In this condition there is a disruption in the normal relationship between the head of the femur (thigh bone) and
the acetabulum (hip socket). Sometimes the acetabulum is too shallow or sloping rather than a normal cup shape. It
cannot hold the femoral head in place. Hip dysplasia can affect one or both hips. It can be mild to severe. In mild cases called unstable hip dysplasia, the hip is in the joint but easily dislocated. More involved cases are partially dislocated or completely dislocated. A partial dislocation is called subluxation.
Early diagnosis in the newborn and young infant is important. If the problem is not diagnosed and treated early, the soft tissues around the hip start to stretch out. There can be changes in the blood supply to the hip. Sometimes the hip joint tries to form another hip socket called a false acetabulum. Without the proper ligaments, soft tissues, and joint capsule to hold the femoral head in place, the false acetabulum creates even more problems.
Using the Pavlik harness to hold the hip firmly in the socket helps form the soft cartilage around the hip and deepen the socket to hold the femoral head. But in about 40 per cent of all cases, the harness doesn’t work. It’s not entirely clear why the treatment works for some, but not all infants. A recent study from the Texas Scottish Rite Hospital for Children in Dallas, Texas might shed some light on the subject.
They used ultrasound studies to examine the hips of children with hip dysplasia who were being treated with a Pavlik harness. By comparing the hips of children who had success with the treatment to children who had a failed response, they were able to see some possible anatomical reasons that might explain differences in response to treatment.
They found that the failure group had an inverted labrum. The labrum is a rim of fibrous cartilage around the hip socket. It is designed to
give the socket a little bit more depth to hold the head of the femur in place and prevent subluxation or dislocation. Instead of acting as a buttress or barrier to movement, the labrum in the failure group was inverted (turned inward) and blunted (short). The angle of the labrum didn’t help stabilize the femoral head in the socket. Without this added support, the harness treatment only kept the hip in its socket while the harness was in place. Once the harness was removed, the hips slid out of the socket.
More study is needed to confirm these findings and possibly look for additional factors that might affect the success or failure of the Pavlik harness. For now, it is recommended that if treatment with the harness doesn’t show improvement within the first four weeks, the treatment approach must be changed. It may be necessary to switch to a different type of brace called an abduction brace. If that fails, then surgery is a last resort.