     Hence, it remains desirable to provide a method and apparatus for modifying a bone graft that does not require excessive time or necessitate extensive handling of the graft. It is further desired to provide a method and apparatus for modifying a bone graft that creates a uniform or standard size and shape of the graft without subjecting the graft to potentially damaging forces.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0008]     Embodiments of the present invention relate to methods and apparatus for modifying the bone cross section of a bone portion of a graft, such as that used in the reconstruction of a damaged anterior cruciate ligament (ACL). Embodiments of the present invention comprise a driving member for threaded engagement with a housing member and a cutting member engaged with the driving member. Upon rotation of the driving member, the cutting member will engage the bone portion of the graft and modify it to have a generally circular cross section. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a view of a disassembled graft modification system;  
         [0010]      FIG. 2  is a perspective view of the housing member of the graft modification system of  FIG. 1 ;  
         [0011]      FIG. 3  is an assembled view of the graft modification system of  FIG. 1 ;  
         [0012]      FIG. 4  is a view of an unmodified graft;  
         [0013]      FIG. 5  is a view of the graft and graft modification system;  
         [0014]      FIG. 6  is a view of a modified graft.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring initially to  FIGS. 1-3 , a graft modification system (GMS)  100  for, modifying a bone/ligament graft  200  (shown in  FIG. 4 ) is displayed. As shown in the unassembled view of the embodiment in  FIG. 1 , GMS  100  comprises a housing member  110 , a driving member  120 , and a cutting member  130 . As best shown in the perspective view of  FIG. 2 , housing member  110  comprises a generally cylindrical body  112  having an outer surface  113  and an recess  118  defined between a drive end wall  106  and a graft end wall  108 . In the embodiment shown, drive end  106  wall has a threaded bore  114  therethrough for receiving driving member  120 , while graft end wall  108  comprises an opening or slot  116 . An openable cover member  119  allows or prevents access to recess  118 . The graft end of recess  118  is defined by an inner wall  115  having a pair of anti-rotation members  117  protruding inwardly therefrom. In the embodiment shown, slot  116  extends radially inwardly from outer surface  113  to an inner portion  111  of graft end wall  108 .  
         [0016]     Referring back to  FIG. 1 , driving member  120  comprises a threaded shaft  124  with a handle  122  disposed on a distal end  126  and a pin or engagement member  129  disposed on a proximal end  128 . In the embodiment shown, cutting member  130  comprises a tubular cylindrical body portion  132  having a cutting edge  134  on a first end  136  and a slot or engagement member  139  disposed on a second end  138 .  
         [0017]     In the assembled view of the embodiment in  FIG. 3 , cutting member  130  is disposed on proximal end  128  of threaded shaft  124 , such that engagement members  129  and  139  are engaged. In addition, threaded shaft  124  is threadably engaged with threaded bore  114 , so that cutting member  130  is disposed within recess  118 .  
         [0018]     As shown in  FIG. 4 , a bone/ligament graft  200  comprises a first bone portion  210  harvested from a first bone and a second bone portion  220  harvested from a second bone. Prior to harvest, first and second bone portions  210 ,  220  are selected from bones that are connected by ligament. Sections of bone surrounding the connection points at each end of the ligament are harvested, so that the ligament  230  still connects them after, harvest. First and second bone portions  210  and  220  each have an inner end  215 ,  225 , respectively, which are connected to ligament portion  230 . As described in the previous discussion of ligament transplants, the bone portions of the graft will be inserted into generally circular holes that have been drilled into the recipient bones (not shown). However, first and second bone portions  210  and  220  are initially irregularly shaped because they are typically removed from the donor bones (not shown) by chiseling or other methods that typically produce irregular shaped portions. As previously described, it is desirable for the bone grafts to have a fairly tight fit into the holes of the recipient bones and to maximize the contact between the grafts and the recipient bones. Therefore, first and second bone portions  210  and  220  typically need to be modified to have a generally circular cross section so as to ensure a proper fit into the holes in the recipient bones.  
