Core Decompression - Femoral Head AVN

Absolute Indications

• Ficat/ARCO Stage I-II AVN with failed conservative management (activity modification, bisphosphonates, protected weight-bearing for 3-6 months)
• Small to medium lesion size: <30% femoral head volume, <250° Kerboul angle on MRI
• Young patient: <50 years (ideally <40 years) - high THA revision risk justifies aggressive preservation
• Preserved joint space: >2mm on AP weight-bearing radiograph
• Symptomatic hip pain: Interfering with activities of daily living, work, or recreation

Relative Indications

• Asymptomatic Stage I-II AVN in high-risk patient (bilateral disease, ongoing steroid use) - controversial but may prevent progression
• Medium-large lesion (15-30%): Consider adjuncts (tantalum rod, vascularized fibula) to improve outcomes
• Ficat Stage IIC (small crescent): Very controversial - most surgeons proceed to arthroplasty but some attempt salvage with vascularized fibula

Contraindications (Absolute)

• Ficat/ARCO Stage III-IV: Established collapse (crescent sign), flattening, or secondary arthritis - proceed to arthroplasty
• Large lesion: >30% femoral head, >250° Kerboul angle - very high failure rate (70-80%), consider primary THA or vascularized fibula
• Active infection: Septic arthritis or osteomyelitis - contraindication to any hip preservation
• Significant osteoarthritis: Joint space <2mm, Tönnis grade 2-3 changes - unlikely to benefit

Contraindications (Relative)

• Elderly/low demand patient: >65 years - THA may be more predictable option
• Severe osteoporosis: Fracture risk during procedure or post-op, consider bone optimization first
• Morbid obesity: BMI >40 - technical difficulty with percutaneous approach, high mechanical load on healing head
• Patient unwilling to comply: With protected weight-bearing protocol for 12 weeks

Staging Systems - Know Both!

FICAT Classification (X-ray based)

• Stage I: Normal X-ray, MRI shows marrow edema/necrosis
• Stage II: Sclerosis, cysts, porosis on X-ray, NO collapse
• Stage III: Crescent sign (subchondral fracture), early collapse
• Stage IV: Flattening, head deformity, secondary acetabular arthritis

ARCO Classification (adds MRI quantification)

• Stage 0: Normal imaging, high-risk patient (bilateral, steroids)
• Stage I: Normal X-ray, MRI positive - subdivided by lesion size (<15%, 15-30%, >30%)
• Stage II: Abnormal X-ray, no collapse - subdivided by lesion size
• Stage III: Subchondral fracture (crescent) - subdivided by flattening (<2mm, 2-4mm, >4mm)
• Stage IV: Acetabular involvement

Kerboul Angle Method (Lesion Size Quantification)

On MRI: Find coronal cut showing largest necrotic extent, measure angle from center of femoral head to edges of necrotic zone. Repeat on sagittal cut. Sum both angles.

• <200°: Good prognosis (80-90% success)
• 200-250°: Intermediate (50-70% success)
• >250°: Poor (30-40% success)

Evidence Base

Success Rates by Stage/Size:

• Ficat I + <15% lesion = 85-90% avoid arthroplasty at 5 years
• Ficat I + 15-30% lesion = 60-75%
• Ficat I + >30% lesion = 40-50%
• Ficat II + <15% lesion = 70-80%
• Ficat II + >30% lesion = 30-40%

AOANJRR Data: Young AVN patients undergoing THA have 25-30% revision rate at 10 years vs 5-7% for OA patients - supports aggressive joint preservation attempts.

Femoral Head Blood Supply (Critical for Understanding AVN)

Normal Vascular Anatomy

• Medial femoral circumflex artery (MFCA): Dominant supply (80-90% of head)
  • Posterior superior retinacular vessels to posterosuperior head
  • Posterior inferior retinacular vessels to posteroinfeiror head
• Lateral femoral circumflex artery (LFCA): Minor supply (10-20%)
  • Anterior retinacular vessels
• Artery of ligamentum teres: Minimal (<5% in adults, more in children)

AVN Pathophysiology

Interruption of MFCA supply (trauma, emboli, thrombosis) → ischemia → osteocyte death → necrotic zone formation → mechanical failure of dead bone → subchondral fracture (crescent) → collapse → arthritis

Typical AVN Lesion Location

Anterosuperior weight-bearing dome (90% of cases) - watershed zone between MFCA and LFCA territories. This is your TARGET for core decompression trajectory.

