Abstract:
A set of femoral orthopedic devices includes a first component having a first size and a second component having a second size. The first component includes a peg positioned a predetermined distance from a first reference point The second component includes a peg positioned said predetermined distance from said first reference point. The method calls for referencing a femoral condyle at a first reference point, locating a peg aperture a predetermined distance from the first reference point, selecting a sized femoral component, and implanting the femoral component. The size of the femoral component is defined by a distance from the peg to a second reference point.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to prosthesis and instruments used during knee surgery for the reinstatement of the natural knee joint. More particularly, the invention relates to a unicondylar femoral prosthesis and the instruments used to properly size and locate the prosthesis using anterior or posterior referencing. 
     For various reasons, the human knee fails at the tibial and femoral juncture causing great pain and suffering to the individual. To correct this problem, surgeons now replace all or part of the natural knee joint with artificial components. In one type of partial knee replacement, an artificial tibial component is placed on the proximal end of the tibia and an artificial femoral component is placed on the distal end of the femur. 
     Because each individual&#39;s femur and tibia are different in size and because the extent of damage to the tibia and femur ends cannot accurately be determined until after the knee has been opened by the surgeon, the size of the implant components cannot be easily determined prior to the operation. Accordingly, it is common practice to initiate the operation, open up the knee, fully evaluate the needs of the patient and, at that time, determine the size of the femoral and tibial components required. In view of this practice, manufacturers of femoral and tibial components typically manufacture five to eight different size component sets to be available to the surgeon during the operation. 
     Additionally, once the knee is open, the surgeon evaluates the patient to determine which of two referencing methods will best suit the patient. In anterior referencing, careful attention is given to the patellofemoral joint by using an anteriorally placed feeler gage. This referencing system focuses on allowing proper ligament balance and stability in extension as well as consistent patellofemoral placement on the anterior surface. 
     A second type of instrument design (posterior referencing) is based on the concept that flexion and extension stability are more important than the patello transition location. Specifically, the flexion gap is better balanced to avoid laxity in flexion or tightness in flexion. 
     In the case of sizing the femoral distal end in determining which of the femoral component sizes to use, the common practice has been to measure the anterior to posterior distance of the femur and, utilizing this measurement, to pick an appropriate size femoral component. Unfortunately, this technique is relatively invasive because the instrument used to measure the anterior to posterior femoral distal end distance is relatively large and unwieldy. 
     Many surgeons wishing to avoid patient morbidity associated with the aforementioned invasive procedure have chosen an instrument free method of resection. In this method, the surgeon removes portions of the femoral distal end with a burr operated by hand without the use of a resection guide. While such a method is less invasive, the resected surface created by the burr is not accurately located relative to a reference point. Unfortunately, variation in the final positioning of the femoral component occurs. 
     Accordingly, an object of the present invention is to provide a method and apparatus enabling implantation of a unicondylar femoral prosthesis with minimal bone removal. 
     Another object of the present invention is to provide a minimally invasive technique for producing reproducible bone resections using either anterior or posterior referencing. 
