Abstract:
A femoral component for a prosthetic knee implant system. The femoral component comprises medial and lateral condyles, wherein the height of the medial condyle is greater than the height of the lateral condyle.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to orthopedic prosthetic devices. More specifically, the invention relates to a femoral orthopedic knee implant for use in conjunction with a total knee arthroplasty (“TKA”), wherein the femoral component is designed to accommodate a broader range of knee flexion than femoral components known in the art.  
           [0003]    2. Description of the Related Art  
           [0004]    Disease and trauma affecting the articular surfaces of the knee joint are commonly effectively treated by surgically replacing the articulating ends of the femur and tibia with prosthetic femoral and tibial implants, referred to as total knee replacements (“TKR”). These implants are made of materials that exhibit a low coefficient of friction as they articulate against one another so as to restore normal, pain free, knee function.  
           [0005]    As a knee joint moves through a ROM, the angle of the distal femur relative to the mechanical axis of the person&#39;s leg changes. During high flexion, this change is even more pronounced. For example, as a person&#39;s natural knee is moved through a ROM from about 0° to about 155°, the angle of femoral rotation about the transverse axis which is perpendicular to the mechanical axis of the person&#39;s leg may move from about 10° at to about 30°.  
           [0006]    Most TKRs, however, include femoral components that are designed to accommodate knee joint articulation from a position of slight hyperextension to approximately 115° to 130° of flexion. However, the healthy human knee is capable of a range of motion (“ROM”) approaching 170° of flexion, and a ROM in around 155° is required for deep kneeling and squatting as may be required during some sporting, religious or cultural events.  
           [0007]    There is a need, therefore, for an improved TKR femoral component that accommodates knee ° flexion, under optimal conditions, of more than 130° (“high flexion”).  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention comprises, in one embodiment thereof, an improved femoral prosthesis for a TKR. The femoral component of the TKR comprises an internal non-articulating bone contacting surface adapted to receive a resected distal femur. In a preferred embodiment, the bone contacting surfaces of the femoral component include anterior, distal, and posterior chamfer surfaces, which may further comprise bone growth promoting surfaces attached thereto.  
           [0009]    The femoral component further comprises anterior, distal, medial posterior and lateral posterior articulating portions, referred to herein as medial and lateral posterior condyles. The medial and lateral condyles each comprise a unique “height.” The height of each condyle is measured from a line tangent to the distal articulating surface to the proximal tip of a particular condyle. The differences in the medial and lateral condylar height of a prosthetic femoral component according to the present invention permit a larger angle of femoral rotation in a TKR about the mechanical axis of a patient&#39;s leg. In addition, the extent to which the medial aspect of the lateral femoral condyle extends into the intercondylar region of the femoral prosthetic component is reduced in the present invention to accommodate high flexion.  
           [0010]    An advantage of the present invention is that it allows greater rotation of the distal femur about a leg&#39;s mechanical axis. This greater rotation is necessary to, and therefore accommodates, high flexion in a patient&#39;s knee.  
           [0011]    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  
       [0012]    The above-mentioned and other features and objects 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:  
         [0013]    [0013]FIG. 1 is a side view of an embodiment of the present invention showing the difference in the medial and lateral condyle heights.  
         [0014]    [0014]FIG. 2 is a posterior view of the embodiment shown in FIG. 1.  
         [0015]    [0015]FIG. 3 is an anterior view of a human femur, tibia, knee joint, and leg mechanical axis.  
         [0016]    [0016]FIG. 4 is an anterior view of the embodiment shown in FIG. 1.  
         [0017]    [0017]FIG. 5 is a superior view of the embodiment of FIG. 1, showing the rotation of the present invention between no flexion and high flexion. 
     
    
       [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 exemplification set out herein illustrates an exemplary embodiment of the invention only and such exemplification.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    As used herein, the following directional definitions apply. Anterior and posterior mean nearer the front or nearer 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 sagittal plane or further from the sagittal plane respectfully. The sagittal plane is an imaginary vertical plane through the middle of the body that divides the body into right and left halves.  
         [0020]    Referring initially to FIG. 1, a femoral component  100  of a TKR according to one embodiment of the present invention comprises an external articulating surface  110  and a bone contacting non-articulating internal surface  150 . Articulating surface  110  comprises an anterior articulating surface  115 , a distal articulating surface  125 , a medial posterior condylar articulating surface  135 , and a lateral articulating condylar surface  145 .  
