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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 mechanical axis. This angle became 4.9" when the full-length femoral anatomic axis was used. When simulating a onelegged weight-bearing stance by shifting t h e 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.Osteoarthritis is a common disorder of both genders, increasing in frequency with age. The knee joint is one of the most common sites of involvement because of its weight-bearing requirement, high mobility,

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