Surgical Approach: Percutaneous Lateral

Entry Point Selection

Anatomic landmark: 2-3cm distal to vastus ridge (palpable prominence on lateral femur at base of greater trochanter)

Fluoroscopic confirmation:

• AP view: Lateral cortex of femur, below and slightly posterior to greater trochanter
• Lateral view: Posterior one-third of femoral shaft

Trajectory Planning (3D Understanding Critical!)

From lateral femur entry → through lateral cortex → into intramedullary canal → across femoral neck → into femoral head → toward anterosuperior dome → STOP 5mm from subchondral bone

AP view trajectory: Directed medially and slightly superiorly toward weight-bearing dome

Lateral view trajectory: Directed anteriorly toward mid-anterior third of head (NOT extreme anterior - risk of anterior cortex perforation)

Tissue Layers (Lateral Approach)

1. Skin (1-2cm incision)
2. Subcutaneous fat
3. Fascia lata (incise in line with fibers)
4. Vastus lateralis muscle (blunt dissection perpendicular to fibers)
5. Lateral femoral cortex (entry point for guidewire)

Critical Anatomic Relationships

What You're AVOIDING (Danger Zones)

• Posterior: Profunda femoris perforating branches (through lateral intermuscular septum)
• Anterior-medial: Femoral neurovascular bundle (far from lateral approach)
• Superior: Superior gluteal neurovascular bundle (above GT - avoid proximal entry)
• Sciatic nerve: Posterior to hip (lateral approach stays far anterior)

What You're TARGETING

• Anterosuperior femoral head: Weight-bearing dome where AVN lesion typically located
• Center of necrotic zone: Based on preoperative MRI correlation
• 5mm from subchondral bone: Safety margin to protect articular cartilage

Fluoroscopy Setup - Biplanar Imaging Essential

AP Pelvis View

• Both hips visible for comparison
• Femoral head perfectly circular (not rotated)
• Allows visualization of mediolateral trajectory
• Shows depth to medial subchondral bone

Cross-table Lateral OR Frog-Leg Lateral

• Shows anteroposterior trajectory
• Confirms depth to anterior subchondral bone
• Identifies femoral neck anterior cortex position

Critical: Must check BOTH views alternately during guidewire advancement - 3D trajectory cannot be judged from single view!

Core Decompression Techniques

Single Large Core (8-11mm diameter)

Technique: Cannulated trephine or reamer over guidewire, creates one large channel

Advantages:

• Allows structural graft placement (non-vascularized fibula, tantalum rod)
• Removes solid core of necrotic tissue intact for histology
• Theoretically better decompression of central lesion

Disadvantages:

• Greater weakening of femoral neck - higher fracture risk
• Larger stress riser at entry point (subtrochanteric fracture risk)
• May need 10-12 weeks protected weight-bearing vs 6-8 weeks for small cores

Best For: Medium lesions (15-30%) where adjunct graft/rod planned

Multiple Small Cores (3-4 × 3.5mm)

Technique: First guidewire to lesion center, then place 2-3 additional parallel wires around first (1cm spacing), drill each with 3.5mm bit

Advantages:

• Less femoral neck weakening
• Multiple drainage pathways
• Allows "gradient" decompression around lesion
• Shorter protected weight-bearing (6-8 weeks)

Disadvantages:

• Cannot place structural graft
• More radiation exposure (multiple wire placements)
• Technically more complex - must ensure wires converge on lesion

Best For: Small lesions (<15%) where adjunct graft not needed

Evidence Comparison

Multiple systematic reviews show NO SIGNIFICANT DIFFERENCE in outcomes between single large core vs multiple small cores. Choice based on surgeon preference and whether adjunct graft planned.

