Hip dislocation

This information addresses hip dislocation that results from a traumatic injury, and will not refer to paediatric developmental hip dislocation (developmental dislocation or dysplasia of the hip - DDH) or to dislocation after total hip replacement.

A traumatic hip dislocation occurs when the head of the thighbone (femur) is forced out of its socket (acetabulum of the pelvis). It typically takes a major force to dislocate the native hip, such as motor vehicle collisions and falls from significant heights, and as a result, other injuries like broken bones are often associated with the dislocation. 

A hip dislocation is a serious medical emergency. Immediate treatment is necessary.

Anatomy

The hip is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the pelvis. The ball is the femoral head, which is the upper end of the femur (thighbone). A smooth tissue called articular (hyaline) 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 a 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.

Description

When there is a hip dislocation, the femoral head is pushed either backward out of the socket (posterior dislocation), forwards (anterior dislocation), and more rarely inferiorly /medially.

• Posterior dislocation. In approximately 90% of hip dislocation patients, the thighbone is pushed out of the socket in a backwards direction.  A posterior dislocation leaves the lower leg in a flexed position, with the knee and foot rotated in toward the middle of the body.  A sciatic nerve palsy is associated in 8-20% of cases.
• Anterior dislocation. When the thighbone slips out of its socket in a forward direction, the hip will be bent only slightly, and the leg will rotate out and away from the middle of the body.  There may be associated femoral nerve palsy.

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.

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Posterior dislocation of the left hip

Symptoms

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

Cause

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. There may be associated fractures of the socket (acetabulum), femoral head, or both. A fall from a significant height (such as from a ladder) or an industrial accident can also generate enough force to dislocate a hip.

With hip dislocations, there are often other related injuries, such as fractures in the pelvis and legs, and back (especially the lumbar spine), abdominal, knee, and head injuries. 

Medical Examination

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

In cases in which 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, your doctor will complete a thorough physical evaluation.

Other imaging tests, such as x-rays and CT scans, are used to show the exact position of the dislocated bones, as well as any additional fractures in the hip or thighbone, as well as other areas noted from the physical examination

Treatment

Reduction Procedures

If there are no other injuries, an anaesthetic will be given and the joint will be manipulated back into its proper position. This is called a closed reduction.

In rare cases, torn soft tissues or small bony fragments block the bone from going back into the socket. When this occurs, open surgery is required to remove the loose tissues and correctly position the bones. Following reduction, the surgeon will request another set of x-rays and possibly a computed tomography (CT) scan to make sure that the bones are in the proper position.

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(Left) This x-ray, taken from the front, shows a patient with a posterior dislocation of the left hip. (Right) Normal alignment after the hip has been reduced.

Complications

A hip dislocation can have long-term consequences, particularly if there are associated fractures.

1. Nerve injury - As the thighbone is pushed out of the socket, particularly in posterior dislocations, it can crush and stretch nerves around the hip. The sciatic nerve, which extends from the lower back down the back of the legs, is the nerve most commonly affected. Injury to the sciatic nerve may cause weakness in the lower leg and affect the ability to move the knee, ankle and foot normally. Sciatic nerve injury occurs in approximately 10% of hip dislocation patients. The majority of these patients will experience some nerve recovery.

2. Osteonecrosis (or avascular necrosis) - As the thighbone is pushed out of the socket, it can tear blood vessels and nerves. When blood supply to the bone is lost, the bone can die, resulting in osteonecrosis (also called avascular necrosis). This is a painful condition that can ultimately lead to the destruction of the hip joint and arthritis.

3. Arthritis - The protective cartilage covering the bone may also be damaged, which increases the risk of developing arthritis in the joint. Arthritis can eventually lead to the need for other procedures, like a total hip replacement.

Recovery and Rehabilitation

It takes months for the hip to heal after a dislocation. The rehabilitation time may be longer if there are additional fractures, or if open surgery has been needed. The doctor may recommend limiting hip motion for several weeks to protect the hip from dislocating again. Physical therapy is often recommended during recovery to regain strength and mobility. Patients often begin walking with crutches within a short time, initially protected/partial weight-bearing. Walking aids, such as walkers, crutches and eventually canes, help patients get mobilized.