Biomechanics of the Patellofemoral Joint (PFJ)

The PFJ consists of the patellar articular surface and the femoral trochlear plane, and its conformity changes depending on the angle of knee flexion. Moro-oka et al. [1] acquired MRI images of healthy volunteers at 0°, 45°, 90°, and 135°of knee flexion and analyzed changes in the shape of the PFJ plane of the normal knee. As the knee is flexed from 0° onward, the patella gradually shifts outward (shift) and rotates inward (tilt), sinking into the femoral intercondylar space (Fig. 27.1). The shape of the articular surface at 135° flexion is characteristic of the PFJ, and the inclination of the femoral lateral condyle matches the shape of the articular surface of the patella; thus, a wide contact surface is accessed even during deep flexion.