Vascular Anatomy of the Humeral Head

1. Anterior Humeral Circumflex Artery (AHCA) - Primary supply (80%):

   • Origin: Axillary artery (lateral to pectoralis minor)
   • Course: Runs along inferior border of subscapularis
   • Arcuate artery branch: CRITICAL vessel
   • Enters humeral head just posterolateral to bicipital groove
   • Ascends within bone to supply anterolateral 2/3 of head
   • Most vulnerable to injury in displaced fractures and surgical dissection
     • Supplies: Greater tuberosity, anterolateral humeral head, long head biceps

2. Posterior Humeral Circumflex Artery (PHCA) - Secondary supply (20%):

   • Origin: Axillary artery (travels with axillary nerve through quadrangular space)
   • Course: Posterior to surgical neck
   • Supplies: Posterior 1/3 of humeral head via multiple capsular vessels
   • Less clinically significant than AHCA (smaller contribution)

3. Terminal Intraosseous Distribution:

   • Vessels arborize in subchondral bone creating terminal vascular network
   • Watershed zone: Superomedial humeral head (junction of AHCA and PHCA territories)
   • Limited intraosseous anastomoses (poor collateral circulation)
   • End-artery pattern makes head vulnerable to single-vessel injury

Anatomical Vulnerabilities:

• Single dominant vessel reliance: AHCA (arcuate artery) disruption causes extensive necrosis affecting 80% of head
• Epiphyseal-metaphyseal junction: Watershed zone most susceptible to ischemia
• Capsular reflection: Creates anatomical separation limiting collateral flow between metaphysis and epiphysis
• Intracapsular location: Limits external soft tissue collateral development
• Terminal vessel architecture: End-artery pattern with minimal anastomoses

Surgical Relevance:

• Fracture fixation: Overzealous dissection anterolateral to bicipital groove risks arcuate artery injury
• Deltopectoral approach: Staying medial to biceps groove protects AHCA
• Inferior capsular release: Avoid extending dissection too far posteriorly (PHCA in quadrangular space)
• Screw placement: Avoid long screws in anterolateral quadrant (may disrupt arcuate artery)

Pathophysiological Cascade

AVN progresses through a predictable sequence from ischemic insult to mechanical failure:

Stage 1: Ischemic Event (Reversible - Hours to Days)

• Interruption of blood supply to subchondral bone (vascular injury, thrombosis, extravascular compression)
• Osteocyte death begins within 2-4 hours of complete ischemia
• Bone marrow necrosis and edema
• Hematopoietic cell death
• Imaging: MRI detectable (marrow edema), X-ray normal
• Reversibility: If blood flow restored quickly, bone may recover

Stage 2: Repair Response (Potentially Reversible - Weeks to Months)

• Revascularization attempts from periphery (creeping substitution)
• Inflammatory response at necrotic-viable bone interface
• Osteoclastic resorption of necrotic bone (removing dead trabeculae)
• Attempted new bone formation by osteoblasts
• Structural consequence: Paradoxical weakening during remodeling (removing dead bone faster than forming new)
• Imaging: MRI double-line sign appears (reactive zone), X-ray may show early sclerosis
• Biomechanics: Strength reduced 70-80% during repair phase

Stage 3: Mechanical Failure (Irreversible - Months to Years)

• Subchondral fracture under physiological loads (crescent sign)
• Trabecular collapse and architectural disruption
• Articular cartilage initially remains viable (synovial fluid nutrition)
• Progressive deformity and head flattening
• Imaging: Crescent sign visible on X-ray (subchondral lucency), MRI shows fracture line
• Point of no return: Joint preservation strategies ineffective after collapse occurs

Stage 4: Secondary Arthritis (Months to Years)

• Articular cartilage fragmentation (loss of congruent support)
• Glenoid cartilage damage from incongruent articulation
• Osteophyte formation
• Joint space narrowing
• Synovitis and capsular contracture
• Imaging: Classic OA changes both sides of joint
• End-stage: Requires arthroplasty for symptom control

Biomechanical Factors:

• Normal humeral head stress: 50-200 MPa during activities of daily living
• Necrotic bone strength: Reduced 70-80% from baseline
• Repair bone strength: Woven bone has 50% strength of mature lamellar bone
• Collapse threshold: Lesions involving over 40% of head volume exceed mechanical tolerance
• Load distribution: Central lesions fail faster than peripheral (higher stress concentration)

