Ultrasonography of the patellofemoral joint in diastrophic dysplasia.

Plain radiographs do not provide adequate information in diastrophic dysplasia (DD) because of abnormal ossification and severe deformation of the knee joint. Radiographically, the lateral femoral condyle is hypoplastic, and the position of patella is difficult to define. In clinical examination, the patella is inferior and lateral. In this study, the anatomy of the patellofemoral joint in DD is described using ultrasound. Both knees of 13 patients with DD were examined. The alignment of patella, the angle of femoral sulcus, and the size of both femoral condyles were measured. Student's paired t test with two-tailed significance probability was applied for differences in mean values, and their 95% confidence limits were computed. The femoral sulcus angle averaged 129 degrees and was deeper than that (142 degrees) in normal knees. The lateral femoral condyle was smaller than the medial condyle. The patella was aligned lateral to the bottom of femoral sulcus. In 10 degrees knee flexion, the patella remained laterally in the sulcus with no true patellar dislocation. Vertical position of the patella averaged 2.9 mm distal to the femorotibial joint. The study showed that, in patients with DD, the anatomic complex of the femoral condyles and patella deviates laterally, and the patellofemoral joint is deformed with a hypoplastic lateral condyle, a deep femoral groove, and a distally aligned patella.