Abstract:
A broaching instrument and method using a segmented broach head. First and second broach segments are laterally engageable with each other in vivo, and are aligned with each other on a common longitudinal axis when so engaged. The method involves making a small anterior incision adjacent a patient&#39;s femur, inserting the broach segments sequentially through the anterior incision, interconnecting the plurality of broach segments in vivo, connecting the broach handle to the broach segments, and broaching the proximal medullary canal with the assembled multi-part broach instrument.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/534,270, filed Jan. 5, 2004, and U.S. patent application Ser. No. 10/912,644, filed Aug. 5, 2004, both of which applications are hereby incorporated by reference along with the following applications filed on Jan. 5, 2005: Attorney Docket No. 13007-24B entitled Method And Instrumentation For Performing Minimally Invasive Hip Arthroplasty and filed in the name of Troy W. Hershberger and Kimberly S. Parcher, and Attorney Docket No. 13007-24C entitled Method And Instrumentation For Performing Minimally Invasive Hip Arthroplasty and filed in the name of Troy W. Hershberger. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to methods and instruments for performing hip arthroplasty, and more particularly to broach instruments and methods for preparing the proximal femur to receive a femoral implant as part of an implantable hip prosthesis.  
         [0003]     In one popular method of performing a total hip arthroplasty through two incisions, the femur is prepared by passing instrumentation through a small posterior lateral incision. This posterior incision is similar to the incision made when performing a conventional femoral intramedullary nailing procedure except that the incision is located somewhat more superior. A second, anterior incision is made to facilitate the introduction of instrumentation for preparation of the acetabulum as well as to expose the femur from the anterior side. The surgeon is able to view the femur and resect the femoral head from this anterior side. Access along the femoral axis for reamers and broaches is most readily accomplished, however, through the posterior lateral incision. The surgeon bluntly divides the fibers of the gluteus maximus through the posterior incision to develop a small tunnel through which he may pass the femoral broaches, reamers and, eventually, the femoral implant. The femur is broached through the posterior lateral incision while the femur is viewed through the anterior incision.  
         [0004]     There are disadvantages associated with the prior method and instrumentation described above. These include the necessity of making the posterior lateral incision large enough to accommodate passage of the femoral broach and other instrumentation. Also, damage may be caused to the muscle fibers as well as the skin margins by excessive stretching of tissue and by repeatedly passing the broach and other instrumentation into and out of the posterior lateral incision.  
       SUMMARY OF THE INVENTION  
       [0005]     According to one aspect of the present invention, a broach instrument for preparing the proximal medullary canal of a femur for receiving a hip stem implant comprises a segmented broach head which includes a first broach segment defining a longitudinal axis, and a second broach segment laterally engageable with the first broach segment in vivo, the second broach segment being aligned with the first broach segment on the longitudinal axis when engaged therewith.  
         [0006]     Another aspect of the present invention is a novel method of preparing the proximal medullary canal of a patient&#39;s femur using a multi-part broaching instrument which includes a broach handle and a segmented broach head having a plurality of broach segments. The method comprises making a small anterior incision adjacent a patient&#39;s femur, inserting the broach segments sequentially through the anterior incision, interconnecting the plurality of broach segments in vivo, connecting the broach handle to the broach segments, and broaching the proximal medullary canal with the assembled multi-part broach instrument.  
         [0007]     The objects and advantages of the present invention will be more apparent upon reading the following detailed description in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a side view of an assembled instrument according to one embodiment of the present invention.  
         [0009]      FIG. 2  is an exploded side view of the instrument of  FIG. 1   
         [0010]      FIG. 3  illustrates placement and insertion of the parts of the instrument of  FIG. 1  within a patient.  
         [0011]      FIG. 4  is an exploded side view of another embodiment of the present invention.  
         [0012]      FIG. 5  is a detail view, partially in cross section, of the embodiment of  FIG. 4 .  
         [0013]      FIG. 6  is a side view of a further embodiment of the instrument of the present invention.  
         [0014]      FIG. 7  is an exploded side view of the embodiment shown in  FIG. 6 .  