Biological Determinants of Progression:

• Lesion size: over 40% volume = 80% progress to collapse
• Lesion location: Central/medial worse than peripheral/lateral
• Age: Younger patients have higher bone turnover (faster remodeling, paradoxically faster progression)
• Continued exposure: Ongoing steroids/alcohol accelerates all stages

Cruess Classification (Most Commonly Used)

The Cruess classification is the most clinically practical system, based primarily on plain radiographic findings and correlating well with treatment algorithms. It is the gold standard for communication among surgeons and in clinical decision-making.

Ficat and Arlet Staging

Originally described for femoral head AVN, this system has been adapted for humeral head with good correlation to MRI findings. It provides more granular staging than Cruess, particularly in early disease.

Stage 0: Pre-radiographic (Asymptomatic)

• Clinical: May be asymptomatic or minimal symptoms
• Radiographs: Completely normal
• MRI: Normal or very subtle marrow signal changes
• Significance: Rarely diagnosed unless screening at-risk patients

Stage I: Pre-radiographic (Symptomatic)

• Clinical: Mild to moderate pain, normal ROM
• Radiographs: Normal (key differentiator from Stage II)
• MRI: Band sign (single or double-line), marrow edema, demarcated lesion
• Significance: Earliest clinically relevant stage, best outcomes with intervention

Stage II: Radiographic Sclerosis

• Clinical: Moderate pain, some ROM restriction
• Radiographs: Sclerosis visible, cystic changes, NO collapse or contour change
• MRI: Well-demarcated lesion, increased signal intensity T2, double-line sign common
• Significance: Still pre-collapse, reasonable outcomes with core decompression

Stage III: Subchondral Fracture

• Clinical: Significant pain, ROM loss
• Radiographs: Crescent sign (subchondral lucency indicating fracture)
• MRI: Fracture line clearly visible on all sequences
• Significance: Mechanical failure, poor outcomes with preservation attempts

Stage IV: Articular Collapse

• Clinical: Severe pain, limited function
• Radiographs: Humeral head flattening, loss of sphericity, possible fragmentation
• MRI: Structural deformity, extent of collapse quantifiable
• Significance: Joint replacement territory

Stage V: Secondary Glenohumeral Arthritis

• Clinical: Disabling arthritis symptoms
• Radiographs: Joint space narrowing, glenoid sclerosis, osteophytes
• MRI: Glenoid involvement evident (edema, cartilage loss)
• Significance: Definite need for arthroplasty, glenoid component likely required

Modified Ficat Classification (MRI-Enhanced)

This enhanced version incorporates MRI volumetric assessment and signal characteristics, providing prognostic information beyond plain radiographs.

Key Prognostic Parameters:

Lesion Volume (Prognostic):

• under 30% of head: Low progression risk (15-20% progress to collapse)

• 30-50% of head: Moderate risk (50-60% progress)

• over 50% of head: High risk (over 80% progress to collapse)

• Measurement: Best assessed on coronal MRI sequences

  Lesion Location (Prognostic):

• Peripheral: Better prognosis (lower stress, easier revascularization)

• Central/medial: Worse prognosis (3x higher collapse rate, high-stress zone)

• Anterior vs posterior: Anterior location slightly worse (higher loads)

  MRI Signal Characteristics:

• T1-weighted: Low signal in necrotic segment (dark = dead marrow fat)

• T2-weighted: Double-line sign (pathognomonic when present)

  • Inner line: Low signal (necrotic bone interface)
  • Outer line: High signal (reactive granulation tissue, revascularization attempt)

• Enhancement: Peripheral enhancement on gadolinium (viable tissue surrounds necrotic core)

Prognostic Scoring: Combining volume, location, and stage improves prediction of progression:

• Low risk: Stage I-II, under 30% volume, peripheral location (20% progress)
• Moderate risk: Stage II, 30-50% volume, central (60% progress)
• High risk: Stage II-III, over 50% volume, central (over 80% progress)

This scoring helps stratify patients for intervention intensity (observation vs core decompression vs early arthroplasty).

