The Hip in Adults with Classic Bladder Exstrophy: A Biomechanical Analysis

Abstract

We studied the untreated pelvic deformity in 14 adult patients with bladder exstrophy to determine the relative hip-joint force and stress and their effects on the clinical status of the hip. Pelvic radiographs were used for biomechanical analysis to calculate joint force and joint stress (force/area) relative to partial body weight, which allowed comparison between patients and age-matched controls. IOWA hip ratings were used for clinical evaluation, and hips were scored radiographically for degenerative joint disease. The mean relative joint force and joint stress was significantly higher for exstrophy patients (p < 0.001). In addition, the mean distance from the body center to the center of the femoral head was significantly increased (p < 0.001) in bladder exstrophy patients. An increase in diastasis correlated with an approximate 30% increase in the distance from the center of the femoral head to the body midline. The mean distance from the greater trochanter to the femoral head center was significantly less (p < 0.02) and the center–edge angle was significantly decreased in exstrophy patients (p < 0.05). Two patients' hips showed significant subluxation, and one of these showed degenerative hip disease in association with poor IOWA and radiographic scores.The force and stress on the hip joint are increased in untreated adult bladder exstrophy patients. Further longitudinal study is indicated to validate these findings and to determine whether clinically important degenerative changes are occurring. This could affect treatment recommendations in childhood.