Abstract:
A femoral component for a prosthetic knee joint has a medial and a lateral condylar portion each having a bearing surface and a bone contacting surface. The medial and lateral condylar portions defining an opening therebetween. The opening is at least partially open to a cavity surrounded by a wall extending proximally from the bone contacting surface of the medial and lateral condylar portions. The wall having an inner surface defining a perimeter of the cavity and medially, laterally and posteriorly facing outer surface portions. The medially laterally and posteriorly facing surface portions being arcuate in shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/846,854 filed Jul. 16, 2013, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present disclosure relates to orthopedic devices and more particularly, to knee prostheses and more particularly to a prosthetic femoral component. 
         [0003]    During articulation of a natural knee joint, flexion between the tibia and the femur takes place about a transverse axis while some relative internal/external rotation occurs between the tibia and the femur about a longitudinal axis. Such flexion and rotation is necessary to carry out a normal gate cycle. It has been established that in full extension the tibia is rotationally displaced, relative to the femur, by approximately 2-3°. As the natural knee flexes, the tibia rotates internally. According to previous studies, about 5° of rotation ordinarily occurs as the knee is articulated from 0° to 10° of flexion, thereafter, little further rotation occurs up to at least about 45° of flexion. Total rotation at 110° of flexion is approximately 20°. 
         [0004]    Rotational stability of the natural knee is provided by the collateral and cruciate ligaments. The cruciate ligaments deter uncontrolled internal rotation within a certain range of flexion of the knee, while the collateral ligaments provide transverse stability and deter uncontrolled external rotation of the tibia. During knee replacement the anterior and posterior cruciate ligaments may be sacrificed. In the instances where the knee prosthesis is constrained to supply the stability ordinarily provided by the sacrifice ligaments, it is desirable for the knee prosthesis to mimic the natural knee as closely as possible. In these instances, the prosthesis usually is provided with tibiofemoral articular constraint to supply the stability ordinarily provided by the sacrificed anterior cruciate ligament and also a stabilizing mechanism for supplying the stability ordinarily provided by the sacrifice posterior cruciate ligament. 
         [0005]    Typically, a femoral component is provided with a housing disposed in a receptacle formed in the trochlear groove area of the femur. The housing provides an internal cavity defined by medial and lateral sidewalls extending from the proximal bone contacting surface of the femoral condyles of the prosthesis. The cavity in the housing typically receives a post formed on the tibial bearing component which post extends proximally. The combination of the post and the cavity within the housing provide the necessary constraint between the femur and tibia during knee flexion so that the stability originally provided by the cruciate ligaments is maintained. 
         [0006]    The housing is typically a box having planar sidewalls. This requires the central area of the femur to have a box-like recess formed therein by the removal of bone. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention relates to a femoral component for a prosthetic knee joint having a medial and a lateral condylar portion each having a bearing surface and a bone contacting surface. The medial and lateral condylar portions define an opening therebetween. The opening is at least partially open to a cavity surrounded by a wall extending proximally from the bone contacting surface of the medial and lateral condylar portions. The wall of the cavity has an inner surface defining a perimeter of the cavity and medially, laterally and posteriorly facing outer surface portions. The medially laterally and posteriorly facing surface portions being arcuate in shape. The arcuate medially, laterally and posterior facing outer surfaces may form a cylinder. The cylindrical medially, laterally and posteriorly facing surface may form part of a single diameter cylinder. The single cylinder has a central axis intermediate anteriorly and posteriorly facing bearing surfaces of the femoral component and may be coaxial with the anatomic axis of the femur. The cylinder central axis may lie in a sagittal plate bisecting the femoral component. The central axis of the cylinder may be located closer to the anteriorly facing bearing surface than the posteriorly facing bearing surface. The cavity inner surface perimeter may have medially, laterally and posteriorly facing proximal surfaces which define a planar proximally facing surface extending therebetween. The cavity may be open in the proximal direction between the planar proximally facing surfaces. The cavity may also have planar medially and laterally facing inner surfaces. 
         [0008]    The femoral component for a prosthetic knee joint which has a medial and a lateral condyle having a bone contacting surface defines a space therebetween capable of receiving a proximally extending post of a tibial component. A wall extends proximally from the bone contacting surfaces on a medial side of the lateral condyle and a lateral side of the medial condyle. The wall has a part-cylindrical outer bone contacting surfaces extending proximally from the bone contacting surface. The medially, laterally and posterior facing outer surfaces may be completely cylindrical. The cylindrical medially, laterally and posteriorly facing surface form part of a single cylinder. The single cylinder has a central axis intermediate anteriorly and posteriorly facing bearing surfaces of the femoral component. The wall defines a cavity having an inner surface. The wall has medially, laterally and posteriorly facing proximal surfaces extending between the inner and outer surfaces which define a planar proximally facing surface extending therebetween. The cavity may open in the proximal direction between the planar proximally facing surfaces. The cavity may have planar medially and laterally facing inner surfaces. 
         [0009]    As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a isometric view of the femoral component viewed from the bone contacting side thereof; 
           [0011]      FIG. 2  is a top view of the proximally facing surface of the femoral component of  FIG. 1 ; 
           [0012]      FIG. 3  is a partial enlarged view of the arcuate central box area of the component of  FIG. 2 ; 
           [0013]      FIG. 4  is an elevation view of the femoral component of  FIG. 2 ; 
           [0014]      FIG. 5  is an isometric view of the femoral component of  FIG. 1  mounted on a tibial tray with a post of the tibial tray extending into the cavity of the femoral component box; and 
           [0015]      FIG. 6  is a posterior isometric view of the femoral component and tray shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1  there is shown an isometric view of a femoral component generally denoted as  10 . The femoral component  10  includes posterior condyles  12  and  14  and an anterior surface  16 . Femoral component  10  includes a bearing surface  18  designed to articulate on a tibial component preferably made of ultrahigh molecular weight polyethylene (UHMWPE). 