Indications:

• Cruess Stage I-II (pre-collapse)
• Ficat Stage I-II
• MRI lesion less than 40% of head volume (greater than 40% has poor outcomes)
• Motivated patient willing to comply with 3-month activity restriction
• Age under 40 years (relative indication - younger patients better compliance, longer to arthroplasty)

Contraindications:

• Crescent sign present (Stage III) - mechanical failure already occurred, low success rate
• Collapse (Stage IV and beyond) - irreversible structural damage
• Greater than 50% head involvement - exceeds mechanical tolerance, very low success rate
• Infected shoulder - absolute contraindication
• Unable to comply with post-operative restrictions - premature loading causes fracture
• Non-modifiable risk factors (continued heavy steroid/alcohol) - relative contraindication

Pre-Operative Planning:

• Review MRI: Lesion location, volume, identify target for decompression
• Review CT if available: Assess bone quality, metaphyseal involvement
• Counsel realistic expectations: 50-70% halt progression (NOT reverse damage)
• Discuss augmentation options: Bone graft, BMAC, PRP (if available in research protocol)
• Optimize medical conditions: Cease smoking, vitamin D repletion, diabetes control
• Coordinate with treating physician: Minimize steroids if possible

Consent Discussion:

• Success rate: 70% Stage I, 50% Stage II (define success as no progression to collapse)
• Failure: 30-50% will progress to arthroplasty within 5 years
• Complications: Fracture (2-5%), infection (less than 1%), neurovascular injury (rare), persistent pain (30-40%)
• Post-operative requirements: Sling 4-6 weeks, no lifting 3 months (strict)
• Timeline: 6-12 months to know if successful (serial imaging)

This procedure "buys time" rather than providing definitive cure - important to set appropriate expectations.

Patient Positioning:

• Beach chair (most common) or lateral decubitus (surgeon preference)
• Ensure C-arm access for AP and axillary fluoroscopic views
• Arm free-draped to allow manipulation
• Mark anatomical landmarks (acromion, coracoid, anticipated entry point)

Approach:

1. Deltoid-splitting approach (anterolateral):

   • 3-4cm vertical incision centered over greater tuberosity
   • Palpate lateral acromion edge, mark 2cm distal
   • Split deltoid fibers in line with fibers (not across)
   • Stay within 5cm of acromion (avoid axillary nerve - runs 5-7cm distal)
   • Use self-retaining retractors (small Gelpi or similar)

2. Identify rotator cuff:

   • Supraspinatus insertion on greater tuberosity (most common entry)
   • Alternative: Rotator interval (between subscapularis and supraspinatus)
   • Minimal cuff splitting (5mm longitudinal split if needed)

Core Decompression Procedure:

1. Determine entry point (fluoroscopy-guided):

   • Goal: Aim guidewire toward center of necrotic lesion (pre-identified on MRI)
   • Entry: Lateral humeral head at supraspinatus insertion typically
   • Angle guidewire 30-45 degrees medially and inferiorly (toward lesion center)
   • Confirm position on AP and axillary views

2. Insert guidewire:

   • 2.0-2.4mm threaded guidewire
   • Advance under fluoroscopy
   • Confirm trajectory targets lesion center on both views
   • Advance until guidewire reaches subchondral bone (within 5mm of articular surface)

3. Cannulated drilling:

   • 8-10mm cannulated drill over guidewire
   • Advance slowly with gentle pressure (avoid fracture)
   • Stop 5mm short of articular surface (protect cartilage)
   • Create 1-3 channels depending on lesion size:
     • Small lesion (less than 30%): 1 channel
     • Medium lesion (30-50%): 2 channels (divergent)
     • Large lesion (greater than 50%): 3 channels (fan pattern)
   • Confirm channel positions on fluoroscopy

4. Curette necrotic tissue (if accessible):

   • Insert small curette through drill channel
   • Gently remove necrotic debris (creates space for new bone)
   • Avoid aggressive curettage (risk fracture)

Augmentation Options:

Non-vascularized Bone Graft:

• Harvest iliac crest cancellous bone (standard approach)
• Alternative: Use reamer contents from channel (autograft)
• Pack graft into decompression channels
• Provides scaffold for new bone formation and osteogenic cells

Bone Marrow Aspirate Concentrate (BMAC):

