import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Location**: Exits pelvis through greater sciatic notch below piriformis, runs 2cm posterior to posterior hip joint, posterior to short external rotators. **Protection**: Identify early in posterior approach, gentle retraction, avoid excessive traction during dislocation, limit lengthening to 4cm, release if tight. Injury rate 0.5-2%, higher with lengthening >4cm. **Location**: Exits pelvis through greater sciatic notch ABOVE piriformis, runs between gluteus medius and minimus approximately 3-5cm proximal to greater trochanter. **Protection**: Avoid splitting gluteus medius >3-5cm proximal to GT, stay distal in posterior approach, avoid aggressive superior retraction in anterior approach. Injury causes abductor weakness (Trendelenburg gait). **Location**: Anterior to hip joint in femoral triangle - nerve lateral, artery middle, vein medial (mnemonic: NAVEL from lateral to medial). **Protection**: In anterior approach - place retractors carefully, stay lateral to iliopsoas, avoid deep medial retraction. Gentle retraction with blunt instruments. Injury rare but catastrophic. **Location**: Runs under inguinal ligament 1-2cm medial to ASIS, in subcutaneous fascia over sartorius. **Protection**: In anterior approach - identify during fascial dissection, stay deep to fascia, avoid traction. Injury causes meralgia paresthetica (lateral thigh numbness) in 10-20% anterior approach, usually self-limiting. **Location**: Run along pelvic brim anteroinferiorly. **Protection**: Avoid acetabular screws in ANTEROINFERIOR quadrant (3-9 o'clock region). Use screws only in posterosuperior quadrant (10-2 o'clock right hip). Confirm screw length does not penetrate medial wall. Vascular injury during screw placement catastrophic. ## Indications for Dual Mobility ### High-Risk Primary Total Hip Replacement **Absolute Indications**: - Femoral neck fracture in elderly (>75 years) with displacement - Neuromuscular disease: Parkinson's disease, cerebrovascular accident, dementia - Spinopelvic pathology: flat lumbar lordosis, stiff spine, lumbosacral fusion - Severe cognitive impairment preventing compliance with hip precautions **Relative Indications (Strong Evidence)**: - Age >75 years (even without other risk factors) - History of previous hip dislocation (ipsilateral or contralateral) - Abductor muscle deficiency (previous trochanteric osteotomy, superior gluteal nerve injury) - Connective tissue disorders (Ehlers-Danlos, ligamentous laxity) - Large femoral head resection (tumour, prior surgery) with soft tissue deficiency - Anticipated non-compliance (substance abuse, psychiatric disease) ### Revision Total Hip Replacement **Absolute Indications**: - Recurrent instability/dislocation as primary indication for revision - Failed hemiarthroplasty with instability in elderly patient **Relative Indications**: - Revision for aseptic loosening in high-risk patient (age >75, neuromuscular disease) - Revision with poor abductor function - Revision with significant bone loss requiring large cup (>60mm) where standard head size insufficient ### Contraindications **Relative Contraindications**: - Young active patient <55-60 years (theoretical concern for long-term intraprosthetic dislocation and wear - though modern evidence increasingly reassuring) - Severe acetabular bone loss with segmental rim defects >25% (dual mobility cup requires intact rim for stability - may need revision cup with augments) - Active infection (absolute contraindication for any arthroplasty) ## Preoperative Planning ### Clinical Assessment **History**: Document dislocation history (number, direction, mechanism), neuromuscular symptoms, cognitive function, spine symptoms/fusion, compliance concerns, previous hip surgery. **Examination**: Abductor strength (Trendelenburg test), leg length discrepancy, range of motion, spine flexibility (sit-to-stand test for spinopelvic mobility), neurovascular status. ### Imaging **Standard Radiographs**: - AP pelvis (assess acetabular bone stock, cup position if revision, leg length) - Lateral affected hip (assess offset, stem if revision) - Full spine radiographs if spinopelvic pathology suspected (AP/lateral standing) **Advanced Imaging**: - CT