Hip Dislocation

Anatomy

The hip joint consists of the junction of the femur (thighbone) and the acetabulum (hip socket). The femoral head is round and fits very snugly in the acetabular cup. Because of how well they fit together and the strong muscles around the hip joint, when the femoral head is dislocated, it can be very difficult to replace in the socket. In some cases, complications may result because the blood supply to the femoral head becomes more tenuous as we age. With dislocation, the vessels do not always stretch to accommodate the new position of the femur. If the blood supply is stretched for too long, the vessels may kink and clot, which prevents adequate circulation from reaching the femoral head, potentially leading to the death of that portion of bone.

There are two main ways in which the hip can dislocate. The dislocation is described by the direction in which the femoral head exits in relation to the acetabulum: anterior (in front) or posterior (behind) (see images next page). The posterior type is by far the more common, with the majority of injuries seen in common practice the result of the knee striking the dashboard in a motor vehicle collision.

The sciatic nerve, one of the main nerves of the leg, runs posterior to the hip joint and may be compressed or damaged by the dislocated femoral head. Symptoms of damage to this nerve include [Page 654]pain and numbness in the foot and leg, as well as difficulty lifting the foot and ankle.

An anteroposterior radiograph of the pelvis demonstrates a posterior-superior dislocation of the right femoral head.

Source: Used with permission of the University of South Carolina, Department of Orthopaedic Surgery.

The same patient is shown after successful closed reduction of the hip.

Source: Used with permission of the University of South Carolina, Department of Orthopaedic Surgery.

Causes

The most common cause of hip dislocation is motor vehicle collision, followed by falls. However, injury has been reported also as a result of impact in contact sports such as football, basketball, and rugby.

Clinical Evaluation