Computed tomography of the normal patellofemoral joint

Radiographic assessment of the patellofemoral joint (PFJ) is problematic because conventional views are cumbersome, difficult to standardize, and not reliable for displaying this joint with flexion of the knee less than about 30 degrees. We used computed tomography (CT) to obtain conveniently a direct transaxial view of the PFJ in ten normal human volunteers at different 0 degree, 20 degrees, and 45 degrees of knee flexion and during both contraction and relaxation of the quadriceps muscle. From the CT images we measured femoral trochlear angle, patellar centralization, femoral trochlear depth, and patella tilt angle. In full extension, with the quadriceps muscle relaxed, 19 of 20 knees showed the patella well centered in the femoral trochlear groove. The tilt and centralization of the patella were largely unchanged at 20 and 45 degrees of knee flexion with quadriceps contraction. CT appears to be an optimal method of studying the PFJ. The normal relationships described in this report can be the basis for evaluating patients with known or suspicious history of recurrent subluxation or dislocation of the patella.