     The present invention relates to a set of femoral orthopedic devices and a method of implanting the devices. The set of femoral orthopedic devices includes a first component having a first size and a second component having a second size. The first component includes a peg positioned a predetermined distance from a first reference point The second component includes a peg positioned a predetermined distance from said first reference point. The method calls for referencing a femoral condyle at a first reference point, locating a peg aperture a predetermined distance from the first reference point, selecting a sized femoral component, and implanting the femoral component. The size of the femoral component is defined by a distance from the peg to a second reference point. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to one skilled in the art by reading the following specification and subjoined claims and by referencing the following drawings in which: 
     FIG. 1 is an anterior view of an embodiment of the present invention implanted in a knee joint; 
     FIG. 2 is a medial view of an embodiment of the present invention implanted in a knee joint; 
     FIG. 3 is a perspective view of a right medial tibial tray of the present invention; 
     FIG. 4 is another perspective view of a right medial tibial tray of the present invention; 
     FIG. 5 is a perspective view of a right medial tibial insert of the present invention; 
     FIG. 6 is a another perspective view of a right medial tibial insert of the present invention; 
     FIG. 7 is a lateral view of a femoral component of the present invention; 
     FIG. 8 is a superior view of a femoral component of the present invention; 
     FIG. 9 is a posterior view of a femoral component of the present invention; 
     FIG. 10 is an anterior view of a spacer positioned within a tibial resection adjacent a femur; 
     FIG. 11 is a medial view of a spacer positioned within a tibial resection adjacent a femur; 
     FIG. 12 is a superior view of the spacer placed within the tibial resection with the femur removed; 
     FIG. 13 is an anterior view of a femoral sizing guide placed on a femur acting in conjunction with the tibial spacer of the present invention for anterior referencing; 
     FIG. 14 is a medial view of a femoral sizing guide mounted on a femur acting in conjunction with a tibial spacer for anterior referencing; 
     FIG. 15 is an anterior view of a posterior resection guide placed on a femur; 
     FIG. 16 is a medial view of a posterior resection guide placed on a femur; 
     FIG. 17 is an anterior view of a femur depicting a distal femoral area of bone to be removed; 
     FIG. 18 is a medial view of a femur depicting a distal femoral area of bone to be removed prior to the implantation of the components of the present invention; 
     FIG. 19 is an anterior view of a posterior resection guide placed on a femur; 
     FIG. 20 is a medial view of a posterior resection guide placed on a femur; 
     FIG. 21 is an anterior view of a femoral sizing guide placed on a femur for posterior referencing; and 
     FIG. 22 is a medial view of a femoral sizing guide placed on a femur for posterior referencing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiments concerning a unicondylar femoral prosthesis and instruments are merely exemplary in nature and are not intended to limit the invention or its application or uses. Moreover, while the present invention is described in detail below with respect to a right medial unicondylar prosthesis, it will be appreciated by those skilled in the art that the present invention may be applied to various other types of knee joint prostheses such as a total knee joint prosthesis. 
     Referring to FIGS. 1 and 2, a unicondylar knee prosthesis implanted using the instruments and method of the invention is shown. A femur  10  is shown in combination with a tibia  12 . Femur  10  has a femoral component  14  implanted therein. Tibia  12  has a tibial component  16  implanted therein. While a right medial surgery is shown, it is known that the method will apply to both medial and lateral components, as well as left and right knees. 
     With reference to FIGS. 3-6, tibial component  16  includes a tibial tray  18  and a tibial insert  20 . Tibial component  16  is designed to resurface the proximal end of the tibia to cooperate with a unicondylar femoral component  14 . Tibial tray  18  includes a generally “D” shaped body  22  having a pair of posts  24  extending orthogonally therefrom. Tibial tray  18  also includes a tab  26  extending from body  22  in the same direction as posts  24 . Body  22  includes a snap groove  28  configured to receive tibial insert  20 . It should be appreciated that the two piece tibial component described is merely exemplary and that singular or other multi-piece designs are contemplated for use with the femoral component of the present invention. 
     Tibial insert  20  may be constructed from any suitable bearing material such as ultra high molecular weight polyethylene (UHMWPE). Tibial insert  20  includes a generally D-shaped body  30  having a wear surface  32 . A pair of snap tabs  34  extend from the opposing surface of body  30 . It should be appreciated that snap tabs  34  of tibial insert  20  engage snap groove  28  of tibial tray  18  once tibial component  16  is assembled. In this manner, a modular unicondylar tibial component may be implanted and subsequently reconstructed by removing only the wearable tibial insert  20 . Accordingly, the tibial tray to tibia interconnection need not be disturbed. 
     With reference to FIGS. 7-9, femoral component  14  is depicted in detail. Femoral component  14  is designed to resurface the distal and posterior portions of one of the femoral condyles of femur  10 . Femoral component  14  has an articulating surface  36  and a bone mating surface  38 . Articulating surface  36  in the preferred embodiment includes a pair of radial surfaces  40  and  42  that are tangent to one another forming a smooth flowing surface when viewed from the lateral direction. Radial surface  42  terminates at an anterior run-out  43  of femoral component  14 . In the other plane (FIG.  9 ), the distal portion of femoral component  14  includes a radius  44  extending from anterior run-out  43  to a posterior portion  45  that is larger than and blends with a radius  46  that is present on posterior portion  45 . This allows for more movement between femur  10  and tibia  12  when in flexion than in extension, similar to the natural knee. 
