Chapter 10. Lower Extremity

Hip Dislocation

Radiographic Summary

Radiographs of the pelvis are sufficient to demonstrate a hip dislocation. Hips can dislocate posteriorly, anteriorly, or inferiorly. With posterior dislocation, the femoral head migrates posteriorly and superiorly and partially projects over the acetabular roof on an AP view of the pelvis. Anterior dislocations, conversely, result in anteroinferior migration of the femoral head. Radiographs can also show associated injuries of the acetabulum and femoral head. CT scan (preferably after reduction) can better define the injury, evaluate for associated fractures, ensure the congruity of the joint, and assess for retained intra-articular fragments.

Clinical Implications

Hip dislocations require a significant amount of force to occur. These patients should be treated as trauma patients and quickly evaluated for other injuries. The most common direction of dislocation is posterior (90%), followed by anterior (approximately 10%) and inferior (much less than 1%). Visual inspection of the patient will reveal a leg that is internally rotated, shortened, and adducted with a posterior dislocation. Patients with an anterior dislocation will have more subtle changes of slight external rotation and abduction. Physical exam should also include a thorough neurovascular exam to ensure distal blood flow and sciatic nerve function. Treatment is reduction (preferably within 6 hours) to reduce the likelihood of avascular necrosis of the femoral head.

Pearls

1. Hip dislocations are caused by a significant amount of force; evaluate the patient for life-threatening concomitant injuries.

2. The most common hip dislocation is posterior.

3. Hips should be reduced within 6 hours to reduce the likelihood of avascular necrosis of the femoral head.

Femoral Head Fractures (Pipkin Fractures)

Radiographic Summary

Plain radiographs can usually identify a femoral neck fracture, which is almost always associated with a hip dislocation. CT scan can be used to better define the fracture and evaluate for associated fractures. Subtle fractures may only be visible on CT.