Total Hip Replacement Dislocation - Comprehensive Assessment and Management

Comprehensive Evaluation Protocol

Infection Workup (MANDATORY - Do NOT Skip)

Laboratory Tests:

• ESR and CRP (elevated suggests infection)
• Joint aspiration GOLD STANDARD: Cell count (>3000 cells/µL), differential (>80% PMNs), aerobic/anaerobic cultures (hold 14 days), Gram stain

Rule: Any revision for instability requires infection exclusion - infection can present as recurrent dislocation (30% of 'instability' cases in some series)

Imaging Protocol

Standard Radiographs:

• AP pelvis (assess cup inclination, leg length, offset)
• Lateral hip (assess cup anteversion on cross-table lateral)
• Shoot-through lateral femur (assess stem version)

CT Pelvis with Metal Artifact Reduction (GOLD STANDARD for Component Position):

• Measure cup inclination (radiographic plane): Normal 35-45°, safe zone 30-50°
• Measure cup anteversion (radiographic plane): Normal 15-25°, safe zone 5-25°
• Lewinnek safe zone: 40±10° inclination, 15±10° anteversion
• Outside safe zone: 4x higher dislocation risk (9% vs 2%)
• Assess impingement: Anterior wall overhang, posterior offset, neck-cup contact
• Spinopelvic parameters: Pelvic tilt, sacral slope, lumbar lordosis (especially if spinal fusion or kyphosis)

Femoral Version Assessment:

• CT femur (measure stem anteversion): Normal 10-15°
• Combined anteversion: Cup + stem should total 25-40° (Ranawat triangle)
• Excessive stem anteversion (>20°) → posterior instability
• Excessive stem retroversion (<5°) → anterior instability

Dislocation Direction Classification

Posterior Dislocation (75-90%):

• Mechanism: Flexion + adduction + internal rotation
• Common scenarios: Getting up from low chair, tying shoes, getting into car
• Component factors: Cup retroversion, excessive stem anteversion, posterior wall deficiency

Anterior Dislocation (10-25%):

• Mechanism: Extension + external rotation + adduction
• Common scenarios: Reaching back, pivoting on affected leg, leg crossing
• Component factors: Excessive cup anteversion, stem retroversion, anterior impingement

Risk Factor Identification

Component Malposition (MOST COMMON CORRECTABLE):

• Cup outside safe zone (inclination or anteversion)
• Stem malposition (excessive anteversion/retroversion)
• Combined anteversion outside 25-40°

Impingement:

• Bony: Anterior acetabular wall overhang, posterior offset deficiency, femoral neck osteophytes
• Component: Neck-cup contact, liner rim contact, modular neck-acetabular bone
• Soft tissue: Iliopsoas over acetabular component (anterior), short external rotators (posterior)

Soft Tissue Deficiency:

• Capsule deficient or absent (PRIMARY PATHOLOGY in many recurrent dislocations)
• Short external rotator attenuation (posterior stability)
• Abductor insufficiency (Trendelenburg positive)

Patient Factors:

• Neuromuscular: Parkinson's disease (40-50% failure despite optimal surgery), dementia, CVA
• Compliance: Cognitive impairment, psychiatric disorders, substance abuse
• Anatomy: Femoral offset not restored, leg length inequality

Dislocation History Documentation

Critical Data:

• Number of dislocations (first vs recurrent)
• Time since surgery (early <90 days vs late)
• Direction (posterior vs anterior)
• Mechanism (high vs low energy)
• Reduction method (closed vs open)
• Previous revisions for instability

Treatment Algorithm Decision Tree

NON-OPERATIVE (First dislocation + well-positioned components + correctable risk factors):

• Closed reduction under sedation
• Hip abduction orthosis 6-12 weeks
• Hip precautions 12 weeks minimum
• Success rate: 60-70% after first, 30% after second, less than 20% after third

OPERATIVE (Recurrent >2 episodes OR first with malposition/uncorrectable factors):

• Component revision if malposition
• Dual mobility liner (gold standard, 85-95% success)
• Soft tissue reconstruction if deficient
• GT advancement if abductor insufficiency

Surgical Decision Making and Options

Hierarchy of Treatment Options

OPTION 1: Isolated Liner/Head Exchange (Least invasive - if components well-positioned):

Indications:

• Cup and stem in safe zones
• Components stable and well-fixed
• No impingement on CT
• Recurrent instability despite good position (soft tissue/head size issue)

Technique:

• Remove head and liner
• Insert dual mobility liner (PREFERRED) OR constrained liner OR lipped liner
• Increase head size (32mm→36mm, 36mm→40mm) if adequate polyethylene thickness (>6mm)

Success Rate: 85-95% with dual mobility

OPTION 2: Acetabular Revision (Cup malposition/impingement/loose):

