What is a PAO?
The periacetabular osteotomy (PAO) was first described in 1988 by a physician in Switzerland, Dr. Reinhold Ganz, to treat hip dysplasia in adolescents and adults.1 The operation is a joint-preserving surgery – this means a hip joint can be restored by reconstruction of the patient’s own socket.
When development of the joint does not occur properly, hip dysplasia is the result. In a healthy hip, the acetabulum (the bony socket) sits over the femoral head (the ball at the top of the femur bone) so that the weight of the body is evenly distributed across the joint and onto the femur. Cartilage sits between the acetabulum and head of the femur and acts as a cushion between the bones to keep the joint moving smoothly.
In patients who need a PAO, the acetabulum does not fit over the femoral head correctly, so the weight of the body is not distributed equally across the joint. If left uncorrected, this leads to wearing down of the cartilage, known as osteoarthritis. Our bodies have limited capacity to repair cartilage. Think of the PAO as an operation that will improve your hip mechanics before more damage is done, thus slowing the disease process and decreasing your chances of pain or more surgeries in the future. Since this surgery was described 20 years ago, follow-up data on the long-term effectiveness of such reconstruction is not yet readily available.

What does the surgeon do during a PAO? 
Basically, the socket is cut from the pelvis in such a way that it can be shifted over the femoral head to make a better fit – “putting the hat on top of the head,” as my doctor says.
A single incision is made, usually on the front side of the body, approximately parallel to the groin crease. Muscles, blood vessels, and nerves are carefully retracted to expose the joint. The physician will use a bone-cutting tool called an osteotome to make a series of cuts in the acetabulum. Then, the freed pieces of bone are rotated over the femoral head to correct the weight-bearing load of the joint. Long screws are inserted to hold the pieces of bone in place. Over six months to a year, the pieces of cut bone will fuse with the surrounding bone, restoring the acetabulum and thus creating a stable joint. The surgical technique of the PAO is continually evolving and each surgeon may practice slight variations on the surgical procedure. Specifics of the operation, such as the length of the incision, the number of screws inserted, whether or not the screws are removed, and post-operative care, will depend on the surgeon.

What kind of patients undergo this operation?
This operation is more commonly, but not exclusively, performed on adolescents and young adults. Each case is unique and requires assessment from the physician. Patients who have the most success from this surgery are those who show little or no osteoarthritis pre-operatively.2,3 Osteoarthritis of joints happens to almost everyone with age, but the process occurs at a faster rate in patients with hip dysplasia. The degree of osteoarthritis can be assessed by looking at a patient’s imaging studies. If there is too much damage to the cartilage, fixing the mechanics of the joint will not relieve pain.
In addition to the physical exam, the surgeon will use imaging studies to decide if you are a good candidate. These include X-rays and sometimes CT and MRI scans. Your hip’s range of motion, the severity of deformities at the joint, and the degree of osteoarthritis will be important in the decision.2 For patients who need a PAO on both hips, the time between operations will depend on recovery from the first surgery, but could be as short as six months.

What can I expect on surgery day?
When you arrive at the hospital, you will be taken to a pre-operative room on the surgery floor. The anesthesiology team will discuss anesthesia options with you. An IV will be started and you may be given medication to reduce your anxiety before being taken into the operating room. Some patients are candidates for an epidural anesthesia, which creates numbness from the waist down. Then the anesthesiologist will put you under general anesthesia; you probably will not even remember falling asleep. Before the surgeon begins, a nurse will insert a catheter into the bladder, which will remain for a few days post-operatively. The operation lasts about 4-6 hours. During surgery, your vital signs will be continually monitored. If too much blood is lost, you will receive a transfusion.
When you wake from the surgery, you should not be in excessive pain because of the medicine being administered through the IV and/or epidural. The anesthesiology team will continually check on your pain and nausea level to make you comfortable. Patients are monitored for a few hours in the recovery unit before being taken to a hospital room.

What will recovery be like during my hospital stay?
Patients stay in the hospital for about 3-6 days. Some patients experience post-operative nausea during this time. Pain management is monitored by the anesthesiology team during your entire hospital stay. You may have a patient-controlled anesthesia device, in which you can self-administer extra medicine into the epidural or IV line by clicking a button. No matter how well your pain is controlled, your hip may still hurt. The hip, entire thigh, and groin will be swollen and bruised for a few weeks.
The surgeon will check if your nerves are intact by asking you to move your leg in certain directions. During the first two days, patients with an epidural anesthesia will be slowly weaned off this medicine and given oral pain pills instead. This is necessary to regain control of the muscles in the pelvis and legs so you can get out of bed.  Doctors want patients out of bed on the first post-operative day with the assistance of a physical therapist. This is especially important for patients who are not given anti-coagulation medication because they are at risk for developing blood clots when sedentary. You will use a walker and cannot bear weight on the side of the operation.
When the epidural is weaned enough that the patient regains control of bladder muscles, the catheter will be removed, thus reducing the risk of contracting a urinary tract infection. At this point, you will use a bedside commode or a bedpan. It may take a day or so to regain full control of your bladder muscles. You will be given a laxative and stool softener each day – do not refuse these because pain medications slow down stool movement through the digestive tract, and you may suffer from painful constipation later.
Your blood will be drawn daily to monitor your body as it makes more red blood cells after the trauma of surgery. If your blood pressure gets too low or if the tests indicate that you need more blood, you may receive a transfusion. You may be given the option to donate your own blood prior to hospital admission if you are able; otherwise you will rely on the blood bank.
Physical and occupational therapists will visit each day to teach the safest way to get in and out of bed and to use walking aids. Some surgeons give patients restrictions on the degree to which they can bend at the hip joint, such as a maximum of 60-degree flexion; this should be explained thoroughly by the physician and therapists. Learning how to use the toilet, sit, and stand with this restriction feels unnatural and takes time getting used to. The therapists will also assist in preparation for recovery at home. They will arrange for equipment you can bring home – such as walker, crutches, bedside commode, and possibly a wheelchair. If there are stairs at your home, the physical therapists will teach you the correct way to use stairs with crutches.
Together, your therapists and physicians will decide when you are ready to be discharged – your pain must be managed with oral pain medication and you must be able to walk several steps using a walker or crutches without too much difficulty.