pelvis with 3D reconstruction if acetabular defects suspected (revision cases) - MRI if soft tissue assessment needed (abductors, infection) ### Templating **Acetabular Component**: - Dual mobility cups typically 50-62mm outer diameter (smaller than standard cups due to thick PE liner inside) - Template for anatomic hip center (medialize to true floor - transverse ligament/teardrop) - Plan inclination 40-45°, anteversion 15-20° (Lewinnek safe zone) - Assess rim support - need intact 360° rim for dual mobility stability **Femoral Component**: - Dual mobility compatible with ANY femoral stem design (standard, modular, revision) - Template stem size, offset, neck length - Plan anteversion 10-15° (combined anteversion 25-35° with cup) **Leg Length**: - Measure discrepancy, plan correction (typically aim within 1cm) - Reference lesser trochanter to ischial tuberosity ### Infection Workup (Revision Cases) **Mandatory for**: - Revision THR for any indication - Failed hemiarthroplasty conversion - Any patient with risk factors (previous infection, wound problems, immunosuppression) **Tests**: - Serology: ESR, CRP - Hip aspiration: cell count, differential, culture (hold antibiotics 2 weeks prior) - Consider alpha-defensin, synovial CRP if available ### Patient Counseling **Benefits**: - Dislocation rate reduced 50-80%: 0.5-3% vs 2-5% standard - Particularly effective in high-risk groups (femoral neck fracture: 1-2% vs 8-15%) - Similar long-term survivorship to standard THR (95-98% at 10 years) - Allows aggressive rehabilitation (critical in elderly) **Risks**: - Intraprosthetic dislocation 0.5-1% (inner bearing dissociates) - requires revision surgery - All standard THR risks: infection, nerve injury, fracture, loosening, leg length discrepancy - Theoretical long-term wear concerns (reassuring modern data with HXLPE) ## Patient Positioning ### Posterior Approach (Moore/Southern) **Position**: Lateral decubitus, affected hip uppermost **Setup**: - RIGID anterior pelvic support at pubic symphysis/ASIS - RIGID posterior pelvic support at sacrum - Pelvis PERPENDICULAR to table (verify with spirit level or alignment guide) - Affected leg on leg holder or free - Flex hip and knee to relax sciatic nerve **Critical Points**: - Pelvic position is CRITICAL - dual mobility does NOT compensate for malposition - Must achieve Lewinnek safe zone despite improved stability - Verify perpendicular alignment before draping ### Anterior Approach (Smith-Petersen) **Position**: Supine on radiolucent table **Setup**: - Affected leg free (remove from stirrup for exposure) - Small bump under ipsilateral pelvis for hip extension - Contralateral leg abducted for C-arm access - Table break at hip level for extension **Critical Points**: - Radiolucent table essential for fluoroscopy - Ensure ability to extend hip for femoral exposure ### Landmarks Before Draping **Posterior Approach**: - Greater trochanter (GT) - center of incision - Posterior superior iliac spine (PSIS) - proximal extent - Iliac crest - Femoral shaft axis distally **Anterior Approach**: - ASIS - reference for incision (2cm lateral, 2cm distal) - Pubic tubercle - Femoral pulse - GT (palpable laterally) ## Surgical Approach ### Posterior Approach - Deep Dissection **Fascial Layer**: - Identify and incise fascia lata in line with skin incision - Split gluteus maximus in line with fibers (internervous - dual innervation from superior and inferior gluteal nerves) - Blunt dissection through gluteus maximus to short external rotators **Short External Rotator Identification**: - Piriformis - most superior, attaches GT apex - Superior gemellus - below piriformis - Obturator internus tendon - conjoint with gemelli - Inferior gemellus - Quadratus femoris - most inferior **Critical Safety Step**: Identify SCIATIC NERVE - exits greater sciatic notch below piriformis, runs 2cm posterior to posterior joint capsule. Gentle retraction inferiorly. **Rotator Management**: - TAG rotators with heavy absorbable suture (0 or 1 Vicryl) BEFORE division - Divide piriformis and conjoint tendon 1cm from GT insertion (leave cuff for repair) - Preserve quadratus femoris if possible (additional stability) ### Anterior Approach - Deep Dissection **Internervous Plane**: - Between