Traumatic hip dislocations in children don’t occur very often. But when they do, the emergency room physician or surgeon must be very alert to possible pitfalls. A careful examination must be done first before any treatment is started. Associated injuries of the nerves, blood vessels, growth plate, and soft tissues must be identified. For best results, reduction must begin within six hours of the injury.
Reduction refers to putting the round head of the femur (thigh bone) back in to the acetabulum (hip socket). In younger children (up to age 10), gentle traction may be all that’s needed to reduce the hip. This can be done as a closed reduction. With a closed reduction, no surgery is required. Older children and teens are more likely to develop a transient hip dislocation.
A transient hip dislocation refers to a hip that has dislocated and then partially, but not completely, reduced. Imaging studies before performing a reduction are a must in order to identify the presence of an incomplete reduction, fractures, or bone fragments in the joint space. Any of these features can cause additional complications later.
X-rays will also show any signs of incongruous reduction, another possible pitfall. Incongruous reduction means the hip has returned to its natural, anatomic position, but cartilage, capsular tissue, or a bone fragment has lodged itself between the femoral head and the acetabulum. This will prevent normal movement and can lead to osteonecrosis of the femoral head (death of the bone due to loss of blood supply).
Sometimes a hip injury in a teen athlete dislocates and relocates spontaneously (on its own). The athlete may not even be completely aware of what has happened but develops hip or knee pain later. Imaging studies are needed to rule out the possibility of incongruous reduction. In other children, an unrecognized dislocation can delay treatment. Hip pain, limp, leg length difference, and loss of hip motion offer red flag symptoms that something’s wrong.
Even when a hip dislocation has been diagnosed correctly, other problems can develop. For instance, there may be other injuries that are subtle. Fractures of the acetabulum, femoral head, or greater trochanter (bump on the femoral bone where muscles attach) may not be recognized when the focus and attention is on the hip dislocation. This is especially true for patients who were involved in car accidents where multiple trauma has occurred.
Even with early diagnosis and treatment, complications can occur. The most common (and serious) problem that can develop is femoral head osteonecrosis. Several factors raise the risk of osteonecrosis. The first is femoral head epiphysiolysis.
This refers to a fracture and then separation of the epiphysis (growth plate) at the upper end of the femoral head. If the physician is unaware of the physeal injury and attempts to reduce the hip with a closed reduction technique, the growth plate can get displaced. The result is an unstable hip and eventual osteonecrosis.
Surgeons are advised to ensure complete relaxation of the leg by using a general anesthesia. The fracture may need to be pinned to stabilize it before attempting the reduction. And continuous imaging during the procedure is best to avoid these pitfalls. This can be done using a special dynamic imaging called fluoroscopy. Fluoroscopy allows the surgeon to see what’s going on inside the hip throughout the procedure.
Besides osteonecrosis, other complications include a dislocation that cannot be reduced, recurrent dislocations, osteoarthritis, and nerve damage. An irreducible dislocation and recurrent dislocations may require surgery. Any tears in the labrum (rim of cartilage around the hip socket) should be repaired. Sometimes repeated dislocations can be treated with immobilization using a hip spica cast (from hip to toes).
Children are not as likely to develop hip osteoarthritis as adults are after a traumatic hip dislocation. But when osteonecrosis occurs, the risk of osteoarthritis goes up significantly. Osteoarthritis is also more likely when there have been associated injuries or when an incongruous reduction wasn’t treated.
And finally, injury to the sciatic and gluteal nerves can occur as a result of a stretch placed on the nerve. The force of an injury great enough to dislocate the hip is also strong enough to cause neurologic damage. Quick reduction of the hip helps nerve recovery. With time enough to heal, the nerves should return to normal function.
In summary, although traumatic hip dislocations don’t occur very often, when they do, the physician must act quickly to avoid pitfalls from complications. Even with early diagnosis of the dislocation, a thorough examination and evaluation is needed to find any other areas of injury or damage. Failure to do so can result in serious, long-term complications. Whether the dislocation is a closed or open reduction, the surgeon has numerous risk factors and pitfalls to watch out for.