FEMOROACETABULAR IMPINGEMENT (FAI)
CAM vs Pincer vs Mixed | Alpha Angle Measurement | FADIR Test Gold Standard | Hip Arthroscopy
FAI MORPHOLOGY TYPES
Critical Must-Knows
- CAM impingement from aspherical femoral head with decreased head-neck offset
- Pincer impingement from acetabular overcoverage (focal or global)
- Alpha angle greater than 55 degrees diagnostic for CAM morphology on MRI
- FADIR test (flexion-adduction-internal rotation) has 94-99% sensitivity
- Mixed morphology present in 85% of symptomatic FAI cases
- Labral tears in 86% of FAI patients requiring surgery
Examiner's Pearls
- "CAM = femoral problem, Pincer = acetabular problem, Mixed = both
- "Alpha angle measured on lateral femoral head-neck junction
- "Crossover sign indicates anterior acetabular overcoverage (pincer)
- "Hip arthroscopy gold standard for treatment - open surgery declining
Critical FAI Exam Points
CAM vs Pincer Distinction
CAM is a femoral problem - aspherical head-neck junction with decreased offset. Pincer is acetabular - overcoverage causing rim impingement. Mixed (both) occurs in 85% of symptomatic cases. Know the radiographic signs for each.
Alpha Angle Measurement
Alpha angle greater than 55 degrees indicates CAM morphology. Measured on lateral view (frog-leg or MRI axial oblique). Angle between femoral neck axis and line to point where head becomes aspherical. Critical diagnostic threshold.
FADIR Test Critical
Flexion-Adduction-Internal Rotation (FADIR) test has 94-99% sensitivity for FAI. Patient supine, hip flexed to 90 degrees, then adducted and internally rotated. Positive = anterior groin pain. Most sensitive clinical test.
Labral Pathology Link
86% of FAI patients have labral tears at time of surgery. CAM causes anterosuperior labral damage from shear forces. Pincer causes posteroinferior labral damage from levering. Address both morphology and labral tear.
Quick Decision Guide - FAI Management
| Patient | Morphology | Treatment | Key Pearl |
|---|---|---|---|
| Young active, mild symptoms | Asymptomatic CAM/pincer on X-ray | Conservative: activity modification, physio | Not all morphology needs surgery |
| Active, failed 3-6 months physio | CAM morphology, alpha angle greater than 60° | Hip arthroscopy: femoral osteoplasty | Address CAM bump and labral tear |
| Active, mechanical symptoms | Pincer with crossover sign | Hip arthroscopy: rim trimming | Don't over-resect - risk instability |
| Young athlete, failed conservative | Mixed FAI with labral tear | Hip arthroscopy: combined osteoplasty + labral repair | Most common scenario (85%) |
| Older patient, established OA | FAI with Tonnis grade 2-3 arthritis | Total hip arthroplasty | Arthroscopy contraindicated with OA |
CAM - Femoral Morphology Features
Memory Hook:CAM = Capital (femoral head) Asphericity in Males - think of a CAMera bump on the femoral neck
PINCER - Acetabular Morphology Features
Memory Hook:PINCER pinches the femoral neck between acetabular walls like pincers
FADIR - Clinical Diagnosis
Memory Hook:FADIR = Position that Forces Anterior impingement and Reproduces pain
SCOPE - Hip Arthroscopy Indications
Memory Hook:SCOPE out the right candidates - not everyone with FAI morphology needs arthroscopy
Overview and Epidemiology
Femoroacetabular impingement (FAI) is a mechanical hip disorder caused by abnormal contact between the femoral head-neck junction and the acetabular rim during hip motion. This repetitive impingement leads to labral and chondral damage, potentially progressing to early hip osteoarthritis.
Two distinct morphological types:
- CAM impingement: Aspherical femoral head with decreased head-neck offset
- Pincer impingement: Acetabular overcoverage (focal or global)
- Mixed impingement: Combination of both (85% of symptomatic FAI)
Why FAI Matters
FAI is increasingly recognized as a major cause of early hip osteoarthritis in young active patients. Without treatment, repetitive impingement causes progressive labral and chondral damage. Early recognition and intervention may prevent or delay the development of osteoarthritis, though long-term data is still emerging.
Epidemiology:
Demographics
- Peak age: 20-40 years for symptoms
- CAM type: 3:1 male predominance
- Pincer type: More common in middle-aged females
- Athletes: Higher prevalence in certain sports (soccer, hockey, dancing)
- Morphology prevalence: 10-15% general population (often asymptomatic)
Clinical Impact
- Activity limitation: Significant impact on young active patients
- Labral tears: Present in 86% of FAI requiring surgery
- Cartilage damage: Chondral lesions in 70% at arthroscopy
- OA progression: May account for 10-15% early hip OA cases
- Sports: Can be career-ending for athletes if untreated
Risk factors for developing symptomatic FAI:
- High-impact sports participation during skeletal development
- Repetitive hip flexion activities (dancers, martial artists)
- Underlying hip dysplasia or acetabular retroversion
- History of Perthes disease or slipped capital femoral epiphysis (SCFE)
- Genetic predisposition (familial clustering observed)
Pathophysiology and Mechanisms
Normal hip anatomy:
The hip is a ball-and-socket joint with exceptional range of motion. Normal anatomy includes:
- Femoral head: Spherical, covered by articular cartilage except at fovea
- Femoral neck: Offset from head creating concave waist at anterior-superior junction
- Head-neck offset: Normal anterior offset allows clearance during flexion and internal rotation
- Acetabulum: Horseshoe-shaped socket covering approximately 40% of femoral head
- Acetabular labrum: Fibrocartilaginous rim deepening socket and sealing joint
Normal Head-Neck Offset
The anterior-superior femoral head-neck offset is critical for normal hip mechanics. During hip flexion and internal rotation, this offset allows the femoral neck to clear the acetabular rim. Loss of this offset (CAM morphology) causes abnormal contact and shear forces on the anterosuperior labrum and cartilage.
