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When identified before the acetabular cartilage has been irreversibly damaged, PAO surgery is the preferred treatment for acetabular (hip) dysplasia. During PAO surgery, the hip socket is repositioned to better cover the femoral head, redistributing the forces concentrated and preserving the patient’s native hip joint.


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The term “Hip Dysplasia” includes a broad spectrum of abnormal shapes (morphologies) of the ball and socket hip joint which may result in abnormal mechanics in the hip joint.  Left untreated, these abnormalities may result in early arthritis. 

Dr. Tania Ferguson _ Normal Hip vs Dyspl

Most commonly, the term hip dysplasia is used to describe the shape of the acetabulum, or socket.  

  • In a “normal” hip the acetabulum covers the femoral ball (head) and is flat in orientation.  This allows the femoral head to remain stable and centralized, and the stress of weight-bearing is distributed throughout the socket evenly.


  • In hip dysplasia, most commonly the acetabulum is a shallow, upward sloping structure that does not adequately cover the femoral head.  The forces become concentrated at the periphery of the acetabulum, and instability may occur.  The force concentration and instability may lead to tearing of the labrum and cartilage injury in area of increased stress.  This may result in irreversible cartilage degeneration and hip arthritis.  The rim may fragment under these poor mechanical forces. 

Dr. Tania Ferguson _ Damage to Labrum an

There is a great range of abnormalities that fall under the umbrella of “hip dysplasia”.  The most drastic example is a congenitally dislocated hip (DDH or CDH) where the femoral head is completely uncovered.  A patient may have shallow, upsloping acetabulum allowing some, but insufficient coverage of the femoral head leading to the excessive stress and instability previously described.  Others may have dysplasia but not develop pain until their later adult years when the cartilage has broken down and arthritis ensues. 

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Sometimes the femoral side has an abnormal morphology that also may require surgery to optimize the biomechanical forces within the hip socket, to preserve the cartilage and labrum. The treatment of dysplasia thus depends greatly each person’s underlying anatomy and the stage at which they seek medical attention.

What are the symptoms of hip dysplasia?

Some patients’ complaints involve pain in the muscles around the hip, particularly in the Gluteus Medius and Minimus (Hip “Abductors”). When there is insufficient boney architecture to support the femoral head (the acetabulum is too shallow and upward sloping), these muscles work extra hard to try to keep the head stabilized under whatever roof there is.  These muscles often fatigue, and pain and weakness in the lateral and posterior hip is experienced.

Dr. Tania Ferguson _ Hip Dysplasia Glute
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At times patients present with pain in the front of the hip or the groin.  This may be caused by injury to the acetabular labrum, which may occur secondary to the instability and/or increased force concentrated on the peripheral soft tissues.  Additionally, fragmentation of the rim of the socket can occur (for the same reasons).  Both of these conditions, amongst other pain generators within the socket itself, are often felt in the groin.


What is the treatment for Hip Dysplasia?

The severity of the dysplasia and the state of the intra-articular soft tissues at the time the patient develops symptoms define the treatment plan for hip dysplasia.

1.  Periacetabular Osteotomy (PAO): When identified before the acetabular cartilage has been irreversibly damaged, PAO surgery is the preferred treatment for acetabular dysplasia.  This is an operation in which Dr. Ferguson creates a series of 4 cuts in the pelvis bone to allow the hip socket itself to be moved, or “reoriented”.   The socket is then repositioned to better cover the femoral head, redistributing the forces concentrated.

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The femoral head becomes covered, the acetabular roof flat, and the forces of weightbearing redistributed to the entire cartilage lining of the socket rather than the rim.  This surgery is aimed at preserving the patient’s native hip joint, and when performed in optimal conditions may prevent hip arthritis for more than 20 years (See below). 

2.  Total Hip Replacement: Unfortunately, many patients present with hip dysplasia late after the cartilage has degenerated beyond repair and progressed to arthritis. In these cases, THA is indicated.


3.  Hip Arthroscopy: In rare circumstances, there may be a role for an arthroscopic-only interventions to address the pain of a labral tear associated with very mild dysplasia, or in patients who have developed some cartilage damage but not so much as to necessitate THA.

more PAO info

What is Periacetabular Osteotomy (PAO) Surgery?

Periacetabular Osteotomy (PAO) is a surgical treatment for hip dysplasia that involves repositioning the acetabulum into a location that best covers the femoral head.  Four cuts (or “osteotomies”) are created in the pelvis bone around the acetabulum, detaching it and freeing it to be repositioned. 

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The acetabulum is then repositioned to provide better coverage of the femoral head, improving the stability of the hip joint and unloading the peripheral cartilage and labrum.   The socket fragment is then secured with screws.

Dr. Tania Ferguson

The shallow, upsloping roof that incompletely covered the femoral head is brought over the head to provide normal coverage and also brings the roof to a horizontal position. This improves the coverage of the femoral head, decreases the instability associated with dysplasia, and unloads the peripheral labrum and articular cartilage.  These changes optimize the mechanics of the hip such that the soft tissues are no longer subject to damaging forces.

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Each dysplastic hip is unique, and therefore Dr. Ferguson must tailor each surgery to each patient’s needs.  About 70% of the time the femoral head has grown into an abnormal shape as well, requiring recontouring during surgery.  Often the labrum has been injured and must be reattached.  And from time to time the top of the femur is abnormally formed requiring an additional “osteotomy” to be performed.

