Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part and claims the benefit of U.S. provisional patent application Ser. No. 60/721,450 filed Sep. 28, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 10/429,435 filed May 5, 2003, which is a divisional of U.S. patent application Ser. No. 10/075,829 filed Feb. 12, 2002 now U.S. Pat. No. 6,723,102, the entireties of which are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   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. Soft tissue such as ligaments, tendons, menisci, and capsule provide support to the bony structures. A smooth and resilient surface consisting of articular cartilage covers the bony 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 fully articulated, 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. 
   The articular surfaces of the bony structures may become damaged by a variety of diseases, accidents, and other causes. A common disorder of joints is degenerative arthritis. Degenerative arthritis causes progressive pain, swelling, and stiffness of the joints. As the arthritis progresses the joint surfaces wear away, resulting in contractures of the surrounding soft tissues that provide stability to the joint. Moreover, 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). 
   A relatively young patient with moderate to severe degeneration of the hip joint is often treated with drug therapies. While drug therapies may temporarily provide relief of pain, progression of the disease, with resulting deformity and reduced function, ultimately necessitates surgery. Alternative treatments such as non-steroidal anti-inflammatory drugs and cortisone injections similarly provide only temporary relief of symptoms. Accordingly, there exists a need for a source of permanent relief of symptoms associated with moderate to severe degeneration of the hip joint. 
   In severe situations, surgery may be indicated in which the articular surface of one or more of the bones related to the joint is partially or entirely replaced with an artificial surface, as, for example, when the acetabular socket and femoral head are replaced with a prosthetic device including an UHMWPE bearing to resurface the acetabulum and a polished metal or ceramic femoral head mounted to a stem extending into the medullary canal of the proximal femur to replace the femoral head. Joint replacement surgery has become a proven and efficacious method of alleviating pain and restoring function of the joint. 
   Current methods of preparing the rigid elements of a joint to receive components as in joint replacement surgery involve extensive surgical exposure. 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. For total hip replacement, the acetabular articular surface and subchondral bone is removed by hemispherical graters, the femoral head is resected with an oscillating saw, and the proximal medullary canal is shaped with broaches. A difficulty with total hip replacement is that the invasiveness of the procedure causes significant intraoperative blood loss and extensive rehabilitation because muscles and tendons must be released from the proximal femur to mobilize the femur and gain exposure of and access to the acetabular fossa. 
   Conventional total hip arthroplasty is indicated for painful arthritis of the hip joint. The procedure involves exposing the hip joint through a large incision to provide the surgeon full visualization of the hip joint and the acetabular region and to provide access for surgical power instruments. In order to appropriately prepare the bony structures of the hip joint, the major muscles spanning the joint are commonly disrupted to gain adequate exposure of the joint. Steps of the procedure include removing the femoral head followed by reaming and broaching the proximal femoral canal to prepare a bony surface to support a hip stem. The stem is implanted and may be cemented in place, or press fit for bony ingrowth. The acetabulum is typically prepared using sequentially sized graters to remove cartilage down to bleeding bone. Once the acetabulum is prepared, an acetabular component is implanted, either by cementing in place or press fitting for bony ingrowth. Extensive surgical exposure is necessary to accommodate the bulk and geometry of the components as well as the instruments for bone preparation. The surgical exposure, which may be between six and twelve inches in length, may result in extensive trauma to the soft tissues surrounding the hip joint along with the release of muscles that insert into the proximal femur. The surgical exposure increases bleeding, pain, and muscle inhibition; all of which contribute to a longer hospitalization and rehabilitation before the patient can be safely discharged to home or to an intermediate care facility. 
   The prepared bony surfaces are technically referred to as the acetabular fossa, femoral canal and metaphyseal region of the femur. Prior to placing the final implants into the prepared spaces, a femoral trial, which may be the broach in some systems, is placed in the proximal femur along with a trial femoral head and neck, and an acetabular trial is placed into the acetabulum to facilitate trial range of motion and evaluation of hip stability prior to placement of the final total hip implants. 