Indications:

• Cup outside safe zone (inclination or anteversion)
• Impingement from cup position/orientation
• Cup loosening

Technique:

• Remove cup (preserve bone)
• Ream to bleeding bone
• Reposition to safe zone: 40° inclination, 15-20° anteversion
• Multiple screws (posterior-superior quadrant)
• Insert dual mobility liner

Success Rate: 80-90% when combined with dual mobility

OPTION 3: Femoral Revision (Stem malposition/loose):

Indications:

• Stem excessive anteversion (>20°) or retroversion (<5°)
• Combined anteversion outside 25-40°
• Offset not restored
• Stem loosening

Technique:

• Extract stem (may need ETO if well-fixed)
• Revise to neutral version (10-15° anteversion)
• Restore offset (modular stem helpful)
• Large head (36-40mm) or dual mobility construct

Success Rate: 80-90% when version corrected

OPTION 4: Dual Mobility (GOLD STANDARD for Instability):

Mechanism:

• Large metal outer bearing (52-60mm) articulates with acetabular cup
• Small polyethylene inner bearing (28-32mm) articulates with femoral head
• Two articulations reduce dislocation by 50-80%

Advantages:

• Delays impingement (large outer bearing increases ROM)
• Preserves head-to-neck ratio (small inner head)
• Lower dissociation rate (1-2% vs 3-5% constrained)
• Less wear than constrained (metal-on-poly vs poly constraint)
• Less torque to fixation (vs constrained locking mechanism)

Evidence: Berry 2012 (0% re-dislocation in 140 revisions for instability), Guyen 2009 (0% at 10 years), Australian registry (reduced revision rate by 50%)

OPTION 5: Constrained Liner (Second-line if dual mobility unavailable):

Mechanism:

• Locking ring captures femoral head
• Prevents dislocation but limits ROM
• Uses polyethylene thickness for constraint

Disadvantages:

• Dissociation 3-5% (locking mechanism failure)
• Accelerated wear (constraint from polyethylene)
• Higher torque to fixation (loosening risk)
• Lower success (75-85% vs 85-95% dual mobility)

Use: Only if dual mobility not available or contraindicated

OPTION 6: Soft Tissue Reconstruction:

Capsular Repair/Reconstruction:

• Primary repair if adequate tissue
• Achilles allograft reconstruction if deficient (attach acetabular rim to femoral neck)
• Reduces re-dislocation when combined with component optimization

Greater Trochanteric Advancement:

• Indications: Abductor insufficiency (Trendelenburg positive)
• Technique: Osteotomize GT with abductors, advance distally 1-2cm, screw fixation
• Increases abductor moment arm and tension
• Protected weight bearing 12 weeks for union

Combined Anteversion Concept (Ranawat Triangle)

Principle: Cup anteversion + stem anteversion should total 25-40°

Examples:

• Cup 20° + Stem 10° = 30° (SAFE)
• Cup 30° + Stem 20° = 50° (HIGH - posterior instability risk)
• Cup 10° + Stem 5° = 15° (LOW - anterior instability risk)

Application: Correct BOTH components if combined anteversion outside 25-40°

Spinopelvic Parameters (Advanced Concept)

Relevance: Pelvic tilt changes cup orientation in standing vs sitting

High-Risk Patients:

• Spinal fusion (rigid spine, changes pelvic tilt)
• Spinal deformity (kyphosis, flatback)
• Elderly with loss of lumbar lordosis

Assessment: Lateral standing and sitting radiographs, measure pelvic tilt change

Management: May need cup anteversion adjustment (more anteversion if anterior tilt, less if posterior tilt)

Step-by-Step Operative Technique

Positioning and Approach Selection

Patient Position:

• Lateral decubitus for posterior approach (90% of primary THRs)
• Supine for anterior approach (if primary done anteriorly)

Approach Choice:

• Use PREVIOUS APPROACH to minimize soft tissue damage
• Posterior approach most common (extended posterior approach for revision)
• Anterior approach if primary done anteriorly

Fluoroscopy: Essential for intraoperative component position assessment

Surgical Exposure

Incision:

• Utilize previous incision, excise scar
• Extend proximally/distally as needed (revision requires longer exposure)

Posterior Approach Exposure:

1. Incise fascia lata over greater trochanter
2. Split gluteus maximus in line with fibers (protect superior gluteal nerve proximally)
3. IDENTIFY SCIATIC NERVE EARLY - vessel loop for protection (higher risk in revision, 3-7% palsy rate)
4. Tag short external rotators if present (often attenuated/absent)
5. Extensive capsulectomy - capsule usually deficient (PRIMARY PATHOLOGY)

Dislocation:

• Posterior: Flex 90°, adduct, internal rotate
• May be scarred in position, require extensive soft tissue release

