Hip dysplasia is a condition characterised by the socket (acetabulum) of the hip joint being too shallow. There is a wide spectrum in this condition ranging from babies whose hips are dislocated at birth or who have unstable hip joints, to those in whom the hip does not quite develop normally. The condition is much more common in women than men (8:2) and is a common cause of hip arthritis in older patients. Patients who have hip dysplasia often start to get symptoms in their early 20’s or 30’s. This is caused by the abnormal stresses that a shallow hip has to withstand and after some time damage starts to occur at the edge of the socket leading to pain. Unfortunately, once symptoms start, it is generally a sign that the joint can no longer compensate for its abnormal shape any longer. The consequence is damage to the articular cartilage (the gliding surface of the joint) and the gradual development of osteoarthritis.
Symptoms
Usually groin pain is the presenting symptom, which is frequently activity related. This may occur intermittently at first and then becomes a more constant feature. There may be episodes of acute sharp pains that almost make the hip give way, and after this the hip may be quite sore for a number of days. This symptom complex has been termed the acetabular rim syndrome indicating that damage starts to occur at the edge of the acetabulum. Often people find they have to give up sporting activities to accommodate the pain they get from the hip. In time, pain may be present with everyday activities such as walking.
Signs
Patients with this problem do not usually lose movement in the hip except when it is acutely irritable. Stiffness usually occurs much later as a result of the development of osteoarthritis. The main problem occurs when the hip is flexed up towards the chest, then internally rotated. This tends to precipitate pain by impinging the neck of the femur against the damaged portion of the acetabulum.
Diagnosis
This condition can be diagnosed by a simple x-ray of the pelvis. Other more specialised investigations such as MRI of CT scan may be needed to more clearly define the abnormal shape of the acetabulum or to assess the damage to the joint more clearly.
Treatment options
Once the condition has been identified, the treatment will depend a lot on the age of the patient, the degree of dysplasia and whether or not arthritis has started to develop in the joint. Ideally the aim is to protect and preserve the hip joint by performing a procedure whereby the acetabulum is redirected so that it provides better coverage of the head of the femur creating more normal contact stresses. This is generally suitable for younger patients (less than 45) where there is no or little evidence of osteoarthritis in the joint. The type of procedure is referred to as an acetabular osteotomy. There are a variety of techniques that can be used to achieve the same aim, and a particularly successful technique is the Bernese periacetabular osteotomy (PAO).
This involves a series of bony cuts around the acetabulum freeing it from its attachment to the pelvis and allowing it to be moved into a new position. The optimal position for the hip is determined by x-rays taken at the time of surgery. The fragment is then fixed with a number of screws. Because of the way the bone is cut and the stability of the fixation, mobility is allowed after surgery without any form of other splintage. The bone usually takes 6-8 weeks to heal during which time patients remain on crutches.
The overall aim of this type of surgery is to reduce pain from the hip and to reduce the chance of the development of arthritis in the joint. How successful this is will depend on the overall shape of the joint and the presence of pre-existing arthritis. In general this type of surgery is successful in allowing patients to return to a high level of activity.
