Periacetabular Osteotomy (PAO)

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Overview

The words “Periacetabular osteotomy” (PAO) simply translate to cutting the bone around the acetabulum (hip socket). A PAO is a surgical procedure developed to correct hip socket (acetabulum) deficiencies by repositioning it (osteotomy). It is most commonly utilized to address developmental dysplasia of the hip in the skeletally mature individual. The goal of the procedure is to separate the socket from the surrounding pelvis by a series of carefully controlled cuts and rotating it into a better position. 

Acetabular dysplasia (congenital or developmental) of the hip is a relatively uncommon diagnosis and is often underappreciated by many healthcare professionals. The normal hip is a ball and socket joint. In the case of hip dysplasia, the socket does not form correctly and can be shallow or properly formed but poorly positioned. The socket abnormalities lead to problems in the way the ball is covered. This leads to abnormal stresses upon the cartilage of the hip. 

Individuals with acetabular dysplasia rarely know they have the diagnosis until these abnormal stresses lead to injury of the labrum and/or cartilage. In many situations, symptoms begin in the early 20’s or 30’s but can occur in childhood/adolescence or later in life. They present with groin or hip pain that prompts the initial medical evaluation. Occasionally, there is a history of having been treated for hip problems as an infant or child.

If left untreated, the abnormal stresses on the hip predictably lead to additional damage within the hip. Commonly the acetabular labrum (the rim cartilage) begins to tear and cysts may form. As the damage progresses, the edge of the acetabular bone subjected to these stresses may fracture. These are usually rather painful events leading to the condition called “Acetabular Rim Syndrome”.

The diagnosis of dysplasia of the hip is usually straightforward. An X-ray of the pelvis is usually all that is required to reveal the abnormality of the hip. Further studies such as an MRI and CT may also be helpful with further characterization of the situation. 

Without correction, damage accumulates and will destroy the hip joint. Hip arthritis is predictable and may progress rapidly. This leads to increasing pain, stiffness, debility, loss of motion, and worsening function of the hip. If the arthritis progresses, hip replacement becomes the only option for salvage. 

Periacetabular Osteotomy (PAO) is a surgical treatment for acetabular dysplasia that preserves and enhances the patient’s own hip rather than replacing it with an artificial joint. The goal of the procedure is to reorient the abnormal socket into a better position, which reduces pain, improves function and avoids or postpones arthritis. Each case is unique in that there are varying requirements of rotation based on the type and degree of dysplasia. In rare cases, an additional femoral osteotomy is required to achieve normalization of the hip anatomy. The PAO is very powerful in that it allows very large corrections to occur with very little deformity of the pelvis.

As with any hip surgery, there is a risk of complications such as blood clots, bleeding and transfusions, infection, nerve or blood vessel injury, non-union (lack of healing), malpositioning, stress reaction, errant osteotomy propagation of the socket fragment. In Dr. Williams’ experience these have been rare, and the procedure overwhelmingly safe.

The usual hospital stay is 1 to 3 days and depends on how rapidly pain subsides and how the patient is progressing with physical therapy. After surgery, the patient will be closely monitored. Physical therapy begins the day after surgery to improve hip motion and muscle function and to learn to use appropriate assistive devices such as crutches or a walker. The patient begins walking with crutches immediately, but weight bearing is restricted to 30 pounds on the operative side for 6 weeks. Placing full weight on the operated side too early can cause the screws to bend or break and the socket 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 complications and arthritis increase. A team of medical specialists will care for the patient after surgery. 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 traveling through veins to the lungs).

The patient will go home after medical stability and physical therapy criteria are met, typically two days after surgery. Before returning home the patient will be provided prescriptions for pain medications, an anticoagulant, and a medication to decrease the chances of extra bone formation. 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 these are natural and generally subside as time progresses. Numbness and a tingling sensation is common around the incision area. Follow-up outpatient visits are necessary to monitor progress by X-ray and physical examination. The first follow-up visit is usually scheduled about 2 weeks after surgery and the second at 6 weeks.

Between 6 and 8 weeks after the surgery the patient is allowed to be full weight bearing and work toward discontinuing use of the crutches. The patient may begin working with outpatient physical therapy at this time. Progress in walking depends on return of muscle strength. The majority of patients are walking without support by 2-3 months after the surgery. Subsequent follow-up visits are at 3 and/or 6 months, 1 year and 2 years after surgery and then at 2 year 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 an outpatient procedure that does not interrupt a patient’s continued full function.