         [0017]    Femoral component  10  has a bone contacting surface comprising a posterior condylar contact surface  20 , a posterior chamfer surface  22 , a distal surface  24 , an anterior chamfer surface  26  and an anterior surface  28 . These surfaces extend across the implant from the medial side to the lateral side and are designed to contact a prepared distal femur having resected surfaces corresponding to the bone contacting surfaces of femoral component  10 . Femoral component  10  also includes a stabilizing box  30  defining a cavity  32  having preferably planar medial and lateral side walls  34  and  36  and an anterior wall  38 . A cam surface  40  is formed at the posterior end of the implant  10  and is adapted to engage a stabilizing post on a tibial component as will be described below. As is well known, the cam surface provides for the anterior-posterior movement of the femoral component with respect to the tibial component as the knee goes from flexion to extension. The stabilizing box  30  includes an arcuate preferably cylindrical wall  42  which extends from a posterior end  44  of stabilizer box  30  on the medial side to a similar location on the lateral side. 
         [0018]    Referring to  FIG. 2  there is shown a top view of  FIG. 1  viewing the bone contacting surface from the proximal direction. It can be seen that box  30  is bisected by an axis  50  in the sagittal plane which is parallel to walls  34  and  36  of inner cavity  32 . Arcuate or cylindrical surface  42  extends from point  44  to point  46  when the medial and lateral sides of the implant. Preferably surface  42  is a cylinder with a single radius from center  48  between points  44  and  46 . As discussed above, the use of a arcuate or cylindrical surface for box  30  results in less bone being removed during preparation of the femur for receiving femoral component  10  as well as eliminating various corners in the prepared bone that may weaken the resected femur. Also shown in  FIG. 2  are the femoral component anterior chamfer surface  26 , the distal surface  24  and the posterior chamfer surface  22 . As can be easily seen in the top view, the anterior and posterior surfaces  38  and  39  of the cavity  32  are preferably arcuate and connect side walls  34  and  36 . 
         [0019]    Referring to  FIG. 3 , there is shown an enlarged view of the arcuate or cylindrical outer surface  42  of  FIG. 2  and walls  34  and  36  defining the medial and lateral side walls of cavity  32 . Also shown in  FIG. 3  are anterior and posterior end walls  38  and  39 . 
         [0020]    Referring to  FIG. 4 , there is an elevation view of femoral component  10  shown in  FIG. 2  with anterior flange  16  and posterior flange  14  and bone contacting surfaces  22 , the distal bone contacting surface  24 , the anterior chamfer bone contacting surface  26  and the anterior bone contacting surface  28 . Cam surface  40  is shown as well as cylindrical surface  42 . 
         [0021]    Referring to  FIG. 5 , there is shown an isometric view of femoral component  10  mounted on a UHMWPE tibial component  60  which includes medial and lateral condyles and a stabilizing post  66  which is received within cavity  32 . As femoral component  10  rotates from flexion to extension, the total joint is stabilized by the interaction of post  66  and cam surface  40  as is well known. 
         [0022]    Referring to  FIG. 6 , there is an alternate isometric view showing the component of  FIG. 5  with the post of the tibial component extending within cavity  32 . Also shown is a portion  66  which forms the proximal posterior end of the intracondylar recess  67  typical in many femoral components. Recess  67  bears against the patella as the knee flexes. 
         [0023]    The method of implantation of femoral component  10  will now be described in brief. As is typical, the distal femur is resected typically first providing a distal femoral cut to match distal surface  24  of the femoral component and then the posterior, posterior chamfer, anterior chamfer and anterior cuts were made which conform to the shape of the corresponding bone contacting surfaces  28 ,  22 ,  26  and  28  of femoral component  10 . In typical stabilized femoral component implantation, a box cutter which is generally a pair of parallel planar chisel-like cutting surfaces is used to form a recess in the femur which has planar medial and lateral and anterior sides. Once this piece of bone is removed, a femoral component with an integral box with planar, medial and lateral sides is implanted on the prepared distal femur or, in some cases, a stabilizing box having the planar, medial lateral and anterior surfaces is attached to a femoral component and then implanted. This would be a modular design where the stabilizing box may or may not be used depending on which ligaments are cut. 
         [0024]    Use of the femoral component  10  of the present invention is simplified because of the cylindrical surface  42  which can be inserted into a cylindrical counterbore in the distal femur. This counterbore can be easily formed by first using a drill or mill to form a cylindrical counter bore in the distal femur and then removing bone from the posterior side of the counter bore to accommodate the posterior cam area of the femoral component. This procedure for implanting femoral component  10  removes less bone and provides for a better distribution of the stresses within the distal femur because of the smooth arcuate bone contacting surface  42  as opposed to planar medial and lateral surfaces with small radius corners. 
         [0025]    While the femoral component  10  shown as being unitary or a one-piece design, as indicated above, it may be a modular design wherein the box  30  may be attached to the femoral component such as by a pair of screws engaging medial and lateral threaded counter bores in the bone contacting surface of the medial and lateral condyles of the femoral component. 
         [0026]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.