Hip PAO explained

The surgical process of periacetabular osteotomy (PAO) is typically prescribed for people with hip dysplasia. Hip dysplasia is a medical condition in which the ball and socket of the joint has not been properly formed. In medical terms, the “ball” is referred to as the femoral head, and the “socket” is referred to as the acetabulum.

How does hip dysplasia occur?

In patients presenting with hip dysplasia, the femoral head is not fully aligned with the acetabulum, often resulting in full or partial dislocation. This misalignment can cause groin pain, stiffness, or osteoarthritis. It is not uncommon, and one in every 1000 babies are born with hip dysplasia.

The surgical answer to this medical condition is hip PAO surgery. By moving the acetabulum closer to the femoral head, the hip joint’s biometrics can be improved. This reduces physical stress and allows for greater hip mobility.

Hip PAO surgery

Prior to the PAO operation, an arthroscopy may need to be performed. This will allow for a more accurate assessment of the patient’s hip joint area and contribute to the optimisation of the surgery as a whole. This operation is typically performed while the patient is under either sedation-induced spinal anaesthetic, or an epidural-induced general anaesthetic.

The process of PAO usually takes two hours overall. It starts with an incision of 10-12cm across the outside of the pelvic bone, followed by a series of bone cuts in close proximity to the acetabulum. This frees the acetabulum, allowing it to be adjusted into proper alignment with the pelvis. While still in surgery, the adjustment will be assessed by X-rays until optimal positioning occurs. This position is then held in place using 3-4 metal screws.


After surgery patients are assisted out of bed by physiotherapists. A self-administered morphine pump is provided for pain. Patients are encouraged to place a small amount of body weight on crutches for rehabilitative support. Approximately 4-6 days post operation, patients may begin gentle exercises in a hydrotherapy pool. Most patients are released from hospital after 5-8 days.

How can PAO surgery help?

The main objective of PAO surgery is to minimise pain coming from the hip joint. Furthermore, it is anticipated that PAO reduces the progression or risk of development of arthritis. However, this will depend greatly on how severe the presence of arthritis is in the patient.

Minimally invasive periacetabular osteotomy

Although the typical incision made during a PAO is 10-12cm, we have developed a newer approach that is less physically invasive and results in minimised scarring. This is Minimally Invasive (MIS) PAO.

The main difference between the original PAO surgical approach and the MIS approach is the length of the incision. With MIS, it is just 8-10cm. This minimised dissection allows for faster healing and a smoother cosmetic result that is significantly less visible. Scarring from MIS is generally not even visible in beachwear. Another advantage of MIS is the increased speed of recovery and rehabilitation time. Patients can put up to 30kg of pressure on the affected leg, making mobility with crutches easier. Bearing full weight is allowed at six weeks, with a steady progression from two crutches to one.

Post-PAO rehabilitation

We recommend that patients continue with hydrotherapy for up to 6 weeks post-operation, with sessions roughly 2-3 times every week. Hydrotherapy improves physical strength and mobility, allowing a gradual adjustment to weight bearing that is supported by the buoyancy of water. Patients are encouraged to consider finding a local hydrotherapy facility prior to the operation for ease of organisation after the PAO.

6 weeks after the operation, patients will return for an assessment and a repeat X-ray to determine how the bone is healing. At this point, patients are allowed to place half their body weight on the affected leg with the support of two crutches for a week, until graduating to full body weight on just one crutch. This phase of the recovery process puts emphasis on the hip muscles and abductors (gluteus minimus and medius). To avoid limping, both muscles must be strengthened.

Most patients can return to a regular lifestyle and activities within 10-12 weeks post-surgery. Impact sports and exercise will require a minimum of six months before patients can partake. Aside from the hip surgery recovery, patients with arthritis will still need to take into account their condition before returning to regular activities.