CAM morphology anatomy:
CAM Morphology Features
| Feature | Normal | CAM Morphology | Clinical Significance |
|---|---|---|---|
| Head shape | Spherical | Aspherical (pistol-grip deformity) | Loss of clearance during motion |
| Head-neck offset | Concave waist anteriorly | Decreased or absent offset | Alpha angle greater than 55° |
| Impact zone | None | Anterosuperior acetabulum | Outside-in chondral/labral damage |
| Mechanism | Smooth articulation | Shear forces on flexion-IR | Progressive cartilage delamination |
Pincer morphology anatomy:
Pincer Morphology Features
| Feature | Normal | Pincer Morphology | Clinical Significance |
|---|---|---|---|
| Acetabular coverage | 40% femoral head coverage | Excessive coverage (focal or global) | Premature rim contact |
| Acetabular version | 15-20° anteversion | Retroversion or coxa profunda | Crossover sign on AP pelvis |
| Impact zone | None | Anterosuperior rim initially | Rim contact causes levering |
| Labral damage | None | Posteroinferior from levering | Contre-coup labral tear pattern |
Outside-In vs Inside-Out Damage
CAM impingement causes outside-in damage - the aspherical head impacts the acetabular rim first, then shears into the labrum and cartilage like a snowplow. Pincer impingement causes inside-out damage - the acetabular rim impacts the femoral neck, causing levering and posteroinferior contre-coup labral damage. Understanding this distinction is critical for surgical planning.
Biomechanics of impingement:
The impingement occurs during specific hip positions:
- CAM: Worse with flexion and internal rotation (FADIR position)
- Pincer: Worse with flexion, adduction, external rotation (FABER position)
- Mixed: Symptoms in multiple positions
Normal vs pathological forces:
Normal Hip Mechanics
- Smooth spherical femoral head
- Adequate head-neck offset allows clearance
- Labrum acts as suction seal
- Cartilage experiences compression forces only
- Full range of motion without impingement
FAI Mechanics
- Abnormal bony contact at extremes of motion
- Shear forces damage labrum and cartilage
- Repetitive microtrauma with each hip flexion
- Progressive delamination of cartilage
- Eventually leads to full-thickness cartilage loss
Classification Systems
FAI Type by Morphology
| Type | Location | Radiographic Signs | Labral Pattern | Treatment |
|---|---|---|---|---|
| CAM | Femoral head-neck | Alpha angle greater than 55° | Anterosuperior tear | Femoral osteoplasty |
| Pincer | Acetabular rim | Crossover sign, coxa profunda | Posteroinferior tear | Acetabular rim trimming |
| Mixed | Both femur and acetabulum | Combined signs | Anterosuperior + posterior | Combined osteoplasty |
Mixed is the Rule
85% of symptomatic FAI cases are mixed type with both CAM and pincer components. Always look for both on imaging. The primary mechanism may be one or the other, but addressing only one component leads to persistent symptoms. Complete assessment requires evaluating both femoral and acetabular morphology.
Clinical Presentation and Assessment
History:
Patients with symptomatic FAI typically present with:
- Pain location: Deep anterior groin pain (85-90% of cases)
- Character: Activity-related, insidious onset
- Aggravating factors: Prolonged sitting (theater sign), getting out of car, squatting, climbing stairs
- Sports: Reduced performance in cutting, pivoting sports
- Mechanical symptoms: Clicking, catching, or giving way (if labral tear present)
CAM Presentation
- Demographics: Young males, athletes (soccer, hockey)
- Pain pattern: Deep groin pain with high-impact activity
- Movements affected: Hip flexion with internal rotation
- Sports limitation: Reduced ability to change direction quickly
- Progression: Gradual worsening over months to years
- Associated: May have labral tear causing clicking
Pincer Presentation
- Demographics: Middle-aged females, endurance athletes
- Pain pattern: Anterior groin pain with prolonged activity
- Movements affected: Hip flexion, especially in adduction
- Theater sign: Pain after prolonged sitting with hip flexed
- Progression: Slower progression than CAM
- Associated: Posterior labral tears from levering
Physical examination:
FAI Physical Examination Findings
| Test | Technique | Positive Finding | Sensitivity |
|---|---|---|---|
| FADIR test | Flexion 90°, adduction, internal rotation | Anterior groin pain | 94-99% |
| FABER test | Flexion, abduction, external rotation | Groin or lateral pain | 70-80% |
| Hip internal rotation | Prone, hip extended, measure IR | Less than 20° suggests FAI | Variable |
| Stinchfield test | Resisted hip flexion at 30° | Anterior groin pain | 60-70% |
| Log roll test | Supine, passive hip rotation | Groin pain or clicking | Variable |
FADIR Test is Gold Standard
The FADIR test (Flexion-Adduction-Internal Rotation) is the single most sensitive clinical test for FAI with 94-99% sensitivity. Position the patient supine, flex hip to 90 degrees, then adduct across the body and internally rotate. Reproduction of anterior groin pain is a positive test. This position maximizes impingement at the anterosuperior acetabulum.
