Revision Total Hip Replacement for Recurrent Instability

Primary Indications

Absolute Indications:

• Recurrent dislocation (≥2 episodes) after primary THR despite closed reduction and rehabilitation
• Chronic instability affecting quality of life and activities of daily living
• Failed conservative management (bracing, activity modification, physiotherapy)
• Identifiable correctable cause (component malposition, soft tissue deficiency)

Relative Indications:

• Single dislocation with identifiable mechanical cause (malpositioned components)
• Persistent subluxation episodes causing pain and apprehension
• Patient request after single traumatic dislocation in context of high-risk activities

Contraindications:

• Active infection (must stage with explant and spacer first)
• Medical comorbidities precluding major revision surgery
• Severe abductor deficiency with no reconstruction option (consider expectant management)
• Neuromuscular disorder causing instability (Parkinson's, seizures) - surgery may not solve problem
• Patient non-compliance with post-operative precautions (relative contraindication)

Preoperative Assessment

History:

• Number of dislocations, direction (posterior 80%, anterior 15%, superior 5%)
• Provocative activities (bending, sitting low chairs, specific movements)
• Timing (early <6 weeks vs late >6 weeks post-primary)
• Previous closed reductions, attempts at conservative management
• Impact on quality of life, activities of daily living

Clinical Examination:

• Trendelenburg test (abductor integrity)
• Hip range of motion, stability testing
• Leg length assessment
• Neurovascular status (baseline documentation)
• Gait assessment

Imaging:

• AP pelvis: Measure cup inclination (normal 40-45°, >50° = superior escape, <35° = instability)
• Lateral hip or cross-table lateral: Assess anteversion (15-25° normal)
• CT with 3D reconstruction: ESSENTIAL for precise cup version measurement, stem version, impingement assessment
• Consider MRI: Abductor integrity, fatty infiltration, capsular deficiency

Laboratory Investigation:

• MANDATORY infection workup: ESR, CRP, joint aspiration
• Aspiration: Cell count (>3000 concerning), differential (>80% PMNs concerning), 14-day culture, alpha-defensin or synovial CRP/IL-6
• Cannot proceed without ruling out infection

Component Assessment:

• Cup position (in/out of Lewinnek safe zone)
• Cup type, liner wear pattern
• Stem version, offset restoration
• Head size (small heads <32mm higher risk)
• Impingement signs (eccentric wear)

Reconstruction Planning:

• Decision: Component repositioning alone? Dual mobility? Constrained liner?
• Soft tissue reconstruction needs (abductor repair, capsule reconstruction)
• Implant ordering (dual mobility system or constrained liner, backups)

Patient Positioning

Lateral Decubitus (Posterior Approach):

• Affected side up on radiolucent table
• Pelvic stabilization with supports (anterior ASIS, posterior sacrum)
• All bony prominences padded
• Careful positioning to prevent pressure injuries
• Cell saver recommended (blood loss typically 400-800mL)

Approach Selection:

• Use the previous surgical approach when possible (minimise soft-tissue trauma)
• Posterior approach is the most commonly used worldwide and carries the highest baseline dislocation risk of the standard approaches
• Extended exposure often needed for component assessment

Exposure Technique

Incision:

• Use previous incision, excise old scar elliptically
• Extend proximally and distally as needed (typically 15-20cm)
• Multiple previous scars: choose most posterior

Deep Dissection:

• Deepen through scarred subcutaneous tissue
• Incise fascia lata in line with previous surgery
• Split gluteus maximus in line with fibers (often scarred, difficult planes)
• CRITICAL: Identify and protect sciatic nerve EARLY
  • Higher risk due to scar encasement
  • Place vessel loop or protected retractor
  • Nerve palsy risk 2-7% (highest of all revision types)

Capsular Assessment:

• Tag any capsule present for repair
• Often deficient or absent in chronic dislocators
• Note deficiency for reconstruction planning
• Assess abductor attachment and quality at greater trochanter

Component Assessment

Dislocation:

• May be easy (chronically unstable) or difficult (scar tissue)
• Gentle maneuvers: flex 90°, adduct, internally rotate
• Bone hook on femoral neck if needed
• Avoid excessive force (fracture risk)

Systematic Assessment:

1. Cup position: Inclination, version (Lewinnek safe zone 40±10° inclination, 15±10° anteversion)
2. Cup fixation: Well-fixed or loose
3. Liner wear: Eccentric wear, scratching (impingement signs)
4. Stem: Version, stability, offset restoration
5. Head size: Small <32mm = higher risk
6. Impingement: Wear on femoral neck
7. Soft tissues: Abductor quality, capsule integrity

Component Removal (If Indicated)

Acetabular Cup:

