Patellofemoral incongruence in chondromalacia and instability of the patella.

We measured the patellofemoral congruence in tangential radiographic projections according to Merchant in 64 patients with unilateral patellar pain. The congruence angle was usually within normal limits. However, compared with the asymptomatic side, the angle was increased in chondromalacia and instability of the patella. A comparison of congruence angles of the two knees seems more valuable than a comparison with normal values.