Patent Publication Number: US-2003225458-A1

Title: Universal femoral component for endoprosthetic knee

Description:
BACKGROUND  
       [0001] The present invention relates to a provisional and final femoral component for an endoprosthetic knee.  
       DESCRIPTION OF THE RELATED ART  
       [0002] Endoprosthetic knees of various designs are well known in orthopaedics. Such devices have often been used to successfully treat knee injuries and ailments.  
       [0003] Generally, endoprosthetic knees comprise a femoral component, a tibial component and a meniscal component, sometimes referred to as an articular bearing surface, disposed there between. The femoral component comprises an internal bone contacting surface and an external articulating surface. The internal surface comprises a specific desired shape.  
       [0004] During a total knee arthroplasty (“TKA”) or partial knee arthroplasty (“PKA”), a surgeon cuts the distal femur of the patient into a shape corresponding to the internal surface of the femoral component. The surgeon also resects the proximal tibia, then chooses and attached a desired tibial component. The surgeon subsequently chooses a provisional femoral component and provisional nenixal components. After attaching the provisional femoral component and inserting the provisional meniscal component, the surgeon “reduces” the knee joint to determine whether the proper sizes of components have been selected. If the patient&#39;s joint is unable to accommodate a desirable range of motion due to the size of the implants or if there is too much laxity in the joint due to the same, the surgeon will remove the provisional implants and replace them with differently sized provisional implants.  
       [0005] If there is a need to change the size of the provisional femoral component, the surgeon must often make new cuts to the distal femur. If necessary, the surgeon may need to repeat this process until he or she is satisfied with the fit of the particular endoprosthetic knee, and can replace the provisional components with final components.  
       [0006] It is desirable, therefore, to provide an endoprosthetic knee implant system that alleviates the need for the surgeon to recut bone in order to achieve the proper fit for a femoral knee implant component.  
       SUMMARY OF THE INVENTION  
       [0007] It is an object of the present invention, therefore, to provide an endoprosthetic knee implant system wherein the components are designed such that the surgeon does not need to cut additional bone from a patient&#39;s distal femur to change the size of a provisional femoral component.  
       [0008] The present invention comprises a set of provisional and final femoral knee implant components, wherein each component comprises a unique external articulating surface geometry, but wherein the components have a constant internal bone contacting surface geometry.  
       [0009] Thus, an advantage of the present invention is that a surgeon performing a total or partial knee arthroplasty who finds that the motion of the patient&#39;s knee is impinged or that the knee is too lax throughout a desired range of motion, may simply remove one provisional femoral implant and replace it with another implant having the same internal surface geometry but a slightly smaller external or larger external geometry without making new cuts on the patient&#39;s distal femur.  
       [0010] Although the present invention is described herein as providing a single internal geometry for a pair of external geometries comprising different anterior to posterior dimensions, those skilled in the art of orthopaedic implants will understand that a single internal geometry could also be used to accommodate any number of implants having unique medial to lateral, inferior to superior, or anterior to posterior external dimensions, and a constant internal geometry. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a side elevational of an endoprosthetic knee according to the present invention.  
     [0012]FIG. 2 is a perspective view of a femoral component of an endoprosthetic knee according to the present invention.  
     [0013]FIG. 3 is a perspective view of a pair of artificial femoral components according to the present invention.  
     [0014]FIG. 4 is a perspective view of a provisional femoral component according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
     [0015] The present invention relates to the femoral component of an endoprosthetic knee.  
     [0016] Referring now to FIG. 1, an endoprosthetic knee comprises femoral component  200 , tibial plate  400  and articulating bearing surface  300  disposed there between. Prosthetic knee joints are generally required where all, or a portion of a patient&#39;s natural knee has become painful, misaligned or dis-functional due to trauma or disease. Where a surgeon replaces an entire knee joint (ie: both femoral condyles, the entire meniscus, and the natural proximal tibia), the surgical procedure is referred to as a total knee arthroplasty. Where only one condyle is replaced the procedure is referred to as a partial knee arthroplasty. For the sake of clarity, the present invention is described in terms of a total knee arthroplasty. However, those skilled in the art will appreciate that the invention is equally applicable to a partial knee arthroplasty.  
