Abstract:
A method of implanting a modular hip stem implant having a stem portion and a body portion into a medullary canal of a patient&#39;s femur utilizing a two-incision technique. The stem portion is inserted through an anterior incision and the body portion is inserted through a posterior incision where they are interconnected in vivo. The modular hip stem implant is then driven into the medullary canal with force applied through either of the two incisions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     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: U.S. patent application Ser. No. 11/030,020 entitled Method And Instrumentation For Performing Minimally Invasive Hip Arthroplasty and filed in the name of Troy W. Hershberger and Kimberly S. Parcher, and U.S. patent application Ser. No. 11/030,019 entitled Method And Instrumentation For Performing Minimally Invasive Hip Arthroplasty and filed in the name of Troy W. Hershberger. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods and instruments for performing hip arthroplasty, and more particularly to methods for implanting a femoral implant as part of an implantable hip prosthesis. 
     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 incision and tunnel must be large enough, of course, to accommodate passage of the full girth of the femoral broach and other instrumentation, and the desired femoral implant. Such a large incision and tunnel can cause damage to the muscle fibers as well as the skin margins by excessive stretching of tissue. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel method employing a two-incision technique to implant a modular hip stem implant into a medullary canal of a patient&#39;s femur. In broad terms, the method comprises making a first incision and a separate second incision in the body of the patient, inserting a first portion of the modular hip stem implant through the first incision, inserting a second portion of the modular hip stem implant through the second incision, interconnecting the portions of the hip stem implant in vivo, and driving the modular hip stem implant into the medullary canal. 
     According to one aspect of the present invention, a novel method of implanting a modular hip stem implant comprises inserting the stem portion of the implant into the medullary canal through a posterior incision, inserting the body portion of the implant through an anterior incision, affixing the body portion onto the stem portion, and driving the hip stem implant into the medullary canal. 
     According to another aspect of the present invention, a novel method of implanting a modular hip stem implant is provided in which the body portion is inserted through the anterior incision, and the stem portion is inserted through the posterior incision and into a bore in the body portion. The stem portion is retained within the body portion, and the hip stem implant is driven into said medullary canal. 
     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 
         FIG. 1  shows a modular hip stem implant and installation instrumentation. 
         FIG. 2  illustrates a method for implanting the modular hip stem implant of  FIG. 1 . 
         FIG. 3  illustrates implanting of the implant in a patient&#39;s medullary canal. 
         FIG. 4  shows another modular hip stem implant design. 
         FIG. 5  illustrates another method for implanting the modular hip stem implant of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     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. One approach to reducing the size of the incisions is to make two smaller incisions having combined size less than the size of an incision typically made in a traditional single-incision hip replacement procedure. According to the present invention, one method of implanting a modular hip stem using a two-incision approach includes placing the stem portion into the medullary canal of the patient&#39;s femur through a posterior incision in the body of the patient using an assembly shaft and inserting the body portion through a separate anterior incision in the body, thus reducing the size of the posterior incision necessary to perform the procedure. 
     A first method according to the present invention uses a hip stem implant design  10 , as shown in  FIG. 1 , generally comprising a stem portion  12 , a body portion  14 , and a locking screw  16 . The hip stem implant  10  is implanted into the femur of the patient using an assembly shaft  18 , slap hammer  20 , hold back handle  22 , lock nut  24  and implant driver  26 . 
     The stem portion  12  has a threaded aperture  34  for receiving the locking screw  16  and securing the body portion  14  to the stem portion  12 . The body portion  14  has a bore  28  therethrough for receiving the locking screw  16  into the top of the tapered head  30  of the stem portion  12  and an open cavity  32  for receiving the tapered head  30  of the stem portion  12 . 
     The method illustrated in  FIGS. 2 and 3  preferably comprises first inserting the stem portion  12  through a posterior incision  36  in the body of the patient  38  with the assembly shaft  18  and loosely positioning the stem portion  12  into the medullary canal  40  of the patient&#39;s femur  42 . Forceps  44  are then preferably used to hold the stem portion  12  while the assembly shaft  18  is detached from the stem portion  12 . Next, the body portion  14  is preferably inserted through an anterior incision  46  in the body of the patient  36  while the stem portion  12  continues to be held with forceps  44 . The assembly shaft  18  is then reattached to the stem portion  12  through the bore  28  of the body portion  14 . Next, the slap hammer  20  is slid over the assembly shaft  18  and the hold back handle  22  and lock nut  24  are secured to the end of the assembly shaft  18 . 
     Once situated, the body portion  14  is then impacted onto the stem portion  12  using the slap hammer  20  while preventing the stem portion  12  from seating into the medullary canal  40  by continuing to hold the stem portion  12  with the hold back handle  22 . Assembly of the body portion  14  onto the stem portion  12  may be visualized through the anterior incision  46  while impaction of the body portion  14  onto the stem portion  12  is accomplished through the posterior incision  34 . The implant driver  26  is then used to hold the body portion  14  while the assembly shaft  18  is detached from the implant  10 . Next, the locking screw  16  is preferably inserted through the anterior incision  46  and threaded into the stem portion  12 , as shown in  FIG. 3 , with a screw driver (not shown) manipulated through the posterior incision  36 , securing the body portion  14  to the stem portion  12 . 
     Finally, the implant  10  can be seated within the medullary canal  40 , as shown in  FIG. 3 , using a standard punch inserter (not shown) manipulated through the posterior incision  36  and anteversion of the implant  10  guided with the implant driver  26 , or by manipulation of the implant driver  26  alone through the anterior incision  46 . 
     Another embodiment of the present invention uses a different hip stem implant design  110  shown in  FIGS. 4 and 5 , generally comprising a stem portion  112 , a body portion and a threaded locking cap  116 . The stem portion  112  has a reverse tapered portion  130  enabling the body portion  114  to be inserted through the anterior incision  146 , prior to the insertion of the stem portion  112  through the posterior incision  136 . The body portion  114  has an open threaded through cavity  132  for receiving the reverse tapered portion  130  of the stem portion  112  and threaded locking cap  116 . 
     The method illustrated in  FIG. 5  preferably comprises first inserting the body portion  114  through the anterior incision  146  in the body of the patient  138  and loosely positioning the body portion  114  into the medullary canal  140  of the patient&#39;s femur  142 . The stem portion  112  is then preferably inserted through the posterior incision  136  with the assembly shaft  118  and advanced through the open threaded through cavity  132  of the body portion  114 . Next, the threaded locking cap  116  is inserted through the posterior incision  136  and threaded into the open threaded through cavity  132  of the body portion  114 , securing the stem portion  112  within the body portion  114 . Finally, the implant  110  can be seated within the medullary canal  140  of the patient&#39;s femur  142  by manipulation of the implant driver  126  through the anterior incision  146 . 
     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.