Range of motion findings:
| Motion | Normal Range | Typical FAI Finding | Clinical Significance |
|---|---|---|---|
| Flexion | 120-140° | 90-110° | Limited by pain at end range |
| Internal rotation | 30-40° | Less than 20° | Most restricted motion in FAI |
| External rotation | 40-50° | Often preserved | Helps distinguish from other pathology |
| Abduction | 40-50° | Usually preserved | Not typically limited |
| Adduction | 20-30° | May be painful | Pain with FADIR position |
Gait and posture:
- Usually normal gait pattern (unless severe OA)
- May have antalgic gait with advanced disease
- Sitting posture: May sit with hip abducted and externally rotated to avoid impingement
C-Sign Positive
The C-sign is highly specific for intra-articular hip pathology including FAI. Patient makes a "C" shape with thumb and fingers, placing it over the anterior and lateral hip to indicate deep groin and lateral pain. Distinguishes intra-articular pathology from extra-articular hip pain (bursitis, muscle strains).
Differential diagnosis:
Must Rule Out
- Hip dysplasia: May coexist with FAI or be separate entity
- Athletic pubalgia: Sports hernia, adductor pathology
- Labral tear without FAI: Traumatic labral injury
- Avascular necrosis: History, risk factors, MRI
- Hip OA: Age, X-ray changes, Tonnis grading
- Inflammatory arthritis: Systemic symptoms, labs
Extra-articular Causes
- Iliopsoas tendinitis: Snapping hip, different pain pattern
- Greater trochanteric pain syndrome: Lateral pain, not groin
- Adductor strain: Medial thigh pain
- Lumbar spine: L2-L3 radiculopathy can mimic groin pain
- Stress fracture: Femoral neck stress fracture in runners
Investigations
FAI Imaging Protocol
Standard views (mandatory):
- AP pelvis: Assess acetabular coverage, crossover sign, center-edge angle
- Frog-leg lateral: Alpha angle measurement, head-neck offset assessment
- False profile: Evaluate anterior coverage
Key measurements:
- Alpha angle (frog-leg lateral): Greater than 55° diagnostic for CAM
- Center-edge angle (AP): Greater than 40° suggests pincer overcoverage
- Crossover sign: Anterior wall crosses posterior wall (acetabular retroversion)
- Tonnis grading: Assess for osteoarthritis (Grade 0-1 for arthroscopy eligibility)
MRI arthrogram is the gold standard for FAI assessment:
- Alpha angle: Measured on axial oblique sequences (most accurate)
- Labral tears: 90% sensitivity with intra-articular gadolinium contrast
- Cartilage damage: Assess for chondral lesions (predictor of outcome)
- Cam deformity extent: Map the CAM lesion circumferentially
- Herniation pits: Synovial herniation into femoral neck (marker of FAI)
Typical MRI findings in FAI:
- Anterosuperior labral tear (CAM pattern)
- Anterosuperior cartilage delamination or defect
- Paralabral cysts (if labral tear present)
- Herniation pit at anterior femoral neck
CT indications (not routine):
- Surgical planning for complex acetabular morphology
- 3D reconstruction to map CAM lesion extent
- Assess bony anatomy when MRI contraindicated
- Measure version and coverage angles precisely
Less sensitive than MRI for soft tissue (labrum, cartilage) assessment.
Dynamic fluoroscopy (during examination under anesthesia):
- Assess impingement location during hip motion
- Guide extent of osteoplasty intraoperatively
- Confirm clearance after CAM resection
- Identify additional impingement sources
Radiographic signs summary:
Key Radiographic Signs in FAI
| Sign | View | Finding | Indicates |
|---|---|---|---|
| Alpha angle greater than 55° | Frog-leg lateral or MRI | Angle between neck axis and asphericity point | CAM morphology |
| Crossover sign | AP pelvis | Anterior wall lateral to posterior wall | Acetabular retroversion (pincer) |
| Posterior wall sign | AP pelvis | Posterior wall medial to femoral head center | Relative anterior overcoverage |
| Center-edge angle greater than 40° | AP pelvis | Angle from femoral head center to lateral rim | Global overcoverage (pincer) |
| Herniation pit | MRI or frog-leg | Pit at anterior femoral neck | Marker of chronic FAI |
| Os acetabuli | AP pelvis | Ossicle at anterosuperior rim | Chronic pincer impingement |
Intra-articular Injection Test
Diagnostic local anesthetic injection into the hip joint under fluoroscopy or ultrasound guidance can be very useful. Temporary relief of pain after injection confirms the hip joint as the pain source. Persistent pain suggests extra-articular pathology. Typically combine anesthetic (lidocaine or bupivacaine) with steroid for therapeutic benefit.
Laboratory investigations:
Generally not required unless ruling out inflammatory arthropathy:
- ESR, CRP if inflammatory arthritis suspected
- Rheumatoid factor, anti-CCP if RA suspected
- HLA-B27 if ankylosing spondylitis suspected
Management Algorithm
Non-Operative Treatment (First-Line)
All patients should trial conservative management for 3-6 months unless severe mechanical symptoms.