   Devices for minimally invasive hip surgery that prepare the acetabulum to receive final total hip implants are known. Hemispherical graters driven with straight drive handles connected to a surgical drill have been used. However, soft tissue structures limited proper orientation of these devices leading to the development of curved drive handles used to avoid soft tissue interference. The resulting reamer device, while partially avoiding soft tissue structures, still required the surgeon to force the handle against soft tissue structures to gain proper orientation of the grater. In addition, such devices still required retraction of the proximal femur to provide access for the handle and grater to the acetabulum. Extensive distraction force is needed to displace the femur resulting in trauma to soft tissue structures because of the magnitude and duration of the force imparted. 
   An acetabular grater that rotates about an axis transverse to the drive handle longitudinal axis is known for preparation of the acetabulum to receive an implant. The reamer device includes a grater and a drive handle. The drive handle has a pivotable head to which the grater attaches. The grater is rotated about the pivotable head to reduce the grater profile for a surgical incision. Once in the acetabulum, the grater rotates normal to the drive handle during operation. The grater includes cutouts in the hemispherical shell to allow rotation over the drive handle. As with the straight and curved drive handles described above, a pivotable head drive handle interferes with soft tissue structures while preparing the acetabulum and requires distraction of the femur to allow access to the acetabulum. 
   Based on the foregoing, there exists a need for surgical methods and apparatuses that may be employed to gain surgical access to articulating joint surfaces, to appropriately prepare the bony structures, to provide artificial, e.g., metal or plastic, articular bearing surfaces, and to close the surgical site, all without substantial damage or trauma to associated muscles, ligaments or tendons. There also exists a need for a system and method that enables articulating surfaces of the joints to be appropriately sculpted using minimally invasive apparatuses and procedures. There exists another need for a surgical navigation system to guide the preparation of articular surfaces and to position the acetabular implant. 
   SUMMARY OF THE INVENTION 
   The present invention provides a system and method for total joint replacement that involves minimally invasive surgical procedures. The instruments disclosed accomplish accurate bone preparation through a limited surgical exposure. 
   Thus, in one embodiment, the present invention provides a method of appropriately sculpting the articular surface of a second bone that normally articulates with a first bone. The method involves 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. Sculpting of the second bone is done by moving one bone with respect to the other. Alternatively, sculpting of the second bone is done by orienting the first bone appropriately relative to the second bone and advancing the sculpting tool into or onto the second bone. In another embodiment, sculpting of the second bone is done by orienting the sculpting tool relative to the second bone while supporting the sculpting tool on the first bone and advancing the sculpting tool into or onto the second bone. Optionally, the bone sculpting tool may be attached to a mount that is attached directly or indirectly to the first bone. Force to advance the sculpting tool into or onto the second bone is provided by a distraction device integral to the sculpting tool. Optionally, the distraction device may be independent of the sculpting tool. Alternatively, the force to advance the sculpting tool into or onto the second bone may be provided by the weight of the extremity or by the surgeon applying force to the extremity. 
   In a further embodiment, the invention provides a method of appropriately preparing the articular surface of a second bone that normally articulates with a first bone and implanting a prosthetic device. The method involves 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 by articulating one of the bones with respect to the other while bone preparation is performed. Optionally, the sculpting tool may be supported by the first bone with the tool in bone sculpting engagement with the articular surface of the second bone, and then sculpting the articular surface by articulating the tool with respect to the first bone. Alternatively, the sculpting tool may be supported by the first bone with the tool in bone sculpting engagement with the articular surface of the second bone, and then sculpting the articular surface by advancing the tool into or onto the second bone while maintaining the relative orientation of the tool to the second bone. The bone sculpting tool may be supported by an implant, a trial, a reamer or a broach placed in or on a bone. Alternatively, the bone sculpting tool may be attached to or integral with an implant, a trial, a reamer or a broach placed in or on a bone. Optionally, the bone sculpting tool may be attached to a bone mount that is directly or indirectly attached to or integral with an implant, a trial, a reamer or a broach placed in or on a bone. 