Adjunct Techniques for Medium-Large Lesions

Tantalum Rod (Porous Trabecular Metal)

Technique: After core decompression (8-10mm), impact tantalum rod (10-12mm diameter, length to within 5mm of subchondral bone) into track. Tantalum is highly porous allowing biologic ingrowth.

Mechanism: Provides structural support to subchondral bone + scaffold for revascularization through porous structure

Outcomes: 50-70% success in Stage II, 40-50% in early Stage III - similar to vascularized fibula but much simpler technique

Advantages:

• No microsurgery required (vs vascularized fibula)
• No donor site morbidity
• Radiopaque - easy follow-up monitoring
• Can revise to THA later without difficulty

Disadvantages:

• Expensive implant
• No active blood supply (relies on host ingrowth)
• Can migrate if undersized
• Metal artifact on MRI (limits post-op imaging)

Vascularized Fibula Graft

Technique: Harvest 8-12cm segment of proximal fibula with peroneal artery pedicle. Insert through 12-15mm core track. Microsurgical anastomosis of peroneal artery to ascending branch of LFCA.

Mechanism: Provides BOTH structural support (load-bearing strut) AND active revascularization via blood supply

Outcomes: 70-90% success even in Stage III (post-collapse) - BEST outcomes for salvage procedures

Advantages:

• Active blood supply provides revascularization
• Structural support prevents collapse
• Can treat larger lesions and post-collapse cases

Disadvantages:

• Requires microsurgical training and equipment
• Significant donor site morbidity (ankle stiffness 20-30%, peroneal nerve injury 5-10%, chronic pain 15-25%)
• 4-6 hour procedure vs 45-60 min for core alone
• Higher complication rate
• Difficult to revise to THA (fibula incorporation)

Best For: Large lesions (>30%, >250° Kerboul) in young patients (<35 years) where THA would have very high revision risk

Non-Vascularized Fibula Strut

Technique: Harvest 8-10cm fibula segment WITHOUT vascular pedicle, insert through core track, impact into subchondral bone

Mechanism: Structural support only (no blood supply) - acts as "internal splint"

Outcomes: 40-60% success - better than core alone for medium lesions but worse than vascularized

Advantages:

• Simpler than vascularized (no microsurgery)
• Structural support
• Lower donor morbidity than vascularized

Disadvantages:

• No revascularization mechanism
• Fibula may resorb over time
• Still has donor site morbidity (though less than vascularized)

Bone Marrow Aspirate Concentrate (BMAC)

Technique: Aspirate 60-120ml bone marrow from iliac crest, centrifuge to concentrate mesenchymal stem cells, inject into core track(s)

Mechanism: Theoretical enhancement of revascularization and bone healing via stem cell and growth factor delivery

Outcomes: CONFLICTING evidence - some studies show 10-15% improvement in success rates, others show no difference

Advantages:

• Minimal additional morbidity (iliac aspiration only)
• Can combine with any core technique
• Relatively low cost

Disadvantages:

• Evidence limited and inconsistent
• No structural support
• Requires centrifuge equipment

Biologic Adjuncts (Investigational)

• BMP-7 or BMP-2: Theoretical enhancement of bone healing but limited evidence, concerns about HO and malignancy
• Cultured stem cells: Multiple small trials show promise but not standard practice, regulatory issues
• Platelet-rich plasma (PRP): Very limited evidence, most studies show no benefit over core alone

Comprehensive Operative Steps

Step 1: Preoperative Planning & Staging

Review imaging systematically:

1. AP pelvis X-ray: Assess stage (normal = I, sclerosis/cysts = II, crescent = III, collapse = IV), joint space (>2mm required), bilateral involvement (30-70% of cases)

2. Lateral hip X-ray (frog-leg best): Look for crescent sign (contraindication!), assess anterior head involvement

3. MRI T1 + T2: Measure Kerboul angle (sum of arcs on coronal + sagittal), identify lesion location (usually anterosuperior), look for double-line sign (pathognomonic), assess for marrow edema (high T2)

