The tangential x-ray investigation of the patellofemoral joint: x-ray technique, diagnostic criteria and their interpretation.

The X-ray technique for the tangential visualization of the patellofemoral joint is described; 3 X-ray signs (patellofemoral angle, patellofemoral index and patellofemoral displacement) are proposed as diagnostic aids in cases of subluxation of the patella and chondromalacia patellae. Theoretically, the pathogenesis of chondromalacia patellae and patellofemoral osteoarthritis may be explained as manifestations of cartilage damage secondary to lateral patellofemoral hyperpressure and medial patellofemoral hyperpressure.