Abstract:
A method and apparatus for minimally invasive total joint replacement. The method involves sculpting the articular surface of a second bone that normally articulates with a first bone by attaching a bone sculpting tool directly or indirectly to the first bone with the tool in bone sculpting engagement with the articular surface of the second bone, and then sculpting the articular surface of the second bone with the joint reduced and moving one bone with respect to the other. An implant is placed to replace the articular surface of the second bone using an impaction device directly or indirectly attached to the first bone.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Patent Application Ser. No. 60/744,535, filed Apr. 10, 2006, the entirety of which is hereby incorporated by reference. 
     
    
     THE FIELD OF THE INVENTION  
       [0002]     The present invention is directed generally to the field of hip arthroplasty. This invention relates generally to surgical instruments and more particularly to an apparatus and method for implanting prostheses during surgery. The invention is specifically directed to an improved acetabular impactor uniquely constructed for use in less and minimally invasive hip surgeries.  
       BACKGROUND OF THE INVENTION  
       [0003]     A joint generally consists of two relatively rigid bony structures that maintain a relationship with each other. Soft tissue structures spanning the bony structures hold the bony structures together and aid in defining the motion of one bony structure relative to the other. In the hip, for example, the bony structures are the pelvis and the femur. Soft tissue such as ligaments, tendons and capsule span the joint and provide stability. A smooth and resilient surface consisting of articular cartilage covers the articulating structures. The articular surfaces of the bony structures work in concert with the soft tissue structures to form a mechanism that defines the envelope of motion between the structures. When the joint is taken through a full range of motion, the motion defines a total envelope of motion between the bony structures. Within a typical envelope of motion, the bony structures move in a predetermined pattern with respect to one another. In the example of the hip joint, the joint is a ball in socket joint that is inherently stable. The capsule and ligaments spanning the hip joint provide stability while the muscles provide motion.  
         [0004]     Degenerative arthritis causes progressive pain, swelling, and stiffness of the joints. As the arthritis progresses the joint surfaces wear away and progression of the disease process increases pain and reduces mobility. Treatment of the afflicted articular bone surfaces depends, among other things, upon the severity of the damage to the articular surface and the age and general physical robustness of the patient. Commonly, for advanced arthritis, joint replacement surgery is necessary wherein the articulating elements of the joint are replaced with artificial elements commonly consisting of a part made of metal articulating with a part made of ultra high molecular weight polyethylene (UHMWPE). More recently, metal on metal and ceramic on ceramic bearing surfaces have gained in popularity. Early techniques for performing total joint arthroplasty involved large incisions and surgical exposures. Excessive trauma to soft tissue structures leads to significant intraoperative blood loss, postoperative pain, prolonged hospital stay, and slower recovery. The exposure must be sufficient to permit the introduction of drills, reamers, broaches and other instruments for cutting or removing cartilage and bone that subsequently is replaced with artificial surfaces.  
         [0005]     For total hip replacement, the acetabular articular surface and subchondral bone are removed by hemi-spherical reamers. The femoral head is resected with an oscillating saw, the femoral canal may be prepared with reamers and the proximal medullary canal is shaped with broaches. Traditionally, the acetabulum is prepared with hemi-spherical reamers supported on straight drive handles and powered by a surgical drill. Extensive surgical exposure is needed to properly orient the acetabular reamer relative to the acetabulum. This has resulted in a need for instruments that take maximum advantage of available space.  
         [0006]     Examples of instruments specifically described as being designed for minimally invasive hip surgery are shown in, for example, U.S. Pub. 2004/0153063 (Harris), U.S. Pat. No. 7,004,946 (Parker et al), U.S. Pat. No. 7,037,310 (Murphy), and U.S. Pub. 2006/0149285 (Burgi et al). While these devices may be acceptable for their intended purposes or described uses, each requires displacement of the femur to some extent to place the impactor handle and to impact the acetabular shell.  