         [0019]     In the view of  FIG. 5 , cutting member  130  is engaged with driving member  120  and threaded shaft  124  is threadably engaged with threaded bore  114 , so that cutting member  130  is disposed within recess  118 . Also shown in  FIG. 5 , first bone portion  210  has been placed in recess  118  with ligament portion  230  disposed within slot  116  of housing member  110 . In the embodiment shown, anti-rotation members  117  are sharp protuberances that extend from inner wall  115  and contact inner end  215  of first bone portion  210 , as explained more fully below. After first bone portion  210  has been placed in recess  118 , cover member  119  is closed to capture bone portion  210  within recess  118 . In the embodiment shown, GMS  100  is operated by rotating handle  122  clockwise so that threaded shaft  124  engages threaded bore  114  and advances cutting member  130  towards bone portion  210 . After cutting member  130  has moved a sufficient axial distance, cutting surface  134  will engage first bone portion  210 .  
         [0020]     Due to the threaded engagement of threaded shaft  124  and threaded bore  114 , cutting edge  134  will rotate as it moves axially towards first bone portion  210 . In the embodiment shown, cutting surface  134  is a circular sharp edge disposed on first end  136  of cutting member  130 . Therefore, as cutting surface  134  rotates and moves axially along bone portion  210 , it will cut first bone portion  210  into a generally circular cross section and tubular cylindrical body portion  132  will be disposed around the modified first bone portion  210 . Anti-rotation members  117  help to hold first bone portion  210  in place so that first bone portion  210  will not rotate when cutting surface  134  acts on it. In other embodiments, cover member  119  can be configured to contact first bone portion  210  so that it also restricts rotation of first bone portion  210  when cutting surface  134  acts on it. Still other embodiments may combine a combination of anti-rotation devices such as anti-rotation members  117  and cover member  119 .  
         [0021]     Handle  122  is rotated until cutting surface  134  passes through the length of bone portion  210  and modifies first bone portion  210  to have a generally circular cross section. At that point, the rotation of handle  122  is reversed so that cutting member  130  moves in the opposite axial direction and away from first bone portion  210 . Cover  119  is then opened and bone/ligament graft  200  is removed and repositioned so that second bone portion  220  is received within recess  118 . The process described above is repeated so that second bone portion  220  is modified to have a generally circular cross section. At this point, first and second bone portions  210  and  220  of bone/ligament graft  200  have each been modified to have a generally circular cross section, as shown in  FIG. 6 . This allows first and second bone portions  210  and  220  to be installed in the holes of the recipient bones (not shown) with a proper fit and allows more contact between the bone portions  210  and  220  and the recipient bones. This in turn improves healing and ultimate graft strength.  
         [0022]     Embodiments of the present invention as described above provide many benefits during surgical procedures such as ligament transplants or reconstructions. For example, embodiments of the invention reduce the amount of time needed to create a generally cylindrical bone portion, resulting in lower costs and decreasing the likelihood of complications during surgery. Time savings are realized by engaging a cutting surface that is distributed around the circumference of the bone (rather than just one portion, as with a rongeur). Time savings are also realized by producing a uniform graft size, minimizing the need to perform trial and error fittings between the graft and a standard gauge used to measure the size of the graft. Producing a uniform graft size also allows for a better fit between the graft and the recipient bone. In addition, embodiments of the present invention allow a surgeon to modify a bone graft without holding the graft in his or her hands. This reduces the likelihood of bacterial contamination of the graft and also minimizes the chance that the graft could be inadvertently dropped, rendering the graft unusable. Furthermore, embodiments of the invention distribute the cutting forces around the circumference of the graft, reducing the likelihood that the bone graft will be damaged during the shaping process.  
         [0023]     While various preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not limiting. Many variations and modifications of the invention and apparatus disclosed herein are possible and are within the scope of the invention. For example, the opening in the graft end of the housing member may be a hole rather than a slot. Other embodiments may also comprise a cutting surface that does not have a completely circular cross section, so long as the cutting surface produces a generally circular bone graft when rotated about the graft. The cutting surface may include teeth, serrations, or other means for enhancing cutting, such as embedded diamond particles. In addition, the cutting member may engage with the driving member in various manners, such as a threaded connection or other suitable mechanical engagement. Other embodiments may also comprise different means for rotating the threaded shaft, such as a wrench. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims that follow, that scope including all equivalents of the subject matter of the claims.