Abstract:
A unicondylar femoral component for use in a partial knee arthroplasty. A femoral component of the present invention comprises a post and a flange having a predetermined angle there between whereby a clamping force is placed on a patient&#39;s distal femur to hold the implant in place. The implant further comprises a porous layer on its bone contacting surface. In an alternative embodiment the femoral component is attached to the distal femur at least two threaded fasteners.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to unicondylar or partial knee arthroplasty, specifically the invention relates to a femoral component used during such an operation.  
           [0003]    2. Description of the Related Art  
           [0004]    Total knee arthroplasty (“TKA”) has long been a successful treatment for patients who have knee joints that have been damaged by disease or trauma. During a TKA a patient&#39;s damaged knee is replaced with an endoprosthetic implant generally comprising a femoral component, a bearing component, and a tibial component wherein the femoral component is attached to the distal femur of the patient. This fixation occurs in part via a clamping force against the distal femur generated between the posterior and anterior flanges of the femoral component. Femoral components used during a TKA may further comprise a porous surface that promotes growth of bone into the implant. Such boney ingrowth provides better fixation of the implant and for a more accurate simulation of a natural knee.  
           [0005]    Sometimes, however, a patient&#39;s knee is only partially damaged, thus it is sometimes only necessary to fix one compartment, or condyle, of the damaged knee. It is desirable in such circumstances to form a partial knee arthroplasty (“PKA”) which normally requires less surgical cutting and therefore less trauma to the patient. Unfortunately, unicondylar femoral components do not have posterior flanges with which the anterior flange can generate a clamping force against a distal femur. It is desirable, therefore, to provide a unicondylar femoral component for a PKA that may be attached to a distal femur despite lacking a posterior flange. It is further desirable to provide a unicondylar femoral component for a PKA that comprises a porous surface useful in promoting boney ingrowth.  
         SUMMARY OF THE INVENTION  
         [0006]    A unicondylar femoral component for use in a PKA according to the present invention comprises, in one embodiment thereof, an articulating surface, a bone contacting surface, a posterior post, a porous layer, and an anterior flange. The post and flange are disposed such that a clamping force is generated there between against a prepared distal femur thereby holding the implant in place.  
           [0007]    In a second embodiment, the present invention comprises an articulating surface, a bone contacting surface, a posterior post, an anterior post, and a porous layer wherein the clamping force against the distal femur is generated between the posterior and anterior posts.  
           [0008]    In a third embodiment, the unicondylar femoral component of the present invention comprises an articular surface, a bone contacting surface, a porous layer disposed on the bone contacting surface and at least two threaded fasteners that are threaded through the femoral component and into the distal femur.  
           [0009]    It is an advantage of the present invention that it allows a unicondylar femoral component to be fixedly attached to a distal femur.  
           [0010]    Another advantage of the present invention is that it accommodates a porous layer disposed on the bone contacting surface of the femoral component.  
           [0011]    Another advantage of the present invention is that it allows for the use of a trabecular metal porous layer.  
           [0012]    Other advantages and features of the present invention will be apparent to those skilled in the art upon a review of the appended claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above mentioned and other features and advantages of this invention and the manner of obtaining them will become more apparent, and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a side elevational view of a first embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is a side elevational view of a second embodiment of the present invention.  
         [0016]    [0016]FIG. 3 is a bottom view of a third embodiment of the present invention.  
         [0017]    [0017]FIG. 4 is a side cross-sectional view of the third embodiment of the present invention. 
     
    
       [0018]    Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent an exemplary embodiment of the present invention the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain the invention. The illustrations set out herein merely illustrate exemplary embodiments of the present invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    As used herein, the following locational definitions apply, anterior or posterior mean near the front or near the back of the body respectively. Thus, for the knee joint described herein anterior refers to that portion of the knee that is nearer the front of the body when the leg is in an extended position. Proximal and distal mean nearer to or further from the root of the structure respectively. For example, the distal femur is a part of the knee joint while the proximal femur is closer to the hip joint. Finally, the adjectives medial and lateral mean nearer the median plane or further from the median plane respectively. The median plane is an imaginary, vertical plane through the middle of the body that divides the body into right and left halves.  
         [0020]    Referring now to FIG. 1, a first embodiment of the present invention, unicondylar femoral component  100 , comprises arcuated articular surface  110 , bone contacting surface  120  disposed generally opposite articulating surface  110 , post  130  extending superiorly from the posterior end of bone contacting surface  120 , flange  140  extending superiorly from the anterior edge of femoral component  100 , and porous layer  150  disposed against the entirety of bone contacting surface  120 .  
         [0021]    In a PKA, femoral component  100  is attached to one condyle of a “prepared” distal femur. (“Prepared” refers to a femur that has been cut appropriately to receive a condylar implant.) Although only one condyle is shown, it will be apparent to those skilled in the art, that the invention described and claimed herein is appropriately used for either femoral condyle.  