   Specifically, for example, the invention may be used for replacing the surfaces of a femur and acetabulum through a minimal incision and with minimal disruption of musculotendinous structures about the hip. A typical incision for a minimally invasive total hip procedure is between two and four inches in length. It is noted that there may be some variation in incision length due to patient physiology, surgeon preferences, and/or other factors; the stated range is illustrative, not limiting. In addition to a small incision, care is taken to approach the joint capsule by separating tissues between muscle groups, rather than sectioning specific muscles. The invention includes, in various embodiments, a reamer system. The reamer system in accordance with the present invention is either a modular or non-modular construct that, for hip applications, comprises a femoral attachment component which is typically a femoral trial, a reamer drive (either integral or separate), a handle, and a hemispherical grater or similar device for removing cartilage and bone from the acetabular fossa. The reamer system is powered by a power source such as a standard surgical drill. Optionally, the reamer system may be powered by an integral power source such as an electric, pneumatic or hydraulic motor, a solenoid, an electromechanical drive or other suitable power source. The reamer system is designed or structured to be placed into the joint cavity via one or more small incisions while leaving most, if not all, muscles intact. Surgical navigation may be used to aid in positioning the reamer system and in monitoring progression of acetabular preparation by attaching a navigational tracker to the pelvis and a second navigational tracker to the reamer drive. Optionally, the second navigational tracker may be attached to the handle. Once the femur and acetabulum have been prepared, the implants are placed without further muscle release or surgical trauma. 
   In a minimally invasive procedure, 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 support a femoral broach which in turn supports the reamer system to prepare the acetabulum. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration of hip anatomy and conventional exposure for total hip replacement; 
       FIG. 2  is an illustration of exposure for minimally invasive total hip replacement with a reamer system; 
       FIGS. 3A ,  3 B and  3 C are perspective views of a reamer system in accordance with the present invention, including a handle, reamer drive, broach and grater, where the reamer system is depicted in collapsed, extended and exploded views, respectively; 
       FIGS. 4A and 4B  are perspective views of the handle in accordance with one embodiment of the present invention; 
       FIG. 5  is a bottom perspective view of the grater in accordance with one embodiment of the present invention; 
       FIGS. 6A ,  6 B,  6 C and  6 D are top and bottom perspective views of the reamer drive in a collapsed position and an extended position, respectively, in accordance with an embodiment of the present invention; 
       FIG. 7  is an exploded view of the grater threadably attached to the reamer drive in accordance with another embodiment of the present invention; 
       FIG. 8  is an exploded view of a quick attachment apparatus to connect the grater to the reamer drive in accordance with another embodiment of the present invention; 
       FIG. 9  is an exploded view of the grater and the attachment bracket shown in  FIG. 8 ; 
       FIG. 10  is an enlarged perspective view of a portion of the attachment bracket shown in  FIG. 9 ; 
       FIGS. 11A and 11B  are perspective views of the reamer drive, handle, grater and grater removal tool in accordance with the present invention; and 
       FIGS. 12A and 12B  are perspective views of the reamer drive, handle, grater and grater release tool in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates the general anatomy of a hip joint and a typical surgical approach  10  to the hip joint to expose a proximal femur  11  and an acetabulum  12 . Four surgical approaches to the hip joint for total hip replacement are known. These approaches include posterior approaches without trochanteric osteotomy, trans-trochanteric approaches, anterior approaches without trochanteric osteotomy, and Smith-Peterson approaches. A direct lateral approach is also known for total hip arthroplasty. The most common surgical approach to the hip is posterior, and the musculature disrupted may include the short internal and external rotators, tensor fascia femoris, quadratus femoris, piriformis, and on occasion part of the gluteus medius and minimus, and the gluteus maximus. 