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Outcomes After PAO Surgery

When performed in young hips without early signs of cartilage damage, PAO surgery has been found to be a successful operation in preserving the hip joint.  Recent data indicate that 80-90% of hips after an optimal PAO surgery may survive 20 years or more.   Thus, while recovery times are meaningful, the operation has the opportunity of successfully maintaining the patient’s hip joint for a very long time, and some patients go a lifetime without THA. 

Why is PAO surgery preferable to THA?

Before the revolutionary advances made in joint replacement seen in the 1970’s, osteotomy surgery was very common in pre-arthritic and even post-arthritic hips. The PAO surgery became a popular surgery practiced world wide in this era.

In the 1970’s, the outcomes after THA improved significantly with the advances in implant engineering and septic technique brought forth by great work of Sir John Charnley and others like him.  Encouraging early good results led many surgeons to abandon osteotomy surgeries and instead treat even young patients with THA instead of preservation attempts. 

However, despite good initial results of total hip replacement, the long-term follow up of these patients demonstrated high rates of failures secondary to implant loosening and complications thought associated with the demands and activities of younger patients.  Osteolysis (bone loss) can cause loosening of the hip prosthesis (artificial hip) when patients outlive the longevity of their artificial hip, which is particularly likely in younger adults.  Failure of THA requiring revision surgeries in active young to middle aged adults began to again underscored 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 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. The sensory capabilities of the joint are preserved, and the patient can continue to remain as active as symptoms or lack thereof permits.

While THA is an excellent (and ever improving) option in patients whose cartilage has degenerated, it is a greatly inferior option to preserving one’s native hip with PAO surgery for these reasons and more.

FAQs and Logistics of PAO Surgery with Dr. Ferguson:

  • Dr. Ferguson does this operation at St. Thomas Midtown Center in Nashville, Tennessee.  Arrangements have been made to allow family members to stay in the room with patients during the hospitalization.

  • Hospital stays average 4 nights but range from 3 nights to 7 nights.

  • Many (if not most patients) fly or drive long distances to Nashville for surgery, and our office will assist with arrangements for “Out of Towners."

  • Surgery may be 4-8 hours depending on what more than the “PAO” itself must be done (femoral osteotomy, labral fixation, femoral head recontouring).

  • Surgery is performed with both a general anesthesia and an epidural catheter, which remains in place for 2 days to minimize the immediate pains after surgery.  Leaving the catheter in place has GREATLY decreased the amount of IV narcotic medications required.

  • Blood loss occurs during surgery, and the blood lost reinfused with a “cell saver” device.  About 30% of patients require a transfusion after the surgery. 

  • The Medical Hospitalist or Pediatric Hospitalist team will meet with you before surgery and assist Dr. Ferguson’s team with the medical management during the hospitalization. 

  • We have developed a multimodal approach to pain control which involves the anti-inflammatory (Celebrex), Tylenol, cryotherapy (see the “Game Ready” information below), and oral narcotic medications (Oxycodone).  On average patients require the Oxycodone about 2 weeks after discharge from the hospital.

  • The “Game Ready” ice machine provides both cryotherapy and compression to the hip.  We recommend this machine during the hospitalization, and it is then taken home for 2 weeks after the surgery.  This is what my patients call a “Game Changer” and has GREATLY reduced the use of narcotic medications after surgery.

  • Physical therapy begins the day after surgery. 

  • Weight-bearing is restricted to 30 lbs on the operative side for 10-12 weeks after surgery to allow the osteotomy sites to begin healing. 

  • Most patients begin walking with a walker.  Many progress to crutches a week or two after surgery

  • A continuous passive motion (CPM) machine is utilized, allowing safe and controlled motion starting the day after the surgery. Patients take this machine home and use if for 2 weeks after surgery to allow controlled motion without threating the fixation of the fragment, in attempts to minimize scar tissue in the joint.

  • There are some restrictions on the range of motion after the surgery, including limitations to active flexion and flexion beyond 90 degrees. 

  • After 2 weeks patients are encouraged to lay on their stomachs to start stretching out the muscles in the front of the hip.

  • If labral surgery is performed, there may be rotational restrictions also. 

  • We try to avoid blood clots by the use of compressive stocking which are worn for 3 weeks after surgery. Aspirin is taken for 6 weeks after surgery.

  • Sometimes, after hip surgery, the muscle around the hip can form islands of bone called “Heterotopic Ossification.”  To minimize this risk these muscles are injected with a prophylactic medication (Toredol) before the incision is closed in surgery, and patients take an anti-inflammatory medication (Celebrex 200 mg) 2x a day for 3 weeks.

  • In women a “bikini line” incision that used.  There are no sutures or staples to remove, and the incision is coated with a glue.  The first bandage is water tight and comes down the day before or the day of discharge, and replaced with paper-based dressings which you will then apply at home for 2 weeks. 

  • In males there may be a few sutures in the mid-portion of the incision to be removed 10 days after discharge.  We can usually arranged this with a local physician or nurse closer to your home.  The bandages are the same as for women.

*Each surgery is individualized, and therefore the specific restrictions and precautions for each patient will be different for each patient.  We will spend a lot of time with you after surgery ensuring that you understand your unique protocols before you leave the hospital.

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