4. Document stage: Ficat and ARCO (exam may ask for both!)

5. Measure lesion size: Percentage of head volume and Kerboul angle - determines prognosis and need for adjuncts

6. Check contralateral hip: 30-70% bilateral in non-traumatic AVN

Step 2: Patient Setup & Fluoroscopy

1. Position: Supine on radiolucent table (fracture table optional but allows traction if needed for C-arm visualization)

2. Hip position: Neutral rotation (slight 10-15° internal rotation may relax anterior capsule and improve visualization)

3. C-arm setup: Test biplanar imaging BEFORE draping

   • AP pelvis: Both hips visible, femoral head perfectly circular
   • Lateral: Cross-table OR frog-leg (surgeon preference)

4. Mark entry point: Under fluoroscopy - lateral thigh, 2-3cm distal to palpable vastus ridge

5. Prep and drape: Wide prep including hip, lateral thigh, and iliac crest (if BMAC planned)

Step 3: Entry Point & Trajectory Planning

1. Skin incision: 1-2cm stab incision over marked entry point

2. Fascia lata: Incise in line with fibers (longitudinal split)

3. Vastus lateralis: Blunt dissection perpendicular to muscle fibers with curved hemostat - spread to bone

4. Identify lateral cortex: Confirm with fluoroscopy on both views

5. Trajectory planning:

   • AP view: Toward weight-bearing dome (slightly superior to head center)
   • Lateral view: Toward mid-anterior third (NOT extreme anterior)
   • Correlate with preoperative MRI lesion location

6. Measure depth: From lateral cortex to subchondral bone on both views, subtract 5mm for safety margin

Step 4: Guidewire Placement

1. Initial wire placement: 2.0-2.4mm smooth or threaded guidewire through entry point

2. Penetrate lateral cortex: With mallet taps or power, confirm intramedullar position

3. Advance across femoral neck: Check AP and lateral views alternately - adjust trajectory as needed

4. Aim for lesion center: Based on preoperative MRI, typically anterosuperior dome

5. Approach subchondral bone: Slow advancement with frequent fluoroscopy checks

6. STOP at 5mm from articular surface: Use depth markings on wire, confirm on BOTH views

7. Final position check:

   • AP: Wire in weight-bearing dome, 5mm from medial subchondral bone
   • Lateral: Wire in mid-anterior head, 5mm from anterior subchondral bone
   • No cortical perforation (neck or shaft)

8. If position suboptimal: Remove wire and redirect - do NOT proceed with wrong trajectory

Step 5: Core Decompression

For SINGLE LARGE CORE (8-11mm):

1. Select cannulated trephine or reamer (8-11mm diameter) over guidewire

2. Advance with gentle pressure and rotation, frequent fluoroscopy checks

3. Irrigate copiously during reaming (prevent thermal necrosis)

4. Stop at predetermined depth (5mm from subchondral bone)

5. Remove trephine and extract solid core of necrotic bone

6. Send core for histology (confirms AVN, rules out tumor/infection)

For MULTIPLE SMALL CORES (3-4 × 3.5mm):

1. Drill first wire track with 3.5mm cannulated drill bit to planned depth

2. Leave first wire in place as reference

3. Place 2-3 additional guidewires parallel to first, spaced 1cm apart, all converging on lesion center

4. Drill each additional wire track with 3.5mm bit

5. Extract cores from each track

6. Send representative core for histology

7. Copiously irrigate all tracks

Step 6: Adjunct Procedures (If Indicated)

TANTALUM ROD (for medium-large lesions 15-30%):

1. Select rod diameter 1-2mm larger than core (10-12mm typical)

2. Measure rod length to within 5mm of subchondral bone

3. Impact rod through core track with mallet until stable

4. Confirm position on biplanar fluoroscopy - within 5mm margin, stable, no migration

BONE GRAFT (structural support for large lesions):

1. Harvest non-vascularized fibula (8-10cm segment from proximal fibula)

2. Trim to fit core track (typically 8-10mm diameter)

3. Measure length to within 5mm of subchondral bone

4. Impact into core track, confirm stability and position

BMAC (adjunct for any core technique):

