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Periacetabular Osteotomy (PAO)

  • Surgical procedure to help preserve the health and function of the hip joint
  • Involves cutting the bone around the acetabulum, repositioning it, then using screws to reattach it to the pelvis
  • Most commonly used to treat hip dysplasia in adolescents and young adults
  • Involves Hip Preservation Program, Orthopaedics & Rehabilitation

Periacetabular Osteotomy (PAO)


A periacetabular osteotomy (PAO) is a hip preservation surgery typically used to treat patients with hip dysplasia, a condition in which the hip joint does not develop properly, and other hip conditions in which the acetabulum—the bowl-shaped socket of the hip joint—is not oriented or positioned correctly. PAO surgery reorients and repositions the acetabulum.

Hip dysplasia increases wear and tear on the joint and can cause pain. Over time, dysplasia can result in osteoarthritis at a young age. Osteoarthritis is often a painful condition marked by stiffness and reduced range of motion in the affected joint. In many cases, people with hip osteoarthritis are treated with total hip replacement surgery. To avoid this outcome, PAO is done before osteoarthritis sets in to preserve hip health.

The term “periacetabular” means all around the acetabulum, while “osteotomy” refers to a surgical procedure in which bone is cut. PAO is a surgical procedure that involves cutting the bone around the acetabulum so it is completely free from surrounding bone (the pelvis). The acetabulum is then reoriented and reattached to the pelvis with screws. In the weeks after surgery, new bone tissue heals where the surgeon cut the bone.

For young people with hip dysplasia and other hip conditions, PAO can reduce pain, improve hip function and quality of life, and allow them to live physically active lives, including playing sports.

How does the hip joint work?

To better understand PAO, it is helpful to review how a normal hip joint works.

The hip is a “ball and socket” joint where the head of the femur—the thigh bone—meets the acetabulum, which is part of the pelvis. The “ball” is the rounded head of the femur, and the “socket” is the acetabulum, a bowl- or cup-shaped part of the pelvis.

Normally, the head of the femur fits within the acetabulum, like a ball inside a socket. The acetabulum covers the head of the femur, providing support and stability to the joint. A layer of tough cartilage, known as articular cartilage (“articular” refers to a joint), covers the surfaces of the femoral head and acetabulum, protecting the bones from wear and tear and helping them glide smoothly over one another when the joint moves. A ring of tough tissue, known as the labrum, wraps around the rim of the acetabulum. It helps cushion and stabilize the joint.

In certain hip conditions, such as hip dysplasia, the acetabulum does not form properly. These problems with the acetabulum alter how forces are distributed to the hip joint during movement and cause excessive wear and tear on the labrum and articular cartilage which can result in injury, eventually leading to osteoarthritis.

What conditions are treated with PAO?

PAO is commonly used to treat hip dysplasia, also known as acetabular dysplasia. “Dysplasia” means abnormal growth. In this case, it refers to the abnormal growth of the acetabulum. More specifically, the acetabulum is too shallow to adequately cover the head of the femur, which can lead to joint instability, pain, and labral tears. It can also result in degenerative changes in the articular cartilage and other structures in the hip joint, eventually causing osteoarthritis.

Less frequently, PAO is used to treat other hip conditions, including acetabular retroversion. In this condition, the opening of the acetabulum is oriented backwards, causing the acetabulum to cover too much of the front of the femoral head and, in some cases, too little of the back. In many cases, the front of the acetabulum protrudes abnormally and causes femoroacetabular impingement (FAI), a condition that can lead to osteoarthritis.

Who is a good candidate for PAO?

To determine whether someone is a good candidate for a PAO procedure, doctors typically review their medical history, perform a physical exam, and order one or more imaging tests.

The doctor may begin by asking about symptoms, including hip or groin pain, and whether the pain occurs during certain activities or hip movements or at night. During the physical exam, the doctor will closely examine the hip, rotating the hip joint to assess range of motion, testing whether certain hip positions cause pain, and observing the patient’s gait.

The doctor will also order imaging tests, such as X-rays, a computed tomography (CT) scan, magnetic resonance imaging (MRI), and/or magnetic resonance arthrography (MRA). These imaging tests allow doctors to visually examine the bones, cartilage, and other structures in the hip.

In general, the best candidates meet these criteria:

  • They are age 40 or younger (the procedure may be performed on people starting around age 12)
  • They have healthy articular cartilage (i.e., no signs of osteoarthritis in the affected joint)
  • They have good hip joint congruency (i.e., how well the curvature of the femoral head matches the acetabulum’s curvature)

Active people over 40 with little evidence of osteoarthritis may still be good candidates for the procedure, though PAO is not typically performed on those over 50.

