Dislocated Hip

A hip dislocation happens when the head of the femur is forced out of its socket in the pelvis.

The hip is a ball and socket joint. The ball is the head of the femur or thighbone and the socket in the pelvis is called the acetabulum. Surrounding muscles and ligaments and a thick band of cartilage called the labrum stabilize the joint. A hip dislocation occurs when the femoral head is forcibly removed from the acetabulum.

Doctors describe hip dislocations according to where the femoral hip bone moves with the acetabulum.

• Posterior dislocations, where the femoral head moves backward, are most common and often occur from car wrecks and athletic injuries.
• Anterior hip dislocations occur when the femoral head pushes forward out of the socket of the acetabulum. This type of hip dislocation can occur in downhill skiing accidents.
• Patients who have had hip replacements can also dislocate their prosthetic hip.
• Developmental dysplasia of the hip (dys=bad + plasia=formation) is an abnormal design of the hip at birth (formerly referred to as congenital hip dysplasia). Developmental dysplasia can lead to hip dislocation in infants and children.

Hip dislocations are uncommon injuries in a normal hip. It takes a lot of energy to dislocate a hip, and most dislocations of the hip are due to motor vehicle injuries. Athletic injuries most often occur in football and rugby, downhill skiing, and snowboarding.

In patients who have had hip replacements, a simple fall or abnormal movement may provide enough energy to dislocate the hip prosthesis.

The risk of a hip dislocation exists with any high-impact, high-energy accident.

Hip dislocations occur most commonly in the following:

• Motor vehicle crashes
• Pedestrians hit by cars
• Athletic injuries (less common)

Pain, deformity, muscle spasm, and inability to move the hip are common symptoms and signs of hip dislocation. The patient will not be able to bear weight or stand on the hip.

On physical examination, the hip and leg will be in an abnormal position and there will be physical deformity.

• For posterior hip dislocations, the hip will be short and internally rotated, meaning that the foot will be pointing inward toward the midline of the body.
• Anterior hip dislocations will have a shortened leg with the foot externally rotated or pointing away from the midline of the body.

Physical examination often clinically diagnoses hip dislocations. The health care provider might be able to observe a deformity at the hip, as well as abnormal positioning of the hip. X-rays confirm the diagnosis of hip dislocation.

The healthcare provider will also look for complications associated with a hip dislocation, including injury to the femoral artery that runs in front of the joint and the sciatic nerve located in the back of the hip.

Depending upon the situation, the healthcare provider may assess the patient for other injuries that might be present.

The initial treatment of a dislocated hip is to try to relocate it, replacing the femoral head with the hip socket. Because of pain and muscle spasms associated with the injury, the patient often requires medications for sedation and muscle relaxation to allow the hip to be relocated. Different techniques can be used to relocate the hip, but all involve traction on the leg to replace the femoral head with the acetabulum. This is called closed reduction.

Sometimes the hip cannot be relocated, even with the patient undergoing general anesthesia. A CT scan may be needed to look for small bone fragments that may have fractured (broken off) off the acetabulum or pieces of torn ligament or cartilage that get in the way of the relocation. In this situation, open reduction is required, meaning that an orthopedic surgeon has to operate to remove any foreign objects in the joint and then reduce or replace the hip into its socket. Sometimes doctors do this using arthroscopic surgery.

After hip reduction, physical therapy and rehabilitation will be required to return the range of motion and regain strength in the muscles surrounding the hip.

Physical therapy is important and begins with non-weight-bearing exercises that can start after the first week. This is important to prevent loss of range of motion.

Strengthening of leg muscles can begin when the patient is pain-free and can walk without crutches, usually after 4-8 weeks.

If all goes well, it may take 3-4 months to return to full activity after a hip dislocation.

Hip dislocations are a significant injury and the prognosis depends upon how long it takes to reduce the dislocation and whether other structures are damaged.

• About 70% of patients with posterior hip dislocations will have an associated acetabulum fracture.
• Approximately 10%-15% of patients with hip dislocation will have sciatic nerve injuries.
• About 2%-10% of patients with a hip dislocation will develop avascular necrosis of the femoral head if it is reduced within 6 hours.
• Approximately 20% of patients with hip dislocation will eventually develop osteoarthritis in the hip joint.

Common complications include the following:

• Sciatic nerve injury: The nerve runs behind the hip and can be stretched and damaged with a hip dislocation.
• Avascular necrosis of the femoral head (a=loss + vascular=blood supply; necrosis=death): The femoral head, or ball of the hip, gets its blood supply from small arteries that run along the ligaments that help hold the hip joint stable. These arteries can be stretched, damaged, or torn with hip dislocation and the part of the bone that they supply can die (necrosis). This causes the hip joint to gradually lose its range of motion and potentially require hip joint replacement. For this reason, the goal is to reduce a dislocated hip as soon as possible. A follow-up MRI of the hip is usually recommended at 6 weeks to look for this complication.
• Osteoarthritis of the hip joint
• Recurrent hip dislocation: The structures that keep the hip stable may not heal adequately, leading to repeated dislocations.

Hip dislocations occur because of unexpected events and cannot be prevented.