Conservative Treatment Protocol
- Avoid provocative positions: Limit deep flexion, internal rotation
- Modify sports: Reduce high-impact activities temporarily
- Lifestyle changes: Avoid prolonged sitting, low chairs
- Weight management: If overweight, weight loss reduces hip forces
- Education: Understand FAI and realistic expectations
Core strengthening and hip stabilization:
- Gluteal strengthening (avoid aggravating impingement)
- Core stability exercises
- Avoid deep hip flexion exercises
- Posterior chain strengthening
- Proprioception and balance training
Goals: Optimize hip mechanics, reduce compensatory patterns, improve functional capacity
- NSAIDs: Short courses for symptom control
- Paracetamol: Regular for baseline pain control
- Avoid long-term NSAIDs: Risk of gastrointestinal and cardiovascular effects
Not disease-modifying but provides symptom relief during rehabilitation.
Steroid injection (fluoroscopy or ultrasound-guided):
- Diagnostic and therapeutic
- Temporary relief (3-6 months typical)
- May allow participation in physiotherapy
- Can be repeated once if helpful
- Not a definitive treatment for FAI
Contraindications: Infection, severe OA, allergy
Success Rate of Conservative Management
Conservative management succeeds in approximately 30-40% of symptomatic FAI patients. Success is more likely in patients with mild morphology (alpha angle 55-65°), no significant labral tear, and good compliance with activity modification and physiotherapy. Failure is indicated by persistent symptoms limiting activities after 3-6 months of appropriate conservative treatment.
Surgical Technique - Hip Arthroscopy
Pre-operative Planning
Consent Points
- Failure to improve symptoms: 15-20% (especially if cartilage damage present)
- Nerve injury: Pudendal, lateral femoral cutaneous (5% transient)
- Heterotopic ossification: 3-5% (usually asymptomatic)
- Infection: Less than 1%
- Conversion to arthroplasty: If severe cartilage damage found intraoperatively
- DVT/PE: Standard orthopedic surgery risk
Equipment Checklist
- Hip arthroscopy traction table (with well-padded perineal post)
- Arthroscopic camera and equipment (30° and 70° scopes)
- Specialized instruments: Curved shavers, burrs, radiofrequency devices
- Fluoroscopy (C-arm positioned for AP and lateral views)
- Labral repair equipment: Suture anchors (2.3mm or smaller)
- CAM resection tools: High-speed burr, arthroscopic osteotomes
Patient Positioning
Setup for Hip Arthroscopy
Supine on specialized hip arthroscopy traction table:
- Well-padded perineal post positioned against medial groin
- Both feet secured in traction boots
- Contralateral leg abducted and secured to allow fluoroscopy
- Operative leg in neutral position initially
Critical padding points:
- Perineal post: Well-padded to prevent pudendal nerve injury
- Lateral femoral cutaneous nerve: Avoid compression at ASIS
- Contralateral leg: Padded at knee and ankle
- Arms: Secured across chest or on arm boards
Maximum traction time: Limit to 2 hours to prevent traction injury
Traction technique:
- Apply approximately 25-50 pounds of traction
- Distract joint 8-10mm (confirmed on fluoroscopy)
- Adequate distraction essential for safe portal placement
- Monitor throughout case, release periodically if greater than 2 hours
Pudendal Nerve Protection
Pudendal nerve injury is a recognized complication of hip arthroscopy from excessive or prolonged traction. Risk factors include prolonged traction time (greater than 2 hours), excessive traction force, inadequate perineal post padding, and female gender. Limit traction time and release traction when working in peripheral compartment. Neurapraxia usually resolves within 6 months but can be permanent.
Portal Placement
Standard Hip Arthroscopy Portals
Established under fluoroscopy:
- Identify intersection of horizontal line from superior aspect of greater trochanter and vertical line from ASIS
- Insert spinal needle under fluoroscopy to confirm intra-articular position
- Incise skin, blunt dissection to capsule
- Insert arthroscope sheath and cannula
Primary viewing portal for central compartment
Established under direct visualization:
- Visualize anterolateral capsule with scope from AL portal
- Insert spinal needle from outside-in under direct vision
- Ensure safe distance from lateral femoral cutaneous nerve
- Create working portal with skin incision and blunt dissection
Primary working portal for labral repair and CAM resection
Posterolateral portal: For posterior labral access Distal anterolateral accessory: For peripheral CAM resection
Generally 2-3 portals sufficient for most FAI cases
Central Compartment Work (Under Traction)
Systematic evaluation of central compartment:
Diagnostic Sequence
- Anterosuperior labrum: Most common tear location in CAM FAI
- Posterior labrum: Check for contre-coup pincer lesion
- Classify tear: Radial flap, longitudinal, bucket-handle, degenerative
- Stability testing: Probe to assess for unstable flap
- Acetabular cartilage: Map areas of damage (Beck classification)
- Femoral head cartilage: Usually better preserved than acetabular
- Delamination: Look for carpet phenomenon (cartilage lifted off bone)
- Wave sign: Indicates delaminated cartilage
- Assess for partial or complete tear
- Debride if degenerative and symptomatic
- Not routinely reconstructed
- Remove any loose bodies
- Common in FAI from cartilage delamination
- May be in anterior or posterior recess
