Periacetabular osteotomy, commonly called PAO, is a joint-preserving hip surgery that repositions the hip socket to improve coverage of the femoral head in people with hip dysplasia. Unlike hip replacement, which substitutes the joint entirely, PAO works with the patient’s own bone and cartilage, making it the preferred surgical option for younger adults whose dysplasia causes pain and threatens long-term joint health. The surgery involves cutting the bone around the acetabulum (the hip socket) and rotating it into better alignment, and the results over the past three decades have made it the standard of care for symptomatic dysplasia in the right candidate.
Who Is a Candidate
PAO is not for everyone with a shallow hip socket. The best outcomes occur in patients who meet a fairly specific profile: symptomatic hip dysplasia with a lateral center-edge angle between roughly 10° and 30°, no more than early-stage arthritis, and an age typically between 18 and 45. Studies consistently show that correcting the bony deformity in these patients improves hip function and slows the march toward osteoarthritis.1PubMed Central. Patient selection criteria for periacetabular osteotomy or rotational acetabular osteotomy The joint also needs to demonstrate good congruency when the hip is placed in an abducted position on X-ray, essentially a test that tells the surgeon the socket and ball will fit together well once realigned.
Several factors push the odds against a good outcome. Patients over 50 and those with more advanced arthritis tend to score worse on function and are more likely to eventually need a hip replacement. A medium-term follow-up study identified severe dysplasia on both conventional X-rays and CT scans, reduced acetabular anteversion, and the presence of an os acetabuli (a calcified fragment from a detached labrum) as predictors of eventual conversion to total hip arthroplasty.2Journal of Bone and Joint Surgery. Medium-Term Outcome of Periacetabular Osteotomy and Predictors of Conversion to Total Hip Replacement Higher age, an incongruent joint, narrow postoperative joint space, and a corrected center-edge angle that lands below 30° or above 40° also predict failure over four to twelve years of follow-up.3PubMed Central. What Factors Predict Failure 4 to 12 Years After Periacetabular Osteotomy? That last point is worth noting: over-correcting the socket can be just as problematic as under-correcting it.
What the Surgery Actually Does to the Joint
A dysplastic hip socket doesn’t cover enough of the ball of the femur, which concentrates weight-bearing forces onto a small area of cartilage. Think of it like standing on the edge of a ledge instead of in the middle of a platform. Over time that concentrated stress damages the cartilage and leads to arthritis. PAO aims to spread the load across a larger surface by rotating the socket into a more anatomically normal position.
Biomechanical studies confirm this works, but with nuances. One analysis using three-dimensional modeling found that peak joint contact pressure dropped by an average factor of about 1.7 after PAO.4PubMed Central. Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up A separate finite-element study of 51 hips showed that peak contact pressure decreased in 98% of cases, though only about two-thirds of those hips reached a truly normal pressure range afterward. The roundness of the femoral head and the degree of surgical correction both influenced whether the pressure fully normalized.5PubMed. Factors Associated With Abnormal Joint Contact Pressure After Periacetabular Osteotomy: A Finite-Element Analysis
Even more telling, contact stress in dysplastic hips after PAO tends to remain higher than in naturally normal hips. One study found that while the contact area during walking increased significantly after surgery (from about 395 mm² to 595 mm²), it was still far smaller than the roughly 1,120 mm² seen in normal hips. Mean contact stress dropped but didn’t reach statistical significance, and it stayed elevated compared to healthy joints.6PubMed Central. Joint contact stress improves in dysplastic hips after periacetabular osteotomy but remains higher than in normal hips PAO substantially improves the mechanical situation, in other words, but it doesn’t create a perfectly normal hip. That gap helps explain why some patients still develop arthritis eventually.
How the Surgery Is Performed
The Bernese PAO, which is the most widely practiced version, involves making a series of carefully planned bone cuts around the acetabulum. The procedure is approached from the front of the pelvis and from the inside, distinguishing it from older osteotomy techniques.7PubMed Central. Bernese periacetabular osteotomy (PAO): from its local inception to its worldwide adoption A critical goal is to keep the back column of the pelvis intact, which preserves the pelvic ring’s structural stability and allows earlier rehabilitation than procedures that cut through the entire ring.
