Abstract:
Methods and apparatus for arthroscopically-assisted preparation of the tibia to accept an unicompartmental implant that includes the step of removing bone from the tibial plateau to correct depth, diameter and proper angle by employing a tibial rasp comprising a cutter with a plurality of teeth on the bottom surface and a side surface (for example, the front side). The tibial rasp may be used in conjunction with an additional starter rasp that can cut only in one direction (for example, cutting to establish only the depth of the tunnel or socket).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/222,747, filed Jul. 2, 2009, the entire disclosure of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of arthroscopic surgery and, more particularly, to improved instrumentation for reconstructive knee surgery. 
     BACKGROUND OF THE INVENTION 
     Partial knee replacement surgery (also called unicompartmental knee arthroplasty) is known in the art for the treatment of osteoarthritis of the knee joint. During partial knee replacement surgery, the bone and cartilage on the end of the femur and top of the tibia are removed. A knee replacement implant made of various biocompatible materials such as metal or plastic is then placed to function as a new knee joint. Depending on the condition of the cartilage on the undersurface of the kneecap, the cartilage may also be replaced. The knee replacement implant typically comprises (i) a femoral component which fits on the femur, (ii) a tibial component which fits on the tibia, and optionally (iii) a patellar component, made of plastic and which replaces the cartilage on the undersurface of the kneecap, and optionally (iv) a plastic insert which fits between the femoral and tibial components. 
     Placement of the knee replacement implant typically involves the steps of: (i) forming a tibial socket in the tibial plateau; (ii) performing at least one cut on the femoral condyle; and (iii) placing implants or components into the socket on the tibial plateau and into the cut in the femur. These steps are performed using precise instruments to create exact surfaces to accommodate the implant. For example, instrumentation and apparatus for arthroscopic unicompartmental knee surgery (which include a femoral component and a tibial component) are described for example in U.S. Patent Application Publication No. 2008/0275512, the disclosure of which is incorporated by reference. U.S. Patent Application Publication No. 2008/0039852 (the disclosure of which is also incorporated by reference) describes the use of a dual-sided cutter for forming the femoral trough and tibial socket by retrograde drilling. 
     SUMMARY OF THE INVENTION 
     The present invention provides techniques and apparatus for unicompartmental knee surgery by utilizing novel tibial rasps (a starter tibial rasp and a second tibial rasp) that allow the surgeon and/or medical personnel to rasp away bone at the tibial plateau to the proper diameter, depth and angle (in a direction about normal to the tibial plateau) to facilitate placement of the tibial implant. 
     The starter tibial rasp of the present invention is provided with a cutter (a first rasping body) designed to cut a tibial socket to a set depth using a guide pin that has been inserted in previous steps of retrodrilling a tunnel through the tibia as described in U.S. Patent Application Publication No. 2007/0233128, the disclosure of which is incorporated in its entirety by reference herein. The cutter of the starter tibial rasp is provided with a plurality of teeth located on the bottom surface of the cutter. The cutter is also cannulated to fit over the guide pin located in the tibial tunnel. The guide pin prevents the rasp from cutting outside the desired diameter of the tibial socket. The rasp can only cut establishing a depth of the socket. This rasp is used to start a socket and then a second tibial rasp (described below) is used to complete to formation of the tibial socket. The guide pin is removed prior to using the second tibial rasp. Removal of the pin allows the second rasp to self adjust to approximately normal to the tibial plateau. 
     The second tibial rasp of the present invention is provided with a cutter (a second rasping body) designed to enlarge (to cut) a tibial socket to a set depth, diameter and proper angle (about perpendicular to the tibial plateau) so that the tibial implant will seat easily and properly in the prepared socket. The cutter of the second tibial rasp is provided with a plurality of teeth located on the bottom of the cutter and along only one side of the cutter (for example, the front side). In this manner, the cutter is used to rasp away bone until the top of the cutter portion of the instrument is flush with the tibial plateau, guaranteeing the depth and angle of the cut. The cutter of the second tibial rasp may be provided in various diameters to match various implant sizes. 
     By utilizing the tibial rasps of the present invention in lieu of a typical cutting instrument, the surgeon can position the instruments close to perpendicular to the tibial plateau (when introducing the instrument from the top of the plateau) and more easily visualize and correctly create the tibial socket (for insertion of the tibial implant during the unicompartmental knee surgery). 
     The present invention also provides a method of arthroscopically-assisted preparation of the tibia to accept a unicompartmental implant that includes the steps of: (i) removing bone from the tibial plateau by employing a first starter tibial rasp comprising a cannulated cutter with a plurality of teeth provided only on one side of the cutter (for example, only on the bottom of the cutter); and optionally (ii) removing additional bone to correct depth, diameter and proper angle by employing a second tibial rasp comprising a cutter with a plurality of teeth on the bottom surface and a side surface (for example, the front side). 