Peripheral Compartment Work (Traction Released)
CAM Resection Technique
- Release hip from traction
- Flex and externally rotate hip to expose femoral neck
- Access peripheral compartment between capsule and femoral neck
- May need to perform limited capsulotomy for access
High-speed burr osteoplasty:
- Identify CAM lesion at anterior-superior head-neck junction
- Use high-speed burr to resect aspherical portion of head
- Goal: Restore concave waist at head-neck junction
- Alpha angle target: Reduce to under 50° (confirmed on fluoroscopy)
- Resect conservatively to avoid creating femoral neck notch
Extent of resection:
- Typically anterosuperior quadrant of head-neck junction
- May extend to 1 o'clock to 4 o'clock positions (right hip)
- Smooth transition from head to neck
- Avoid creating stress riser
Fluoroscopic confirmation:
- AP view: Check head-neck offset restored
- Lateral view: Alpha angle under 50-55°
- Dynamic examination: Flex hip and confirm no impingement
- May use arthroscope to visualize from anterolateral portal
If capsulotomy performed:
- Repair capsule with arthroscopic sutures
- Restoration of capsular integrity may reduce post-op instability
- Some surgeons leave capsulotomy open (controversial)
Technical Pearls and Pitfalls
Do's (Pearls)
- Preserve labrum whenever possible - repair is better than debridement
- Conservative CAM resection - avoid creating femoral neck notch
- Dynamic fluoroscopy - confirm clearance after osteoplasty
- Limit traction time - release every 2 hours to prevent nerve injury
- Address both components - CAM and pincer if mixed morphology
- Smooth osteoplasty - avoid sharp edges or stress risers
Don'ts (Pitfalls)
- Over-resect acetabular rim - causes iatrogenic instability
- Create femoral notch - stress riser, risk of neck fracture
- Excessive traction - pudendal nerve injury risk
- Ignore labral tears - address all pathology found
- Incomplete CAM resection - residual impingement leads to failure
- Leave capsulotomy open (controversial) - may increase instability risk
Closure
Closure Steps
- Release traction completely
- Perform final arthroscopic inspection
- Confirm no retained instruments or debris
- Ensure hemostasis achieved
- Remove all cannulas and instruments
- Close portal sites with simple interrupted sutures
- Typically 1-2 sutures per portal (small incisions)
- Apply sterile dressings
- Apply compression dressing
- Ice and elevation
- Mobilize with crutches (partial weight-bearing initially)
- DVT prophylaxis as per protocol
Complications
Hip Arthroscopy Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Nerve injury (transient) | 5-8% | Prolonged traction, excessive force | Usually resolves 3-6 months, observe |
| Nerve injury (permanent) | Less than 1% | Same as above | May require nerve specialist referral |
| Heterotopic ossification | 3-5% | Extensive CAM resection, genetic predisposition | Usually asymptomatic, excision if limiting motion |
| Failure to improve symptoms | 15-20% | Severe cartilage damage, persistent morphology | May require revision or conversion to THA |
| Hip instability (iatrogenic) | 1-2% | Excessive rim trimming, capsulotomy not closed | Activity modification, may need capsular plication |
| Femoral neck fracture | Less than 1% | Excessive CAM resection creating notch | Usually requires ORIF or arthroplasty |
| Infection | Less than 1% | Standard surgical risk factors | Arthroscopic washout, antibiotics |
| DVT/PE | Less than 1% | Standard orthopedic risk factors | Anticoagulation as per protocol |
| Instrument breakage | Less than 1% | Technical error | Retrieve broken instrument intraoperatively |
Nerve injuries:
The most common nerve injuries in hip arthroscopy are:
- Pudendal nerve: From perineal post pressure or excessive traction (numbness, sexual dysfunction)
- Lateral femoral cutaneous nerve: From portal placement or positioning (lateral thigh numbness)
- Sciatic nerve: From traction or positioning (rare)
- Femoral nerve: Very rare
HO Prophylaxis Controversial
Heterotopic ossification (HO) occurs in 3-5% of hip arthroscopy cases, usually asymptomatic. Risk factors include extensive CAM resection, history of HO, male gender, and genetic predisposition. Prophylaxis is controversial - options include indomethacin 75mg daily for 2-3 weeks or single-dose radiation (7 Gy). Not routinely used by all surgeons. More common in revision cases or after open surgery.
Failure to improve symptoms:
The most common "complication" is failure to achieve symptom improvement (15-20% of cases). Causes include:
- Severe cartilage damage at surgery (Outerbridge grade 3-4)
- Incomplete correction of morphology (residual impingement)
- Progression of osteoarthritis despite surgery
- Incorrect diagnosis (pain from other source)
- Unrealistic patient expectations
- Poor rehabilitation compliance
Prevention: Careful patient selection (Tonnis 0-1, confirmed FAI morphology, mechanical symptoms), complete correction of both CAM and pincer, realistic counseling.
Femoral Neck Fracture Risk
Femoral neck fracture after CAM resection is rare (less than 1%) but devastating. Risk factors include excessive resection depth (greater than 30% neck diameter), creating a notch at the femoral neck, and early weight-bearing before healing. Prevention: Conservative resection depth, smooth gradual transition from head to neck, avoid creating sharp corners or notches, protected weight-bearing for 6 weeks post-op.
