Posterior acetabular wall deficiency in Down syndrome.

Trisomy 21 or Down syndrome is the most common chromosomal anomaly and is associated with musculoskeletal abnormalities related to a generalized ligamentous laxity. Approximately 1% to 7% of Down syndrome patients have hip instability. Prior studies on the topic recommend Salter innominate osteotomy, capsular plication, and a varus derotational osteotomy of the proximal femur, which typically is in an anteverted and valgus position. The authors present a previously unreported bilateral finding in two patients noted on three-dimensional reconstruction computed tomography: deficiency of the posterior acetabular wall. Each was treated using a modification of the Pemberton osteotomy in which a wedge of iliac crest graft is placed posteriorly to hinge the posterior wall into a position of better posterior coverage of the femoral head. Both patients' hips have remained stable more than 10 years postoperatively. Follow-up imaging demonstrates well-remodeled osteotomy sites and excellent posterior coverage of the femoral heads.