     [0017] Referring still to FIG. 1, there is shown femur  100  having a series of cuts made to its distal end (a resected femur). Although a specific shape of femoral cuts is shown and described herein, those skilled in the art will appreciate that any series of cuts may be made to the distal femur and any matching internal femoral component geometry may be used within the scope of the present invention. During a total knee arthroplasty this series of cuts, commonly referred to as “box cuts,” is made to the distal femur in order to remove diseased or damaged bone and to prepare the distal femur to receive femoral component  200 . Similarly, a generally flat cut is made to proximal tibia  500  to prepare the tibia  500  to receive tibial plate  400 . The box cuts made to distal femur  100  are adapted to allow femoral component  200  to be fixedly attached thereto. The fixed attachment may be accomplished by any, or a combination of, several means known to those of skill in the art, such as using bone cement, using threaded bone screws, or using a porous surface that allows bone ingrowth to secure distal femur  100  and femoral component  200 .  
     [0018] One issue with which physicians must contend is accommodating the size of an endoprosthetic knee in the amount of space available in a particular patient&#39;s knee joint cavity. Soft tissues, including skin, ligaments, tendons and the like operate to restrict the space available to an endoprosthetic joint.  
     [0019] Presently, when a physician must change a femoral component to a larger or smaller size, new box cuts must be made to distal femur  100 . The present invention comprises a system or set of femoral components and provisional components having a universal box cut geometry suitable for an infinite array of femoral component sizes, while prior devices and methods have required measuring the size of a distal femur  100  and cutting the bone to fit a specific size of prosthesis. Surgeons also sometimes try more than one size of provisional femoral component  200  to achieve an optimal range of motion between knee flexion and extension for a patient&#39;s knee joint given the soft tissue spacing issues described herein. Upon finding a provisional component of appropriate size, the physician chooses a final implant of equal size to use in the actual joint replacement. However, if a physician tries a first provisional femoral implant  200  according to the present invention and finds that it is too large or too small to operate properly in a patient&#39;s knee joint, a new provisional or final femoral component may be used in its place without the need to make additional cuts to distal femur  100 .  
     [0020] Referring now to FIG. 2, femoral component  200  comprises: anterior flange  210 ; medial and lateral condylar flanges  220  and  230 ; interior femoral bone contacting surface  240  and exterior articulating surface  250 .  
     [0021] Anterior flange  210  comprises superior and inferior ends  211  and  212 . Extending posteriorly from, and fixedly attached to, inferior end  212  of anterior flange  210  are parallel medial and lateral condylar flanges  220  and  230 .  
     [0022] The condylar flanges comprise anterior ends  221  and  231  respectively which anterior ends  221  and  231  are fixedly attached to interior end  212  of anterior flange  210 .  
     [0023] Referring to FIG. 2 and FIG. 3, each flange  210 ,  220  and  230  comprises a portion of interior bone contacting surface  240 . Interior  240  comprises a series of connected, segmented planes adapted to be attachable to resected distal femur. The number of connected planes may be as many or as few as desired. Similarly any desired geometry of said planes is acceptable.  
     [0024] In an alternative embodiment of the present invention, condylar flanges  420  and  430  are removably attached to provisional femoral component  400 . Such a modular configuration allows a surgeon to alter the size of femoral component  400  without removing the entire provisional component.  
     [0025] Referring again to FIG. 2, femoral component  200  further comprises exterior articulating surface  250 . Articulating surface  250  is generally convex and comprises the exterior of each flange  210 ,  220  and  230 . Anterior flange  210  preferably comprises patella tracking groove (not shown) disposed on articulating surface  250  along the longitudinal axis of anterior flange  210 .  
     [0026] Femoral component  200  preferably comprises a bio compatible metal. A cobalt chrome alloy is preferred, but any rigid, resilient bio compatible material is acceptable.  
     [0027] The planes comprising interior  240  of femoral component  200  comprise a desired geometry matching the cuts made by the surgeon to distal femur  100 . The geometric relationship between the planes remains relatively constant over an array of implant sizes.  
     [0028] Referring now to FIG. 3, there is shown a set of femoral implants  200  according to the present invention. Therein, interior bone contacting surface  240  comprises a series of interconnected planes having a geometric relationship to one another that is unchanged even as the dimensions or shape of articulating surface  250  are changed to accommodate soft tissues in the knee.  
     [0029] It will be appreciated by these skilled in the art that the foregoing is a description of the preferred embodiment of the present invention. Variations in design and construction may be made to the preferred embodiment without departing from the scope of the invention as defined by the appended claims.