Postoperative Care and Rehabilitation
Hip Arthroscopy Rehabilitation
Protection phase:
- Partial weight-bearing with crutches (20-30 pounds foot-flat)
- Hip brace optional (some surgeons, especially if capsulotomy)
- Ice and elevation
- DVT prophylaxis (aspirin or LMWH as per protocol)
- Pain management (multimodal analgesia)
- Passive ROM exercises (avoid extremes)
- Avoid hip flexion greater than 90°, avoid combined flexion-IR
Progressive weight-bearing:
- Week 2: Increase to 50% weight-bearing if comfortable
- Week 4: Wean off crutches to full weight-bearing
- Week 6: Should be walking normally without aids
ROM exercises:
- Gentle active-assisted ROM
- Supine hip flexion to 90° (avoid end-range flexion)
- Hip abduction and extension exercises
- Avoid combined flexion and internal rotation (impingement position)
Stationary cycling: Start at 3-4 weeks (high seat position)
Progressive loading:
- Advance ROM exercises (gradual increase in flexion)
- Begin closed-chain strengthening (squats, leg press - limited depth)
- Hip abductor strengthening (gluteus medius focus)
- Core stability exercises
- Pool exercises if available
- Avoid impact activities
Goals: Full ROM, normalized gait, good hip control
Sport-specific training:
- Progress to jogging (flat surface) at 3 months
- Agility and cutting drills at 4-5 months
- Sport-specific training at 5 months
- Return to full sport at 6 months if strength testing adequate
Criteria for return:
- Pain-free full ROM
- Hip strength 90% of contralateral side
- Functional testing: Single-leg squat, hop tests
- No effusion or mechanical symptoms
- Continue hip strengthening indefinitely
- Avoid high-impact activities if possible (controversial)
- Monitor for symptom recurrence
- Follow-up X-rays at 1 and 2 years (assess for OA progression)
Key rehabilitation principles:
Do's
- Protected weight-bearing first 6 weeks
- Progressive ROM avoiding impingement positions
- Hip strengthening focus on gluteal muscles
- Patience - full recovery takes 6-12 months
- Communication with therapist about procedure details
- Criteria-based progression not time-based
Don'ts
- Early full weight-bearing risks femoral neck stress
- Aggressive ROM early risks labral repair failure
- Return to sport too early increases failure risk
- Ignore persistent symptoms - may indicate problem
- Skip strengthening - hip control is critical
- Resume high-impact too soon - need full healing
Outcomes and Prognosis
Outcomes with modern hip arthroscopy:
Modern hip arthroscopy for FAI produces good to excellent outcomes in approximately 85% of appropriately selected patients at 2-year follow-up. Patient satisfaction is high, with significant improvements in pain, function, and return to sport.
Outcomes by Patient Selection
| Patient Group | 2-Year Success | Prognostic Factors |
|---|---|---|
| Ideal candidate | Greater than 90% | Age under 40, alpha angle 55-70°, Tonnis 0, minimal cartilage damage |
| Good candidate | 80-90% | Age 40-50, mixed morphology, Tonnis 0-1, moderate cartilage damage |
| Marginal candidate | 60-70% | Age over 50, Tonnis 1, significant cartilage damage (Outerbridge 3) |
| Poor candidate | Less than 50% | Tonnis 2-3, severe cartilage loss, unrealistic expectations |
Return to sport:
- Recreational athletes: 80-90% return to sport at 6-12 months
- Elite/professional athletes: 70-85% return to pre-injury level
- Contact sports: May have lower return-to-play rates
- Time to return: Average 6 months (range 4-12 months)
Predictors of Poor Outcome
Poor prognostic factors for hip arthroscopy in FAI:
- Tonnis grade 2-3 osteoarthritis - strongest negative predictor
- Severe cartilage damage (Outerbridge grade 3-4 or Beck grade 3-4)
- Age over 50 years - lower success rates
- Severe joint space narrowing (less than 2mm)
- Worker's compensation claim - psychosocial factor
- Isolated pincer morphology - worse than CAM or mixed
- Previous hip surgery - revision cases have worse outcomes
These patients should be counseled about higher failure risk and potential need for arthroplasty.
Long-term outcomes and OA progression:
The critical question: Does FAI surgery prevent osteoarthritis?
- Short-term (2-5 years): High satisfaction, improved function
- Medium-term (5-10 years): Good outcomes maintained in most
- Long-term (10+ years): Data emerging - 20-30% may develop OA despite surgery
Factors affecting OA progression:
- Severity of cartilage damage at surgery (most important)
- Completeness of morphology correction
- Age at surgery (younger better for prevention)
- Genetic factors and joint loading patterns
Surgery May Not Prevent OA
While hip arthroscopy for FAI improves symptoms and function, it may not prevent progression to osteoarthritis in all patients, especially those with significant cartilage damage at time of surgery. The goal is to improve symptoms and delay OA progression, not necessarily prevent it entirely. Long-term studies (15-20 years) are still lacking.