     Bone mating surface  38  is comprised of a distal surface  48 , a posterior surface  50 , and a posterior chamfered surface  52 . Extending from bone mating surface  38  is a first peg  54  and a second peg  56 . Pegs  54  and  56  aid in alignment and stability. Preferably, a rib  58  interconnects first peg  54  and second peg  56  to resist rotation of femoral component  14  after implantation. 
     First peg  54  is positioned a pre-determined distance  60  from anterior run-out  43 . In addition, second peg  56  is positioned a pre-determined distance  62  from posterior portion  45 . As will be described in greater detail hereinafter, distances  60  and  62  remain constant as femoral component size changes. A surgeon has the option of choosing anterior or posterior referencing while using a common femoral component. Accordingly, as the size of the femoral component increases, a distance  64  between first peg  54  and second peg  56  increases in order to maintain distances  60  and  62  constant. 
     It should be appreciated that the femoral component previously described as having both first and second pegs is merely exemplary. For example, another embodiment of a femoral component constructed in accordance with the teachings of the present invention includes a single peg positioned predetermined distance  60  from anterior run out  43 . Similarly, another femoral component embodiment exists having a single peg positioned predetermined distance  62  from posterior portion  45 . Therefore, alternate femoral component embodiments may be constructed by simply removing one of first peg  54  or second peg  56 . 
     Another embodiment of the present invention positions first peg  54  a pre-determined distance  65  from chamfer  52 . In this manner, the size and location of chamfer  52  are also standardized. One skilled in the art should appreciate that first peg  54  may also be positioned a constant distance from posterior surface  50  without departing from the scope of the present invention. 
     The method of implantation for the unicondylar knee prosthesis will now be described including a description of the instruments used for the method. With reference to FIGS. 10-14, the knee is articulated in flexion and an incision is made to open the knee as is known by those skilled in the art. After exposure of the joint, tibia  12  is resected using a tibial cutting guide (not shown). A tibial spacer  66  is inserted at the tibial resection. At this time, the surgeon determines the proper joint tension by articulating the joint through flexion and extension with spacer  66  in place. If the joint is too lax, a spacer having a greater thickness is inserted. Conversely, if the joint tension were too tight, a spacer having a lesser thickness would be inserted. Once the proper joint tension is set, the corresponding spacer remains positioned between the posterior distal femur and the tibial resection. Alternatively, the joint tension may be set using a tensioning device. The tensioning device (not shown) loads and positions femur  10  relative to tibia  12  to properly define the distance between resected tibia  12  and femur  10  without the use of spacer  66 . 
     At this time, the surgeon must decide which referencing method is best suited for the patient. The anterior referencing method will be described first. Femur  10  is sized using a sizing guide  68 . Sizing guide  68  includes a body  70  having a first portion  72  and a second portion  74 . First portion  72  includes a peg aperture  76  and a pin aperture  78 . Second portion  74  extends anterior of first portion  72 . Second portion  74  includes a first face  80  and a second face  82  generally converging at a point  84 . 
     Sizing guide  68  also includes an indexable probe  86 . A sizing scale  88  is imprinted on an exterior surface of indexable probe  86 . Indexable probe  86  has a first end  90  disposed within a probe aperture  92  located within first portion  72 . Indexable probe  86  also includes a second end  94 . 
     To determine the proper femoral component size to be implanted, sizing guide  68  is placed over a distal end of femur  10  as shown in FIG.  14 . Body  70  is aligned such that first face  80  contacts anterior reference point  96  at the edge of the anterior run-out. It should also be appreciated that sizing guide  68  is placed at a slight angle in relation to tibial spacer  66  along the line formed by the anterior and posterior portions of distal femur  10 . Once aligned, sizing guide  68  is pinned in place while a first peg aperture  98  is drilled. Preferably, first pin apertures  100  are machined using relatively small, headless drill bits that are left in place to align sizing guide  68  and a resection guide as will described in greater detail hereinafter. Once sizing guide  68  has been aligned and pinned as previously discussed, indexable probe  86  is translated until second end  94  contacts tibial spacer  66 . The size is determined by noting where sizing scale  88  meets first portion  72  of body  70 . Sizing guide  68  is removed. 