• Harvest 60mL bone marrow from iliac crest
• Centrifuge to concentrate stem cells (if equipment available)
• Inject 3-5mL BMAC into each channel
• Theoretical benefit: Mesenchymal stem cells aid revascularization

Vascularized Fibular Graft (rarely used in shoulder):

• Consider for very large lesions (greater than 50%) in young patients
• Technically demanding (microsurgical anastomosis)
• Better evidence in hip AVN, limited shoulder data

Closure:

• Repair rotator cuff if violated: Absorbable suture (2-0 Vicryl), side-to-side
• Close deltoid split: Absorbable suture
• Subcutaneous: 2-0 absorbable
• Skin: Subcuticular 3-0 or staples
• Sterile dressing and sling application

Post-Operative Protocol:

Weeks 0-6 (Protection Phase):

• Sling immobilization continuously (remove for exercises only)
• No lifting (not even coffee cup with operative arm)
• Pendulum exercises: Start day 1 (gentle passive motion)
• Passive ROM by therapist: Forward elevation and external rotation only
• Goals: Prevent stiffness while protecting channels

Weeks 6-12 (Early Motion):

• Wean sling gradually (start with removing at home)
• Active-assisted ROM exercises
• Light ADLs permitted (eating, light grooming)
• Still no lifting (bone not healed yet)
• Goals: Regain motion, continue protecting bone

Months 3-6 (Strengthening):

• Commence active ROM (all planes)
• Progressive strengthening: Isometric → light resistance → moderate resistance
• Return to light work and ADLs
• Lifting restriction gradually increased: 5kg month 3, 10kg month 4, 15kg month 5
• Goals: Restore function, progressive loading

Month 6 onwards (Return to Activities):

• Full ROM and strength goals
• Return to normal activities (within reason)
• Avoid: Heavy overhead lifting (greater than 20kg), contact sports
• Serial imaging: X-rays at 3, 6, 12 months (assess progression vs stabilization)

Critical Post-Operative Instructions:

• "The bone is weaker during healing (like removing pillars from a building during renovation). Premature loading causes fracture. Strict adherence to restrictions is essential."
• "Success is defined as halting progression, not reversing damage. We will monitor with X-rays to see if the bone stabilizes."

Success Rates: (Success defined as no radiographic progression to collapse or need for arthroplasty)

• Stage I: 70-80% at 5 years
• Stage II: 50-65% at 5 years
• Stage III (with crescent sign): 20-30% at 5 years (controversial indication)
• Overall: 68% success at mean 4-year follow-up (systematic review)

Factors Associated with Success:

• Lesion volume less than 30%: 75-80% success vs 40% if greater than 50%
• Pre-collapse stage: 2-3x better outcomes than post-crescent
• Peripheral location: Better than central (easier revascularization)
• Younger age (under 40): Better compliance, similar biological outcomes
• Non-alcohol etiology: Slightly better than alcohol-related (cease alcohol easier than cease steroids)
• Augmentation with bone graft: Trend toward better outcomes (not statistically significant in most studies)
• Biologics (BMAC, PRP): Promising small series but no RCTs, unclear benefit

Failure Patterns:

• Progressive collapse: 30-50% by 5 years in Stage II patients
• Time to conversion: Mean 2-4 years post-decompression (range 1-8 years)
• Predictors of failure: Large lesion, central location, continued steroid/alcohol exposure
• Salvage: Conversion to arthroplasty (usually TSA or hemiarthroplasty depending on age)

Evidence Base:

• Level III-IV evidence: Case series, retrospective cohorts (no RCTs in shoulder AVN)
• Largest series: Mont et al. systematic review (n equals 268 shoulders, 68% success)
• Better evidence in hip AVN: Extrapolated to shoulder (same biological principles)
• Biological augmentation: Mostly Level IV-V evidence, remains investigational
• No high-quality studies comparing decompression vs observation (ethical challenges randomizing)

Complications:

Intraoperative:

• Fracture during drilling: 1-2% (avoid aggressive reaming, use fluoroscopy)
• Neurovascular injury: Less than 1% (axillary nerve if deltoid split too distal, circumflex vessels if aggressive)
• Failure to target lesion: 5% (technical error, importance of fluoroscopy)

Post-Operative:

