Axial computed tomography of the patellofemoral joint with and without quadriceps contraction.

Computed tomography was used to analyze the patellofemoral relationship during the first 60 degrees of knee flexion in patients with chronic patellofemoral pain syndrome (49 knees) and a healthy control group (15 knees). The patellofemoral joints were imaged axially through the center of the patella articular cartilage with the knee flexed 0 degrees, 0 degrees with maximal quadriceps muscle contraction, 30 degrees, and 60 degrees. In 0 degrees of knee flexion, the sulcus angle was greater in the symptomatic group than in normal controls. The patella displaced further laterally, and the lateral patellar tilt was greater. The patellar lateral index was found to be greater at 0 degrees and indicated severe abnormality with full quadriceps muscle contraction. The Laurin angle was pathologic with increased medial opening, especially with muscle contraction. At 30 degrees of knee flexion, these differences were less marked than at 0 degrees. No relevant differences were found with 60 degrees of knee flexion. This study showed that the sulcus angle, lateral patellar displacement, lateral patellar tilt, patella lateral condyle index, and Laurin angle are relevant diagnostic features in 0 degrees of knee flexion, indicating a pathological femoral patellar gliding mechanism. Our evaluation also demonstrated the influence of full quadriceps muscle contraction, especially regarding lateral patellar displacement and the Laurin angle, and it was most prominent on the patella lateral condyle index. Thus, quadriceps muscle contraction often creates a more pathological displacement of the patella, which can be depicted using axial computed tomography.