     With reference to FIGS. 15 and 16, an appropriately sized resection guide  102  is mounted to femur  10 . Posterior resection guide  102  includes a generally rectangular body  104  having a peg  106  extending therefrom. Body  104  also includes at least one pin aperture  108  used to align resection guide  102  relative to femur  10 . As mentioned earlier, in the preferred technique, the surgeon leaves the headless drill bit used to create first pin aperture  100  therewithin. Accordingly, proper alignment of posterior resection guide  102  is guaranteed by disposing peg  106  within first peg aperture  98  while disposing the headless drill bit within pin aperture  108 . 
     Posterior resection guide  102  includes a slot  110  used to guide the saw blade when making the posterior chamfer cut. Body  104  includes a posterior surface  114  used to guide a saw blade when making the posterior cut. The posterior chamfer cut is designed to correspond to bone mating surface  52 . The posterior cut acts in conjunction with bone mating surface  50 . Posterior resection guide  102  may also include a second drill guide used to guide a drill for forming a second peg aperture (not shown) if desired. Alternatively, a separate drill guide may be introduced to align a drill bit when forming the second peg aperture. 
     The posterior resection guide and headless drill bit are removed to perform a final bone removal step. As shown in FIGS. 17 and 18, a distal portion  118  is removed to correspond to distal surface  48  of femoral component  14 . If the specific femoral component chosen includes rib  58 , an additional cut is made in the distal femur to allow complete insertion of rib  58  within the cut. 
     To complete the unicondylar implantation process, femoral component  14  is cemented to femur  10 . Similarly, tibial component  16  is cemented to tibia  12  using a conventional cementing technique that is well known to those skilled in the art. The wound is then closed and post-operative care is given. 
     As mentioned earlier, the present invention is directed to both anterior and posterior referencing methods and instruments. If the surgeon decides after initially opening the joint, that a posterior referencing method is more desirable than an anterior referencing method, a different procedure and set of instruments are used as described below. 
     As shown in FIGS. 19 and 20, the posterior referencing method begins by making a tibial resection as previously described in the anterior referencing method section. Next, a posterior resection guide  120  is coupled to femur  10  using pins  122 . Pins  122 , are preferably headless drill bits temporarily left in place to provide alignment for posterior resection guide  120 . Posterior resection guide  120  includes a body  124  having a contact face  126  in contact with distal end of femur  10 . Body  124  also includes a first slot  128  and a second slot  130  for guiding a saw blade. First slot  128  is used to create a posterior cut. Second slot  130  is useful when making a posterior chamfer cut. A leg  132  extends from guide  120  and includes a contacting surface  134  in contact with posterior femur  10 . Posterior resection guide  120  also includes a first drill guide  136  for guiding a drill to create a first peg aperture  138 . 
     After the posterior cut, posterior chamfer cut and first peg aperture are formed, posterior resection guide  120  is removed and a sizing guide  140  is placed on the distal femur as depicted in FIGS. 21 and 22. Sizing guide  140  includes a body  142  and an extending leg  144 . Body  142  includes a face  146  in contact with the distal surface of the femur. Leg  144  includes a face  148  in contact with and positioned adjacent to the posterior cut. An alignment peg  150  extends from body  142  and is disposed within first peg aperture  138 . An indexable probe  152  includes a shaft  154  slidably mounted within body  142 . Shaft  154  has a graduated sizing scale  156  imprinted thereon indexable probe  152  also includes a finger  158  extending from shaft  154 . Finger  158  includes a contact surface  160 . To determine the correct femoral component size, indexable probe  152  is translated until contact surface  160  contacts an terior run-out  43  of femur  10 . At this time, the surgeon reads graduated sizing scale  156  to determine the proper femoral component size. 
     After removal of sizing guide  140 , a drill guide (not shown) is coupled to femur  10  to guide a bit to drill a second peg aperture if required. Lastly, distal bone portion  118  (FIG. 18) is removed as previously discussed. Both the femoral and tibial components are implanted and the wound is closed.