1. Aspirate 60-120ml bone marrow from posterior iliac crest

2. Centrifuge to concentrate stem cells (follow device protocol)

3. Inject 5-10ml BMAC into each core track under fluoroscopy

Step 7: Hemostasis & Closure

1. Copious irrigation of all core tracks to remove debris and blood

2. Hemostasis: Usually minimal due to avascular nature of necrotic bone

3. Final fluoroscopy check:

   • No iatrogenic fracture (femoral neck, subtrochanteric, femoral shaft)
   • Appropriate depth (5mm from subchondral bone on both views)
   • Graft/rod position if used (stable, correct depth, no migration)
   • No articular penetration

4. Closure:

   • Fascia lata: 2-0 absorbable suture (close split in fibers)
   • Subcutaneous: 3-0 absorbable
   • Skin: 3-0 monocryl subcuticular OR staples

5. Sterile compressive dressing

6. Postoperative imaging: AP and lateral radiographs in recovery for documentation

Postoperative Protocol

Weight-Bearing Restrictions (CRITICAL for Success)

Rationale: Reduce mechanical stress on weakened femoral head during revascularization phase (takes 3-6 months)

Standard Protocol:

• Weeks 0-6: Non-weight bearing (NWB) with crutches or walker
• Weeks 6-12: Touch-down weight bearing (TDWB) - 10-20kg foot contact only
• Weeks 12-16: Progressive weight bearing as tolerated
• Month 4-6: Full weight bearing if X-rays stable (no collapse)

Alternative Protocol (some centers):

• Weeks 0-8: Touch-toe weight bearing (TTWB) throughout with crutches
• Weeks 8-12: Gradual progression to full weight bearing

With Large Core or Adjunct Graft:

• Consider extended NWB to 8-12 weeks due to greater femoral neck weakening

Rehabilitation Protocol

Phase 1 (Weeks 0-6): Protection Phase

• ROM exercises (supine): Hip flexion, abduction, external rotation
• Ankle pumps and quad sets
• Upper body and contralateral leg strengthening
• Transfer training with NWB
• Aquatic therapy (if available) - reduces load while maintaining ROM

Phase 2 (Weeks 6-12): Progressive Loading

• Continue ROM exercises
• Begin hip strengthening (isometric first, then progressive resistance)
• Core and pelvic stabilization
• Proprioceptive training (single-leg balance once TDWB)
• Gait training with assistive device

Phase 3 (Weeks 12-24): Functional Restoration

• Advanced strengthening (hip, core, lower extremity chain)
• Sport-specific training (if appropriate)
• Gradual return to impact activities after Month 6 if X-rays stable
• Continue monitoring for pain or mechanical symptoms

Imaging Follow-up

X-rays (AP pelvis + lateral hip):

• 6 weeks: Check for fracture, early collapse
• 3 months: Assess for progression
• 6 months: Critical time point - most failures evident by now
• 1 year: Long-term stability assessment
• Annually for minimum 5 years: Late failures can occur up to 2-3 years

MRI (optional but informative):

• 3-6 months: Assess revascularization
  • Success: Decreased marrow edema (lower T2 signal), resolution of double-line sign
  • Failure: Persistent or increased edema, progressive lesion size
• MRI can predict outcome earlier than X-ray changes

Medications

Thromboprophylaxis:

• Aspirin 100mg daily for 6 weeks OR
• LMWH for 4-6 weeks (local protocol dependent)
• Higher risk if NWB/immobility

Bisphosphonates (consider for specific etiologies):

• Steroid-induced AVN: Alendronate 70mg weekly or zoledronic acid 5mg IV annually
• Evidence shows reduced progression risk
• PBS coverage for steroid-induced AVN in Australia

Analgesia:

• Paracetamol regular for 2-4 weeks
• NSAIDs cautiously (theoretical concern about bone healing, limit to 2 weeks)
• Avoid narcotics if possible

