Patellar instability in juvenile amputees.

Forty-three ipsilateral knees in 41 juvenile amputees were studied for determination of the extent and severity of patellar instability. The amputation was performed for trauma in 13 patients and congenital anomalies in 28 patients. Eleven patients had instability, and three had patellofemoral pain. All symptomatic patients had patella alta, lateral subluxation, and hypoplastic patellae on radiographs. Of the asymptomatic patients, 68% had patella alta, and 35% had hypoplasia. Amputees with patella alta had more below-knee amputations and had worn prostheses longer. It is hypothesized that the pressure of the prosthesis on the patellar tendon may lead to patella alta and predispose to instability.