The surgeon typically makes four cuts. The pubic bone is cut completely through the superior pubic ramus, while the ischial cut (the bone you sit on) is an incomplete separation. Two additional cuts are made in the iliac bone, and when the final cut connects the posterior iliac and ischial cuts, the acetabular fragment is freed and can be rotated into the desired position.8PubMed Central. Surgical Anatomy of the Rectus-Sparing Approach for Periacetabular Osteotomy: A Cadaveric Study Once repositioned, the fragment is held in place with screws. The overall objective is to optimize femoral head coverage and increase the weight-bearing surface of the acetabular cartilage without distorting the natural shape of the pelvis.9PubMed Central. Master’s Surgical Technique Ganz periacetabular osteotomy: How to make the osteotomy cuts easier?
Because this surgery demands precise three-dimensional spatial judgment, researchers have been exploring technology to help. Three-dimensional printed navigation templates, designed from CT scans and virtual surgical planning, have been tested in cadaver studies and shown to accurately translate the pre-planned bone cuts and rotation into the operating room.10PubMed Central. Application of a 3-dimensional printed navigation template in Bernese periacetabular osteotomies: A cadaveric study Inertial measurement units, small motion sensors attached to instruments, have also been proposed as a way to track the orientation of the acetabular fragment in real time without the line-of-sight limitations that optical navigation systems have.11PubMed. A cost-effective surgical navigation solution for periacetabular osteotomy (PAO) surgery These technologies are still evolving, but they point toward a future where the precision of PAO is less dependent on the individual surgeon’s spatial intuition.
When Hip Arthroscopy Is Done Alongside PAO
Many patients with hip dysplasia also have labral tears, cartilage damage, or features of femoroacetabular impingement, conditions where the bones of the hip pinch the soft tissue of the joint. In these cases, performing hip arthroscopy before or at the same time as PAO allows the surgeon to inspect and repair the inside of the joint, addressing problems that realigning the socket alone would leave untouched.12PubMed Central. Combined hip arthroscopy and periacetabular osteotomy: indications, advantages, technique, and complications
The approach can be staged (arthroscopy first, PAO weeks or months later) or combined in a single session. Staged arthroscopy with labral repair, femoroplasty (reshaping the femoral head-neck junction), and capsular plication followed by PAO has shown improved patient-reported outcomes and 100% survivorship at a minimum of two years for patients with both impingement and dysplasia.13PubMed. Staged Hip Arthroscopy With Labral Repair, Femoroplasty, and Capsular Plication Followed by Periacetabular Osteotomy for Hip Dysplasia Results in Improved Outcomes and 100% Survivorship at Minimum 2-Year Follow-Up The combined approach is gaining traction as surgeons recognize that dysplasia rarely exists in isolation and that leaving intra-articular damage untreated can limit the benefit of the osteotomy itself.
Recovery and Rehabilitation
Recovering from PAO is a long process. Most protocols start partial weight-bearing on the first day after surgery, typically at about 25% of body weight with a flat-foot technique, and continue that restriction for six to eight weeks while the bone heals.14PubMed Central. Rehabilitation Guidelines for Use Following a Periacetabular Osteotomy (PAO): A North American Based Delphi Consensus Crutches are the standard assistive device and are used until X-rays confirm bony healing and the patient can walk with a normal gait pattern. A systematic review found that most studies recommended partial weight-bearing lasting six to eight weeks, with crutches recommended in nearly half the studies and bracing rarely used.15PubMed Central. Postoperative weight-bearing restrictions and rehabilitation after periacetabular osteotomy: a systematic review
Return to sport varied widely across studies, typically somewhere between six and twelve months after surgery. The weight-bearing restrictions are not arbitrary: postoperative stress fractures are a recognized complication, reported at rates between 2% and 18% across the literature. Early full weight-bearing, non-union at the pubic bone, larger preoperative deformity, older age, and an aggressive postoperative correction have all been linked to higher stress fracture risk.16PubMed Central. Rehabilitation Guidelines for Use Following a Periacetabular Osteotomy (PAO): A North American Based Delphi Consensus
Long-Term Survivorship
The biggest question for most PAO patients is: how long will this last before I need a hip replacement? The answer depends on the severity of the initial dysplasia and the quality of the correction, but the numbers are generally encouraging. A large study of 1,385 hips reported a cumulative hip survival rate (with conversion to total hip arthroplasty as the failure endpoint) of 96% at five years, 90% at ten years, and 80% at fourteen years.17PubMed Central. 14-year hip survivorship after periacetabular osteotomy: a follow-up study on 1,385 hips Among those who did need a hip replacement, the average time from PAO to that surgery was about five years.