Outcomes & Prognostic Factors

Success Definition

• No radiographic progression to collapse (no crescent sign development, no flattening)
• Pain improvement (VAS decrease ≥3 points)
• Maintained joint space (no narrowing >1mm)
• Return to desired activities
• Avoiding arthroplasty at 5 years

Success Rates (Evidence-Based)

By Ficat Stage:

• Stage I: 70-85% avoid arthroplasty at 5 years
• Stage II: 50-70%
• Stage III: 20-30% (most proceed to arthroplasty - core decompression not indicated)

By Lesion Size (Kerboul Angle):

• <200°: 80-90% success
• 200-250°: 50-70%
• >250°: 30-40%

By Lesion Size (% of Head):

• <15%: 80-85% success
• 15-30%: 55-70%
• >30%: 35-45%

Combined Stage + Size (Most Predictive):

• Stage I + <15% lesion: 85-90%
• Stage I + 15-30%: 60-75%
• Stage I + >30%: 40-50%
• Stage II + <15%: 70-80%
• Stage II + 15-30%: 45-60%
• Stage II + >30%: 30-40%

With Adjuncts:

• Tantalum rod (Stage II, medium lesions): 50-70%
• Vascularized fibula (Stage II-III, large lesions): 70-90%

Prognostic Factors

Good Prognosis:

• Early stage (Ficat I, ARCO I-II)
• Small lesion (<15%, <200° Kerboul)
• Young age (<40 years)
• Non-weight bearing location (less common)
• Compliance with protected weight-bearing protocol

Poor Prognosis:

• Advanced stage (Ficat IIC-III)
• Large lesion (>30%, >250° Kerboul)
• Anterosuperior weight-bearing location (most common)
• Older age (>50 years)
• Continued steroid use or alcohol consumption
• Non-compliance with weight-bearing restrictions

Failure Management

Recognition of Failure:

• Progressive collapse on X-ray (crescent sign development if not present initially, increasing flattening)
• Joint space narrowing (>1mm loss)
• Worsening pain despite initial improvement
• Decreased ROM and function

Timing: Most failures occur within 18-24 months post-op, but can occur up to 3-5 years

Salvage Options:

1. Total Hip Arthroplasty (most common):

   • Standard treatment for failed core decompression
   • Good long-term outcomes but HIGH revision rate in young patients
   • AOANJRR: 25-30% revision at 10 years for AVN patients <55 years vs 5-7% for OA
   • Challenges: Young age, good bone stock, high activity demands

2. Hip Resurfacing (controversial):

   • Preserves bone stock
   • Concerns about bone quality in AVN
   • Higher failure rates than for OA patients
   • Not standard in Australia

3. Vascularized Fibula Graft (salvage attempt):

   • For very young patients (<35 years) with small-medium lesions who failed core decompression
   • 60-80% success as salvage in carefully selected cases
   • Buys time before inevitable THA

4. Rotational Osteotomy (transtrochanteric):

   • Rarely considered in Australia
   • Rotates defect away from weight-bearing zone
   • Only for small, contained anterosuperior lesions
   • Technically demanding, unpredictable outcomes

Australian-Specific Data (EXAM ESSENTIAL!)

AOANJRR Registry Data

• Young AVN patients (<55 years) undergoing THA: 25-30% revision rate at 10 years
• Comparison OA patients same age: 5-7% revision rate at 10 years
• 4-5× higher revision risk justifies aggressive joint preservation attempts
• Most common failure modes: Aseptic loosening, instability, fracture

PBS (Pharmaceutical Benefits Scheme)

• Alendronate covered for "corticosteroid-induced osteoporosis" (includes AVN prevention)
• Zoledronic acid covered for similar indication
• Requires minimum 3 months prednisolone ≥7.5mg daily (or equivalent)

MBS Item Numbers

• 49548: Excision of bone, femur (includes core decompression) - $600-800
• 49318: Bone graft to femoral head - additional $400-500
• Combined procedure typically $1000-1300

eTG (Therapeutic Guidelines) Antibiotic Prophylaxis

• Cefazolin 2g IV at induction (single dose)
• If penicillin allergy: Vancomycin 25-30mg/kg IV (over 1-2 hours pre-incision)