• Infection: Less than 1% (minimally invasive procedure)
• Persistent pain: 30-40% (often represents progression despite decompression)
• Progression to collapse: 30-50% (definition of failure)
• Fracture through decompression site: 2-5% (premature loading, non-compliance with restrictions)
• Stiffness: 5-10% (inadequate physiotherapy, capsular contracture)

Comparison to Other Treatments:

• Core decompression vs observation: No Level I evidence, but decompression widely accepted as superior in Stage I-II
• Core decompression vs early arthroplasty: Arthroplasty definitive but destroys native joint in young patients
• Augmentation vs no augmentation: No clear benefit proven, but low morbidity if using BMAC/PRP

Long-Term Outcomes (Successful Cases):

• Pain relief: 60-70% achieve good to excellent pain control
• Function: Near-normal shoulder function if successful
• Radiographic: Lesion may persist but not progress (stable disease acceptable outcome)
• Opposite shoulder: 30-40% require intervention on contralateral side during follow-up

The key message for examiners is that core decompression is a joint preservation strategy with moderate success rates that buys time in young patients, but requires careful patient selection and post-operative compliance.

Pre-Operative Planning:

Imaging Review:

• CT scan: Assess glenoid version (normal 5-10 degrees retroversion), bone stock, humeral deformity from collapse
• Templating: Size humeral and glenoid components, plan version correction if needed
• MRI review: Confirm rotator cuff integrity (critical for anatomic TSA success)
• Assessment of bone quality: AVN often has mixed sclerosis and cystic areas (may need cement even in young patients)

Risk Stratification:

• Bleeding risk: Anticoagulation (common in AVN patients), immunosuppression affecting platelets
• Infection risk: Current immunosuppression (steroids, transplant medications), diabetes, malnutrition
• Bone quality: Osteoporosis from steroids/alcohol (fracture risk, component fixation concerns)
• Medical optimization: Vitamin D repletion, diabetes control (HbA1c less than 7.5%), nutrition (albumin greater than 35)

Implant Selection:

• Stemmed vs stemless humeral: Stemless preferred in AVN if metaphyseal bone quality adequate (bone preservation, easier revision)
• Cemented vs uncemented: Consider cement if osteoporotic bone (alcohol, steroids) even in younger patients
• Glenoid component: Cemented all-polyethylene standard (metal-backed higher failure in AVN population)
• Size: Avoid over-sizing (increases stiffness and nerve injury risk)

Patient Positioning:

Beach Chair (Most Common):

• Head secured in horseshoe headrest or specialized device
• Torso 30-45 degrees upright
• Operative arm free to extend and rotate
• Non-operative arm tucked or on arm board
• C-arm access from opposite side for intraoperative imaging
• Advantages: Familiar anatomy, easier assistant positioning, lower neuro risk

Lateral Decubitus (Alternative):

• Patient on beanbag or lateral positioning device
• Axillary roll under down-side axilla
• Arm suspended in traction device or supported
• Advantages: Easier humeral preparation, better visualization with gravity, more stable glenoid exposure
• Disadvantages: Unfamiliar anatomy orientation for some surgeons

Deltopectoral Approach:

1. Skin Incision:

   • Start 2cm lateral and inferior to coracoid tip
   • Extend 10-12cm distally along deltopectoral groove (palpable)
   • Can extend proximally toward clavicle or distally toward deltoid insertion if needed

2. Superficial Dissection:

   • Identify cephalic vein in deltopectoral groove
   • Ligate crossing tributaries with electrocautery
   • Retract vein laterally with deltoid (most common) or medially with pectoralis (alternative)
   • Develop plane between deltoid (lateral) and pectoralis major (medial)

3. Deep Exposure:

   • Incise clavipectoral fascia lateral to conjoined tendon
   • Identify and protect conjoined tendon (retract medially)
   • Coracoid process is medial landmark
   • Tag muscle edges with stay sutures for later closure

4. Rotator Interval Exposure:

   • Identify interval between subscapularis (inferior) and supraspinatus (superior)
   • Long head biceps tendon lies in interval
   • Tenotomy or tenodesis LHB: Routine in AVN (tendon often attritional, simplifies exposure)
   • Open rotator interval capsule

Subscapularis Management:

