Bilateral recurrent patellar dislocation in a patient with isolated patella aplasia-hypoplasia.

Patella aplasia-hypoplasia is a rare condition characterized by the congenital absence or marked reduction of the patellar bone. It is well known that patella aplasia-hypoplasia occurs in nail-patella syndrome, small patella syndrome, and several other syndromes. However, isolated patella aplasia-hypoplasia without associated clinical or radiologic anomalies, first described by Kutz in 1949, is an extremely rare condition. This report describes 12 years' follow-up after medial patellofemoral ligament reconstruction surgery performed for bilateral recurrent patellar dislocation in a 29-year-old patient with isolated patella aplasia-hypoplasia. The patient had no radiographic findings of elbow abnormalities, exostoses of the ilia, or abnormal ossification of the ischiopubic junction. The right patella was severely subluxated, and the left patella was mildly subluxated. The preoperative Kujala score was 28 points for the right patella and 23 points for the left. Medial patellofemoral ligament reconstruction, wide lateral release, and patellaplasty with multiple drilling were done in July 1993 for the left knee and in August 1993 for the right. At 12 years' follow-up, the Kujala score was 68 points for the right patella and 73 points for the left, and the patient was satisfied with the result. Magnetic resonance images showed both patellae without subluxation and bulky regenerated ligaments.