         [0007]     For patients who require hip replacement surgery it is desirable to provide surgical methods and apparatuses that enable preparation of implant support surfaces and implant placement without substantial damage or trauma to associated muscles, ligaments or tendons. Such minimally invasive total hip surgery reduces exposure of the joint cavity, and the size and location of the minimally invasive incision may not be optimal for proper orientation and application of force to adequately seat and stabilize an acetabular implant. Thus, an impaction device is needed that allows for impaction of the acetabular component with the hip reduced or articulated for use with a minimally invasive exposure for total hip arthroplasty. It may also be desirable to use an alignment guide or surgical navigation to aid the surgeon in positioning the acetabular implant. To attain this goal, a system and method is needed to enable articulating surfaces of the joints to be appropriately sculpted and implants to be placed using minimally invasive apparatuses and procedures. What is needed is an acetabular cup impactor that is more easily placed into the joint space, maintains the femur in an anatomical position and enables cup impaction.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides an apparatus and method for acetabular cup impaction during hip arthroplasty involving minimally invasive surgical procedures. The acetabular cup impactor disclosed accomplishes accurate implant orientation and implant fixation through a limited surgical exposure.  
         [0009]     An acetabular component, such as a press fit shell, is implanted following preparation of the acetabulum. An impaction device is provided that allows for impaction of the acetabular component with the hip reduced or articulated in order to fully seat a press fit acetabular component into the acetabulum. In hip arthroplasty, the hip is accessed through an incision adequate to expose the trochanteric fossa and allow resection of the femoral neck and removal of the femoral head and neck segment. The femoral canal is accessed through the trochanteric fossa and trochanteric region. Reamers, rasps and other devices as are known to those skilled in the art are used to prepare the proximal femur to receive a femoral implant by a sequence of reaming and broaching steps. Once prepared, the intramedullary canal and retained area of the femoral neck and trochanteric region are used to support the acetabular cup impactor of the current invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of the surgical incision through which the present invention is structured to be used.  
         [0011]      FIG. 2  is an orthogonal view of cup impactor according to embodiment of the present invention.  
         [0012]      FIG. 3  is a perspective view of the acetabular cup impactor, femoral broach and acetabular cup superimposed on a femur according to embodiment of the present invention.  
         [0013]      FIG. 4  is a schematic view of a femoral broach.  
         [0014]      FIGS. 5 and 6  are exploded views of cup impactor according to embodiment of the present invention.  
         [0015]      FIGS. 7, 8  and  9  are cross section views of implant attachment assembly according to embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     As described above, the present invention is applicable to orthopedic surgical procedures for total hip arthroplasty; optionally the invention may be used in resurfacing hip arthroplasty. Optionally, the cup impactor of this invention may be used with an attachable alignment guide to aid in aligning and orienting the acetabular shell. Optionally, the cup impactor of this invention may be used with an attachable surgical navigational tracker to aid in aligning and orienting the acetabular shell.  
         [0017]     Referring to  FIG. 1 , there is depicted a surgical incision  100  for a less invasive total hip arthroplasty. The muscles and soft tissues spanning the hip joint are exposed and either bluntly dissected along muscle fibers or separated along muscle boundaries. Optionally, select muscles may be taken down to increase surgical exposure and access to the hip joint. Anatomy of interest to this embodiment of the invention includes the pelvis  102 , the acetabulum  104 , the femur  106 , the joint capsule (not shown) and the muscles  105  and ligaments spanning the hip joint. The femoral head is resected at the base of the femoral neck  107  as shown in  FIG. 1  to provide access to the medullary canal to prepare the canal to receive a femoral hip stem. In total hip arthroplasty, the articular surfaces of the proximal femur and the acetabulum are resurfaced. In general, after resecting the femoral head, the femur is prepared by reaming and broaching to prepare the femoral canal to receive a hip stem implant and femoral head implant there on. Alternatively, the femoral head may be sculpted to receive a resurfacing implant structured to fit over the prepared femoral head, this representing another embodiment of the present invention to place an implant onto a prepared bone surface. The acetabulum is generally prepared by reaming a hemispherical cavity to receive an acetabular cup.  
