Diagnosis and imaging studies of traumatic hip dislocations in the adult.

Traumatic dislocation of the hip represents a major injury that is associated with significant morbidity. In particular, the risk of osteonecrosis of the femoral head is greatly affected by the time it takes to reduce the hip. Therefore, thorough understanding of the clinical and radiologic features is essential if this injury is to be recognized and treated promptly. Most patients present in severe distress after a high-energy injury such as a motor vehicle accident. Associated injuries, particularly of the knee, are common and the leg usually is held in a specific posture characteristic of the direction of dislocation. Plain anteroposterior radiographs of the pelvis will clearly show the dislocation in most patients but lateral views or a computed tomography scan may be required to confirm the diagnosis and to show the direction if the signs are subtle. Associated acetabular wall fractures and femoral head fractures also may be identified by computed tomography scans. After reduction, plain radiographs alone are not adequate to assess reduction; computed tomography is more sensitive in detecting osteochondral fragments and may reliably detect residual subluxation of 2 mm in any part of the joint. Magnetic resonance imaging is useful in detecting changes of osteonecrosis but rarely is indicated in the early treatment of this condition.