Hip dislocation


A hip dislocation is a disruption of the joint between the femur and pelvis. Specifically it is when the ball-shaped head of the femur comes out of the cup-shaped acetabulum of the pelvis. Symptoms typically include pain and an inability move the hip. Complications may include avascular necrosis of the hip, injury to the sciatic nerve, or arthritis.
Dislocations are typically due to significant trauma such as a motor vehicle collision or fall from height. Often there are also other associated injuries. Diagnosis is generally confirmed by plain X-rays. Hip dislocations can also occur follow a hip replacement or from a developmental abnormality known as hip dysplasia.
Efforts to prevent the condition include wearing a seat-belt. Emergency treatment generally follows advanced trauma life support. This is generally followed by reduction of the hip carried out under procedural sedation. A CT scan is recommended following reduction to rule out complications. Surgery is required if the joint cannot be reduced otherwise. Often a few months are required for healing to occur.
Hip dislocations are uncommon. Males are affected more often than females. Traumatic dislocations occurs most commonly in those 16 to 40 years old. The condition was first described in the medical press in the early 1800s.

Signs and symptoms

The affected leg is virtually immovable by the person, and is usually extremely painful. Dislocations are categorized as either posterior or anterior, based on the location of the head of the femur.

Posterior dislocation

Nine out of ten hip dislocations are posterior. The affected limb will be in a position of flexion, adduction, and internally rotated in this case. The knee and the foot will be in towards the middle of the body. A sciatic nerve palsy is present in 8%-20% of cases.

Anterior dislocation

In an anterior dislocation the limb is held by the person in externally rotated with mild flexion and abduction. Femoral nerve palsies can be present, but are uncommon.

Cause

Dislocations of the hip typically take a high degree of force. About 65% of cases are related to motor vehicle collisions, with falls and sports injuries being the cause of many of the rest.

Mechanism

The hip joint includes the articulation of the femoral head and the acetabulum of the pelvis. In hip dislocation, the femoral head is dislodged from this socket. Posterior dislocation is the most prevalent, in which the femoral head lies posterior and superior to the acetabulum. This is most common when the femur is adducted and internally rotated. The opposite is true for the shoulder, where the most common dislocation occurs in the anterior and inferior directions. Motor vehicle traffic collisions are responsible for almost all posterior hip dislocations. The posterior side of the hip exhibits primarily hip extension, dealing with the muscles: gluteus maximus, hamstring muscles, and the six deep external rotators.
To actually dislocate a healthy hip, a great amount of force needs to be applied. Falls from a height, such as a ladder, can also generate enough force to dislocate a hip. In older individuals, even a slight fall could cause this type of injury. Wear and tear that the body undergoes throughout the years leads to increased incidents of hip dislocation in the older population.
Several other injuries are also associated with hip dislocation. Fractures in the pelvis and legs, and minor back or head injuries can also occur, along with a hip dislocation, that is caused by a fall or athletic of injury.

Diagnosis

X-rays of the pelvis, AP and lateral views of the femur are ordered for diagnosis. The size of the head of the femur is then compared across both sides of the pelvis. The affected femoral head will appear larger if the dislocation is anterior, and smaller if posterior. A CT scan may also be ordered to clarify the fracture pattern.

Classification

Posterior dislocation

Posterior dislocations with an associated fracture are categorised by the Thompson and Epstein classification system, the Stewart and Milford classification system, and the Pipkin system.

Anterior dislocation

There is also a Thompson and Epstein classification system for anterior hip dislocations.

Central dislocation

Central dislocation is an outdated term for medial displacement of the femoral head into a displaced acetabular fracture. It is no longer used.

Hip dysplasia

is a condition in which a child is born with a hip problem. Hip dysplasia is when the formation of the hip joint is abnormal. The ball at the top of the thighbone which is known as the femoral head is not stable within the socket.
Hip dysplasia is the preferred term because it provides a more accurate description of the spectrum of abnormalities that affect the immature hip. The term "congenital" dislocation is no longer recommended, except for very rare conditions, in which there is a fixed dislocation location present at birth.

Management

Uncomplicated

The hip should be reduced as quickly as possible to reduce the risk of osteonecrosis of the femoral head. This is done via inline manual traction with general anesthesia and muscle relaxation, or conscious sedation. Fractures of the femoral head and other loose bodies should be determined prior to reduction. Common closed reduction methods include the Allis method and Stimson method. Once reduction is completed management becomes less urgent and appropriate workup including CT scanning can be completed. Post-reduction, people may begin early crutch-assisted ambulation with weight bearing as tolerated.

Complicated

If the dislocated hip cannot be reduced by manipulation alone, an immediate open reduction is necessary. A CT scan or Judet views should be obtained prior to transfer to the surgical suite.

Rehabilitation

Hip dislocation rehabilitation can take anywhere from two to three months, depending on the person. Complications to nearby nerves and blood vessels can sometimes cause loss of blood supply to the bone, also known as osteonecrosis. The protective cartilage on the bone can also be disturbed from this type of injury. For this reason, it is important for people to contact a physician and get treatment immediately following injury.
Individuals suffering from hip dislocation should participate in physical therapy and receive professional prescriptive exercises based on their individual abilities, progress, and overall range of motion. The following are some typical recommended exercises used as rehabilitation for hip dislocation. It is important to understand that each individual has different capabilities that can best be assessed by a physical therapist or medical professional, and that these are simply recommendations.
16-40 year-old males are responsible for the majority of hip dislocations. These hip dislocations are typically posterior, and a direct result of motor vehicle traffic collisions.

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