Abstract:
A surgical kit for minimally invasive total hip replacement includes a guide for inserting a guide wire into the body at the appropriate angle for reaming an Acetabulum. A shaft is inserted along the path of the guide wire. Working heads are sequentially attached to the shaft. The working heads of the reamers, impactors, trials and screw drivers are changed in the primary surgical incision thereby reducing the size of the incision and the trauma.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of orthopedic surgery and particularly to the instrumentation and methods for minimally invasive total hip replacement.  
         BACKGROUND OF THE INVENTION  
         [0002]    A conventional total hip replacement is performed through a 10-14 inch incision located either anterior, lateral or posterio-lateral overlying the hip joint. The hip is dislocated either anteriorly or posteriorly.  
           [0003]    This large incision is necessary to allow preparation of the acetabulum and proximal femur using instruments held at various angles to the acetabulum and proximal femur. The soft tissue dissection through skin, subcutaneous tissue, deep fascia, and muscles is associated with significant pain and time for healing.  
           [0004]    The head and part of the neck of the femur is visualized and removed using a saw. The acetabulum is prepared by reaming to the desired size and using various sized trials until the optimum size is determined. The desired acetabular prosthesis is impacted in optimum position in the acetabulum and one of various sized liners is impacted into the posthesis. The prosthesis is fixed to bone either by cement or by porous coating that allows fixation by bony ingrowth into the prosthesis.  
           [0005]    The proximal femur is then prepared by reaming and adjustment of neck length and varying sized trials are used to determine the optimum size. Trial neck lengths are used to determine the proper fit and leg length and the femoral stem is fixed top bone either by cement or porous coating on the prosthesis. The proper prosthetic head and neck length is then attached and the final fit, stability, and leg length are confirmed.  
           [0006]    What is needed in the art is instrumentation along with procedures which reduce the soft tissue trauma and facilitate placement of the acetabular prosthesis.  
         DESCRIPTION OF THE PRIOR ART  
         [0007]    U.S. Pat. No. 6,010,535 issued Jan. 4, 2000 to Shah discloses a surgical technique performed through arthroscopic and fluoroscopic guide procedures in which the natural ball of the Femur and the natural Acetabulum are left, largely, intact. A small hole is drilled through the Trochanter and ball of the Femur. The hole is extended, in the same plane, into the Acetabulum. A guide wire is inserted through the hole in the Femur and anchored in the Acetabulum. A reamer follows the guide wire enlarging the hole in the Femur to about an inch. Another reamer is inserted along the guide wire to ream a small spherical cavity in the natural Acetabulum. A small cup member is then secured in this cavity in the Acetabulum. A small ball may then attached to the exterior of the natural ball to be seated in the small cup member in the Acetabulum. The small ball and cup member, respectively, are secured by bone screws. This approach avoids the large conventional incisions with accompanying hospital stay and rehabilitation period. This procedure is obviously limited to those situations in which the ball-and-socket of the natural hip joint are still functional and pain free.  
           [0008]    Sharratt, U.S. Pat. No. 6,315,718, issued Nov. 13, 2001, discloses the conventional surgical procedure for total hip replacement. Sharratt is concerned with the physical strength required on the part of the surgical team to retract and hold the Femur distant from the Acetabulum during surgery. To that end the patent is related to a surgical table mounted retractor apparatus capable of fixing the leg during surgery.  
         SUMMARY OF THE INVENTION  
         [0009]    Accordingly, it is an objective of the instant invention to teach a minimally invasive technique for total hip replacement using a small incision to create a surgical field to visualize the acetabulum.  
           [0010]    It is a further objective of the instant invention to teach the use of instrumentation to facilitate anatomically correct placement of an artificial acetabulum.  
           [0011]    Another object of the invention is to teach the insertion of a properly oriented guide wire from the exterior of the patient&#39;s body into the surgical field.  
           [0012]    It is yet another objective of the instant invention to teach the use of instrumentation with removable working heads for changing components within the surgical field.  
           [0013]    The minimally invasive technique of this invention includes making a small, 2½ to 3 inches, incision to create a surgical field to view the head of the femur and the acetabulum during the preparation of each for implantation of the prosthesis. One end of a guide is inserted into the acetabulum through the surgical field and manipulated to the correct angle for reaming the acetabulum. This results in placing the other end of the guide at the proper point exteriorly of the patient&#39;s body to access the surgical field at the correct angle.  
           [0014]    A guide wire is inserted through the other end of the guide and through the patient&#39;s body, at the correct angle, to engage the first end of the guide in the surgical field. In some cases, a second small incision, approximately 1 inch, is used for positioning the other end of the guide and inserting the guide wire. A common shaft may be inserted along the guide wire to operatively connect the surgical field and the exterior of the body, without an incision. As the stages of the hip replacement progress, the surgeon may replace different working heads on the end of the shaft which is in the surgical field without the necessity of removing the shaft from the body.  
           [0015]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0016]    [0016]FIG. 1 is a side view of the acetabular alignment guide of this invention;  
         [0017]    [0017]FIG. 2 is a side view of the instrument shaft changeable in the surgical field;  
         [0018]    [0018]FIG. 3 a  is a side view of a working head reamer with a shaft connector;  
         [0019]    [0019]FIG. 3 b  is a side view of a trial with a shaft connector;  
         [0020]    [0020]FIG. 3 c  is a side view of a screw driver with a shaft connector; and  
         [0021]    [0021]FIG. 3 d  is a side view of an impactor with a shaft connector. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    The surgical approach for the minimally invasive hip replacement begins with an incision over the postero-lateral area of the hip approximately 3 to 5 cm. distal to the greater trochanter. The exact position of the incision depends upon the anatomical location of the trochanter in relation to the acetabulum. The incision extends approximately 2½ to 3 inches in a postero-superior direction, in line with the fibers of the Gluteus Maximus. The surgical field is increased exposing the posterior capsule of the hip.  