Intraoperative Assessment (CRITICAL)

Component Position:

• Fluoroscopy: Measure cup inclination and anteversion
• Direct visualization: Stem version assessment
• Combined anteversion calculation

Impingement Testing:

• Reproduce dislocation mechanism (flex/adduct/IR for posterior)
• Identify neck-cup contact, liner rim impingement
• Check throughout ROM

Soft Tissue Quality:

• Capsule: Intact vs deficient vs absent
• Short external rotators: Present vs attenuated
• Abductors: Strong vs weak (Trendelenburg test)

Range to Dislocation:

• Test stability in all positions
• Identify safe vs unsafe ROM

Component Removal and Exchange

Acetabular Cup Removal (if indicated):

1. Remove modular liner
2. Loose cup: Usually levers out with curved osteotomes
3. Well-fixed cup: Circumferential osteotomes, stay on metal (preserve bone), may need Explant system
4. Remove all cement if cemented
5. Preserve bone stock (critical for revision)

Femoral Stem Removal (if indicated):

1. Remove head and liner
2. Loose stem: Extract with gentle impaction and extraction devices
3. Well-fixed stem: Extended Trochanteric Osteotomy (ETO)
   • Anterior 1/3 of femur for 10-12cm
   • GT attached to vastus lateralis
   • Repair with cerclage wires after stem insertion
4. DO NOT FORCE - will fracture femur
5. Remove cement (high-speed burr, osteotomes, ultrasonic)

Component Revision and Repositioning

Acetabular Revision:

1. Ream acetabulum to bleeding bone
2. Size for press fit (1-2mm under-ream)
3. Position to safe zone: 40° inclination, 15-20° anteversion
4. Use fluoroscopy to confirm position
5. Multiple screws (posterior-superior quadrant, avoid anterior/medial neurovascular structures)
6. Augments if bone loss (porous metal to fill defects, achieve 50% host bone contact)
7. Insert dual mobility liner (gold standard)

Femoral Revision:

1. Ream/broach canal to appropriate size
2. Select revision stem:
   • Adequate metaphyseal bone → modular stem (adjust offset and version independently)
   • Bone loss → extensively coated diaphyseal-fit stem
3. Position in neutral version (10-15° anteversion)
4. Restore offset (compare to contralateral)
5. If ETO performed, repair with 2-3 cerclage wires before final head
6. Large head (36-40mm) or dual mobility construct

Isolated Liner Exchange (if components well-positioned):

1. Dislocate hip, remove head
2. Remove modular liner (locking tabs, specialized tools)
3. Clean cup taper (remove debris, inspect for wear)
4. Insert dual mobility liner (large metal outer bearing locks into cup, small poly inner bearing for head)
5. Alternative: Constrained liner (locking ring) or lipped liner (elevated rim)
6. Insert large head (36-40mm if adequate poly thickness >6mm)

Soft Tissue Reconstruction

Capsular Repair/Reconstruction:

1. If adequate capsule: Primary repair to femoral neck/GT with heavy non-absorbable sutures (#2 or #5 Ethibond)
2. If inadequate capsule: Achilles tendon allograft reconstruction
   • Attach to acetabular rim (drill holes, secure with sutures)
   • Attach to femoral neck/GT (transosseous sutures)
   • Recreate anterior and posterior restraints

Short External Rotator Repair (Critical for posterior stability):

• Repair piriformis, gemelli, obturators, quadratus femoris to GT/posterior capsule
• Transosseous sutures if bone quality adequate
• May be attenuated - do best possible repair

Greater Trochanteric Advancement (if abductor insufficiency):

1. Osteotomize GT with attached gluteus medius/minimus
2. Advance distally 1-2cm (increases abductor moment arm and tension)
3. Fix with screws and washers OR cables
4. Protected weight bearing 12 weeks until union

Trial Reduction and Stability Testing (CRITICAL)

Stability Protocol:

1. Posterior stability (MOST IMPORTANT): 90° flexion + adduction + IR, apply posterior force - must be stable with firm endpoint
2. Anterior stability: Extension + ER + adduction - must remain reduced
3. Mid-range: 45° flexion, neutral rotation, abduction/adduction
4. Extremes of motion: Full flexion, extension, abduction, adduction - identify impingement
5. Shuck test: Quantify translation (should be minimal)

Rule: Must be STABLE throughout ROM with no impingement. If unstable, options:

• Increase head size
• Change to dual mobility or constrained
• Adjust component position
• Increase soft tissue tension

DO NOT ACCEPT INSTABILITY - will fail post-operatively

Closure

Layered Closure:

1. Capsule and short external rotators to femoral neck/GT (heavy non-absorbable sutures)
2. If GT osteotomy, confirm stable fixation (2-3 screws + washer OR cables)
3. Gluteus maximus fascia (close securely)
4. Deep fascia and subcutaneous layer
5. Skin (monofilament or staples)