Decision: Lesser Tuberosity Osteotomy (Preferred in AVN)

Rationale for Osteotomy in AVN:

• Preserves subscapularis insertion (anatomic healing potential)
• AVN bone may be soft or sclerotic (osteotomy technically easier than tendon dissection through abnormal tissue)
• Easier revision surgery (landmarks intact)
• Lower failure rate (5% vs 10-15% for tenotomy)

Osteotomy Technique:

1. Mark osteotomy line: 5-8mm medial to bicipital groove (preserve tendon insertion)
2. Oscillating saw: Create 10-15mm thick bone wafer including subscapularis insertion
3. Extend medially: 2-3cm along subscapularis-capsule junction
4. Protect axillary nerve: Stay on bone, no retractors beyond 6 o'clock position
5. Complete osteotomy: Use osteotome to finish (avoid saw exiting posteriorly near nerve)
6. Tag with sutures: Place two Number 2 non-absorbable sutures through osteotomy fragment
7. Reflect medially: Gently mobilize subscapularis-osteotomy unit, release adhesions to glenoid neck

Repair at Closure (see later tab):

• Transosseous tunnels or suture anchors
• Anatomic positioning with arm in neutral rotation
• Number 2 non-absorbable suture

Humeral Head Osteotomy:

1. Exposure:

   • Place Fukuda or similar humeral head retractor (deep to subscapularis, lever head into wound)
   • Externally rotate and extend arm to deliver head
   • Assistant maintains position

2. Assess Anatomy (AVN Distorts Landmarks):

   • Anatomic neck: Usually identifiable despite collapse
   • Version reference: Bicipital groove (aim 20-30 degrees retroversion from groove)
   • Collapse pattern: Note deformity (affects templating)
   • Bone quality: Assess sclerosis vs cystic areas (impacts fixation choice)

3. Osteotomy:

   • Guide: 1cm superior to pectoralis major insertion (approximate anatomic neck)
   • Angle: 30-40 degrees to humeral shaft (creates retroversion when stem placed)
   • Saw: Oscillating saw, preserve posterior soft tissue hinge initially
   • Remove head: Complete osteotomy, extract humeral head
   • Inspect glenoid: Confirm arthritis if doing TSA vs hemiarthroplasty

4. Humeral Canal Preparation:

   • Entry point: Center of cut surface (slightly posterior to bicipital groove)
   • Starter: Box chisel or entry reamer to open canal
   • Sequential reaming: Progressively larger reamers to cortical contact
   • Goals:
     • Press-fit stability (if uncemented) - light cortical contact
     • Cement mantle 3-4mm (if cemented) - slightly under-ream
   • AVN considerations: Variable bone density (necrotic soft, sclerotic hard) - careful reaming

5. Version Control:

   • Reference: Bicipital groove equals 0 degrees
   • Target: 20-30 degrees retroversion (groove rotated posteriorly)
   • Assess with trial: Fluoroscopy, ensure correct version

6. Height Assessment (Critical):

   • Landmark: Greater tuberosity should be 5-8mm below top of humeral head
   • Trial reduction: Assess stability, ROM, soft tissue tension
   • Over-stuffing: Causes stiffness, nerve stretch (avoid)
   • Under-stuffing: Causes instability, poor cuff mechanics
   • Use intraoperative references: Compare to pre-op X-rays, opposite shoulder if normal

Glenoid Exposure:

1. Retraction:

   • Humeral head retractor (Fukuda, Kolbel) placed deep to subscapularis
   • Lever humerus posteriorly (creates space for glenoid work)
   • Externally rotate and extend arm (assistant or mechanical arm holder)
   • Adequate retraction critical (poor exposure causes malposition)

2. Capsular Release (360-degree):

   • Inferior capsule: Most critical release
     • Stay directly on bone (axillary nerve runs 5-7mm from glenoid rim inferiorly)
     • Use electrocautery or elevator
     • Release until inferior glenoid fully visible
   • Posterior capsule: Release from posterior glenoid rim
   • Superior capsule: Preserve rotator cuff insertions, release just enough for exposure
   • Remove labrum and osteophytes: Identify native glenoid rim

Glenoid Reaming:

