The forces involved in car crashes can be so severe that a hip dislocation can occur. The force can travel up the outstretched leg and then release itself in the form of a dislocation of the hip. About 90 percent of hip locations are when the ball of the hip goes posterior to the socket, called posterior dislocations. Anterior or central dislocations occur just ten percent of the time. The hip is the most dislocated joint in the body with up to 5 percent of people sustaining one at some point in their lives.
A total of 74 percent of hip fractures are able to be reduced through closed (no surgery) reduction. Up to 12 percent of relocated fractures will spontaneously dislocate again. The incidence of hip fractures is increasing worldwide, in part because of an increase in high speed motor vehicle accidents. A hip dislocation should be considered a marker for a high impact event with high forces so other injuries that can be life threatening need to be looked for if the hip is dislocated.
There are a lot of people with long term disability following dislocation of their hip. Half will have chronic pain or limited use of the hip after the dislocation. If the diagnosis is delayed, the prognosis will be worse. There are multiple complications including a deep vein thrombosis, pulmonary embolism, avascular necrosis, recurrent dislocation, arthritis, vascular injury and chronic unrelenting pain.
The most severe complication of a dislocated hip is a pulmonary embolism, caused by a deep vein thrombosis or blood clot in the leg that travels to the lungs causing a lack of blood flow to the lungs and the possibility of sudden death. For this reason, patients with hip fractures are given blood thinners to prevent clots. Injury to the sciatic nerve happens up to 19 percent of the time. This can result in nerve damage to much of the leg. If the nerve is damaged but not torn, there is usually full recovery.
In 2-17 percent of dislocations, there is what’s called “avascular necrosis” of the femoral head. This results from a lack of circulation to the head or ball of the femur so that it dies off, leading to chronic pain and arthritis. If the hip is put together quickly, it limits the chances of getting this complication.
The most common long term complication after hip dislocation is post-traumatic arthritis. It occurs in around 16 percent of affected individuals and is associated with problems with gait and with pain requiring medications. The rate of arthritis is as high as eighty percent if the acetabulum (socket) is also injured in a fracture.
When the hip dislocation is due to a trauma, it is considered an orthopedic emergency. Surgeons and orthopedists must quickly relocate the joint and must evaluate the person for the presence of other trauma. Timely reduction makes for the best possible outcome without later complications and problems. Two thirds of traumatic hip dislocations are due to motor vehicle crashes but people can dislocate their hip after a fall from a great height. Rarely sports injuries can cause a hip fracture. Fractures are defined as being posterior (most common), anterior, or centrally dislocated.
Most dislocations are treated without having to do surgery. Some, especially when the acetabulum is fractured, require open surgery and replacement of the joint.