Fig. 16.

With large anterior (and, to a lesser degree, posterior) rotation of the acetabulum (curved arrow), the rising pubic end of the fragment leads to a ventral lift of the femoral nerve (straight arrow), especially when additional lateral coverage has to be performed. Full hip extension may lead to intolerable stretching of the nerve. Massive medial fragment displacement as necessary in posttraumatic dysplasia may be followed by a similar adverse translation of the nerve. 1 = acetabular fragment, 2 = iliacus muscle, 3 = iliac crest, 4 = Schanz screw, and AIIS = anterior inferior iliac spine.