Axial and lateral radiographs in evaluating patellofemoral malalignment

This is a prospective study of 431 patients (862 knees) with patellofemoral pain, patellar dislocation, or other abnormalities of the knee joint. There were 217 asymptomatic knees with no contralateral problems for comparison. All patients had a history and physical and radiographic examination of both knees. The radiographs included standard anteroposterior views, axial views at 30 degrees of knee flexion, and standing lateral views at 0 degree and 30 degrees of flexion. The presence of patellar tilt or subluxation was noted on the axial view. The lateral view of the patella, with precise overlap of the posterior femoral condyles, allowed determination of relationships between the patella's medial edge, median ridge, and lateral edge to assess patellar tilt. Sixty-two percent of patients with patellar dislocations demonstrated subluxation on the axial view, while 98% demonstrated an abnormal lateral view. Eighteen percent of the control knees revealed evidence of subluxation on the axial view while 35% demonstrated subluxation on the extended lateral view. The axial view demonstrated 62% sensitivity for dislocation, while the lateral view taken in full extension demonstrated 98% sensitivity. The specificity for previous dislocation was 82% for the axial view and 93% for the lateral flexed view. Given the high sensitivity of the lateral view for detecting prior patellar dislocation, a normal result on this view can virtually eliminate the question of previous dislocation. Also, with the high specificity of the axial view and lateral view with knee flexion, the two views combined can confirm a clinical impression of patellofemoral malalignment.