CT detection of cortical fracture of the femoral head associated with posterior hip dislocation.

Posterior dislocation of the femoral head is a common injury in automobile accidents and is frequently associated with fractures of the posterior acetabular rim. Fractures of the anterior cortex of the femoral head have not been described. One hundred sixty-four cases of posterior hip dislocation presenting consecutively to our shock trauma unit and emergency department during a 3-year period were evaluated with plain film radiology and CT. In 21 cases (13%), CT showed an anterior cortical fracture of the femoral head that could not be seen on plain radiographs. This injury is similar to the Hill-Sachs lesion of the humerus that results from anterior dislocation. The anterior cortical fracture was associated with fractures of the posterior acetabulum in 18 cases (86%). The anterior fracture is caused by impaction of the anterior femoral head against the posterior acetabular rim at the time of dislocation. We conclude that anterior cortical fracture of the femoral head is a common accompaniment to posterior acetabular dislocation.