Normal axial alignment of the lower extremity and load-bearing distribution at the knee

Based on a series of 120 normal subjects of different gender and age, the geometry of the knee joint was analyzed using a full-length weight-bearing roentgenogram of the lower extremity. A special computer program based on the theory of a rigid body spring model was applied to calculate the important anatomic and biomechanical factors of the knee joint. The tibiofemoral mechanical angle was 1.2° varus. Hence, it is difficult to rationalize the 3° varus placement of the tibial component in total knee arthroplasty suggested by some authors. The distal femoral anatomic valgus (measured from the lower one-half of the femur) was 4.2° in reference to its mechanically axis. This angle became 4.9° when the full-length femoral anatomic axis was used. When simulating a one-legged weight-bearing stance by shifting the upper-body gravity closer to the knee joint, 75% of the knee joint load passed through the medial tibial plateau. The knee joint-line obliquity was more varus in male subjects. The female subjects had a higher peak joint pressure and a greater patellotibial Q angle. Age had little effect on the factors relating to axial alignment of the lower extremity and load transmission through the knee joint.