     The present invention also provides a method of arthroscopically-assisted preparation of the tibia to accept an unicompartmental implant that includes the step of removing bone from the tibial plateau to correct depth, diameter and proper angle by employing only one tibial rasp comprising a cutter with a plurality of teeth on the bottom surface and a side surface (for example, the front side). 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a tibial rasp of the present invention; 
         FIG. 2  illustrates an expanded view of the tibial rasp of  FIG. 1 ; 
         FIG. 3  illustrates a close-up view of the cutter of the tibial rasp of  FIG. 1 : 
         FIG. 4  illustrates a perspective view of a starter tibial rasp of the present invention; 
         FIGS. 5A-C  illustrate various views of the starter tibial rasp of  FIG. 4 ; and 
         FIG. 6  illustrates the tibial socket created by the tibial rasps of  FIGS. 1 and 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, where like elements are designated by like reference numerals,  FIGS. 4 and 5  illustrate various views of a starter tibial rasp  100  (a first tibial rasp  100 ) of the present invention, while  FIGS. 1-3  illustrate details of a second tibial rasp  10  of the present invention. The first and second raps  100 ,  10  of the present invention may be provided as an assembly, pre-packaged before surgery and ready for use, or may be assembled during the surgery by medical personnel. 
     The starter tibial rasp  100  of the present invention is provided with a handle  115  and a cutter  120  (rasping body  120 ) designed to create a bone socket or tunnel. Cutter  120  has a generally cylindrical configuration and is provided with an outer cylindrical surface  120   a  and opposing surfaces  120   b . The cutter  120  is cannulated (provided with a hole  130  through it) for placement over a guide pin secured in the tibia by retrograde drilling. The cutter  120  has a plurality of teeth  122  on bottom surface  120   b  (for example, the bottom surface of the two opposing surfaces  120   b ) for creating the socket or tunnel. 
     The second tibial rasp  10  of the present invention is provided with a handle  15  attached to a shaft  16  and a cutter  20  (rasping body  20 ) designed to enlarge (to cut) the tibial tunnel or socket created with the starter tibial rasp  100  to a set depth, diameter and proper angle (about perpendicular to the tibial plateau) so that the tibial implant will seat easily and properly in the prepared tunnel. Preferably, cutter  20  is releasably attached to shaft  16 . Cutter  20  has preferably a general cylindrical configuration, with an outer cylindrical side or surface  20   a  and two opposing sides or surfaces  20   b  ( FIG. 2 ). 
     The cutter  20  of the tibial rasp  10  is provided with a plurality of teeth  22  located only on a portion of outer cylindrical surface  20   a . In an exemplary embodiment, cutter  20  is provided with a plurality of teeth  22  on one side of the cutter (for example, only on the front side  25  of surface  20   a ). A second plurality of teeth  27  is provided on one of the other two opposing surfaces  20   b  (for example, on the bottom side or surface  20   b ) of the cutter  20 . In this manner, the cutter  20  is used to rasp away bone until the top of the cutter  20  is flush with the tibial plateau, guaranteeing the depth of the cut. The cutter  20  of the tibial rasp  10  may be provided in various diameters to match various implant sizes. 
     Tibial rasp  10  of the present invention allows the surgeon and/or medical personnel to rasp away bone at the tibial plateau to the proper diameter, depth and angle (in a direction about normal to the tibial plateau) to facilitate placement of the tibial implant. 
     By utilizing the starter tibial rasp  100  of the present invention in lieu of a typical cutting instrument used in the art, the surgeon can position the instrument perpendicular to the tibial plateau (when introducing the instrument from the top of the plateau over the guide pin) and more easily create a socket having the correct orientation for further insertion of the tibial implant during the unicompartmental knee surgery. The second tibial rasp  10  follows the starter rasp and removes the additional bone not only for the proper depth of the socket but also for the proper orientation of the socket. 
       FIG. 6  illustrates the tibial tunnel  160  created from the retrograde drilling step which is at an angle α2 of 45° also referred to as the parallax error. The proper orientation of the tibial socket for placement of the tibial implant is about perpendicular to the tibial plateau (angle α1 of 90°). The plurality of teeth  22  along the front side  25  of the second tibial rasp  10  removes the area of bone depicted as dotted lines  180  in  FIG. 6 , to create the socket with the desired orientation (i.e., at angle α1 relative to surface  150  of the bone). 
     In an exemplary embodiment only, cutters  20 ,  120  are detachable from the handle  15  of the tibial rasp  10 . In this manner, an additional instrument (for example, an impactor) may be attached to handle  15  in lieu of the cutter so that the instrument (i.e., the impactor) may be employed to drive in the tibial implant, for example, subsequent to the step of enlarging the tibial socket. 
     Although the present invention has been described in connection to a tibial rasp used for removing bone from a tibial socket, the invention is not limited to this exemplary only embodiment, and contemplates an instrument employed for enlarging any socket or tunnel formed into a bone (for example, a hip replacement rasp, among others). 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.