   In conventional total hip replacement surgery the hip joint is exposed through a large incision to provide the surgeon full visualization of the hip joint and the acetabular region, and to provide access for surgical power instruments. The femoral head is removed and the femoral canal is reamed and broached to prepare a bony surface to support a hip stem. The stem may be cemented in place, or press fit for bony ingrowth. The acetabulum is prepared, most typically using a grater attached to a surgical hand drill to remove cartilage down to bleeding bone. The skin incision for surgical exposure as shown in  FIG. 1  generally ranges between eight and twelve inches in length with partial or complete release of hip abductors and external rotators resulting in extensive trauma to the soft tissues surrounding the hip joint. 
   In minimally invasive total hip surgery, an incision  21  is typically two to four inches in length as shown in  FIG. 2 . While a two to four inch surgical incision is typical for less or minimally invasive hip surgery, there may be some variation due to patient physiology, surgeon preferences, 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. Those skilled in the art can appreciate that variations to the surgical approaches described herein can be varied according to individual patients, preference of the surgeon and the like. 
   Referring again to  FIG. 2 , incision  21 , muscle dissection and capsular incision are limited to what is necessary for adequate visualization, placement and operation of instrumentation and placement of implants. The general approach is posterior with no muscle release. Alternately, the surgeon may elect to release the piriformis tendon alone or in conjunction with partial or total release of the external rotators, quadratus femoris and gluteus minimus muscles. The incision is just large enough to expose the femoral head and acetabulum  12 , and to enable placement of a reamer system including a grater  22 , a reamer drive  24 , a handle  20 , and a femoral broach  26  as depicted in  FIGS. 3A through 3C . A grater removal tool  88 , as shown in  FIGS. 11A and 11B , and a grater release tool  92 , as shown in  FIGS. 12A and 12B , can also be used with the reamer system. Optionally, one or more tissue distractors  18  may be used to hold soft tissue out of the line of sight or to distract tissue for instrument placement. Alternately, one or more of the tissue distractors may be integral to the handle  20 , or may be integral to the reamer drive  24 , or a combination thereof. 
   Reamer drive  24 , handle  20 , grater  22 , femoral broach  26 , grater removal tool  88 , grater release tool  92 , and/or structural sub-components of each of these are generally manufactured from a suitable stainless steel either by machining, metal injection molding or stamping. Alternately, materials, including but not limited to titanium and titanium alloys, cobalt chromium alloys, and other biocompatible metals, can be used. Biocompatible plastics such as PEEK, Ultem, Celcon, Delron and Radel may also be used for some sub-components. Sub-components fabricated from biocompatible plastics may be machined or injection molded. 
   Reamer drive  24 , as shown in  FIG. 3C , is used with handle  20 , grater  22  and femoral broach  26  to prepare the acetabulum  12 . Referring to  FIGS. 3A and 3B , the femoral broach  26  is structured to prepare the proximal femur and remains in the femur to support the reamer drive  24 . The reamer drive  24  is structured to extend once placed in the hip joint cavity. As shown in  FIG. 3A , reamer drive  24  is collapsed to reduce the profile of reamer system for placement through a small incision. Reamer drive  24  is placed onto femoral broach  26  and hydraulically telescoped to distract femur  11  from acetabulum  12  while applying force to grater  22  in order to prepare acetabulum  12  to receive an implant. At least one passageway  59  is placed in a circumference of grater  22  to allow clearance of handle  20  when reamer drive  24  is fully retracted. Hydraulic pressure is applied to a spline tube  39  to extend a linear spline  48 , which elevates grater  22  to allow a face  60  of grater  22  to pass over handle  20  while grater  22  rotates. Hydraulic pressure is applied to a piston tube  40  to extend a piston  47  that advances grater  22  into acetabulum  12  and provides a distraction force between femur  11  and acetabulum  12  to engage cutting elements  15  with material, such as cartilage and bone, of the acetabulum. 