         [0018]     In traditional total hip arthroplasty the surgical exposure generally ranges between eight and twelve inches in length and may result in extensive trauma to the soft tissues surrounding the hip joint. In minimally invasive total hip surgery, the incision  100  is typically two to four inches in length as shown in  FIG. 1 . While this is a typical length for a minimally invasive surgical incision, there may be some variation due to patient physiology, surgeon preferences, and/or other factors. The surgical approach involves separating the gluteus maximus muscle through blunt dissection to gain access to the hip joint capsule and the trochanteric fossa. Muscle disruption is usually limited to release of the piriformis tendon at the trochanteric fossa. It should be noted that there are variations to the surgical approaches described that are known to someone skilled in the art.  
         [0019]     Referring now to  FIG. 2 , The impactor  1  having a first end and a second end. The first end having a strike plate  16  structured to receive mallet blows to impact acetabular shell  6 . The second end structure to receive acetabular shell  6 . Impactor  1  generally includes a handle  14 , a distraction assembly  44 , an implant attachment assembly  45  and a pressure input assembly  46 .  
         [0020]     Handle  14  includes a handle shaft  24  having a grip  15  thereon, grip  15  being of a size and shape for grasping in a hand to stabilize impactor  1 . Strike plate  16  generally covers surface of handle  1  first end and is joined to handle shaft  24  such that mallet blows applied to strike plant  16  are transferred to handle shaft  24 . Implant attachment assembly  45  is joined to handle shaft  24  such that mallet blows applied to strike plate  16  are transferred to acetabular shell  6 . Referring to  FIG. 6 , handle shaft  24  includes external thread  53  to threadably receive internal thread  54  of strike plate  16 .  
         [0021]     Distraction assembly  44  includes a piston  8  and a piston extension  9 . Referring to  FIGS. 2, 3  and  4 , piston  8  is structured to slidably broach post  110 . Broach  108  is supported within femur  2 . Distraction assembly  44  is structured to receive pressure input assembly  46  to provide pressure to elongate piston  8  and piston extension  9  as described in greater detail hereinafter. Syringe pump (not shown) or similar hydraulic or pneumatic pressure source connected to pressure input assembly  46  to pressurize distraction assembly  44 .  
         [0022]     Implant attachment assembly  45  is structured to releasably receive acetabular shell  6  and includes latch  28  to activate lock to secure adaptor link  7  as described in greater detail hereinafter.  
         [0023]     Pressure input assembly  46  includes Luer Lock  4  for sealable connection to syringe pump (not shown) and elongated tube  19 . Elongated tube  19  sealably received by distraction assembly  44  as described in greater detail hereinafter.  
         [0024]     Turning now to  FIG. 5 , second end of handle  1  is structured to slidably receive piston extension  9  therein retained by piston retainer  13 . Piston extension  9  is structured to slidably receive piston  8 . Distraction assembly  44  includes o-rings  10 ,  11  and  12  sealing interfaces between piston  8  and piston extension  9 , piston extension  9  and piston retainer  13 , and piston retainer  13  and handle shaft  24 , respectively, as illustrated in cross section view in  FIG. 7 . Piston retainer  13  is structured to slidably receive piston extension  9  and to be assembled into handle shaft  24  by threaded interface  47 .  
         [0025]     Referring to  FIGS. 5 and 8 , pressure input assembly includes attachment end  51  slidably and sealably received in receiving hole (not shown) in handle shaft  24 . The receiving hole is in communication with handle shaft cylinder  49  via port  52 , which is in communication with piston extension cylinder  49 .  
         [0026]     Implant attachment assembly  45 , shown in cross section in  FIGS. 6, 7 ,  8  and  9 , includes adaptor link  7  structured to be slidably and lockably received by handle shaft  24 , and structured to be assembled with acetabular shell  6 . Implant attachment assembly  45  further includes latch  28 , safety lock  29 , lock spring  30 , latch spring  31 , and retaining pin  55 , each of which is assembled into handle shaft  24 .  