• Remove if malpositioned or converting to dual mobility/constrained
• Well-fixed cup: Curved osteotomes circumferentially, stay on metal, preserve bone
• Specialized extraction tools if needed
• Goal: Minimize bone loss

Femoral Stem:

• Usually NOT removed for instability alone unless:
  • Malaligned (excessive version)
  • Loose
  • Wrong offset
• Well-fixed cementless: May need Extended Trochanteric Osteotomy
• Cemented: Remove cement with high-speed burr, ultrasonic tools

Head Exchange:

• Often simple head size change (28mm → 36mm)
• Keeps well-fixed stem in place

Acetabular Reconstruction - Dual Mobility (Preferred)

Preparation:

• Remove scar tissue to bleeding bone
• Assess bone stock (Paprosky classification)
• Ream to appropriate size (dual mobility needs larger component)
• Medialize to anatomic hip center when possible

Cup Positioning (CRITICAL):

• Still must be in Lewinnek safe zone
• Target: 40-45° inclination, 15-20° anteversion
• Use guide or fluoroscopy for accurate placement
• Combined anteversion: Cup + Stem = 35-50°

Cup Insertion:

• Press fit (1-2mm larger than final reamer)
• Check stability (should not move)
• Add screws in SAFE ZONES if questionable stability
• Posterosuperior quadrant safest
• Avoid: anteroinferior (vessels), medial (intrapelvic), inferior (obturator nerve)

Liner Insertion:

• System-specific (snap or screw mechanism)
• Insert small inner bearing into large outer bearing
• Verify smooth articulation

Acetabular Reconstruction - Constrained Liner (Alternative)

Indications:

• Dual mobility not available
• Prior dual mobility failure
• Severe abductor deficiency
• Severe bone loss preventing dual mobility

Technique:

• Ream acetabulum to appropriate size
• Insert specific constrained cup system
• Position in safe zone (EVEN MORE CRITICAL)
• Screw fixation MANDATORY (high torque)
• Insert constrained liner
• Insert and LOCK femoral head (verify locking)
• Check ROM (constrained reduces ROM)

Disadvantages:

• Higher loosening (5-15% at 5 years) due to torque
• Liner dissociation risk (3-8%)
• Reduced ROM
• Higher wear (thicker polyethylene)

Femoral-Sided Optimization

Assessment:

• Stem version (excessive anteversion >25° or retroversion <5°)
• Offset restoration (compare to contralateral)
• Stem stability (loose requires revision)
• Modularity options (adjust with modular head/neck)

Head Size Change:

• Larger heads reduce dislocation (32mm → 36mm or 40mm)
• 36mm has ~50% lower dislocation than 28mm
• Limited by cup inner diameter
• Appropriate size for dual mobility system (28-32mm inner)

Stem Revision (If Needed):

• Excessive anteversion/retroversion: Revise to neutral (10-15°)
• Wrong offset: Higher offset stem
• Loose: Revise regardless
• Combined anteversion rule: Cup + Stem = 35-50°

Trial Reduction and Stability Testing

Comprehensive Testing (CRITICAL):

1. Posterior stability (most common): 90° flexion + maximal adduction + maximal IR = shuck test (should be ROCK SOLID)
2. Anterior stability: Full extension + 40° ER + slight adduction
3. Superior escape: Full abduction + ER (rare)
4. Full ROM testing: Flex 110-120°, extend neutral, abduct 45°, adduct to midline, rotations
5. Impingement assessment: Look/feel for prosthetic impingement at extremes
6. Soft tissue tension: Snug but not excessively tight (nerve palsy risk)
7. Leg length: Overlapping patellae, ASIS to medial malleolus, compare to templating (aim <1cm difference)
8. Fluoroscopy: Visualize head centering, no subluxation

If unstable: Must address before proceeding (reposition cup, more constraint, better soft tissue repair)

Soft Tissue Reconstruction

Abductor Repair (CRITICAL):

• Assess quality and attachment
• If detached: Repair with #5 non-absorbable sutures through bone tunnels or anchors
• If poor quality: Advance or augment with allograft (Achilles tendon wrapped around GT)
• Repair gluteus medius and minimus to GT anatomically
• Poor abductors = instability and Trendelenburg

Capsule Repair:

• Repair meticulously if tissue present (#1 or #2 non-absorbable sutures)
• Evidence: 50-70% reduction in posterior dislocation with repair
• If deficient: Consider allograft reconstruction (dermal/fascial)
• Creates posterior restraint

Short External Rotators:

• Repair to posterior capsule or GT with transosseous sutures
• Provides posterior soft tissue stability

Closure

Irrigation:

• 3-6 liters normal saline or antibiotic solution
• Remove all debris, bone fragments, PMMA particles

Layered Closure:

