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Periacetabular osteotomy
Introduction
Periacetabular Osteotomy is a hip preserving procedure performed to correct a congenital deficiency of the acetabulum, acetabular dysplasia, or to treat some cases of hip impingement where the acetabulum is malformed.
About the Acetabulum
Two parts comprise the hip joint; a ball on the upper end of the thigh bone (femur), called the head of the femur, and a socket in the pelvis known as the acetabulum. The hip joint, like other joints, is made up of specialised structural elements that serve as precisely fitting moving parts. The head of the femur rotates freely within the smooth, concentric surface of the acetabulum. An extremely low friction tissue, hyaline cartilage, lines this joint as well as others in the human body. The friction between two hyaline cartilage surfaces is much less than the best man-made bearing.

A normal acetabulum “covers” the upper (superior) portion of the head of the femur as well as a partial portion of the front (anterior) and back (posterior) of the femoral head.
About Acetabular Dysplasia
Acetabular dysplasia is a condition defined by inadequate development of an individual’s acetabulum. The resulting acetabulum is shallow and “dish shaped” rather than “cup shaped”. The upper portion (roof) of the acetabulum is obliquely inclined outward rather than having the normal horizontal orientation. Because of these abnormalities, the superior and usually anterior femoral head are incompletely covered by this dysplastic acetabulum.

Individuals with acetabular dysplasia usually develop through childhood and adolescence without symptoms or knowledge of their abnormality. Between the ages of 18-30 however the patient typically experiences pain from their hip and they often seek medical evaluation and an x-ray discloses the abnormality (acetabular dysplasia). Other patients may have been treated for hip problems as an infant or child.

Acetabular dysplasia is often also associated with abnormalities in the shape of the upper femur which may contribute to the patient’s hip symptoms.

Acetabular dysplasia is associated with an abnormally high stress on the outer edge (rim) of the acetabulum leading to degeneration of the articular cartilage (arthritis). It is also possible for breakdown of the acetabular labrum (rim cartilage of the acetabulum) or a fatigue fracture of the rim of the acetabulum to occur as a result of this rim overload. Any one or a combination of these conditions can cause hip pain sufficient for the patient to seek medical evaluation or treatment.

When the diagnosis of acetabular dysplasia is made, the x-ray may also show signs of some arthritis which is most commonly an acetabular cyst, though increased bone density, a femoral head cyst, osteophytes (bone spurs) and/or cartilage thinning may also be present. If the dysplasia is left uncorrected, worsening of the arthritis is predictable and often progresses to a severe degree within a few years and sometimes even a few months. For the patient, this means increasing hip pain, progressive loss of hip motion and worsening functional capabilities.
About Periacetabular Osteotomy
Periacetabular Osteotomy (PAO) is a surgical treatment for acetabular dysplasia and some patients with hip impingement, that preserves and enhances the patient’s own hip joint rather than replacing it with an artificial part. The goal is to alleviate the patient’s pain, restore function, and maximize the functional life of their dysplastic hip.

PAO is a procedure that was developed and first performed in 1984 in Bern, Switzerland, by Professor Reinhold Ganz. Mr Clayson visited Professor Ganz in Bern and has developed expertise in this procedure as part of the North West Pelvic, Acetabular and Young Adult Hip Service provided by him since 1994.

“Periacetabular” means around the acetabulum. “Osteotomy” means to cut bone. Simply put, the PAO cuts the bone around the acetabulum that joins the acetabulum to the pelvis. Once the acetabulum is detached from the rest of the pelvis by a series of carefully controlled cuts, it is rotated to a position of ideal coverage as dictated by the specific acetabulum’s unique anatomy. PAO thereby reorients the acetabulum by changing its rotational position.

The dysplastic roof that incompletely covers the femoral head is brought over the head to give the head a normal coverage and also brings the roof from an oblique to a horizontal position. Other subtle changes typically also occur. Anterior coverage may increase. Also the shortening of the extremity and lateralization of the joint which are often a part of acetabular dysplasia can also be improved.

A dysplastic acetabulum before and after periacetabular osetetomy
     X-ray     X-ray
Individual cases of dysplasia present with their own unique deficiencies and the PAO must often be tailored to solve these unique problems. Xrays taken during surgery confirm the correct position of the acetabulum and screws are inserted into the bone to maintain the acetabulum’s new corrected position during bone healing.

A proximal femoral osteotomy (cutting and repositioning the bone of the upper femur) may be required in about one in ten patients who undergo PAO surgery in order to correct the abnormalities related to the femur. If required, a second incision is necessary and this would be discussed before surgery.
Potential Surgical Complications
As with any other major hip surgery, there is some risk of complications. Surgical wound infection and injury to major nerves or arteries is possible. Non union (lack of healing) of the bone following the osteotomy is also possible.
Post-Operative Care
Patients are initially observed following surgery in the recovery room where nurses closely monitor them. The first night after surgery may be spent in the high dependency ward to allow close monitoring and the following day the patient is returned to the normal ward. Included among the team’s post surgical priorities are pain management, preventing infection, and the prevention of deep vein thrombosis (blood clots in large veins) and pulmonary embolus (blood clots travelling through veins to the lungs).