Revision surgery:
- Incidence: 10-15% require revision within 5 years
- Reasons: Incomplete initial correction, progression of cartilage damage, adhesions
- Outcomes: Revision surgery has lower success rates (60-70%) than primary
Conversion to total hip arthroplasty:
- Rate: 5-10% progress to THA within 10 years
- Risk factors: Severe cartilage damage at index surgery, older age, incomplete correction
- Timing: Average 5-7 years after failed arthroscopy
Evidence Base and Key Trials
UK FASHIoN Trial - FAI Surgery vs Conservative Care
- Multicenter RCT: 222 patients with FAI syndrome
- Hip arthroscopy vs personalized physiotherapy at 8 months
- Arthroscopy showed greater improvement in iHOT-33 score (mean difference 6.8 points)
- Both groups improved, but surgery group had significantly better outcomes
- 23% of conservative group crossed over to surgery
FIRST Trial - FAI Randomized Controlled Trial
- RCT: 222 patients, arthroscopic surgery vs conservative care
- Significantly better outcomes with surgery at 12 months
- Mean iHOT-33 difference of 7.4 points favoring surgery
- Higher satisfaction in surgery group (71% vs 43%)
- Minimal clinically important difference achieved by surgery group
Labral Repair vs Debridement - Systematic Review
- Systematic review and meta-analysis of labral treatment strategies
- Labral repair superior to labral debridement for patient-reported outcomes
- Lower revision surgery rates with labral repair (5.6% vs 12.3%)
- Better return to sport rates with repair
- Modern trend toward labral preservation whenever possible
Danish Hip Arthroscopy Registry (DHAR) - 10-Year Data
- Registry study: 1079 hip arthroscopies for FAI over 10 years
- Overall satisfaction rate 79% at mean 3.4 years follow-up
- Revision rate 9.8% within 5 years
- Progression to THA in 4.4% within 5 years
- Predictors of failure: age over 40, Tonnis grade 1, previous surgery
Australian Hip Arthroscopy Outcomes - Multi-center Study
- Australian multi-center cohort: 505 patients with FAI
- Significant improvements in modified Harris Hip Score at 2 years
- 85% patient satisfaction, 78% return to sport
- Lower success in patients with Tonnis grade 1 vs grade 0
- Complication rate 5.2%, mostly transient nerve symptoms
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Athlete with Groin Pain
"A 28-year-old semi-professional soccer player presents with 12 months of progressive right groin pain. Pain is worse with running, changing direction, and getting out of his car. He has tried rest and physiotherapy without improvement. On examination, he has a positive FADIR test reproducing his groin pain. X-rays show an alpha angle of 68 degrees on frog-leg lateral view. What is your assessment and management?"
Scenario 2: Hip Arthroscopy Technique
"You are planning hip arthroscopy for a 32-year-old female with mixed CAM-pincer FAI and anterosuperior labral tear on MRI. Alpha angle is 62 degrees, and she has crossover sign indicating acetabular retroversion. Tonnis grade 0. Walk me through your surgical approach and decision-making."
Scenario 3: Failed Hip Arthroscopy
"A 45-year-old patient had hip arthroscopy for FAI 18 months ago with CAM osteoplasty and labral debridement. She initially improved for 6 months but now has recurrent groin pain, mechanical symptoms, and limited hip flexion. X-rays show alpha angle now 52 degrees (was 70 degrees pre-op), but joint space has narrowed from 4mm to 2mm with Tonnis grade 2 changes. What is your assessment and management?"
MCQ Practice Points
Definition Question
Q: What are the two main morphological types of femoroacetabular impingement? A: CAM impingement (aspherical femoral head with decreased head-neck offset) and Pincer impingement (acetabular overcoverage, focal or global). Mixed morphology with both CAM and pincer components is present in 85% of symptomatic FAI cases.
Alpha Angle Question
Q: What is the diagnostic threshold for CAM morphology based on alpha angle measurement? A: Alpha angle greater than 55 degrees is diagnostic for CAM morphology. The alpha angle is measured on frog-leg lateral X-ray or MRI axial oblique view. It represents the angle between the femoral neck axis and the point where the femoral head becomes aspherical. Normal is under 50-55 degrees.
Clinical Test Question
Q: Which clinical test has the highest sensitivity for diagnosing FAI and how is it performed? A: The FADIR test (Flexion-Adduction-Internal Rotation) has 94-99% sensitivity. Patient supine, flex hip to 90 degrees, then adduct across the body and internally rotate. Positive test = reproduction of anterior groin pain. This position maximizes impingement at the anterosuperior acetabulum.
Radiographic Sign Question
Q: What is the crossover sign and what does it indicate? A: The crossover sign is when the anterior acetabular wall projects lateral to (crosses over) the posterior wall on AP pelvis X-ray. It indicates acetabular retroversion (focal anterior overcoverage), a type of pincer morphology. Normal acetabulum has anterior wall medial to posterior wall throughout.
Treatment Question
Q: What is the contraindication to hip arthroscopy for FAI based on osteoarthritis status? A: Tonnis grade 2-3 osteoarthritis is a contraindication to hip arthroscopy. Only Tonnis grade 0-1 (no OA or mild OA) should be considered for arthroscopy. Patients with established OA (grade 2-3) have poor outcomes with arthroscopy and should be offered total hip arthroplasty instead.
Surgical Technique Question
Q: In hip arthroscopy for FAI, is labral repair or labral debridement preferred, and why? A: Labral repair is preferred over labral debridement. The labrum functions as a suction seal maintaining negative intra-articular pressure. Studies show labral repair has better patient-reported outcomes, higher return-to-sport rates, and lower revision surgery rates (5.6% vs 12.3%) compared to simple debridement. Preserve the labral seal whenever possible.