1. Gluteus maximus fascia (#1 absorbable)
2. Subcutaneous (2-0 or 3-0 absorbable)
3. Deep dermal (3-0 or 4-0 absorbable)
4. Skin (staples or subcuticular)

Dressing:

• Sterile dressing
• Consider negative pressure wound therapy if high risk

Abduction Pillow:

• Place immediately (15-20° abduction)
• CRITICAL for posterior dislocation prevention

Additional Complications

Intraoperative Fracture:

• Femoral (1-3%): Often during stem removal or dislocation. Cable plates or strut grafts
• Acetabular (1-2%): During cup removal or insertion. Protected weight bearing, consider screws or augments

VTE (3-5% with prophylaxis):

• Prevention: LMWH or DOAC for 4-6 weeks, mechanical compression, early mobilization
• Management: Anticoagulation, consider IVC filter if contraindication to anticoagulation

Leg Length Discrepancy (10-15%):

• Balance stability (lengthening) vs nerve palsy risk
• Aim <1cm, maximum 2cm to avoid nerve palsy
• Shoe lift if persistent >1cm and symptomatic

Heterotopic Ossification (10-15%):

• Prevention: NSAIDs for 6 weeks (indomethacin 25mg TDS) or single-dose radiation
• Management: Observe if asymptomatic, excision if limiting ROM after maturation (12-18 months)

Immediate Postoperative (0-6 weeks)

Positioning:

• Abduction pillow CONTINUOUSLY for 6 weeks (15-20° abduction)
• Remove only for therapy under supervision
• Log roll for position changes

Hip Precautions (STRICT for 12 weeks MINIMUM):

• No hip flexion >90° (elevated toilet seat, no low chairs, no bending to floor)
• No adduction past midline (no crossing legs, pillow between legs in bed)
• No internal rotation (posterior approach) or external rotation (anterior approach)
• Sleep supine or on operative side only with pillow between legs

Weight Bearing:

• Touch-down or partial (20kg) for 6 weeks if soft tissue repair or questionable fixation
• Progress to weight bearing as tolerated if well-fixed components and no soft tissue concerns
• Walker or crutches for first 6 weeks

Physiotherapy:

• Day 1-2: Supervised mobilization
• Gait training with assistive device
• Gentle ROM within precautions
• Abductor strengthening when healed (6-12 weeks)

Medications:

• Anticoagulation: LMWH (enoxaparin 40mg SC daily) or DOAC (apixaban 2.5mg PO BID) for 4-6 weeks
• Antibiotics: IV cefazolin 2g q8h or vancomycin for 24-48 hours
• Analgesia: Multimodal (paracetamol, NSAIDs if not contraindicated, opioids PRN)
• VTE prophylaxis: TED stockings, mechanical compression

Monitoring:

• Neurovascular checks (foot dorsiflexion, sensation) - document any deficit immediately
• Wound inspection daily
• Hemoglobin (transfusion if <70-80 g/L or symptomatic)

Imaging:

• Post-op AP pelvis and lateral hip within 48 hours
• Document component position, leg length, exclude fracture

Follow-Up Schedule

2 Weeks:

• Wound check, remove sutures/staples
• Reinforce hip precautions
• Assess pain control and mobility

6 Weeks:

• Clinical assessment (wound healing, pain, mobility, neurovascular status)
• X-rays (AP pelvis, lateral hip) - compare to post-op films
• Advance to full weight bearing if protected WB used
• Continue hip precautions
• Advance physiotherapy (ROM, abductor strengthening)

3 Months:

• Functional assessment (Oxford Hip Score, WOMAC, Harris Hip Score)
• Discontinue hip precautions if soft tissues healed and appropriate patient compliance
• May extend to 6 months if high risk
• Advance to full activities gradually
• X-rays (assess for loosening, HO)
• Discontinue anticoagulation if no VTE

6 Months:

• Assess function, return to activities
• X-rays (establish baseline for component position)
• Monitor for complications (dislocation, infection, nerve palsy recovery)

Annual (Lifelong):

• Clinical assessment, functional scores
• Radiographs (AP pelvis, lateral hip)
• Surveil for late complications (loosening, wear, late dislocation/infection)

Long-Term Outcomes

Re-Dislocation Rate:

• 5-15% with dual mobility (excellent vs historical 30-40%)
• Most occur in first 6 months
• 60-80% reduction compared to standard revision

Function:

• Significantly improved from chronic instability state
• Not to level of uncomplicated primary THR
• Hip scores improve average 30-40 points

Survivorship:

• 10-year implant survival 85-90%
• Failure from loosening, infection, recurrent instability

Patient Satisfaction:

• 70-80% satisfied or very satisfied
• Improvement over chronic instability
• Anxiety about re-dislocation persists in many