Post-PAO physiotherapy guidance

0-6 weeks post-PAO surgery

This first phase of rehabilitation focuses on promoting hip mobility using crutches and active movements. The weight-bearing limitation is 20kg on the affected leg.

Patients are encouraged to practice a regular heel-to-toe gait, checking weight-bearing progress by pressing down with the leg on a scale. Encouraged hip movements include abduction, extension, and flexion exercises. Sliding the heel up and down while lying down is also a helpful way to encourage flexibility of the hips.

Due to the location of the osteotomy, inhibition and stiffness of the hip flexors are anticipated at this point. Hydrotherapy is strongly recommended for supporting the recovery of these exercises, but it is not mandatory.

At 4 weeks, more exercises are added to the recovery programme, including:

  • Side-lying hip abductor raises with extended hips and knees. If this is particularly difficult for a patient, starting with clam abductor raises may be helpful. Patients should aim to hold the leg in position for 10 seconds at a time, building up to 25 repetitions twice per day (50 repetitions in total).

  • Straight leg raise exercises. Raise the leg roughly 30cm upwards and hold in position for 10 seconds. This exercise can be repeated up to 15 times per day, but no more than that as the iliopsoas may become irritated.

  • Passive hip flexion towards the chest. Patients are to pull the knee and hold it towards the chest until it becomes moderately painful. This position can be held for up to 10 seconds and repeated up to 20 times per day.

  • Hip abductor strengthening. Strengthening and activating the adductor musculature is very important at this stage. This can be done by sitting with a bolster between both knees and squeezing towards the middle for 10 seconds at a time. This can be repeated.

  • Prone lying hip extension. The iliopsoas can become quite tight, so it is very important to perform exercises that strengthen it. Simultaneously, this will also help to activate the posterior gluteal musculature.

6-12 weeks post-PAO surgery

After 6 weeks have passed, patients will return for another X-ray to determine whether the hip is recovering satisfactorily. Should the progress be on track, weight bearing will be increased to 30kg. This will be the new limit for the next two weeks, after which it will be increased to 50% of the patient’s overall weight, supported by two crutches for a week. At that point, the patient can then begin using just one crutch until their Trendelenburg gait withdraws.

The focus during this stage of recovery is on stretching and progressive strengthening exercises. The same muscle groups as before will remain a part of the rehabilitation routine, but with increased resistance from using therabands.

From 8 weeks onwards, using an upright stationary bicycle may be helpful for promoting overall hip flexion and mobility. The bicycle should be set at light resistance with 50-60rpm, with the aim being 30 minutes at a time. From 10 weeks onwards, the rpm and resistance level can be increased to the patient’s comfort level.

At 8-10 weeks, patients with access to a swimming pool are encouraged to start doing their exercises both in the water and on land.

From 10 weeks, a cross-trainer can also be useful for assisting recovery.

12 weeks post-operation

From 12 weeks onwards, the osteotomy should have consolidated. However, depending on the correction required for the acetabulum, the osteotomy may take longer to fully unite – sometimes up to 18 months. This is not an issue on its own, but the callus and changes that the osteotomy may have brought can affect the iliopsoas and cause discomfort or irritation.

Strengthening and stretching the iliopsoas should be the focus at this point in the recovery programme. Patients are encouraged to do their exercises while standing as opposed to lying down, so as not to strain the tendons during strengthening sessions.

Strengthening work on the hip adductor and abductor will continue to promote mobility and stamina of the muscles. It is normal for patients to report feeling fatigued towards the end of the day as their muscles acclimatise to the movement. Individual comfort levels will play a role in how resistance work is increased and adjusted.

Those wishing to take part in impact sports should build up an exercise programme using the swimming pool, stationary bike, and a cross trainer where possible. At 5 months, impact sports may be introduced, with close monitoring after 6 months.

PAO frequently asked questions (FAQs)

PAO surgery usually only takes between 1 and 2 hours.

The typical hospital stay for PAO surgery is 3 to 7 days, but it depends on the patient.