What will recovery be like when I go home?
Patients cannot bear weight on the operated side for 6-8 weeks after surgery. If your left hip was operated on, for example, you can touch your left toe to the floor but should not put the full weight of your body on the left foot. The recovery period sounds overwhelming, especially for the active parent or student, but it can be done. Reading this document in advance will help you make the proper accommodations so that the recovery is smoother and you can return to your normal routine sooner.
It is important that patients arrange a support system with friends and family for the recovery period. Some patients may have access to more assistance than others, but during the first 1-2 weeks of recovery, it will be difficult to take care of yourself – getting up from a lying or sitting position, eating, using the bathroom, and bathing are activities with which you will need help. Sleeping positions may also take some getting used to – at first you will only be able to sleep on your back. After a couple weeks when pain subsides, you may be able to roll onto your unoperated side. Having several different sized pillows for positioning is helpful.
Pain will be managed as needed with prescription pain medication. During each recovery milestone, such as moving from a walker to crutches, starting to bear weight again, or starting physical therapy, it may be necessary to adjust medication intake. Since narcotic pain pills slow down movement through your digestive tract and may cause constipation, stool softener and laxative pills can be taken while using the medication. Urinating can also be difficult for several days after surgery due to internal swelling. Burning sensation during urination or unexpected voiding may occur. A bedside commode or an elevated toilet seat will make using the bathroom much easier, and is essential for those patients who cannot violate the 60-degree hip flexion.
The incision cannot get wet until you see the surgeon again a week or two after surgery and bandages are removed. Until then, you can get creative as far as how to bathe – using washcloths or covering the incision well and using a shower hose while sitting on a shower chair are options. After the bandages are removed, you may choose to crutch into a shower and stand, carefully balancing your weight on the unoperated leg.
Patients will graduate from a walker to crutches when the pain of swinging the pelvis subsides. It is important to get up and walk around several times each day to maintain strength in both legs. Patients’ arms and wrists may hurt because they are not accustomed to using walking aids. The foot on the unoperated side of the body that bears all the weight may also cramp and be sore from overuse. Strengthening arms and legs in the months before surgery can make recovery much easier. The operated leg will weaken from lack of use, so moving around and trying to be active will make walking on that leg easier later.

You may notice other changes in your hip, such as clicking and popping of the hip for weeks after surgery as the joint heals. A frequent complication of surgery is damage to the nerve that provides sensation to the skin of the thigh, due to the nerve’s anatomic location.4 You may notice numbness or uncomfortable sensation here when touched, but this resolves within about two years.
The time it takes to return to a work or school routine will vary from patient to patient. To function normally, pain must be under control since no one can be productive while taking a lot of pain medication. You should not drive until you are off medication and have been cleared by the physician at about the twelve-week mark.
Slowly, you will regain strength and range of motion in the operated leg. At the six-week mark, you will have an X-ray and see the surgeon, who will decide if your bone has healed enough to resume weight bearing on that side. It will be important to begin the appropriate muscle strengthening exercises, as discussed between your physician and physical therapist.
Through physical therapy and becoming active again, you will re-learn how to walk on the operated leg. It takes months after surgery to regain strength and a normal way of walking. You may use one crutch or a cane until you can walk without an aid, which happens by the three month mark for most patients3.  A slight limp will fade as the leg and pelvis muscles become stronger, and eventually you can resume normal activities and sports at a more functional level than prior to surgery.
Your physician may be able to put you in contact with patients who have undergone a PAO and are willing to share their experience and advice with you.

Will this surgery affect childbirth?
The PAO does not change the size of the birth canal, so the majority of women are able to deliver vaginally. One study showed that back and hip pain during pregnancy were frequently reported in the 24 pregnancies among 16 PAO patients, but it is unknown if these were due to the surgery or were just symptoms of pregnancy itself.5 Your obstetrician/gynecologist should be made aware of your condition.

References
1. Ganz R, Klaue K, Vinh TS, Mast JW. A new periacetabular osteotomy for the treatment of hip dysplasias. Clin Orthop 1988; 232: 26-36.
2. Murphy S and Deshmukh R. Periacetabular osteotomy: preoperative radiographic predictors of outcome. Clinical Orthopaedics and Related Reseach 2002; 405: 168-174.
3. Sanchez-Sotelo J, Trousdale RT, Berry DJ, Cabanela ME. Surgical treatment of developmental dysplasia of the hip in adults: I. Nonarthroplasty options. J Am Acad Orthop Surg 2002; 10(5):321-333.
4. Biedermann R., Donnan L, Gabriel A, Wachter R, Krismer M, Behensky H. Complications and patient satisfaction after periacetabular osteotomy. International Orthopaedics 2007.
5. Valenzuela RG, Cabanela ME, Trousdale RT. Sexual activity, pregnancy, and childbirth after periacetabular osteotomy. Clin Orthop 2004; 418: 146-152.

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