         [0023]    The hip is dislocated by internal rotation providing lateral access and view of the acetabulum, along with the trochanter, neck of the Femur and ball. The exposed hip joint is evaluated to determine necessary repair. An osteotomy of the femoral neck may be performed and the head and neck of the femur removed and replaced with an artificial ball supported by a femoral rod, as part of the total hip replacement. Of course, other procedures may be indicated and performed.  
         [0024]    The acetabular alignment guide  10 , shown in FIG. 1, is then used to determine the location of the insertion point of the guide wire. The leading end  11  is placed in the acetabulum. The leading end  11  has a dome shaped attachment  50  similar to the shape of the acetabulum and fits in the acetabulum. The leading end  11  is of a length to extend from the center of the acetabulum outwardly to a docking port  19  located within the surgical incision. The trailing end  12  of acetabular alignment guide  10  is then adjusted to obtain the desired angle used for preparation of the acetabulum by reaming, trialing, and, finally, impacting the acetabular prosthesis and liner. Depending on the size of the patient, the handle  16  attaching the leading end  11  and the trailing end  12  can be adjusted to accommodate the patient. As shown in FIG. 1, the height and length of the acetabular alignment guide is adjustable by couplings  21  and  23 . The leading end  11  and the trailing end  12  of the guide  10  are separated by a space approximating the distance from the acetabulum and a point where an imaginary line from the acetabulum would exit the body and have a common longitudinal axis. In surgery, soft tissue occupies this space between the surgical field and the point on the skin where the imaginary line would exit. Both the leading end and the trailing end of the acetabular alignment guide have a bore or channel extending through the longitudinal axis  13 . Leading end  11  has a channel  14  terminating in the docking port  19  and trailing end  12  has a through channel  15  in line with each other.  
         [0025]    The handle portion  16 , extending between the leading end and the trailing end, is strong and rigid enough to maintain the alignment of the channels  14  and  15 . Further, the handle  16  may be used by the surgeon to secure the guide  10  once the final alignment is accomplished. The specific shape of the handle  16  is important only to the extent that it is displaced from the trailing and leading ends to allow movement of the trailing end over the patient&#39;s body to orient the channels with the mouth of the acetabulum and locate the exit point. To this end the handle may be arched or angled. It may be integral with the leading and trailing ends or made of assembled parts. It may be made in different sizes and/or it may be adjustable in length.  
         [0026]    The entire guide  10  may be made of materials acceptable for repeated surgeries or it may be disposable after a single use.  
         [0027]    Once the acetabular alignment guide  10  has been manipulated to the proper position, the trailing end contacts the patient&#39;s skin in line with the optimum angle for reaming the patient&#39;s acetabulum. A small incision, e.g. one inch, may be made through the skin at the forward edge of the trailing end  12 . A guide wire  20  or Steinman pin is inserted into the channel  15  through the small incision, through the intervening tissue and into channel  14  of the leading end. The resistance to farther insertion indicates the leading end of the guide wire  20  is in contact with the docking port  19  of the channel  14 . This establishes the proper angle for reaming the acetabulum.  
         [0028]    The channels  14  and  15  have an opening  17  and  18  along the bottom wall opposite the handle  16 . Alternatively, the channels may be formed as bores with a removable lower wall portion, e.g. a telescoped lower wall to be removed after insertion of the guide wire or a laterally retractable partition. In any event, the guide wire  20  exits the guide  10  through the longitudinal openings  17  and  18  in the channels  14  and  15  as the handle is lifted from the patient&#39;s body leaving the guide wire in place.  
         [0029]    The common shaft  30 , shown in FIG. 2, is inserted along the path of the guide wire between the surgical field and the exit point and small incision, if there is one. Once the shaft  30  is in place the guide wire  20  may or may not be removed, as desired by the surgeon. On the outside of the patient&#39;s body the shaft  30  may be connected to a power source or may be manually operated. The leading end  31  of the shaft appears in the surgical field. The surgeon fits a particular sized reamer, suitable to the patient&#39;s acetabulum size, to the shaft within the surgical field. The attachments  22  are conventional Hudson or Trinkle fittings.  
         [0030]    As shown in FIG. 3, the reamer or other working head, may be provided with a short shaft  41  for ease of connection with the elongated shaft  30 . Alternatively, each working head could be supplied with its own shaft or the shaft  30  could be connected directly to the working head.  
         [0031]    As the acetabulum is progressively cleaned, larger reamers may be exchanged through the surgical field, without changing shafts, until the a suitable size is obtained.  
         [0032]    At this point, a trial artificial acetabulum  42  is placed on the end of the shaft  30 , in the incision, for ascertaining the best union with the pelvic bone. Several different trials  42  may be needed before an acceptable fit. Once selected, the properly sized artificial acetabulum is then driven into place by the impactor  45  attached to the shaft  30 . The acetabulum liner is then inserted and attached.  
         [0033]    The artificial acetabulum may require bone screws for additional support. In that case, the shaft  30  is attached to a screw driver  44  inserted to tighten the screws. The screw driver shaft  41  may be fitted with a hinge  43  to accommodate different screw angles.  
         [0034]    Once the acetabulum is securely in place, the guide wire is withdrawn through the minor incision and it is closed. The remaining procedures of the total hip replacement may be accomplished in the major surgical field. Upon completion, it is closed.  
         [0035]    This procedure obviates the need for lengthy incision to properly position an instrument to ream, trial, and impact an acetabular prosthesis and liner. This invention improves subsequent hospital care and patient rehabilitation.  
         [0036]    The instruments of this invention may be supplied individually or as a kit.  
         [0037]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and drawings.