         [0015]      FIG. 8  illustrates insertion and assembly of the parts of the instrument of  FIG. 7  within a patient.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0017]     It is desired to reduce the size of incisions necessary to perform a total hip arthroplasty in order to minimize trauma to the gluteus muscles and other underlying tissue adjacent the hip joint. According to the present invention, one approach to reducing the size of the incisions is to divide the broaching instrument used to broach the proximal medullary canal of the patient&#39;s femur into separate pieces, allowing the size of the incisions necessary to accommodate passage of the broach pieces to be reduced. The multi-piece broach instrument may include a laterally segmented broach head that may be inserted through the incisions and assembled within the patient, further reducing the size of the incisions necessary to accommodate passage of the broach segments into the patient.  
         [0018]     In a first embodiment of the present invention, shown in  FIG. 1 , a multi-part broaching instrument  10  generally comprises a core shaft  12 , a laterally divided or segmented broach head  14 , and a broach handle  16 . Core shaft  12 , shown in  FIG. 2 , has a rigid shaft  18  terminating in a threaded distal end portion  20  and a proximal grip or knob  22 . Broach handle  16  has an impact surface  24 , an axial bore  26  for receiving the core shaft  12 , a recess  28  for receiving the grip  22  and an anti-rotation key  30  for preventing the broach head  14  from rotating about the core shaft  12  during use.  
         [0019]     The broach head  14  may be laterally divided or segmented into a plurality of broach segments as shown in  FIG. 2 . A distal broach segment  32  has a tip  34  sized and shaped to guide the instrument  10  into the femoral canal, a threaded aperture  36  for receiving the threaded end portion  20  of the core shaft  12 , and a receiver slot  38  about the threaded aperture  36 , shown as a dovetail type design. An intermediate broach segment  40  has an axial bore  42  therethrough positioned to align with the axial bore  26  of the broach handle  16  when assembled, a second receiver slot  44  about the axial bore  42  and a connector portion  46 , shown as a dovetail type design, for insertion into the receiver slot  38  of the distal broach segment  32 . A proximal broach segment  48  has an axial bore  50  therethrough positioned to align with the axial bores  42 ,  26  of the intermediate broach segment  40  and the broach handle  16  when assembled, and a second connector portion  52 , also shown as a dovetail type design, for insertion into the second receiver slot of the intermediate broach segment. The broach segments and the handle may have a rectangular or curved cross-section, and the broach segments may be serrated partially or completely around the circumference thereof.  
         [0020]     The instrument  10  is assembled during a total hip arthroplasty procedure as shown in  FIG. 3 . First, the broach segments  32 ,  40  and  48  are preferably inserted one at a time through the anterior incision  54  in the body of the patient  56 . Segment  32  may be inserted first and positioned in the proximal medullary canal, then segment  40  may be inserted and laterally connected to segment  32 , and then segment  48  may be inserted and laterally connected to segment  40 . Alternatively, intermediate segment  40  may be inserted after segments  32  and  48  and connected therebetween. Next, the broach handle  16  is preferably inserted through the posterior incision  58  in the body of the patient  56 . Next, the core shaft  12  is preferably advanced through the axial bores  26 ,  42  and  50  of the broach handle  16  and broach segments  40 ,  48 . Finally, the core shaft  12  is rotated so that the threaded end portion  20  engages the threaded aperture  36  of the distal broach segment  32  so that the broach segments  32 ,  40  and  48  are drawn together against the broach handle  16 . The core shaft restrains lateral movement of the broach segments to a degree by simple insertion therein, but its threaded tip is preferably screwed into broach segment  32  sufficiently to create a compression force which tightly secures the broach segments. Once assembled, the instrument  10  is manipulated through the posterior incision  58  of the patient  56  to broach the femoral canal  60  in preparation for receiving the hip stem implant.  
         [0021]     When the broaching procedure is completed, the instrument  10  is preferably removed and disassembled in reverse order. First, the core shaft  12  is preferably rotated so that the threaded end portion  20  disengages the threaded aperture  36  of the distal broach segment  32  and is then removed from the broach segments  32 ,  40 ,  48  and broach handle  16 . Next, the broach handle  16  is preferably removed from the posterior incision  58  of the patient  56 . Finally, the broach segments  32 ,  40 ,  48  are then preferably removed from the patient  56  through the anterior incision  54  one at a time.  