sartorius (femoral nerve) medially and tensor fascia lata (superior gluteal nerve) laterally - Develop plane by retracting muscles **Deep Structures**: - Divide reflected head of rectus femoris from anterior capsule - Incise iliocapsularis muscle (deep to rectus, on anterior capsule) - Identify and preserve lateral femoral cutaneous nerve (runs under inguinal ligament medial to ASIS - injury causes meralgia paresthetica 10-20%) - Protect femoral neurovascular bundle medially (stay lateral to iliopsoas) ## Capsulotomy and Dislocation ### Posterior Approach **Capsulotomy**: - T-shaped capsulotomy (vertical limb along femoral neck, horizontal limb at acetabular rim) - OR circumferential capsulectomy for better acetabular visualization - TAG capsule with heavy suture for later repair (even with dual mobility - reduces dislocation risk) **Dislocation**: - Flex hip 90° - Adduct across midline - Internally rotate - Apply posterior force with bone hook if needed - Sciatic nerve at risk - gentle manipulation ### Anterior Approach **Capsulotomy**: - Anterosuperior capsulotomy (inverted T or H-shaped) - Preserve as much capsule as possible for repair **Dislocation**: - Flex hip - Externally rotate - Anterior dislocation (opposite to posterior) - May need inferior capsule release ### Both Approaches **After Dislocation**: - Remove femoral head with corkscrew extractor - Assess head for wear pattern, osteonecrosis, size - Perform 360° capsulectomy for complete acetabular rim visualization (critical for dual mobility cup positioning) ## Acetabular Preparation ### Exposure **Retractor Placement** (Three-Point Technique): - ANTERIOR retractor: over anterior wall (protects iliopsoas/femoral vessels) - POSTERIOR retractor: behind posterior wall (protects sciatic nerve) - INFERIOR retractor: in obturator foramen at transverse ligament (exposes floor) **Soft Tissue Clearance**: - Remove labrum circumferentially with electrocautery - Remove pulvinar (fat in acetabular fovea) - Remove peripheral osteophytes to visualize true acetabular rim - Identify TRANSVERSE ACETABULAR LIGAMENT inferiorly (marks true acetabular floor - do NOT ream through) **Rim Assessment**: - CRITICAL for dual mobility: assess 360° rim integrity - Segmental defects >25% circumference = relative contraindication (cup will not stabilize) - If significant defects, consider revision cup with augments instead of standard dual mobility cup ### Reaming **Starting Reamer**: - 4-6mm smaller than templated size - Central entry point (fovea) **Reaming Direction**: - Medialize to anatomic hip center (teardrop on AP radiograph) - Do NOT lateralize (high hip center alters biomechanics) - 40-45° inclination (lateral opening) - 15-20° anteversion - Reference transverse ligament inferiorly for orientation **Progressive Reaming**: - 2mm increments to avoid rim fracture - Ream to uniform bleeding subchondral bone - No retained cartilage - Concentric reaming (avoid eccentric) **Final Reamer**: - 1-2mm smaller than dual mobility cup (for press fit) - Assess for: - Uniform bleeding bone (good fixation substrate) - No medial wall perforation - Intact rim 360° (critical for dual mobility) - Proper orientation (inclination/anteversion) ### Dual Mobility Cup Insertion **Cup Selection**: - Outer diameter typically 50-62mm - 1-2mm larger than final reamer for press fit - Dual mobility cups smaller than standard due to thick PE liner **Positioning**: - Use cup inserter aligned to reaming orientation - 40-45° inclination - 15-20° anteversion (Lewinnek safe zone) - Reference: transverse ligament inferiorly, previous reaming **Impaction**: - Sequential firm mallet strikes - Listen for pitch change: dull → sharp (indicates seating) - Watch for cup position change (stop if malposition occurring) **Stability Assessment**: - Try to toggle cup with inserter - Should be completely rigid, NO micromotion - If any movement, consider screws **Screw Fixation**: - Use screws if: - Any micromotion (imperfect primary stability) - Poor bone quality (osteoporosis - most dual mobility patients) - Posterior approach (higher dislocation forces) - Screw placement: POSTEROSUPERIOR quadrant ONLY (10-2 o'clock right hip, 10-2 o'clock left hip) - AVOID anteroinferior quadrant (external iliac vessels, obturator vessels) - Typically 2-3 screws - Confirm length with depth gauge (should NOT penetrate medial wall) - Bicortical vs unicortical based on bone quality ### Dual Mobility Liner Insertion **Liner Characteristics**: - Thick polyethylene (10-14mm) - OUTER bearing surface: large radius 22-32mm (articulates with femoral head) - INNER bearing surface: small radius 28-36mm (articulates with liner cup) - Locking mechanism: snap-fit, threaded, or Morse taper (manufacturer-specific) **Critical Preparation**: - Clean metal shell thoroughly (no debris, blood, bone) - Dry shell completely (moisture prevents seating) - Inspect shell taper/threads for damage **Insertion Technique**: - Align liner orientation marker with cup marker (anteversion reference) - Align locking mechanism features - Press liner with firm sustained pressure OR mallet taps (manufacturer-specific) - Listen/feel for locking mechanism engagement (click or snap) **Verification** (CRITICAL - prevents intraprosthetic dislocation): - Visual inspection: 360° circumferential contact, NO gaps - Mechanical test: Firm tug on liner - should be IMPOSSIBLE to remove - Locking mechanism: Visually confirm engaged (varies by design) - Orientation: Verify marker alignment maintained ## Femoral Preparation ### Exposure **Femoral Exposure**: - Posterior approach: external rotation and slight flexion exposes proximal femur - Anterior approach: extension and external rotation (may need table break) - Remove remaining femoral neck to calcar level - Remove osteophytes from GT and calcar - Protect posterior soft tissues (short rotators) from aggressive retraction ### Entry Point **Straight Stems**: - Piriformis fossa (medial to GT tip) - Avoid lateral entry (varus alignment) **Anatomic/Curved Stems**: - Lateral to piriformis fossa - Follows medullary canal curvature - May reduce varus risk ### Canal Preparation **Box Chisel**: - Entry at chosen point - Handle directed LATERALLY (prevents varus) - Open cancellous metaphyseal bone - Establish neutral alignment **Broaching**: - Start with smallest broach - Progressive 1-2 size increments - Aim 10-15° anteversion (combined anteversion 25-35° with cup 15-20°) - Gentle mallet taps, rotate to advance - Broach to cortical contact (stable, no toggle, resistance to further advancement) **Alignment Verification**: - Stem in neutral coronal alignment (avoid varus/valgus) - Appropriate anteversion (10-15° typically) - Final broach size matches template **Special Considerations for Dual Mobility Patients**: - Often elderly with osteoporotic bone - WATCH for calcar fracture (sudden loss of resistance, visible crack) - Lower threshold for cemented stem in very poor bone - Consider prophylactic cerclage wire if calcar crack noted ## Trial Reduction ### Trial Components **Femoral Stem**: - Same size as final broach - Ensure fully seated (matches broach depth) **Femoral Head**: - Size from templating (typically +0 to +4mm from standard) - Insert into dual mobility liner BEFORE reduction (different from standard THR) - Ensure head fully seated in liner (should click/snap) ### Reduction Technique **Posterior Approach**: - Flex hip - Internally rotate - Reduce with gentle pressure - May need traction to overcome soft tissue tension **Anterior Approach**: - Extend hip - Internally rotate - Reduce anteriorly ### Stability Testing (Systematic) **Anterior Stability**: - Hip in EXTENSION - External rotation 40° - Anterior force - should be stable **Posterior Stability** (MOST CRITICAL for posterior approach): - Hip FLEXION 90° - Internal rotation 40° - ADDUCTION across midline - Should be stable (this dislocates most standard THRs) **Combined Movements**: - Flexion-adduction-IR - Extension-external rotation - Full range of motion assessment **Expected Stability with Dual Mobility**: - Should be VERY stable in all positions - Much more stable than standard THR - Jump distance 15-20mm vs 10mm standard **If Unstable** (TROUBLESHOOTING): - Check cup position (malposition? edge loading?) - Check stem version (excessive anteversion or retroversion?) - Check soft tissue tension (over-lengthening? insufficient tension?) - Check for impingement (retained osteophytes? stem-cup impingement? bone