   Referring now to  FIGS. 4A and 4B , handle  20  is structured with an internal drive shaft  31  structured at one end with a Hudson fitting for attachment to a standard surgical drill. Alternately, the drive shaft  31  may be structured with a Hall adaptor, cylindrical, square, hexagonal or other shaped fitting suitable for attachment to a surgical drill can be used. A grip  32  is structured for easy handling by the surgeon and secured to a base  33  of handle  20 . A barrel  35  is threaded onto base  33 . A lock sleeve  34  is also threaded onto base  33  in order to secure barrel  35  to base  33 . A barrel opening  37  is structured to slidably receive reamer drive  24 , which engages a bayonet lock  36  in barrel  35 . Referring to  FIG. 6A , an attachment boss  45  on reamer drive  24  is structured to be slidably received into barrel opening  37 . An external square drive  44  of a pinion gear  43 , as shown in  FIG. 6A , is structured to be slidably received into an internal square drive  29  of a drive shaft  38 , as shown in  FIG. 4B . Two bosses  46  protruding from attachment boss  45  of reamer drive  24  engage bayonet lock  36  in barrel  35  of handle  20 . Barrel  35  extends along base  33  to provide clearance for attachment boss  45  to slide into barrel  35 . Reamer drive  24  is rotated clockwise to engage bayonet lock  36  with bosses  46  protruding from attachment boss  45 . Barrel  35  is threaded further onto base  33  thereby securing bosses  46  on attachment boss  45  of reamer drive  24  within bayonet lock  36 . Lock sleeve  34  is then advanced to secure barrel  35  in place. 
   Referring to  FIGS. 6A ,  6 B,  6 C and  6 D, reamer drive  24  is configured to extend in order to provide a distraction force between femur  11  and acetabulum  12  during acetabular reaming. Linear spline  48  is slidably received by a bevel gear  50  and housing base  52 . Hydraulic pressure delivered to the cylinder housing the linear spline  48  by a fluid, such as sterile saline or other suitable liquid, via the spline tube  39  extends the linear spline  48 . Spline tube  39  has a standard Luer fitting  41  for attachment to a syringe pump or other suitable pressurizing device. Piston  47  is configured to slidably receive a broach post  27  on femoral broach  26  as depicted in  FIG. 3C . Hydraulic pressure, via a suitable fluid such as sterile saline, is applied to piston tube  40  to extend piston  47 . Piston tube  40  has a standard Luer fitting  42  for attachment to a syringe pump or other suitable pressurizing device. In one embodiment as shown in  FIGS. 3B and 6A , grater  22  is structured for threaded attachment to linear spline  48 . In another embodiment, grater  22  is structured for quick attachment to reamer drive  24 . 
   Referring now to  FIG. 5 , grater  22  is structured for threaded attachment to reamer drive  24 . A bracket  54  is secured to an inner surface  57  of grater  22  with bracket  54  at three attachment points  55 . Those skilled in the art can appreciate that bracket  54  can be structured with one or more attachment points  55  to be attached to grater  22  as suitable for attachment around cutter openings  58 . In one embodiment, bracket  54  is structured with an internal thread  56  for threaded attachment to linear spline  48  of reamer drive  24 . Bracket  54  can be further attached to grater  22 , for example via welding, soldering, and the like. A right hand thread is used at the bracket-to-linear-spline interface and the cutting action of grater  22  is in right hand rotation of grater  22 . Operation of grater  22  to remove bone in accordance with this embodiment tends to tighten bracket  54  onto linear spline  48 . Alternately, bracket  54  is structured to attach to grater  22  by a threaded attachment, bayonet attachment, press-fit attachment or bonded attachment, or with threaded fasteners, press-fit pins, mechanical clips, or other attachment means know to those skilled in the art. 
