Our knowledge of orthopaedics. Your best health.

The hip is a ball-and-socket joint.

• The socket is formed by the acetabulum, which is part of the large pelvis bone.
• The ball is the femoral head, which is the upper end of the femur.

A smooth tissue called articular cartilage covers the surface of the ball and the socket. It creates a low friction surface that helps the bones glide easily across each other.

The acetabulum is ringed by strong fibrocartilage called the labrum. The labrum forms a gasket around the socket, creating a tight seal and helping to provide stability to the joint. Strong bands of tissue called ligaments provide additional stability to the hip joint.

In a healthy hip, the head of the femur stays firmly within the acetabulum.

When there is a hip dislocation, the femoral head is pushed either backward out of the socket, or forward.

• Posterior dislocation. In approximately 90% of hip dislocation patients, the femur is pushed out of the socket in a backward direction. This is called a posterior dislocation. A posterior dislocation leaves the lower leg in a fixed position, with the knee and foot rotated in toward the middle of the body.
• Anterior dislocation. When the femur slips out of its socket in a forward direction, the hip will be bent only slightly, and the knee and foot will rotate out and away from the middle of the body.

When the hip dislocates, the ligaments, labrum, muscles, and other soft tissues holding the bones in place are often damaged, as well. The nerves around the hip may also be injured.

Motor vehicle collisions are the most common cause of traumatic hip dislocations. The dislocation often occurs when the knee hits the dashboard in a collision. This force drives the thigh backwards, which drives the ball head of the femur out of the hip socket. Wearing a seatbelt can greatly reduce your risk of hip dislocation during a collision.

A fall from a significant height (such as from a ladder) or an industrial accident can also generate enough force to dislocate a hip.

While far less common, hip dislocations can result from a collision while playing a sport, like football or hockey.

With hip dislocations, there are often other related injuries, such as fractures in the pelvis and legs; and back, abdominal, knee, and head injuries. Perhaps the most common fracture occurs when the head of the femur hits and breaks off the back part of the hip socket during the injury. This is called a posterior wall acetabular fracture-dislocation.

A hip dislocation is very painful. Patients are unable to move the leg, and, if there is nerve damage, they may not have any feeling in the foot or ankle area.

A hip dislocation is a medical emergency. Call for help immediately. Do not try to move the injured person, and keep them warm with blankets.

When hip dislocation is the only injury, an orthopaedic surgeon can often diagnose it simply by looking at the position of the leg. Because hip dislocations often occur with additional injuries, however, your doctor will complete a thorough physical evaluation.

Your doctor will order imaging tests, such as X-rays and likely a CT scan, to show the exact position of the dislocated bones, as well as any additional fractures in the hip or femur.

It takes time — sometimes 2 to 3 months — for the hip to heal after a dislocation. The rehabilitation time may be longer if there are additional fractures. The doctor may recommend limiting hip motion for several weeks to protect the hip from dislocating again. Physical therapy is often recommended during recovery.

Patients often begin walking with crutches within a short time. Walking aids, such as walkers, crutches, and, eventually, canes, help patients regain their mobility.