Periacetabular osteotomy (PAO)

Periacetabular osteotomy (PAO) is a surgical treatment for hip dysplasia which preserves and improves the function of the patient’s own hip joint rather than replacing it with an artificial one.

The goal of the PAO is to reduce or eliminate pain, restore function, and maximize the functional life of the dysplastic hip.

PAO is designed to correct the major primary mechanical problems in acetabular dysplasia. These problems include excessive pressure of the femoral head on the rim of the acetabulum and instability of the femoral head within the acetabulum.

The analogy is one of your car tyres; when first purchased, the manufacturer's guidelines might indicate that they should last 25,000kms. If however the tyres are wearing down quickly, the problem is usually of being out of alignment. The local tyre store usually then performs an alignment test and re-aligns the wheels.

The ideal PAO patient has no or minimal damage to the interior of the joint, and sufficient, undamaged cartilage remaining within the acetabulum. In general, such patients have little or no narrowing of the cartilage space on regular x-rays and can flex their hips to at least 90° with minimal pain.

The surgeon performing a PAO cuts the bone around the acetabulum in order to rotate it into a more stable, horizontal position of coverage on top of the femoral head. The pressure from the femoral head is now on the central portion of the acetabulum, where the cartilage is designed to accept this pressure. Additional hip procedures are sometimes indicated at the same time as the periacetabular osteotomy. These may include arthrotomy (work inside the joint to repair rim damage) and proximal femoral osteotomy (cutting and realigning the head and upper end of the femur). Between four and twelve months after PAO surgery, most patients undergo screw removal as a brief outpatient procedure.

Case Example 1

This 17 year old girl presented with a 3 year history of hip pain. She had a sudden deterioration resulting in her using a wheelchair. She had been reffered to Dr Balakumar from an orthopaedic surgeon for joint preservation surgery. Again using the hat analogy, it is noted that the hat is sitting on the back of the head. So as the patient continues to walk the head would erode the edge of the socket.

The patient was walking without a limp by 3 months and had her other side operated on 12 months later. She is now 4 years post operatively and plays tennis and participates in competitive netball. Dr Balakumar states “This operation can dramatically change a young person’s function not just preserve their joint.”

After the PAO has healed and motion and strength have returned to a steady state, we encourage the highest level of “reasonable” activity that the hip joint will allow. A corrected dysplastic acetabulum is still at risk for damage by overuse. Pounding types of activities, such as jogging are not encouraged. Though many of our patients are able to jog and even run marathons without a problem, the long-term impact on their joints is not yet known.

In general, since dislocation is not a risk after periacetabular osteotomy, there are no positional restrictions as there can be after total hip replacement.

We consider failure of periacetabular osteotomy to mean lack of improvement in pain, or an increase in hip joint stiffness serious enough to be limiting. In such situations, a joint-replacing procedure of some type often becomes necessary.

Of our more than 300 patients who have had various types of periacetabular osteotomies over the last 7 years, only 1 has required a Total Hip Replacement (THR). The patients who have required THR have been the ones who had the most damaged cartilage before the PAO surgery. Dr Millis et al have shown that at ten years or more post-PAO, more than 90% of patients have little or no pain and well-functioning hips.

In patients who, along with their physician, select periacetabular osteotomy as the treatment of choice, we expect that their pain and function will be greatly improved by the surgery for a minimum of ten years and, hopefully, for a lifetime. In all cases, the decision making process is one of open and honest communication between the surgeon and the patient.

Case Example 2

Another example is a 20 year old patient that saw Dr.Balakumar for previously treated Perthes with residual dysplasia.  She had continues groin pain, pain with sitting and a severe limp. If you examine her left hip it is apparent that both the socket and ball look very different to the other hip. This patient went onto have treatment of both the socket (acetabulum) and the ball (femur). She had a combined Periacetabular osteotomy and femoral osteotomy and neck lengthening procedure.

This patient was asymptomatic 12 months post op. She is 3 years post operatively and is pain free and works as a gym instructor.

Post Operatively you can see that the patient has excellent coverage of her right hip. Again the patient felt significant improvement of her symtoms. Dr. Balakumar utilized the cartilage mapping sequence to help him and the patient prognosticate the success of joint preservation procedures.

[Updated August 2014]