1. Identify Anatomic Center:

   • Center of native glenoid face (NOT worn surface if eccentric wear)
   • Typically junction of upper 2/3 and lower 1/3
   • Mark with electrocautery

2. Determine Version:

   • Normal: 5-10 degrees retroversion
   • AVN: Usually concentric wear (less version abnormality than primary OA)
   • Goal: Restore normal version (perpendicular to scapular body)
   • Use CT plan for correction if significant deformity

3. Sequential Reaming:

   • Start with curved curette (debride cartilage, define subchondral bone)
   • Spherical reamers progressively larger (start small, increase by 2mm increments)
   • Critical: Aim perpendicular to native version (correct any excessive retroversion)
   • Endpoint: Circumferential bleeding subchondral bone (adequate preparation)
   • Avoid over-reaming: Preserves bone stock, optimizes cement fixation

4. Version Correction (if needed):

   • Excessive retroversion: Ream more posteriorly (correct to 5-10 degrees)
   • Assess with trial component and fluoroscopy/direct visualization
   • Ensure component sits flush (no anterior or posterior rocking)

Glenoid Component Preparation:

Cemented All-Polyethylene (Standard in AVN):

1. Drill Peg/Keel Holes:

   • Use drill guide specific to implant system
   • Pegged component: 3-4 holes (anchor points for cement)
   • Keeled component: Single central keel slot
   • Depth: Per manufacturer (typically 15-20mm)
   • Direction: Perpendicular to glenoid face (avoid cortical perforation)

2. Prepare Bone for Cementation:

   • Pulsatile lavage: Remove debris, blood, marrow
   • Dry with sponges (cement bonds to dry bone)
   • Pack peg holes with sponge (remove just before cementing)

3. Cementation:

   • Mix cement per manufacturer (low-viscosity bone cement preferred)
   • Pressurize cement into peg holes with syringe or finger pressure
   • Apply thin layer to glenoid surface
   • Insert component with steady pressure (use impactor specific to system)
   • Hold in position until cement polymerizes (2-3 minutes)
   • Remove excess cement carefully (avoid leaving debris)

4. Confirm Position:

   • Flush seating (no gaps)
   • Correct version (no tilt)
   • Fluoroscopy: Check component position, cement mantle, no perforation

Metal-Backed Glenoid (Rarely Used in AVN):

• Higher failure rate in all populations (especially AVN)
• Consider only if excellent bone stock and young patient
• Screw or press-fit fixation per manufacturer
• Not recommended as first choice in AVN

AVN-Specific Glenoid Challenges:

• Sclerotic bone: Harder to ream (use sharp reamers, patient progression)
• Cystic bone: Poor cement fixation (may need bone grafting of large cysts)
• Mixed quality: Variable density complicates reaming (risk perforation in soft areas)
• Concentric wear: Generally easier than eccentric (less version correction needed)
• Bone grafting rarely needed: Unlike inflammatory arthritis, bone stock usually adequate

Component Trialing and Final Implantation:

1. Trial Reduction:

   • Insert humeral trial stem and head
   • Reduce into glenoid component
   • Assess stability: Anterior, posterior, inferior load-and-shift
   • Assess ROM: Forward elevation (target 90+ degrees passive), external rotation (40+ degrees), internal rotation
   • Check impingement: Tuberosities should NOT contact glenoid at any ROM position
   • Soft tissue tension: Not over-tight (limits motion) or too lax (instability)

2. Adjust if Needed:

   • Over-stuffed: Use smaller head, reduce height
   • Under-stuffed: Use larger head or taller head
   • Unstable: Increase head size, check version, assess soft tissue repair quality
   • Impingement: Adjust version, consider smaller head

3. Final Humeral Implantation:

   • Remove trial components
   • If cemented: Mix cement, insert into canal with cement gun, insert stem, remove excess
   • If uncemented: Impact stem to final position (press-fit)
   • Insert humeral head onto taper (Morse taper)
   • Impact head fully seated (use head impactor, NOT mallet directly on head)
   • Confirm Morse taper fully engaged (should not spin or come off with gentle pull)

4. Final Reduction and Assessment:

   • Reduce shoulder (confirm smooth reduction)
   • Repeat stability and ROM checks
   • Fluoroscopy: Confirm component positions, no fracture, good alignment
   • Copious irrigation (remove debris, cement particles)