Incisions are 8-10cm and very cosmetically advanced.

Should the screw heads become uncomfortable for you, removing them at 6-8 months post-PAO is a very simple procedure that will not cause any weakening of the bone.

A labral tear is very common in patients with hip dysplasia. After assessing the position of the acetabulum, the labrum is put under less stress, resulting in decreased pain. If the femoral head is a particularly abnormal shape, a hip arthroscopy may be necessary. If this is the case, the arthroscopy will be scheduled roughly 8 weeks after the PAO and it should not interfere with the overall recovery process.

The overall length of time that a patient will need to use crutches is 10-12 weeks. Throughout this period, patients will gradually increase weight on the affected leg and shift from two crutches down to one before being able to walk freely.

Using crutches can contribute to some local tenderness or numbness, but this can be alleviated by wrapping the handles of the crutch in soft fabric or tennis racquet grips.

While a wheelchair is not necessary, renting one for a few weeks can make movements less stressful for outings or movements around the home.

The majority of the healing will happen within 4-6 months, but there may be some residual achiness that lingers. This should disappear over time.

The aim of PAO is geared more towards pain reduction than anything else. Although a PAO may eliminate or decrease the chances of you needing a hip replacement at a later stage, the outcome will greatly depend on your personal history with arthritis.

This depends entirely on the nature of work you do. 3 months is the standard period of recovery time needed for PAO. However, if your work is mainly sedentary, any time between 6 and 10 weeks away from work is deemed suitable. If your work requires significant physical movement, up to 4 months may be necessary.

8 weeks after surgery is considered a suitable time for patients to perform their exercises in a gym. Activities like stationary cycling and light stretches in particular are safe to do at this point. However, more strenuous exercises like cross training or treadmill running are more suitable for week 12 of the recovery programme.

If you drive an automatic and it is your left leg that has been operated on, driving can commence at 6 weeks onwards. If you have a manual car or have had your right leg operated on, you may need to wait until 8 weeks to drive.

This will depend on your personal levels of physical comfort, but for most people it takes 6 weeks before sexual activity feels comfortable.

There is no evidence to suggest that PAO specifically affects pregnancy or childbirth.

As with all surgeries, there are some risks and potential complications that may occur. However, PAO is a relatively low-risk procedure. With the appropriate level of experience, PAO can be performed with a fairly small incision that produces a favourable and predictable result.

Blood vessel and nerve injury

The acetabulum is naturally surrounded by important blood vessels and nerves that are at low risk of damage. Should this occur, the lower leg could suffer some weakness, causing pulmonary embolus or deep vein thrombosis.

However, the risk of a major complication like this sits at 2%. Additionally, patients are administered thromboembolic deterrent stockings and blood-thinning medications to further decrease this risk.


Pelvic bones are surrounded by blood vessels that are fed a particularly large supply of blood, which means significant bleeding has the potential to occur. During the PAO surgical process, a cell saver is utilised to replenish any blood that a patient loses during the procedure. It is considered quite uncommon for patients to require a blood transfusion.


The surgical process of PAO may cause the hip joint to become arthritic, but this will depend on the level of arthritic damage present pre-operation. It will also depend on how shallow the respective acetabulum is. Although the objective of PAO is to restore as much normality to the hip joint as possible, the strain of the procedure may trigger the development of arthritis over time.

Leg numbness

There are numerous small sensory nerves around the upper and outer thigh, which means there is a high likelihood of some numbness or sensitivity developing in the area of operation. Some patients may experience numbness between the outer hip and knee, but any extensions below this point would be unusual. Generally speaking, sensations of numbness that do occur are likely to diminish over time.

Wound infections

With PAO, there is small risk of the osteotomy failing to unite. Should this occur, the patient will be given antibiotics and scheduled for a second surgery to stimulate bone healing. However, due to the strong muscle cover and blood supply fed to the pelvis, the risk of a wound infection is extremely low (1%).