CLINICAL AND BIOMECHANICAL ANALYSIS OF HIPS IN ADULTS WITH BLADDER EXSTROPHY

Background: We analyzed shape and stress on the hip joint in exstrophy and reviewed the status of hips in adults with uncorrected exstrophy. Methods: Fourteen patients aged 16 to 52 years born with classic bladder exstrophy were studied. Patients were matched for age and gender with 14 controls. AP pelvis radiographs were used for biomechanical analysis based on the single-stance phase of gait. Joint force and joint stress (force/area) were calculated relative to partial body weight by the method of Legal (1987). Clinical assessment was by Iowa hip score and radiographic grading. Statistical analysis was done using t tests. Results: For the exstrophy patients, the mean relative joint force was significantly higher than control (4.2 [+ or -] 0.91; 3.0 [+ or -] 0.3) (p [is less than] 0.01). The mean relative joint stress for exstrophy patients was significantly higher as well (p [is less than] 0.05). The increase in force and stress appeared to be due to three factors: (1) the mean distance from the body center to the center of the femoral head was significantly increased (p [is less than] 0.001) in bladder exstrophy (12.35 [+ or -] 1.05 cm) versus controls (10.31 [+ or -] 0.70 cm) (approximately 30% increased). (2) The mean distance from the greater trochanter to the femoral head center (f) was significantly less (p [is less than] 0.02) for exstrophy patients (5.2 [+ or -] 1.2 cm) compared to controls (6.5 [+ or -] 0.8 cm). (3) The center-edge angle (CO angle) was significantly decreased in exstrophy patients (25.0 [+ or -] 9 deg.) Versus control (33 [+ or -] deg) (p [is less than] 0.05). Two of the adults with exstrophy had decreased Iowa hip scores and radiographic evidence of arthrosis. Conclusions: The force and stress on the hip joint are increased in adult bladder exstrophy patients. Increased joint load and stress can lead to an earlier onset of DJD. These results need corroboration by larger series. It remains to be seen whether closing the pelvic ring at exstrophy closure may help reduce these factors and affect the outcome of the hip.
M.M. Jani, BA, Paul D. Sponseller, M.D., FAAP, John P. Gearhart, M.D., FAAP. Johns Hopkins Hospital, Baltimore [...]