         [0021]    Femoral component  100  may comprise any biocompatible material having the mechanical properties necessary to function as a human knee distal femoral prosthesis. Preferably, femoral component  100  comprises titanium, titanium alloy, cobalt chrome alloy, stainless steel, or a ceramic.  
         [0022]    The internal non-articulating portion of femoral component  100  is adapted to receive a resected distal femur  105 , as shown in FIG. 5. The surgical cuts made to distal femur  105  can be made by any means, in any sequence and in any configuration known to those of skill in the art of knee arthroplasty. In a preferred embodiment, femoral component  100  comprises a plurality of chamfer surfaces corresponding to a plurality of chamfer surfaces made in distal femur  105 . Surface  150  may comprise a porous metal surface or any surface likely to promote the growth of bone therein.  
         [0023]    Non-articular surface  150  of femoral component  100  preferably comprises anterior non-articular surface  155 , distal anterior non-articular surface  165 , distal non-articular surface  175 , two distal posterior non-articular surfaces  185 , and two posterior non-articular surfaces  195 .  
         [0024]    Distal non-articular surface  175  is generally flat and adapted to receive the distal most surface of resected femoral component  105 . Surface  175  comprises two opposing ends. One end of surface  175  abuts one end of distal anterior non-articular surface  165 , which surface  165  also comprises two opposing ends. The remaining end of surface  165  extends from surface  175  anteriorly and superiorly such that an obtuse angle is formed between each surface  165  and surface  175 . Anterior non-articular surface  155  extends superiorly from the remaining end of surface  165 .  
         [0025]    The opposing end of distal non-articular surface  175  abuts one end of each distal posterior non-articular surface  185 , which surfaces  185  also comprise two opposing ends. The remaining end of surface  185  extends from surface  175  posteriorly and superiorly such that an obtuse angle is formed between each surface  165  and surface  175 . Posterior non-articular surfaces  195  extend superiorly from the remaining ends of surfaces  185 , respectively.  
         [0026]    Referring still to FIG. 1, external articulating surface  110  of femoral component  100  comprises an anterior articulating surface  115 , a distal articulating surface  125 , a medial posterior condylar articulating surface  135 , and a lateral articulating condylar surface  145 . The various articulating surfaces comprising articulating surface  110  of the present invention form a single curved surface having a variable radius adapted to engage cooperatively with a prosthetic knee meniscal component.  
         [0027]    In the preferred embodiment of the present invention, condylar surfaces  135  and  145  comprise differing intermediate radii  136  and  146 , respectively. The intermediate radius of each condylar surface is that portion of the articular surface between the distal articular surface and the posterior articular surface. The medial condylar intermediate radius  136  is larger in the preferred embodiment than the lateral intermediate radius  146 .  
         [0028]    Referring again to FIG. 1, there is shown line  101  tangent to distal articulating surface  125 , and heights “A” and “B” showing the heights of medial and lateral condylar articulating surfaces  135  and  145 , respectively. As shown in FIG. 1, the height A of lateral condyle  145  is less than the height, B, of medial condyle  135 . This difference in condylar heights is also shown in FIG. 2. In the preferred embodiment, the difference in condylar heights is from about 1 mm to about 5 mm; however those of skill in the art will appreciate that a broad range of height differentials may be employed with the present invention.  
         [0029]    Referring now to FIG. 3, there is shown a front view of right leg  101  in full extension comprising femur  105 , artificial femoral component  100 , prosthetic meniscal component  102 , prosthetic tibial component  104 , and tibia  107 . There is further shown line  109  representing the mechanical axis of leg  101 . As leg  101  flexes, it is necessary for femoral component  100  to rotate medially about mechanical axis  109 . The condylar height differential of femoral component  100  in the present invention allows sufficient rotation to accommodate high flexion. In addition, the medial aspect of lateral condyle  145  is truncated such that the distance between the lateral and medial sides of lateral condyle  135  is less than the distance between the lateral and medial sides of medial condyle  145  to further enhance the ability of femoral component  100  to achieve high flexion in a range from about 130° to 170°, or at least above about 150° without interfering with adjacent soft tissues.  
         [0030]    It will be appreciated by those skilled in the art that the foregoing is a description of a preferred embodiment of the present invention and that 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.