         [0022]    As viewed from the distal portion to the superior portion of the implant, femoral component  100  comprises articulating surface  110 . Articulating surface  110  comprises a generally arcuated shape between its anterior and posterior ends. The arcuated shape of articulating surface  110  is adapted to slidingly engage a unicondylar bearing component or a natural meniscus (neither of which is shown) disposed between femoral component  100  and a tibial component (also not shown).  
         [0023]    Referring again to FIG. 1, femoral component  100  further comprises bone contacting surface  120  disposed generally superiorly and opposite to articulating surface  110 . Bone contacting surface  120  preferably comprises a plurality of interconnected flat planes corresponding to bone cuts made to the distal femur. These bone cuts are made in order to prepare a compartment of the femur, i.e. one condyle, to receive femoral component  100 .  
         [0024]    Referring still to FIG. 1, femoral component  100  further comprises posterior post  130  extending generally superiorly from bone contacting surface  120 . Post  130  may comprise any geometric shape including a rectangle or pyramid, but a generally cylindrical shape is preferred.  
         [0025]    The anterior tip of femoral component  100  comprises flange  140 . Flange  140  extends generally superiorly from femoral component  100  such that articular surface  110  extends anteriority and superiorly as shown in FIG. 1.  
         [0026]    Anterior flange  140  and posterior post  130  are arranged such that an angle theta, as shown in FIG. 1 of about 1 degree to about 15 degrees is included between post  130  and flange  140 . However, an angle of about 5 degrees is optimal. Included angle theta allows femoral component  100  to generate a clamping force on the distal femur thereby securing femoral component  100  to the distal femur via a press fit.  
         [0027]    Continuing to refer to FIG. 1, porous surface  150  is disposed against bone contacting surface  120 . Porous layer  150  generally comprises a depth of about 0.5 mm to about 5 mm. Porous layer  150  may comprise a beaded layer of commercially pure titanium, commercially pure cobalt alloys of the same, or a layer of structured porous tantalum such as Trabecular Metal™ a trademark of Implex corporation. Porous layer  150  provides a surface that promotes bony ingrowth of the distal femur into femoral component  150 . This boney ingrowth provides for better fixation of femoral component  150  onto the distal femur. Such boney ingrowth also allows femoral component  100  to more accurately simulate a natural knee in terms of transferring load between femoral component  100  and the patient&#39;s femur.  
         [0028]    Referring now to FIG. 2, there showed a second embodiment of the present invention wherein femoral component  200  comprises arcuated articular surface  110 , bone contacting surface  220  disposed generally opposite to articulating surface  210 , posterior post  230  extending superiorly from bone contacting surface  220 , anterior post  235  extending superiorly from bone contacting surface  220 , flange  240  extending superiorly from the anterior edge of femoral component  200 , and porous layer  250  disposed against the entirety of bone contacting surface  220 .  
         [0029]    Referring still to FIG. 2, there is shown femoral component  200  which generally comprises the same configuration as femoral component  100 . However, femoral component  200  further comprises anterior post  235 . Anterior post  235  and posterior post  230  are arranged along bone contacting surface  220  such that an angle of about 1 degree to about 15 degrees is disposed there between. In the embodiment shown in FIG. 2, the clamping force on the distal femur is generated between anterior post  235  and posterior post  230 . It is preferred for the angle between these posts to be about 5 degrees.  
         [0030]    Referring now to FIG. 3 and FIG. 4, there is shown a bottom view of unicondylar femoral component  300  according to a third embodiment of the present invention. Generally, the configuration of femoral component  300  is identical in a preferred embodiment to that of femoral component  100  or femoral component  200  except that femoral component  300  further comprises threaded fasteners  360 . Femoral component  300  preferably comprises arcuated articular surface  310 , bone contacting surface  320 , post  330 , bone contacting surface  320 , flange  340 , porous layer  150  disposed against bone contacting surface  320 , and at least two threaded fasteners disposed in a desired arrangement through femoral component  300  and into a patient&#39;s distal femur such that threaded fasteners  360  fixedly attach femoral component  300  to the distal femur. Threaded fasteners  360  are arranged such that the heads of the threaded fasteners  360  do not interfere with the motion of articulating surface  310  relative to artificial or natural bearing surface  400  of a patient&#39;s knee. It is further preferred that femoral component  300  comprise four screws relatively symmetrically arranged through articulating surface  310  of femoral component  300 . However, fewer threaded fasteners  360  may be employed while remaining within the scope of the appended claims. Moreover, while it is preferred to use one post extending superiorly from bone contacting surface  320 , of femoral component  300 , two or no posts may be used as well as porous layer  350  or no porous layer while still remaining within the scope of the appended claims.  
         [0031]    It will be appreciated by those skilled in the art, that the foregoing is a description of preferred embodiments of the present invention and that variations in design and construction may be made to the preferred embodiments without departing from the scope of the invention as defined by the appended claims.