Subscapularis Repair (CRITICAL for Outcome):

Lesser Tuberosity Osteotomy Repair:

1. Prepare bone bed:

   • Debride to bleeding bone (remove soft tissue, sclerotic bone)
   • Maintain flat surface for osteotomy fragment seating

2. Transosseous Tunnel Technique:

   • Drill 2-3 tunnels through greater tuberosity/proximal humerus (medial to lateral)
   • Use 2.0mm drill bit
   • Tunnels spaced 1cm apart
   • Pass Number 2 non-absorbable suture through tunnels (braided polyester or high-strength)

3. Position osteotomy fragment:

   • Bring lesser tuberosity back to anatomic position
   • Arm in neutral rotation (NOT internal rotation - risks over-tensioning)
   • Sutures pass through holes in fragment or around fragment

4. Tie sutures:

   • Secure knots with fragment compressed to bed
   • Ensure firm fixation (should not pull apart with gentle traction)

5. Augment repair:

   • Side-to-side capsular sutures (reinforce repair)
   • Close rotator interval (reduces anterior instability risk)

Alternative: Subscapularis Tenotomy Repair (if Osteotomy Not Performed):

• Prepare lesser tuberosity footprint (abrade to bleeding bone)
• Suture anchors (2-3 anchors) or transosseous tunnels
• Side-to-side tendon repair with Number 2 sutures
• Arm in neutral rotation
• Higher failure rate (10-15% vs 5% for osteotomy)

Wound Closure:

1. Deep layer: Close clavipectoral fascia (absorbable 0 or 2-0 suture)
2. Deltopectoral interval: Ligate any bleeding vessels, ensure cephalic vein intact
3. Subcutaneous: 2-0 absorbable (Vicryl or Monocryl)
4. Skin: Subcuticular 3-0 Monocryl or staples (surgeon preference)
5. Dressing: Sterile dressing, apply sling

Immediate Post-Operative:

• Neurovascular examination: Axillary nerve sensation (lateral shoulder), motor function (deltoid contraction), distal pulses
• Radiographs: AP, scapular Y, axillary lateral (confirm component position, no fracture, no dislocation)
• Pain control: Multimodal (interscalene block + oral/IV analgesics)
• DVT prophylaxis: Mechanical (TED stockings, foot pumps) ± pharmacological (if appropriate)

Rehabilitation Protocol:

Phase 1: Protection (Weeks 0-6)

• Sling immobilization: Continuously (remove for exercises only)
• Pendulum exercises: Start day 1 (gentle passive motion, pain control)
• Passive ROM: Therapist-assisted only (forward elevation to 90 degrees, ER to 20 degrees)
• NO active subscapularis use: Protect osteotomy/tendon repair
• Goals: Prevent stiffness while protecting repair (90 degrees elevation, 20 degrees ER by week 6)

Phase 2: Active Motion (Weeks 6-12)

• Wean sling: Progressively (week 6-8 depending on repair quality)
• Active-assisted ROM: Pulley exercises, cane-assisted
• Begin gentle active ROM: All planes (subscapularis healing sufficient by 6 weeks)
• Isometric strengthening: Deltoid, rotator cuff (no resistance)
• Goals: 120 degrees elevation, 40 degrees ER by week 12

Phase 3: Strengthening (Months 3-6)

• Progressive resistance exercises: Theraband, light weights (1-2kg)
• Functional activities: ADLs unrestricted
• Return to light work: Sedentary or light duty
• Goals: 140+ degrees elevation, 60+ degrees ER, strength 70% of opposite

Long-Term (6 months onwards)

• Full ROM expected: Near-normal or normal
• Return to normal activities: Within restrictions
• Permanent activity restrictions:
  • No overhead heavy lifting (limit 20kg)
  • No contact sports or high-impact activities
  • Swimming, golf, recreational activities generally permitted
• Annual radiographs: First 2 years, then every 2-3 years or if symptomatic

Rehabilitation Milestones (Expected Timeline):

• Week 6: Passive ROM 90/20 (elevation/ER), wean sling
• Week 12: Active ROM 120/40, return to ADLs
• Month 6: ROM 140/60, strength 70%, return to light work
• Month 12: ROM near-normal, strength 80-90%, full function within restrictions