Patellofemoral abnormalities in renal osteodystrophy.

Seven patients with renal osteodystrophy demonstrated characteristic abnormalities of the patellofemoral compartment of the knee. The abnormalities consisted of narrowing of the patellofemoral space and ill-defined osseous erosions on the posterior surface of the patella, which in some cases were accompanied by similar alterations on the anterior surface of the femur. Clinical manifestations were not infrequent, including restriction of joint motion and a traumatic synovitis with accumulation of intra-articular fluid. The mechanism accounting for the patellofemoral alterations appears to be subchondral fracture of weakened trabeculae due to the presence of osteomalacia or osteitis fibrosa cystica, or both. Calcium pyrophosphate dihydrate crystal deposition is not required to produce these characteristic abnormalities.