Patellar pain and incongruence. I: Measurements of incongruence.

In 150 normal asymptomatic knees, the average Q angle was 15 degrees. The patellar length was equal to the patellar ligament length, and the average congruence angle was -8 degrees. In 53 knees with recurrent subluxation, the patella was high-riding (TP, 1.23), the sulcus angle was shallow (147 degrees), and the average congruence angle was +16 degrees. In 53 knees with "chondromalacia," the Q angle was increased (20 degrees), and the average congruence angle was -2 degrees.