What happens during a PAO procedure?

Before the procedure begins, patients are given general anesthesia so they will not feel pain during the surgery.

During the procedure, the patient lies on a radiolucent operating table, which allows doctors to use X-rays to see real-time images of the hip joint during the surgery.

The surgeon begins by making an incision in the skin at the hip. The surgeon then dissects through the muscles in the hip to gain access to the hip joint. Next, the surgeon cuts the bone around the acetabulum. These bone cuts are called osteotomies.

Once the acetabulum is free from the surrounding bone, the surgeon reorients it to provide better coverage of the femoral head. The surgeon then uses screws to reattach the acetabulum to the surrounding bone. The screws hold the bones in place while they heal. After the bone is securely in place, the surgeon assesses the hip’s range of motion.

In some cases, patients have other hip conditions that may be addressed during the surgery. For example, if a patient has a misaligned femoral head, the surgeon may perform a femoral osteotomy (cutting the femur and realigning the bone). Other procedures, such as hip labral tear repairs and surgical treatment of FAI, may also be done during surgery or in a staged fashion (at a later date).

At the end of the procedure, the surgeon closes the incision with stitches.

What is recovery like after a PAO procedure?

Patients typically spend one to two days in the hospital after the procedure. Usually, they are able to sit in a chair a day after the procedure, and within one to two days after the surgery, they typically begin to walk with crutches. In most cases, people need to use crutches for six to eight weeks after a PAO.

By two to three months after the surgery, most patients can put their full weight on the affected hip and return to everyday activities. A guided physical therapy program that lasts four to six months will be recommended to help people regain strength and range of motion in the hip. Patients are typically able to return to sports and other physical activities, though it may take six to 12 months of rehabilitation to do so.

Regular follow-up appointments are necessary to monitor recovery and evaluate bone healing with X-rays.

What are some potential complications of a PAO procedure?

As with any surgical procedure, there is a risk for complications during and after a PAO procedure.

Surgical complications may include:

  • Infection
  • Blood loss
  • Blood clots

Other complications that may occur include:

  • Damage to nearby nerves and/or blood vessels
  • A bone fracture
  • A bone cut during the procedure fails to heal, or healing is delayed
  • Osteonecrosis (death of bone tissue due to a disruption in blood flow within a bone)
  • Heterotopic ossification (abnormal bone growth in muscles or other soft tissues)
  • Failure of screws, plates, or other hardware used in the procedure
  • Reduced range of motion
  • Overcorrection or undercorrection of the acetabulum

What is the outlook for people who undergo a PAO procedure?

The outlook for people who undergo PAO is typically excellent, though it can vary based on a number of factors, including age, the degree of osteoarthritis prior to surgery, and hip joint congruency.

Most people who undergo a PAO have reduced pain and improved hip function and quality of life. After the procedure and a rehabilitation program, people can successfully return to normal activities, including sports. Studies have shown that in the long term, the procedure helps preserve the health of the hip joint by preventing or delaying the development of osteoarthritis.

While outcomes after undergoing a PAO are generally excellent, some people still develop osteoarthritis and may eventually need to undergo a total hip replacement procedure in the future.

What makes Yale unique in its approach to PAO?

“Yale's approach to PAO is distinguished by several key factors,” says Andrew Jimenez, MD, a Yale Medicine orthopaedic surgeon who specializes in sports medicine and hip preservation. “First, all surgeons in the Yale Hip Preservation program have additional training specifically in hip preservation and PAO. This specialized training ensures that the surgeons are highly skilled and focused on this procedure. Hip preservation is the focus of their practice. Second, the Yale Hip Preservation program uses the most up-to-date techniques and technology. This commitment to staying at the forefront of medical advancements helps ensure that patients receive the highest level of care. Third, Yale leverages the expertise of experienced surgeons in multiple fields of hip care. This multidisciplinary approach allows for comprehensive treatment plans and improved outcomes for patients with challenging conditions. Most importantly, Yale emphasizes a patient-centered approach, ensuring that care plans are tailored to the individual needs of each patient. This approach involves thorough consultations, personalized treatment strategies, and ongoing support throughout the recovery process, prioritizing the patient’s comfort, preferences, and overall well-being. These elements combine to create a robust and advanced program that is well-equipped to handle all hip-related issues with a high level of expertise, care, and empathy.”