Abduction Pillow: Place between legs

Drain: Consider if large dead space (remove 24-48hr)

Salvage Options for Failed Revision

Indications: Multiple recurrent dislocations despite optimal revision, unreconstructable bone loss, chronic infection

Girdlestone Resection Arthroplasty:

• Remove all components, accept shortened painful limb
• Patient: Elderly, low demand, walker dependent baseline
• Outcome: Significant functional limitation but pain relief

Hip Arthrodesis:

• Patient: Young (<40), unilateral, high demand, no hip/spine arthritis
• Position: 20-25° flexion, 0° adduction/abduction, neutral rotation
• Outcome: Stable painless hip but causes back/knee pain (rare, last resort)

Bipolar Hemiarthroplasty:

• Indication: Severe acetabular bone loss precludes stable cup
• Accepts higher dislocation rate but avoids complex acetabular reconstruction

Evidence-Based Outcomes

Treatment-Specific Success Rates

Non-Operative Management (First Dislocation):

• First episode: 60-70% success (Patel 2007)
• Second episode: Success drops to 30%
• Third episode: Success less than 20%
• Method: Closed reduction, hip abduction orthosis 6-12 weeks, precautions 12 weeks

Isolated Liner Exchange to Dual Mobility (Well-positioned components):

• Success: 85-95% (Berry 2012, Guyen 2009)
• Re-dislocation: 0-5%
• Least invasive option if components stable and in safe zones

Component Revision + Dual Mobility:

• Success: 80-90% (Philippot 2009)
• Re-dislocation: 10-20%
• Best for malpositioned components outside safe zone

Constrained Liner:

• Success: 75-85% (Lombardi 1991, Anderson 1994)
• Re-dislocation OR dissociation: 15-25%
• Dissociation rate: 3-5% (higher than dual mobility 1-2%)

Component Revision Alone (No dual mobility or constraint):

• Success: 60-75%
• Re-dislocation: 25-40%
• Inferior to dual mobility - no longer recommended as sole treatment

Dual Mobility Evidence Base

Berry 2012 (Landmark Study):

• 140 patients revised for instability with dual mobility
• 0% re-dislocation at mean 4.5 years
• Conclusion: Dual mobility is gold standard

Guyen 2009 (Long-term Follow-up):

• 113 primary THRs with dual mobility (high-risk patients)
• 0% dislocation at mean 10 years
• 5% cup revision for aseptic loosening
• Conclusion: Durable long-term solution

Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR):

• Dual mobility reduces revision rate for dislocation by 50% compared to standard bearings
• Increasingly used for primary THR in high-risk patients (prior hip surgery, neuromuscular disorders, spine disease)

Factors Affecting Outcomes

Better Prognosis:

• Correctable component malposition (just outside safe zone)
• Adequate soft tissue for repair
• Compliant patient
• First or second revision

Worse Prognosis:

• Neuromuscular disorders: Parkinson's 40-50% failure despite optimal surgery (Meek 2011)
• Dementia/cognitive impairment (non-compliance with precautions)
• Severe abductor deficiency (Trendelenburg despite GT advancement)
• Multiple prior revisions (bone stock loss limits options)
• Spinopelvic abnormalities (spinal fusion, flatback deformity)

Long-Term Surveillance

Follow-Up Schedule:

• 2 weeks: Wound check
• 6 weeks: Radiographs, advance activity
• 3 months: Radiographs, wean brace
• 6 months: Radiographs and function assessment
• 1 year: Radiographs
• Annually for life: Radiographs, function (Oxford Hip Score, HOOS)

Surveillance for:

• Late dislocation (can occur years later)
• Accelerated wear (dual mobility metal-on-poly, constrained poly)
• Component loosening (especially constrained liner - increased torque)
• Neuromuscular progression (Parkinson's, dementia)

Australian Context

AOANJRR Data (2023 Report):

• THA dislocation accounts for 15% of all revisions
• Dual mobility use increasing: 5% of primary THRs in 2022 (vs 1% in 2012)
• Dual mobility in revision: 40% for instability (vs 10% constrained, 50% standard)
• Re-revision rate lower with dual mobility (5-year: 8% dual mobility vs 15% constrained)

Medicare MBS Item Numbers:

• 49318: Revision of acetabular component
• 49319: Revision of femoral component
• 49321: Revision of both components
• 49327: Greater trochanteric osteotomy

PBS/eTG Antibiotic Guidelines:

• Prophylaxis: Cefazolin 2g (>120kg: 3g) within 60min of incision
• Penicillin allergy: Vancomycin 15mg/kg OR clindamycin 600mg
• Duration: Single dose (cease within 24hr)