A longer-term study followed patients out to 18 years and found a survival rate of about 74%, with about one in five hips eventually undergoing hip replacement at an average of nine years after PAO.18PubMed Central. Survivorship of the Bernese Periacetabular Osteotomy: What Factors are Associated with Long-term Failure? These numbers mean that a large majority of patients get a decade or more of preserved joint function, and many get much longer. For a 25-year-old with dysplasia, that can mean the difference between needing a first hip replacement in their 30s versus their 40s or 50s, and potentially needing fewer replacements over a lifetime.
Risks and Complications
PAO is a major operation involving controlled fractures of the pelvis, and it carries real risks. Nerve injury is among the most concerning. In a series of 1,760 patients, about 2% developed a major deficit of the sciatic or femoral nerve. No specific patient or surgical risk factor could be reliably linked to who developed these injuries. Roughly half recovered completely, with the median time to recovery or plateau at about five and a half months.19PubMed Central. Prevention of Nerve Injury After Periacetabular Osteotomy
A separate and more common nerve issue involves the lateral femoral cutaneous nerve, which provides sensation to the outer thigh. In one study, half of patients had symptoms of injury to this nerve at one year, and a third still had persistent numbness or tingling at three or more years. While the sensory symptoms didn’t significantly affect overall physical health scores, patients with persistent nerve symptoms reported lower satisfaction and worse mental health scores on hip-specific questionnaires.20PubMed. Incidence and clinical outcome of lateral femoral cutaneous nerve injury after periacetabular osteotomy This is something potential PAO patients should know about in advance: thigh numbness after surgery is common and sometimes permanent, even though it’s not functionally disabling.
Bone healing complications are another consideration. In a cohort of 621 hips (in adolescents), stress fractures occurred in 4% of cases, delayed healing in about 2%, and non-union in roughly 6%. Stress fractures appeared exclusively in female patients and were localized to the inferior pubic bone. Higher body mass index, a lower preoperative center-edge angle, and a higher acetabular index angle all predicted these bone healing problems. Smoking was an independent risk factor for non-union specifically.21Archives of Orthopaedics. The Incidence and Risk Factors of Pelvic Stress Fracture, Delayed-healing and Non-union Following Periacetabular Osteotomy in Adolescents
Hardware Removal After PAO
The screws used to hold the repositioned bone fragment can sometimes become a problem. Reported rates of symptomatic hardware removal sit around 14% in the literature, though one series found that nearly a quarter of patients ultimately had their screws taken out.22PubMed Central. Clinical and surgical factors influencing screw breakage during hardware removal following periacetabular osteotomy The irritation can come from screws pressing against soft tissue or simply being palpable under the skin of the pelvis. When removal is needed, surgeons have found that waiting longer increases the chance of screws breaking during extraction, and smaller 3.5-mm screws are more prone to breakage than 4.5-mm screws. Earlier removal (within about 12 months) and the use of larger screws both reduce the probability of breakage during the removal procedure.
Returning to Sports and Daily Life
Getting back to an active life is often the driving motivation for PAO. A systematic review of athletes with symptomatic hip dysplasia found that return-to-sport rates after PAO ranged from about 63% for dancers at one year to over 80% in studies looking at broader sport participation. Competitive athletes returned at slightly lower rates of roughly 73% to 78%. The time to get back to sport ranged from about 9 to 13 months. Participation shifted somewhat toward lower-impact activities after surgery, but patients did participate across all impact categories, from walking and swimming to running and team sports.23PubMed. Periacetabular Osteotomy in Athletes With Symptomatic Hip Dysplasia Allows for Participation in Low-, Moderate-, and High-Impact Sports, With Greater Than 70% Return to Sport for Competitive Athletes: A Systematic Review
Among patients who played sports before surgery, about 70% returned to sport, mostly at a recreational level. Interestingly, about 27% of patients who were not active in sports before surgery took up a sport afterward, suggesting that pain relief and improved hip function opened doors that were previously closed.24PubMed. Return to Function Implications After Periacetabular Osteotomy Psychological factors matter, too: preoperative depression, anxiety, and somatization (the tendency to experience physical symptoms from psychological distress) all affect postoperative quality of life, perceived function, and pain perception after PAO.25PubMed Central. Psychological status affects postoperative quality of life, function, and pain after periacetabular osteotomy Addressing mental health before and during recovery isn’t an afterthought; it’s part of getting the best outcome.