Australian Context and Medicolegal Considerations
Australian Practice Patterns
- Hip arthroscopy availability: Major centers in all capital cities
- Training: Increasing number of surgeons trained in hip arthroscopy
- Subspecialty: Usually performed by sports medicine or hip preservation surgeons
- Public vs private: Mostly performed in private sector, limited public access
- Waiting lists: Public system waiting times 12-24 months in some states
- Cost: Private procedure with Medicare rebate available
PBS Considerations
- Gap payments: Significant out-of-pocket costs typical in private
- Public access: Limited - long waiting lists, restricted indications
- DVT prophylaxis: PBS-listed LMWH or direct oral anticoagulants
- Physiotherapy: May be partially covered by private health insurance
Australian FAI research contributions:
Australia has contributed significantly to FAI research and surgical technique development:
- Dr. John O'Donnell - Melbourne pioneer in hip arthroscopy, developed techniques
- Australian multi-center studies - Published outcomes data for hip arthroscopy
- Training programs - Hip arthroscopy fellowships available in Melbourne, Sydney
Clinical practice guidelines:
Informed Consent Requirements
Documentation requirements for hip arthroscopy consent:
- Procedure-specific risks: Nerve injury (5-8% transient, less than 1% permanent), heterotopic ossification (3-5%), infection (less than 1%), failure to improve (15-20%)
- Outcomes counseling: 85% satisfaction rate at 2 years, may not prevent progression to OA, potential need for future arthroplasty
- Alternative treatments: Conservative management with physiotherapy (discuss and document trial), total hip arthroplasty if OA present
- Return to work/sport: Timeline expectations (6 months to full sport, 3-6 months return to work depending on demands)
- Financial costs: Out-of-pocket expenses in private system
- Revision risk: 10-15% within 5 years
Ensure discussion documented in medical records. Use of standardized consent forms recommended.
Medicolegal considerations:
Common areas of litigation in FAI surgery:
- Inadequate conservative management trial - Operating too early without documented 3-6 months physiotherapy
- Poor patient selection - Operating on Tonnis grade 2-3 OA (contraindication)
- Nerve injury - Pudendal or lateral femoral cutaneous nerve from traction/positioning
- Incomplete correction - Residual alpha angle greater than 55° causing persistent symptoms
- Over-resection complications - Iatrogenic instability from excessive rim trimming or femoral neck fracture from excessive CAM resection
- Inadequate outcomes counseling - Patient expectations not managed regarding realistic success rates
Risk mitigation strategies:
- Document conservative management trial duration and interventions
- Document patient selection criteria (Tonnis grading, alpha angle, symptoms)
- Standardized consent process with written materials
- Intraoperative fluoroscopy to confirm adequate correction
- Detailed operative notes including measurements before and after osteoplasty
- Realistic post-operative expectations discussion and documentation
Australian Orthopaedic Association (AOA) guidelines:
While no specific FAI guidelines exist, general principles apply:
- Appropriate training and credentialing for hip arthroscopy
- Annual procedural volume maintenance for skill retention
- Participation in outcomes audits and quality improvement
- Continuing professional development in hip preservation
FEMOROACETABULAR IMPINGEMENT (FAI)
High-Yield Exam Summary
Key Anatomy and Biomechanics
- •Normal head-neck offset = concave waist at anterosuperior junction allows clearance
- •CAM = aspherical femoral head, decreased offset, shear forces cause outside-in damage
- •Pincer = acetabular overcoverage, rim contact causes inside-out damage via levering
- •Labrum = suction seal maintaining negative intra-articular pressure and load distribution
- •Impingement zone: CAM damages anterosuperior labrum/cartilage, pincer damages posteroinferior
Classification and Diagnosis
- •CAM (25%) = alpha angle greater than 55°, male predominance 3:1
- •Pincer (10%) = crossover sign, coxa profunda, center-edge angle greater than 40°
- •Mixed (85%) = both CAM and pincer components - most common
- •FADIR test = 94-99% sensitivity (flex 90°, adduct, internal rotate)
- •Tonnis 0-1 = arthroscopy candidate, Tonnis 2-3 = contraindication (need THA)
Imaging and Measurements
- •X-rays: AP pelvis + frog-leg lateral (alpha angle, crossover sign, Tonnis grade)
- •Alpha angle greater than 55° = CAM morphology (measure on frog-leg or MRI)
- •MRI arthrogram = gold standard (labral tears 90% sensitivity, cartilage assessment)
- •Crossover sign = anterior wall crosses posterior wall (acetabular retroversion)
- •Center-edge angle greater than 40° = pincer overcoverage
Treatment Algorithm
- •Conservative first: 3-6 months physio, activity modification, NSAIDs (30-40% success)
- •Surgery if: failed conservative, confirmed morphology, Tonnis 0-1, positive FADIR
- •Hip arthroscopy (95% of cases): CAM osteoplasty + labral repair + pincer trimming if needed
- •Target: alpha angle under 50°, center-edge angle 25-35° if pincer resection
- •Contraindications: Tonnis 2-3 OA, active infection, severe dysplasia, unrealistic expectations
Surgical Pearls and Complications
- •Labral repair superior to debridement (better outcomes, lower revision 5.6% vs 12.3%)
- •Conservative resection: avoid femoral notch (fracture risk) or over-trimmed rim (instability)
- •Limit traction under 2 hours (pudendal nerve injury risk 5-8% transient, less than 1% permanent)
- •Post-op: partial weight-bearing 6 weeks, return to sport 6 months if criteria met
- •Complications: nerve injury 5-8%, HO 3-5%, failure to improve 15-20%, revision 10-15% at 5 years
Key Evidence and Outcomes
- •UK FASHIoN/FIRST trials: arthroscopy superior to conservative at 1 year (Level 1)
- •85% patient satisfaction at 2 years, 78% return to sport at 6 months
- •Poor predictors: Tonnis grade 2-3, severe cartilage damage, age over 50, worker's comp
- •Long-term: 20-30% may develop OA by 10 years despite surgery
- •Conversion to THA: 5-10% within 10 years, higher if severe cartilage damage at index surgery