PAO: Definition, Uses, and Clinical Overview

PAO Introduction (What it is)

PAO most commonly refers to periacetabular osteotomy.
It is a hip-preserving pelvic surgery used to improve how the hip socket covers the femoral head.
PAO is most often discussed in the context of hip dysplasia in adolescents and adults.
Orthopedic hip specialists use PAO to reorient the acetabulum (hip socket) to better distribute joint forces.

Why PAO used (Purpose / benefits)

PAO is used to address a structural problem: the hip socket may be too shallow or maloriented, so the “ball” (femoral head) is not well covered by the “socket” (acetabulum). When coverage is inadequate, joint forces concentrate over a smaller area of cartilage and labrum, which can contribute to pain and tissue damage over time.

At a high level, the purpose of PAO is to:

• Improve femoral head coverage by repositioning the acetabulum.
• Reduce abnormal contact stresses across the hip joint by spreading load over a larger cartilage surface.
• Improve hip stability in a dysplastic (under-covered) hip.
• Relieve symptoms linked to mechanical overload (often activity-related groin or lateral hip pain).
• Preserve the native hip joint, potentially delaying the need for joint replacement in appropriately selected cases.

Benefits vary by clinician and case. Outcomes are influenced by factors such as cartilage health, the degree of dysplasia, and whether other hip conditions are present.

Indications (When orthopedic clinicians use it)

PAO is typically considered when the hip’s bony anatomy is a key driver of symptoms and mechanics. Common indications include:

• Symptomatic acetabular dysplasia (under-coverage of the femoral head) in adolescents or adults
• Hip pain with imaging showing dysplasia, often with associated labral injury or early cartilage wear
• Mechanical symptoms (e.g., catching, activity-related pain) where abnormal joint loading is suspected
• Hip instability patterns related to insufficient socket coverage
• Early degenerative changes where hip preservation is still considered feasible (varies by clinician and case)
• Residual dysplasia after childhood hip conditions once skeletal maturity is reached (case-dependent)

Contraindications / when it’s NOT ideal

PAO is not ideal for every painful hip, even when imaging shows structural differences. Situations where PAO may be less suitable, or where other approaches may be considered, include:

• Advanced hip osteoarthritis with substantial cartilage loss (hip preservation may be less effective)
• Severely limited hip range of motion suggesting significant joint degeneration or stiffness
• Poor bone quality or conditions that may impair bone healing (suitability varies by clinician and case)
• Active infection or other medical conditions that raise surgical risk (assessment is individualized)
• Hip pain primarily driven by non-structural causes (e.g., referred pain from spine, primary muscle/tendon disorders) where correcting the socket may not address the main problem
• Anatomy not amenable to acetabular reorientation (for example, certain patterns of deformity may require a different osteotomy or femoral procedure)
• Inability to participate in follow-up and rehabilitation, which can be important for recovery (circumstances vary)

How it works (Mechanism / physiology)

PAO works through biomechanical realignment, not medication-like physiology. There is no “onset” in the pharmacologic sense; instead, PAO immediately changes socket orientation, while symptom improvement and functional gains typically evolve over healing and rehabilitation.

Core biomechanical principle

In dysplasia, the acetabulum may provide insufficient coverage—often anteriorly and laterally—leading to higher contact pressures. PAO involves cutting the pelvic bone around the acetabulum and reorienting the socket so that:

• The femoral head is better covered
• Load is distributed more evenly
• The hip may become more stable during movement

Hip anatomy and structures involved

Key structures and concepts commonly discussed with PAO include:

• Acetabulum: the hip socket, part of the pelvis
• Femoral head: the ball at the top of the femur
• Articular cartilage: smooth lining on the femoral head and acetabulum that allows low-friction motion
• Labrum: fibrocartilage rim around the socket that contributes to stability and sealing of joint fluid
• Pelvic bones around the acetabulum: typically including areas of the ilium, ischium, and pubis (details vary by technique)

Because PAO changes bony orientation, it can also change how the labrum and cartilage are loaded. In some cases, additional procedures (such as addressing femoroacetabular impingement or labral pathology) may be considered, depending on findings and surgeon preference.

Reversibility and durability

PAO is generally considered non-reversible in the way a temporary treatment is; it permanently changes bone position once healed. Long-term durability depends on factors such as correction quality, healing, cartilage condition, and activity demands.

