High incidence of hip dysplasia but not slipped capital femoral epiphysis in patients with Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is characterized by hypotonia, obesity, hypogonadism, small hands and feet, and mental deficiency. Obesity and hypogonadism are also frequently associated with slipped capital femoral epiphysis (SCFE), suggesting that children with PWS might be at increased risk of developing SCFE. Members of the Prader-Willi Syndrome Association (U.S.A.) were surveyed regarding the history of orthopaedic problems in general and of SCFE in particular. A total of 565 (63%) responses were received. The prevalence of orthopaedic conditions included 47% with flat feet, 41% with scoliosis, 19% with knock knees, 10% with hip dysplasia, 9% with osteoporosis, 7% with patellofemoral instability, 3% with bowlegs, 2% each with clubfeet, nursemaid's elbow, or leg-length inequality, and one patient (0.2%) with SCFE. The results of the survey indicate that SCFE is uncommon in patients with PWS, but the prevalence of hip dysplasia is increased approximately 10-fold compared with the general population.