The effect of knee immobilization on degree of hip flexion: a clinical correlation with posterior wall acetabular fractures.

The purpose of this investigation was to determine whether maintaining the knee in extension substantially limits hip flexion. The dominant lower extremity in 22 male subjects was goniometrically evaluated to determine hip flexion both when the knee was allowed to flex and when the knee was held in extension. Pelvic rotation values were subtracted from thigh rotation values to show true flexion of the femur in relation to the pelvis. Hip flexion averaged 49.25 degrees +/- 9.08 degrees in the straight-leg raise test and 94.14 degrees +/- 4.94 degrees in the flexed-knee raise test. This study shows that using a knee immobilizer in the postoperative treatment of posterior wall acetabular fractures should serve to protect the fracture site while still affording early ambulation.