PAO Procedure overview (How it’s applied)

PAO is a surgical procedure, usually performed by orthopedic surgeons with hip preservation expertise. Exact steps and perioperative protocols vary by clinician and case, but the workflow commonly looks like this:

1. Evaluation / exam – Clinical history and physical exam focusing on hip pain location, range of motion, gait, and stability patterns
   – Imaging to assess bony structure and joint health, often including X-rays and sometimes MRI (for labrum/cartilage) or CT (for detailed bony anatomy), depending on the clinical question

2. Preparation – Preoperative planning based on imaging measurements and intended correction
   – Discussion of goals, anticipated rehab constraints, and potential risks (information and planning vary)

3. Intervention (the operation) – Controlled bone cuts (osteotomies) around the acetabulum
   – Reorientation of the socket to improve coverage and alignment
   – Fixation of the repositioned bone, commonly with surgical screws (implant type varies by material and manufacturer)

4. Immediate checks – Intraoperative and/or postoperative imaging checks to confirm alignment and fixation
   – Early monitoring for pain control, mobility, and surgical site issues

5. Follow-up – Scheduled follow-up visits and imaging to monitor bone healing and alignment
   – A rehabilitation plan that typically progresses activity and strengthening over time; weight-bearing status and timelines vary by clinician and case

This overview is intentionally general; surgical approaches, incision strategies, and adjunct procedures differ across centers and patient anatomy.

Types / variations

PAO most commonly refers to the Bernese (Ganz) periacetabular osteotomy, but “PAO” can be used broadly to describe periacetabular reorientation osteotomies. Variations may include:

• Technique variations
• Modified approaches to the classic Bernese PAO (differences in cuts, exposure, and workflow)

• Differences in fixation strategy (e.g., screw number/placement), which can vary by surgeon and case

• Isolated PAO vs combined procedures

• PAO alone when dysplasia-related mechanics are the dominant issue
• PAO plus femoral procedures (e.g., femoral osteotomy) when femoral version, neck-shaft angle, or other femoral factors contribute to mechanics (case-dependent)

• PAO plus hip arthroscopy or open labral/cartilage procedures in selected situations when intra-articular pathology also needs attention (practice patterns vary)

• Related acetabular osteotomies (not always labeled “PAO”)

• Triple pelvic osteotomy (more common in younger patients in some settings)
• Rotational acetabular osteotomy (RAO) in certain regions and surgical traditions
• Other pelvic reorientation procedures chosen based on age, anatomy, and surgeon expertise

Pros and cons

Pros:

• Preserves the native hip joint rather than replacing it
• Targets the underlying bony mechanics of dysplasia by improving socket coverage
• Can improve hip stability and load distribution when correction is appropriate
• May reduce mechanical overload contributing to labral and cartilage stress
• Often performed in younger or middle-aged patients where joint preservation is a priority (selection varies)
• Can be combined with other procedures when multiple anatomic issues exist (case-dependent)

Cons:

• It is a major bone surgery with a meaningful recovery and rehabilitation process
• Risks can include blood loss, infection, blood clots, nerve injury, nonunion or delayed healing, heterotopic ossification, and need for additional surgery (risk profiles vary)
• Results depend on accurate correction and the condition of existing cartilage and labrum
• Not ideal for advanced arthritis, where symptom drivers may not be correctable by reorientation alone
• Temporary limitations are common, including restricted weight-bearing and reduced activity during healing (timelines vary)
• Some patients may later require additional hip surgery, including arthroplasty, depending on disease progression (varies by clinician and case)

Aftercare & longevity

Aftercare following PAO is often discussed in terms of bone healing, protection of the correction, and progressive rehabilitation. Specific protocols differ, but several themes are common.

What affects recovery and outcomes

• Severity and pattern of dysplasia: different coverage deficits require different corrections
• Cartilage and labral condition: pre-existing degeneration can influence symptom improvement and long-term joint health
• Quality of correction and fixation: alignment goals are individualized and surgeon-dependent
• Bone healing capacity: influenced by overall health, bone quality, and other medical factors
• Rehabilitation participation: consistency with therapy goals (mobility, strength, gait) can affect functional recovery
• Weight-bearing status: restrictions are often used to protect healing bone; the exact plan varies by clinician and case
• Comorbidities and lifestyle factors: general health, nutrition, and activity demands can influence healing and conditioning

Longevity (how long the benefits can last)

Longevity is not a fixed number and cannot be guaranteed. In general, PAO aims to create a more favorable mechanical environment for the hip joint, but long-term durability depends on joint health at the time of surgery and how the hip responds over time. Follow-up imaging and clinical assessments are commonly used to track healing and joint status.

