The hip joint is formed between the 'ball' of the femoral head and the 'socket' of the acetabulum (hipbone) or the socket in the pelvis, which is surrounded by a cartilage. Strong supporting muscles and ligaments at the joint capsule make this a stable joint. Extreme force is required to cause hip dislocation (except in prosthetic hips) and this means that such injury may be associated with other life-threatening injuries and other fractures. Diagnosing it during the early stages can be beneficial.
Mechanism of injury
Direct trauma, especially road traffic accidents and falls, is the most common cause of hip dislocation. Dashboard injuries have been implicated in this injury as well. Hip dislocation due to car accidents have come down with the development of air bags and use of seat belts.
Congenital dislocation of the hip in infants is a different entity and has been discussed separately in the paediatric orthopaedic section.
Types of Hip Dislocations
Depending on the direction in which the femoral head (ball) moves out of the acetabulum (socket in the pelvis) dislocations are classified as anterior, posterior or central dislocations. Of these, posterior dislocation occurs in 90% of cases.
- Can be diagnosed by x-rays
- CT scans may be ordered if there is suspicion of an associated fracture. Central dislocations are associated with fracture of the floor of the acetabulum
Hip dislocations are associated with a high incidence of avascular necrosis of the femoral head, a condition where the blood supply to the bone is interrupted due to the injury. Here, the blood supply to the femoral head is disrupted as a result of the dislocation and leads to a slow death of the bone. This then leads to the bone collapsing and eventually leads to arthritis of the hip. This may then require a total hip replacement procedure if the pain doesn't respond to conservative treatment. Hence hip dislocations are treated as an orthopaedic emergency.
Treatment of hip dislocations is by emergency closed reduction. If this fails, the surgeon may need to open the hip joint surgically and reduce the dislocation under vision. This may be all that's necessary for treatment as long as the hip is stable. In central fracture dislocations, once the dislocation is reduced, the acetabulum may need to be reduced and stabilised surgically using plates and screws.