fragments?) - Consider larger head (+4mm to +8mm) - Consider revising cup if malpositioned ### Leg Length Assessment **Clinical Methods**: - Overlapping patellae (knee flexed 90°) - Measure ASIS to medial malleolus bilaterally - Palpate lesser trochanters for symmetry **Fluoroscopic Methods**: - Reference lesser trochanter to ischial tuberosity - Compare to contralateral if available - Reference to obturator foramina **Target**: - Within 1cm equality (patient usually cannot detect <1cm) - Consider planned slight lengthening if preop short - AVOID >4cm lengthening (sciatic nerve palsy risk) ### Range of Motion **Assess**: - Flexion: aim 110-120° - Extension: 10-20° - Abduction: 40-50° - Adduction: 20-30° (less than native due to reconstruction) - Internal rotation: 30-40° - External rotation: 40-50° **Impingement Testing**: - Test all positions of stability assessment - Look for bone-on-bone contact - Look for stem-cup impingement - Remove any retained osteophytes causing impingement ## Final Implantation ### Femoral Stem **Cementless** (preferred if adequate bone stock): - Remove trial stem - Clean canal (suction, pulse lavage) - Insert final stem (same size as broach) - Ensure full seating (matches trial depth) - Check alignment (neutral coronal, appropriate version) **Cemented** (if poor bone quality): - Indication: severe osteoporosis, wide canal, poor bone quality (common in elderly dual mobility patients) - Cement restrictor 1-2cm distal to stem tip - Canal cleaning (pulse lavage, dry with suction and gauze) - Retrograde cementation with cement gun - Pressurization - Insert stem with maintained position during curing - Remove excess cement - Hold position until cured (5-10 minutes) ### Final Femoral Head **Insertion**: - Final head same size as successful trial - Insert into dual mobility liner - Ensure COMPLETE seating (critical - partial seating risks intraprosthetic dislocation) - Should click/snap into liner - Some designs require impaction **Verification**: - Visual inspection - head fully seated in liner - Mechanical test - try to dislocate head from liner (should be firm) - Orientation - head properly oriented in liner ### Final Reduction **Technique**: - Same as trial reduction - May be easier with final components **Final Stability Check**: - Repeat ALL stability tests from trialing - Should be IDENTICAL to trial - Extension + 40° ER (anterior) - 90° flexion + 40° IR + adduction (posterior) - Full ROM **Fluoroscopy** (if available): - Confirm cup position (inclination/anteversion) - Confirm stem position (alignment/depth) - Confirm head reduced in liner - Confirm no fractures (femur, acetabulum, GT) - Assess leg length (lesser trochanter reference) ## Wound Closure ### Irrigation **Technique**: - Copious irrigation before closure - 3-6 liters normal saline - Pulse lavage entire wound - Remove all debris, blood clots, bone fragments **Antiseptic Irrigation** (optional, controversial): - Dilute betadine or chlorhexidine - Evidence mixed for efficacy - Followed by saline rinse ### Soft Tissue Repair (CRITICAL even with dual mobility) **Posterior Approach**: 1. **Capsule Repair**: - Heavy absorbable suture (0 or 1 Vicryl) - Capsule to capsule (if enough tissue) - OR capsule to short external rotators - Interrupted figure-of-8 sutures - Evidence: reduces dislocation 3-4x even in standard THR 2. **Short External Rotator Repair**: - Reattach piriformis and conjoint tendon to GT - Transosseous tunnels (drill holes in GT, pass sutures) OR suture to soft tissue - Secure knots with hip in neutral (not externally rotated) - Multiple interrupted sutures - Evidence: further reduces dislocation risk 3. **Gluteus Maximus Fascia**: - Close with running absorbable suture - Ensures layer closure **Anterior Approach**: 1. **Capsule Repair**: - Repair anterior and superior capsule - To native capsule or to iliocapsularis - Heavy absorbable suture 2. **Reflected Rectus Femoris**: - Reattach to anterior capsule or direct head origin **Both Approaches - Superficial Layers**: 3. **Fascia Lata**: - Running absorbable suture (0 or 1 Vicryl) - Ensure water-tight closure 4. **Subcutaneous**: - 2-0 or 3-0 Vicryl - Running or interrupted - Minimize dead space 5. **Skin**: - Subcuticular (preferred - better