Sydney Hip and Knee - Dr.Michael Solomon Dr.David Broe
Patient Info

Periacetabular Osteotomy

Periacetabular osteotomy is the surgical procedure indicated in hip dysplasia and it involves cutting the bone around the acetabulum so as to fit the head of the femur bone into acetabular socket. This method was developed and performed by Professor Reinhold Ganz and therefore it is also called as Ganz osteotomy.


Periacetabular Osteotomy is a hip preserving procedure performed to correct a congenital deficiency of the acetabulum:

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.
By the age of 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 which leads 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 and treatment.

When the diagnosis of acetabular dysplasia is made, the X-ray also usually shows a sign of 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 status 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.
Periacetabular Osteotomy (PAO) is a surgical treatment for acetabular dysplasia 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.
The Anatomy      
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 specialized 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  "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 re-orientates 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. Individual cases of dysplasia however present with their own unique deficiencies and the PAO must often be tailored to solve these unique problems. X-rays take during surgery confirm the correct position of the acetabulum and screws (typically 3) 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) is also advisable in about one out of 20 patients who  undergo PAO surgery in order to correct abnormalities related to the femur. The indication for this is not always known until during the PAO operation. The femoral osteotomy is then completed during the same surgery though a second incision is  necessary.
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.

Studies have shown PAO to be a relatively safe operation with the chance for any one of these complications to be less than one percent.

The Natural History of an untreated shallow hip is to develop osteoarthritis in the patients 30’s or 40’s

The periacetabular osteotomy is designed to delay the onset and progression of hip arthritis.  There is still a possibility that despite the surgery hip arthritis will continue to progress and very rarely may develop sooner if a complication arises

The Operation and Aftercare:

A cell saver is used in the operation to reduce the degree of blood loss.

An Epidural Anaesthetic as well as a General Anaesthetic is used during the surgery. The Epidural is for pain relief and is usually kept in for 3 days. A urinary catheter is placed in your bladder for 3 to 4 days. It is common for the vaginal or scrotal skin to swell for about 1 week post operatively. The swelling will always resolve. Patients spend the two hours following surgery in the recovery room where nurses closely monitor them.

The same team of medical specialists and nursing staff cares for each patient pre- and post-operatively. 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 emboli  (blood clots traveling through veins to the lungs).

Patients begin physical therapy as soon as possible to improve hip motion and muscle function and to learn to use appropriate assistive devices such as crutches or a walker.   During the first eight weeks following surgery, the operated hip should bear no more than a limited weight of 5Kg’s. Placing full weight on the operated side prior healing may lead to screw breakage and for the osteotomy to lose its position. Too vigorous exercise such as resistive exercise against weights can also cause failure. If failure occurs, re-operation may be necessary and the chance of developing arthritis is greatly increased.

The usual hospital stay is 5 to 7 days and depends on how rapidly pain subsides and progress in physical therapy. 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 is common around the incision area. It is usual to feel numb on the outer aspect of the thigh due to bruising of a small skin nerve. This usually resolves but if not it does not cause any functional problems in the future.

After discharge if you experience severe or consistent pain or have redness, swelling and/or wound drainage please contact the hospital

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 12 weeks.

At 8 weeks after the surgery the patient is allowed to progress to full weight bearing and work toward discontinuing use of the crutches. Muscle strengthening exercises often with the help of a physical therapist are also started. Progress in walking depends on return of muscle strength. The majority of patients are walking without support by 3 months after the surgery Subsequent follow-up visits are at 6 months, I year and 2 years after surgery and then at 2 year intervals.  Screws are usually removed after 6 to 8 months as a small day only procedure with minimal discomfort.

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 what 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. 

It is improtant to understand that a pelvic ostetomy (PAO) is not going to make your joint "normal" again. The surgery is indicated to releave pain from a dysplastic (shallow)  joint and to try and delay the progression of osteoarthritis. Osteoarthritis will always develop if one has a shallow hip. A well done PAO will delay (or possibly even prevent) the development of end stage arthritis of the shallow hip. After recovering from a PAO you should not participate in high impact running sports or competetive impact sports. You are able to walk, hike, play tennis, swim, cycle, excersise sensibly in the gym and snow ski. One always looses a little hip flexibility after a PAO.


Appropriately selected patients have an 85% chance of a successful operation and pain free hip 20 years after the surgery.

Results of periacetabular ostetomies show the majority of patients with poor results did not have an immediate poor result but were benefited by the PAO for a variable period (6-12 years) before requiring further surgery.

For patients who develop a poor result some time after their PAO surgery the cause is typically advancing 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.

I trust the information provided in this handout will give you a better understanding about your hip problem and the surgical treatment available. Please do not hesitate to ask any questions.

Michael Solomon

Oct 2014

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