Alternatives / comparisons

PAO is one option within a broader set of hip pain and hip dysplasia management strategies. Comparisons are most useful when framed around the primary problem: structural under-coverage, soft tissue injury, inflammation/pain, or degenerative arthritis.

• Observation / monitoring
• May be considered when symptoms are mild or intermittent and function is largely maintained.

• Does not change socket mechanics; it focuses on tracking symptoms and joint status over time.

• Physical therapy and activity modification

• Often used to improve hip and core strength, movement control, and symptom management.

• Can help some patients function better but does not reorient the acetabulum.

• Medications

• Commonly used for symptom relief (e.g., anti-inflammatory medications), depending on individual health factors.

• They do not address the underlying bony alignment.

• Injections

• Sometimes used diagnostically (to help localize the pain source) and/or therapeutically for short-term symptom reduction.

• Effects and appropriateness vary by injection type and clinical scenario.

• Hip arthroscopy

• Can address labral tears or certain impingement features in selected patients.

• In a dysplastic hip, arthroscopy alone may not correct instability or abnormal loading; whether it is appropriate depends on anatomy and clinician judgment.

• Other osteotomies

• In some cases, a femoral osteotomy or a different pelvic osteotomy may better match the deformity pattern.

• Choice depends on whether the main driver is acetabular orientation, femoral version/shape, or both.

• Total hip arthroplasty (hip replacement)

• More commonly considered when arthritis is advanced and cartilage loss is a dominant cause of pain and stiffness.
• Changes the joint surfaces rather than reorienting native bone; it is a different category of treatment with different goals and trade-offs.

PAO Common questions (FAQ)

Q: Is PAO a hip replacement?
No. PAO is a hip-preserving procedure that reorients the hip socket to improve coverage and mechanics. Hip replacement resurfaces or replaces the joint with implants.

Q: What kind of pain is PAO meant to address?
PAO is most often discussed for mechanical hip pain linked to dysplasia-related overload or instability. Pain patterns vary and can include groin pain, lateral hip pain, or activity-related symptoms. Not all hip pain is caused by dysplasia, so evaluation focuses on identifying the main pain generator.

Q: How long does it take to recover after PAO?
Recovery is typically described in phases: early healing, progressive mobility and strengthening, and return to higher-level activities. Exact timelines vary by clinician and case, and they depend on bone healing, rehabilitation progress, and whether other procedures were performed.

Q: Will I be allowed to put weight on the leg right away?
Weight-bearing plans after PAO commonly include a period of restricted or protected weight-bearing, but the specifics vary by surgeon and individual factors. The restriction is generally intended to support bone healing and protect fixation during early recovery.

Q: When can someone drive or return to work after PAO?
Driving and return-to-work timing depend on factors such as which side was operated on, pain control, mobility, reaction time, and job demands. Sedating medications and limited weight-bearing can also affect readiness. Plans are individualized and vary by clinician and case.

Q: How long do the results of PAO last?
PAO creates a permanent change in socket orientation, but long-term benefit depends on cartilage health, quality of correction, and how the joint responds over time. Some people maintain improvement for many years, while others may develop progressive arthritis and require additional treatment later. Durability varies by clinician and case.

Q: Is PAO considered safe? What are the main risks?
PAO is a commonly performed hip preservation surgery in specialized centers, but it is still major surgery. Potential risks include infection, blood clots, bleeding, nerve injury, delayed or failed bone healing, and the possibility of additional surgery. Individual risk varies based on health status and surgical details.

Q: Does PAO prevent arthritis?
PAO is intended to improve joint mechanics and reduce overload, which may be favorable for joint health. However, it cannot restore cartilage that is already significantly damaged, and it does not guarantee that arthritis will not progress. The relationship between correction and long-term joint degeneration varies by clinician and case.

Q: Can PAO be combined with labral repair or treatment for impingement?
Yes, in selected cases. Some patients have both dysplasia-related instability/under-coverage and intra-articular problems such as labral tears or femoroacetabular impingement features. Whether to combine procedures, and how, depends on anatomy, imaging findings, and surgeon preference.

Q: How much does PAO cost?
Costs vary widely by region, hospital setting, insurance coverage, surgeon fees, implants, and rehabilitation needs. Because PAO involves surgery, imaging, anesthesia, and follow-up care, total cost can be substantial. The most accurate estimate comes from the treating facility and payer policies.