         [0027]     Adaptor link  7  includes external thread  40  sized to be threadably received by threaded receiving hole  41  in acetabular shell  6 . Adaptor link  7  being one of a set of adaptor links (not shown) of various lengths as appropriate for the size range of acetabular shells typically included in a total hip implant kit. Optionally, adaptor link set (not shown) may include various thread  40  sizes as appropriate for assembly with acetabular shells generally available. Optionally, adaptor link set may include adaptor links structured for assembly with generally available acetabular shells structured with fasteners other than threaded fasteners, for example bayonet mounts, expanding collets, or snap fits.  
         [0028]     Assembly of latch  28 , safety lock  29 , lock spring  30 , latch spring  31 , retaining pin  55  and handle shaft  24  is as follows. Latch spring  31  is placed into receiving hole  60 . Lock spring  30  is placed into receiving hole  61 . Safety lock  29  is slidably received in slot  67  retained therein by tabs  66  slidably received in grooves  65  and by latch  28 . Latch  28  is slidably received in slot  59  and slidably retained by retaining pins  55  placed into upper receiving hole  57  and lower receiving hole  58  in handle shaft  24 . Retaining pins  55  secured in place by welding, bonding, press fit, or other suitable means know to those skilled in the art. Retaining pins  55  slidably received in upper receiving slot  34  and lower receiving slot  35  in latch  28 . Latch  28  thus assembled is free to slide up and down by force applied by the operator to release button  56 . In an unlocked position, shown in  FIG. 8 , latch  28  is depressed into handle shaft  24  and retained therein by safety lock  29  tab  64  resting on latch  28  surface  68 . Sliding safety lock  29  away from latch  28  releases latch  28  to slide upward to a locked position. Tab  64  engages latch  28  slot  63  thereby retaining latch in locked position. The top face of safety lock  29  tab  64  is ramped to allow slidable release of safety lock  29  by pressing on release button  56  thereby moving the latch to unlocked position. Latch spring  31  provides bias force tending to move latch  28  towards a locked position. Lock spring  30  provides bias force tending to move safety lock  29  towards engagement with latch  28 .  
         [0029]     Turning now to connecting an acetabular shell  6  to impactor  1 , handle  14  second end  71  is generally cylindrical with radius leading edge and includes six bayonet slots  21  circumferentially equally spaced. Optionally, one or more bayonet slots  21  may be used or other fasteners, for example threaded fastener, slip fit, taper fit, snap fit, etc., know to those skilled in the art. Adaptor link  7  cavity  70  is structured to slidably receive handle  14  second end  71  and releasably lock thereon. Cavity  70  including six tabs  69  circumferentially equally spaced to be received by corresponding bayonet slots  21 . Lower end of latch  28  includes a tab  33  positioned to close off one of the bayonet slots  21 . Latch  28  unlocked position, as shown in  FIG. 8 , positions tab  33  deeper than bayonet slot  21  opening. Latch  28  locked position, as shown in  FIG. 9 , positions tab  33  within bayonet slot  21  opening to block one adaptor link  7  tab  69  from turning out of bayonet slot  21 .  
         [0030]     Adaptor link  7  is first assembled with acetabular shell  6 . With latch  28  in unlocked position, adaptor link  7  is slidably received on handle  14  second end  71  and rotated to secure tabs  69  in bayonet slots  21 . Safety lock  29  is slid away from latch  28  to release latch  28  to locked position.  