PAO Versus Hip Replacement in Younger Adults
One of the trickiest decisions in hip surgery is whether a young adult with hip dysplasia and some existing arthritis should undergo PAO or skip straight to total hip arthroplasty. A study comparing the two procedures in matched groups found strikingly similar results at ten years: complication rates were identical at about 5%, and the rate of ultimate revision (PAO converting to replacement versus a replacement needing re-revision) was around 8% and 7% respectively. Both groups achieved significant improvements in function scores, and their final scores were not statistically different from each other. Clinical success was achieved in about 81% of PAO hips and 84% of replacement hips.26PubMed Central. Comparison of modern periacetabular osteotomy for hip dysplasia with total hip arthroplasty for hip osteoarthritis-10-year outcomes are comparable in young adult patients
A study focused specifically on patients in their 40s found that 72% of PAO patients and 61% of hip replacement patients reached a patient-acceptable symptomatic state, with similar reoperation rates and survivorship free of reoperation at five and eight years.27The Journal of Arthroplasty. Patient Acceptable Symptomatic State Achievement and Survivorship Following Periacetabular Osteotomy Versus Total Hip Arthroplasty in Patients Aged 40 to 49 Years The implication is that for patients in their 40s, both options are reasonable. The advantage of PAO is preserving native bone stock, which makes a future hip replacement easier if one becomes necessary. The advantage of replacement is a faster, more predictable recovery. A cost-effectiveness analysis found PAO is more cost-effective than hip replacement for patients with mild to moderate arthritis who are young and value sports participation, but becomes both more expensive and less effective for advanced arthritis.28PubMed. Cost-effectiveness analysis of periacetabular osteotomy
Other Types of Pelvic Osteotomy
PAO is not the only pelvic osteotomy for hip dysplasia. Pelvic osteotomies fall into three broad families: redirectional procedures (including the Salter, Pemberton, and Dega osteotomies) that reduce and redirect the acetabulum, mainly used in younger children; reorientation procedures like PAO and triple osteotomies that rotate the entire acetabular fragment; and salvage procedures like the Chiari and shelf osteotomies that enlarge the weight-bearing surface without truly correcting the socket’s position.29Journal of the American Academy of Orthopaedic Surgeons. Pelvic Osteotomies in the Child and Young Adult Hip: Indications and Surgical Technique
Biomechanical modeling has compared some of these approaches head to head. Rotational acetabular osteotomy (a reorientation procedure used more commonly in Asia) reduced hip strain more effectively than both the shelf procedure and the Chiari osteotomy, while the Chiari osteotomy failed to significantly reduce strain at all in one modeling study.30PubMed Central. The biomechanical differences of rotational acetabular osteotomy, Chiari osteotomy and shelf procedure in developmental dysplasia of hip The Bernese PAO has become the dominant reorientation technique worldwide because it preserves the posterior column, allows a large correction, and doesn’t require cutting through the entire pelvic ring. Salvage procedures are still used when the joint is too far gone for reorientation but the patient is too young for replacement.
Pregnancy and Delivery After PAO
Because PAO patients skew young and female, pregnancy after surgery is a common concern. The procedure changes the shape of the pelvis, and many patients worry about whether vaginal delivery is still possible. The evidence is reassuring but complicated. In one study, about 55% of patients who became pregnant after PAO delivered by cesarean section, which is higher than the national average of about 32%. However, most of those cesarean deliveries were for standard obstetric reasons like breech presentation or failure to progress in labor, not because of the PAO itself. Only about 27% of the cesarean patients reported that the surgery was cited as the reason.31PubMed Central. Periacetabular Osteotomy and Postoperative Pregnancy—Is There an Influence on the Mode of Birth?
A related finding is that over half of patients were told by their obstetrician that their PAO history could affect their ability to carry to term or deliver vaginally, contributing to anxiety around pregnancy planning.32PubMed Central. Is Previous Periacetabular Osteotomy Associated with Pregnancy, Delivery, and Peripartum Complications? The gap between obstetrician concern and actual surgical necessity is notable. Many obstetricians who haven’t encountered PAO patients before may err on the side of caution and recommend cesarean delivery without a clear biomechanical reason. Patients planning pregnancy after PAO benefit from having their orthopedic and obstetric teams communicate directly about the specific changes to their pelvic anatomy.