Acetabular dysplasia in the adolescent and young adult.

Hip dysplasia is a major cause of osteoarthrosis in adults. Early aggressive osteotomy has the potential of preventing the development of arthritis, but carries with it significant risks. The problem is further complicated because the surgeon has no means of quantifying the dysplastic deformity or of predicting what a particular combination of osteotomies would do to correct the deformity. This study describes methods of quantifying hip-joint geometry in three dimensions based on computed tomography and magnetic resonance studies, and of simulating pelvic osteotomy to correct the deformities. The study analyzes 49 normal hip joints and 20 dysplastic hip joints. The results show that the normal acetabulum is nearly a full hemisphere, which is anteverted 20 degrees and abducted 53 degrees. The normal lateral center-edge angle is 37 degrees. The dysplastic acetabulum is not anterolaterally maldirected, as has been assumed, but is globally dysplastic. Analysis of the individual dysplastic hip joints showed a wide variability. Some patients were deficient globally, some anterolaterally, and some posterolaterally. Methods of analyzing a patient's hip joint, quantifying abnormalities, simulating surgery, and predicting results are demonstrated in a case example.