         [0031]     Distraction assembly  44  is initially retracted as shown in  FIG. 9 . Pressure, either hydraulic or pneumatic, applied to pressure input assembly  46  deploys piston  8  and piston extension  9  to tension the joint capsule as described in more detail hereinafter. Distraction assembly  44  is shown in full distraction position in  FIG. 7 . Strike plate  16 , shaft handle  24 , adaptor link  7 , piston  8  and extension piston  9  are constructed of rigid material, such as metal or carbon-carbon composite, to withstand mallet blows typical of impacting an acetabular shell. Grip  15  is constructed of metal or plastic or laminated linen material as is know by those skilled in the art.  
         [0032]     As shown most clearly in  FIG. 3 , handle shaft  24  angles abruptly, generally perpendicular, away from acetabular shell  6  axis. Optionally, handle shaft  24  may angle more acutely away from acetabular shell  6  axis in a range from 45° to 90°. Curved portion  72  of handle shaft  24  is structured for co-axial alignment of acetabular shell axis, grip  15  and strike plate  16 . Curve portion  72  sized and shaped to provide clearance around anatomical features of hip joint and surrounding tissues. Such abrupt angulation of shaft handle  24  is advantageous when performing hip surgery through a limited or minimal exposure as the muscles spanning the hip are preferably left intact thereby limiting the space outside of the acetabulum.  
         [0033]     The current invention is designed to provide alignment and orientation of the acetabular shell based on the anatomy of the pelvis, femur and on the kinematics of the hip joint. This is accomplished by tissue guided surgery “TGS” as described in patents U.S. Pat. No. 6,723,102 and patent applications US 2002/0193797 and US 2003/0236523, the entireties of which are incorporated by reference. Impactor  1  is designed to attach to a femoral broach  3  supported by femur  2 . In applying TGS to hip arthroplasty, orientation of acetabular shell  6  is guided by soft tissue envelope surrounding the hip joint. This envelope of tissue defines the limits of hip motion. The soft tissue capsule working in combination with muscles spanning the hip and the articular joint surfaces of the hip define hip kinematics. TGS utilizes such kinematics to first prepare the acetabulum, then to orient and place acetabular shell  6 . Femur  2  is used as a reference to guide impactor  1  to orient acetabular shell  6  relative to acetabulum by using the joint capsule to properly position and orient the femur with respect to the acetabulum.  
         [0034]     Surgical Procedure  
         [0035]     Impactor  1  is structured for partially disassembled for cleaning and sterilization. The components of the impactor are housed in an instrument tray which is brought to the operating room sterile. The instrument tray has fixtures to hold individual components and markings to show where components are to be placed. Impactor  1  is assembled in the operating room under sterile conditions. Distraction assembly  44  is fully retracted. A syringe pump (not shown) or suitable sterile fluid pressurizing source is charged with sterile saline and attached to pressure input assembly  46 .  
         [0036]     After reaming the acetabulum and with the femoral broach in place, the appropriate size acetabular shell  6  is selected. The corresponding adaptor link  7  is selected and assembled to the shell  6 . The adaptor link  7  is attached to handle shaft  24  as described above.  
         [0037]     Impactor  1  with acetabular shell  6  attached is used to place the shell  6  into the prepared acetabulum. Acetabular shell  6  is oriented with respect to the acetabulum by properly aligning the femur with the pelvis then deploying distraction assembly  44  as previously described to tensioning joint capsule. Cup alignment may be confirmed with a mechanical alignment guide (not shown) or with a surgical navigation system and tracker (not shown).  
         [0038]     Acetabular shell  6  is now in proper position and orientation with respect to the acetabulum. The surgeon uses a mallet (not shown) to impact acetabular shell  6  by striking the strike plate  16 . Mallet blows are repeated until acetabular shell  6  is fully seated in the acetabulum. Distraction assembly  44  is retracted. Handle shaft  24  is released from adaptor link  7  as described above and removed from surgical site. Adaptor link  7  is removed from acetabular shell  6  using a hex driver (not shown) attaching to the hex drive  39 . The cup is now placed in the acetabulum and the total hip arthroplasty procedure continues per the surgical technique.  
         [0039]     While a preferred embodiment of the present invention has been described, it should be understood that various changes, adaptations and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.