         [0022]     In another embodiment of the present invention, shown in  FIGS. 4 and 5 , a multi-part broaching instrument  110  employs a push-type design in which a core shaft  112  pushes against the distal broach segment  132  of a laterally segmented broach head  114 , cooperating with the broach handle  116  to put the broach segments  132 ,  140  and  148  in tension. In this embodiment, the core shaft  112  may have an unthreaded distal tip  120  and the distal broach segment  132  may have an unthreaded mating aperture  136 . Alternatively, the distal broach segment  132  may have no aperture other than the receiver slot in its dovetail joint. The broach segments  132 ,  140 ,  148  and the broach handle  116  are restrained longitudinally by their interconnected dovetail joints, and the core shaft  112 , which is threaded into the broach handle  116 , is used to create a tension force in the broach segments  132 ,  140 ,  148  by turning the knob  122  clockwise (for a right-handed thread as illustrated) to advance it toward the adjacent surface of the broach handle  116 . The advancing distal tip  120  of the core shaft  112  engages the closed distal end of aperture  136  in the distal broach segment  132  and thus applies a distally directed force against that broach segment, thereby putting all the broach segments and the handle in tension.  
         [0023]     A push-type design may alternatively be implemented with oppositely threaded portions on the two opposite ends of the core shaft. For example, instead of having an unthreaded distal tip, core shaft  112  may have left-hand threads on its distal end which act in opposition to the right-hand threads on its proximal end in the handle. That is, when rotated clockwise, the core shaft tends to back out of the distalmost broach segment and thereby further pushes on that segment as the threaded proximal end of the core shaft moves distally in the broach handle. The same core shaft may alternatively be used to put the broach segments in compression, by rotating the core shaft sufficiently in the counter-clockwise direction and thereby tending to draw the broach segments tightly together. In another alternative embodiment, the core shaft may have a hook-type end which engages the distalmost broach segment and pulls it toward the other broach segments as the core shaft is retracted in the broach handle. The broaching instrument is otherwise assembled and used in the same way as broaching instrument  10  previously described and illustrated.  
         [0024]     In a further embodiment of the invention, shown in  FIGS. 6-8 , a multi-part broaching instrument  210  generally comprises a flexible core shaft  212 , an offset broach handle  216  and, a laterally segmented broach head  214  as previously described and shown. Flexible core shaft  212  may be made of nitinol (NiTi) or wound cable terminating in a threaded end  220  and a tightening grip or knob  222 . Offset broach handle  216  has an internal bore  226  for receiving core shaft  212 , a recess  228  for receiving the tightening grip  222  and an anti-rotation key  230  for preventing the broach head  214  from rotating about core shaft  212  during use.  
         [0025]     The instrument  210  is assembled during a total hip arthroplasty procedure as shown in  FIG. 8 . First, the broach segments  232 ,  240 ,  248  are preferably inserted one at a time through an anterior incision  254  made in the body of the patient  256  as previously described. Next, the offset broach handle  216  is then preferably inserted through the anterior incision  254  and positioned adjacent the broach head segments  232 ,  240 ,  248 . Next, the flexible core shaft  212  is then preferably advanced through the internal bore  226  of the offset broach handle  216  and the axial bores  242 ,  250  of the broach head segments  240 ,  248 . Finally, the core shaft  212  is rotated so that the threaded end  220  of the core shaft  212  is threadedly engaged with the threaded aperture  236  of the distal broach segment  232 , creating a compression force that draws the broach segments  232 ,  240 ,  248  tightly against the offset broach handle  216 . Once assembled, the instrument  210  is manipulated through the anterior incision  254  in the body of the patient  256  to broach the femoral canal  260  in preparation for receiving the hip stem implant.  
         [0026]     When the broaching procedure is completed, the instrument  210  is preferably removed and disassembled in reverse order. First, the flexible core shaft  212  is preferably rotated so that the threaded end  220  disengages the threaded aperture  236  of the distal broach segment  232  and is then removed from the broach segments  232 ,  240 ,  248  and offset broach handle  216 . Next, the offset broach handle  216  is preferably removed from the anterior incision  254  in the body of the patient  256 .  
         [0027]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, while a core shaft is described above as a preferred means for applying an axial force to the parts of the segmented broach head, alternative means are contemplated, such as a peripheral strap, a pair of peripheral straps, or other device extending alongside the broach segments, e.g., in a longitudinal groove therein, for creating a compression force. Rigid and semi-rigid rods and other peripheral devices are also contemplated in certain embodiments for creating tension in the broach segments.