Plain patellofemoral radiographs

Abstract

Plain radiographs of the patellofemoral joint can show patellar location, bone shape, trabecular pattern, and articular space thickness. With stress application, stability can be measured. Radiographs may be obtained in the lateral, anterior-posterior, oblique or axial projections, with or without weight-bearing, with or without muscle contraction, with or without stress application to the ligaments, and with the knee in varying degrees of flexion. In addition to trabecular pattern, the lateral radiograph can reveal patellar subluxation, height, or trochlear dysplasia. The axial view is rarely useful until 30° of knee flexion and then may show joint space loss, patellar shift or tilt, and trochlear geometry. Stress radiographs may be required to show how far the patella can be displaced from the trochlea with a given force, and thus, it may be the most accurate method of determining patellar instability. Weight-bearing films may be necessary to show loss of joint space.