Immediately following surgery a CPM (continuous passive motion) machine is applied to the leg to commence hip movement from 0-50 degrees and this is increased by 10 degrees per day. The epidural remains in place for 3 days to control post operative pain and after 3 days patients commence active hip exercises and mobilisation with crutches for support. They can put weight fully through the operated leg. During the first 6 weeks following surgery, patients require the use of two crutches but the osteotomy is fully stable allowing weight bearing.

Xrays will be taken at 2 or 3 days after surgery for a final assessment of the result.
After Discharge
The usual hospital stay is 7 days and depends on how rapidly pain subsides and progress with physiotherapy. At discharge pain medication is prescribed as well as an anticoagulant to prevent blood clots. Some degree of pain after discharge is natural which may increase or decrease on different days but the general trend should be toward decreasing pain. Some patients may sense an occasional “click” or “pop” in or around the hip. Numbness and a tingling sensation are common around the incision area and sometimes in the upper leg

Follow up outpatient visits are necessary to monitor progress by x-ray and physical examination. The first follow up visit is usually scheduled about 6 weeks after surgery and the second at 3 months.

At 6 weeks after the surgery, patients work towards discontinuing use of the crutches. Muscle strengthening exercises often with the help of a physiotherapist also continue. Progress in walking depends on return of muscle strength. The majority of patients are walking without support by 2 months after the surgery. Subsequent follow up visits are at 6 months and 1 year after surgery and then at yearly intervals.

A minority of patients request removal of one or more screws that were used to fix the PAO and this can be performed as a day case procedure that does not interrupt a patient’s continued full function.
Why is an Osteotomy preferable to Total Hip Replacement?
During the past 15 years there has been a renewed and growing interest in adult hip osteotomy. Osteotomy was used more frequently as a treatment for adult hip problems before the advent of Charnley’s low friction arthroplasty (the first successful artificial hip joint) in the 1960’s. The encouraging early good results regarding function and pain relief after Charnley total hip replacement in young patients led many surgeons to abandon osteotomy. Osteotomy was considered to be difficult and have results that were less predictable and less satisfactory to the patient.

Despite the good initial results of total hip replacement, the long term follow up of these patients has shown problems, especially in the young active population. Osteolysis (bone loss) associated with loosening of the hip prosthesis (artificial hip) within the bone affects those patients who outlive the longevity of their artificial hip. Hip revision surgery can present problems particularly with the production of hundreds of new hip prosthesis designs claimed to solve the problems of loosening and osteolysis. Unfortunately, the overwhelming majority of new designs have not performed as well as the original Charnley prosthesis and none have been proven better in the long term follow up of young patients Therefore, despite the fact that the modern hip replacement has been used for more than 30 years, its problems for active young to middle aged adults have emphasised the importance of preserving the hip rather than replacing it.

Osteotomy should not be thought of as an inferior second choice to total hip replacement that the young patient with early arthritis must undergo because he or she is too young for total hip replacement. The results after PAO, which preserves the patient’s own hip, justify its use and the long term results can be better than the patient could have obtained from a hip replacement. The patient’s own hip is a living tissue with self maintenance capabilities, whereas deterioration with time is inevitable for an artificial part. The sensory capabilities of the joint are preserved and the patient can continue to remain as active as symptoms permit. The patient with a total hip replacement however always must be cautioned regarding possible hip dislocation and be restricted from vigorous activity.
Longer Term Treatment
For patients whose symptoms deteriorate some time later in life after their PAO surgery, the cause is typically hip arthritis. These patients are almost always best treated by total hip replacement surgery. For these patients the previous PAO has typically enhanced the acetabular bone with the increased femoral head coverage. Enhancement of a dysplastic acetabulum contributes to the success of a later total hip replacement by making the stability of the prosthetic acetabulum more reliable.
References:
1. Finerman, G.A.;Dorey, EJ;Grigoris, P.;McKellop, H.A.;Total Hip Arthroplasty Outcomes, Churchill Livingstone, Inc.; 1998 2. Ganz, R;Klaue, K.;Vinh, T.S.;Mast, A.J.; A new periacetabular osteomy for the treatment of hip dysplasias; Technique and preliminary results. Clin Orthop Re) 3. Matta, J.N; Stover, M.D. – Siebenrock, K.A.; Periacertaular Osteotomy Through the Smith Petersen Approach. Clin Orthop Rel Res 363;21-32 1999. 4. Siebenrock K.A; Sch611, E.; Lottenbach, M.; Ganz, R.; Bernese periacetabular osteotomy Clin Orthop Re) Res 363;9-20, 1999. 5. Trousdale, R.T.l Ekkernkamp, A. – Ganz, R; Wallrichs, S.L.; Periacetabular and intertrochanteric osteotomy for the treatment of osteoarthritis in dysplastic hips. J Bone Joint Surg 77A;73-85, 1995. 6. Trumble, S.J.; Mayo, K.A.; Mast, J.M; The periacetabular osteotomy: Minimum 2 yearfollow up in more than 100 hips. Clin Orthop Rel Res 363:54-63, 1999.
Mr A D Clayson FRCS Orth
Consultant Orthopaedic Surgeon
 
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