   In one embodiment, grater  22  is secured to linear spline  48  of reamer drive  24  such that linear spline  48  is removable from reamer drive  24 . In this embodiment, linear spline  48  is structured to attach to grater  22  by a threaded attachment, bayonet attachment, press-fit attachment or bonded attachment, or with threaded fasteners, press-fit pins, mechanical clips, or other attachment means know to those skilled in the art. In another embodiment, linear spline  48  is permanently attached to grater  22  via welding, soldering, and the like. 
   In one embodiment of the present invention, as shown in  FIG. 7 , grater  22  has formed tabs  61  to which a bracket  62  is attached. In this embodiment bracket  62  is structured with an internal thread  65  for threaded attachment to external thread  49  on linear spline  48  of reamer drive  24 . Alternately, bracket  62  can be permanently attached to formed tabs  61  at contact points formed by one or more bosses  63  extending from bracket  62  to corresponding formed tabs  61 . In another embodiment, the bracket-to-grater interfaces are secured with pins  68  placed through a clearance hole  66  in formed tabs  61  and fitted into a press-fit hole  64  in bracket bosses  63 . Alternately, bracket  62  is structured to attach to grater  22  by a threaded attachment, bayonet attachment, press-fit attachment or bonded attachment, or with threaded fasteners, press-fit pins, mechanical clips, or other attachment means know to those skilled in the art. 
   Referring now to  FIGS. 7 and 11A  and  11 B, grater  22  is removed by unthreading it from reamer drive  24  and/or linear spline  48 . To simplify this step, a grater removal tool  88  is provided. Grater removal tool  88  has one or more protruding bosses  90  corresponding to each of a plurality of receiving pocket  89  in grater  22 . Grater removal tool  88  is placed onto grater  22  with bosses  93  extending into respective receiving pockets  89  in grater  22 . A reaction arm  91  on grater removal tool  88  rests against barrel  35  of handle  20  while the surgical drill (not shown) attached to handle  20  is run in reverse thereby unthreading grater  22  from reamer drive  24  and/or linear spline  48 . Optionally, a T-handle driver (not shown) is used in place of the surgical drill to unthread grater  22  from reamer drive  24 . Grater removal tool  88  and grater  22  are then lifted from reamer drive  24 . 
   Referring now to  FIG. 8  there is shown an embodiment of a bracket  67  including clips  69  for quick attachment to grater  22  in order to enable grater exchange without threading. Grater  22  has formed tabs  61  to which one or more clips  69  are attached. In this embodiment bracket  67  is structured with an internal thread  70  for threaded attachment to external thread  49  on linear spline  48  of reamer drive  24 . Referring to  FIGS. 8 ,  9  and  10 , clip  69  is comprised of two flex arms  73  and  74  each having an internal latch  75  and  76 , respectively. Internal surfaces  81  and  82  of clip  69  are spaced to snuggly receive formed tabs  61  resting on sides  71  and  72  of formed tab  61 . Receiving surfaces  83  and  84  above internal latches  75  and  76  taper outwardly such that the spacing between upper edges  85  and  86  of each receiving surface  83  and  84 , respectively, is greater than the spacing between sides  71  and  72  of formed tabs  61  when flex arms  73  and  74  are in their resting position. As grater  22  is pressed into clips  69  of bracket  67 , formed tabs  61  slide along their respective receiving surfaces  83  and  84 , thereby spreading flex arms  73  and  74  of clip  69 . As formed tabs  61  pass over their respective internal latches  75  and  76  on bracket  67 , internal latches  75  and  76  retain formed tabs  61  within clips  69  thereby locking grater  22  to bracket  67 . When in the locked position, an inner face  87  of formed tabs  61  rests against a support face  79  of bracket  67  thereby centering grater  22  with respect to bracket  67 . Sides  71  and  72  of formed tabs  61  are slidably received by internal support surfaces  77  and  78  of bracket  67  providing the ability to transfer torque from bracket  67  to grater  22 . A right hand thread is used at the bracket-to-linear spline interface and the cutting action of grater  22  is in right hand rotation of grater  22 . Operation of grater  22  to remove material, such as cartilage and bone, with cutting elements  15  on the hemispherical surface tends to tighten bracket  67  onto linear spline  48 . 
