A hip dislocation occurs when the head of the thighbone (femur) slips out of its socket in the hip bone (pelvis). In approximately 90% of patients, the thighbone is pushed out of its socket in a backwards direction (posterior dislocation). This leaves the hip in a fixed position, bent and twisted in toward the middle of the body. The thighbone can also slip out of its socket in a forward direction (anterior dislocation). If this occurs, the hip will be bent only slightly, and the leg will twist out and away from the middle of the body.
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.
The hip is a ball-and-socket joint: the ball-shaped head of the femur fits inside a cup-shaped socket in the pelvis. The structure of a ball-and-socket joint gives it a great deal of stability and allows it to move freely. A great amount of force is required to pop the thighbone out of its socket, but that's just what happens in a hip dislocation.
Motor vehicle accidents are the most common cause of hip dislocations. (Wearing a seatbelt can greatly reduce your risk.)
Falls from a height (such as a fall from a ladder) or industrial accidents can also generate enough force to dislocate a hip.
With hip dislocations, there are often other injuries, including fractures in the pelvis and legs, back injuries, or head injuries.
A hip dislocation is an orthopaedic emergency. Call for help immediately. Do not try to move the injured person, but keep him or her warm with blankets.
Usually, a physician can diagnose a hip dislocation simply by looking at the position of the leg. X-rays will show whether there are any additional fractures in the hip or thighbone.
If the patient has no other complications, the physician will administer an anesthetic or a sedative and manipulate the bones back into their proper position (this is called a reduction).
In some cases the reduction must be done in the operating room with anesthesia. A formal procedure with an incision may be required to reduce the hip.
Following treatment, 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.
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. An orthopaedic surgeon may recommend traction for a short period of time, followed by controlled exercises using a continuous passive motion machine.
Patients can probably begin walking with crutches when free of pain. A walking aid, such as a cane, should be used until the limp disappears.
A hip dislocation can have long-term consequences, particularly if there are associated fractures. As the thighbone is pushed out of its socket, it can disrupt blood vessels and nerves. When blood supply to the bone is lost, the bone can die, resulting in avascular necrosis or osteonecrosis. The protective cartilage covering the bone may also be damaged, which increases the risk of developing arthritis in the joint.