   Referring to  FIGS. 9 ,  10  and  12 A and  12 B, grater  22  is removed by releasing clips  69  of brackets  67  with the use of a grater release tool  92 . Grater release tool  92  has one or more protruding bosses  93  each corresponding to clips  69  on bracket  67 . Grater release tool  92  is placed onto grater  22  with bosses  93  extending into respective receiving pockets  89  in grater  22 . A bottom surface  96  of each boss  93  comes to rest on an upper surface  97  of each formed tab  61  on grater  22 . Boss sides  94  and  95  are slidably received by clip  69  receiving surfaces  83  and  84  thereby spreading flex arms  73  and  74  of clip  69  and releasing grater  22 . Grater release tool  92  and grater  22  are then lifted from bracket  67 . 
   In one embodiment of the present invention reamer drive  24 , handle  20  and grater  22  are reusable components. Alternatively, handle  20  and grater  22  are reusable and reamer drive  24  is a single use or multiple use disposable device. In another embodiment, handle  20  is a reusable instrument and reamer drive  24  and grater  22  are single use or multiple use disposable devices. In yet another embodiment of the present invention grater  22  is integrally formed with reamer drive  24 . 
   Now that each component of the present invention has been discussed, following is a discussion of a method of use of reamer system of the present invention. The hip joint cavity is exposed according to known techniques, including but not limited to those described above. The femoral canal is prepared using reamer drive  24  and femoral broach  26 , where femoral broach  26  is left in the femoral canal. Reamer drive  24  and grater  22  are assembled and placed onto femoral broach  26 . Those skilled in the art can appreciate that the sequence of instrument placement into the surgical site may vary based on surgeon preference and joint cavity access. Reamer drive  24  and grater  22  may be assembled outside the surgical site or within the joint cavity. Reamer drive  24  is assembled to handle  20  outside of the surgical site. An appropriately sized grater  22  is selected an attached to reamer drive  24 . The surgeon selects grater  22 , which is part of a set of graters of appropriate size range for preparing a patient&#39;s acetabulum. Grater  22  typically ranges from a diameter of 36 mm to 80 mm in one mm increments. In general, the surgeon will select an initial grater size smaller than the acetabular diameter for initial acetabular reaming. 
   In order to position grater  22  within acetabulum  12  in a minimally invasive manner, reamer drive  24  is initially collapsed as shown in  FIG. 3A  to reduce size for placement into the joint cavity. Once in position, reamer drive  24  is structured to expand as shown in  FIG. 3C  to provide a distraction force between the femur and acetabulum and grater  22  is positioned within acetabulum  12  in order to initiate the reaming process. The initial grater  22  is then exchanged for a larger grater, typically one mm larger in diameter, and the acetabular reaming step is repeated. This process is repeated until the acetabulum is appropriated prepare as determined by the surgeon to receive an implant. In order to allow interchangeability of grater  22  sizes with reamer drive  24 , each grater  22  in the grater set is structured with a corresponding linear spline  48 . In this manner, exchanging various size graters  22  is quick and efficient. To further simplify grater  22  exchanging during the reaming process, grater removal tool  88  and greater release tool  92  can be used to remove grater  22  from reamer drive  24  and/or linear spline  48 . Upon completion of reaming process, acetabulum  12  is prepared for implantation of total hip replacement device according to techniques known in the art. 
   While the invention has been described with reference to the specific embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope of the invention as defined in the following claims and their equivalents.

Technology Category: a