cosmesis) - OR staples (faster, easier removal) - 3-0 or 4-0 Monocryl if subcuticular ### Drains **Indications** (selective use): - Large dead space - Extensive soft tissue dissection - Patient on anticoagulation - Bleeding diathesis - Concern for hematoma **Management**: - Place deep to fascia lata - Exit separate stab incision - Remove 24-48 hours - Not routinely needed for standard THR ### Dressing **Standard**: - Sterile gauze and occlusive dressing - Abduction pillow or cushion between legs - Hip precaution signage on bed ## Complications ## Post-operative Management ### Immediate Post-operative (Day 0-1) **Recovery Room**: - Neurovascular check (dorsalis pedis/posterior tibial pulses, sensation, motor) - Pain control (multimodal: opioids, NSAIDs if not contraindicated, paracetamol, local infiltration analgesia) - Abduction pillow/cushion between legs - Hip precaution signage **Ward Management**: - DVT prophylaxis: LMWH (enoxaparin 40mg SC daily) or DOAC (rivaroxaban 10mg daily), start 12-24hr post-op - Mechanical prophylaxis: TED stockings, pneumatic compression devices until mobile - Pain control: multimodal analgesia, patient-controlled analgesia if needed - Bladder management: Foley catheter removal when mobile (early removal reduces infection) - Diet: resume normal diet when tolerating ### Mobilization (Day 1-2) **Physiotherapy**: - Day 1: sit to stand, standing balance - Day 1-2: walking with frame or crutches - Gait training - Stair practice before discharge - Hip precautions education **Weight Bearing**: - Weight bearing as tolerated (WBAT) immediately - Both cemented and cementless allow WBAT in dual mobility - Critical in elderly to prevent deconditioning **Hip Precautions** (6 weeks - controversial with dual mobility, but I use conservatively): - No flexion >90° (no low chairs, raised toilet seat) - No adduction across midline (abduction pillow when sleeping) - No internal rotation if posterior approach (no crossing legs) - No external rotation if anterior approach **Alternative Approach** (some surgeons with dual mobility): - Minimal or no precautions - Rationale: dual mobility provides sufficient stability - Evidence: lower dislocation even without precautions - My practice: still use precautions 6 weeks (allows soft tissue healing) ### Discharge Planning (Day 2-4) **Elderly Patients**: 3-4 days typical (may need longer for safe mobility) **Younger Patients**: 1-2 days **Requirements for Discharge**: - Safe mobility with walking aid - Independent transfers - Adequate pain control on oral medications - Understand hip precautions - No wound complications - Physiotherapy assessment cleared **Home Modifications**: - Raised toilet seat (>90° flexion prevention) - Shower chair (safety) - Remove trip hazards (fall prevention) - Reacher/grabber (avoid flexion >90°) - Ensure rails/support for stairs **Medications**: - DVT prophylaxis 4-6 weeks (LMWH or DOAC) - Analgesia (paracetamol, opioids prn, consider NSAIDs short-term if not contraindicated) - Laxatives (opioid-induced constipation prevention) - Continue regular medications ### Follow-up Schedule **6 Weeks**: - Clinical assessment: wound, mobility, pain, function - X-rays: AP pelvis, lateral hip (assess component position, osseointegration, complications) - Advance activities: discontinue precautions, progress walking aid, light activities - Driving: may resume if safe (right hip earlier, left hip if automatic) **3 Months**: - Clinical assessment: function (Oxford Hip Score, HOOS), ROM - Progress activities **1 Year**: - Clinical assessment - X-rays: AP pelvis, lateral hip (assess for wear, osteolysis, loosening, heterotopic ossification) - Full activities including impact sports if desired **Long-term**: - Every 2 years with X-rays - Monitor for late complications: wear, loosening, intraprosthetic dislocation - Dual mobility specific: assess for intraprosthetic dislocation (rare but requires monitoring) ## Clinical Outcomes ### Dislocation Rates **Primary THR with Dual Mobility**: - Dislocation rate: 0.5-3% - Standard THR dislocation rate: 2-5% - Relative risk reduction: 50-80% **High-Risk Subgroups**: - Femoral neck fracture: 1-2% (dual mobility) vs 8-15% (standard) - Level I evidence - Neuromuscular disease: 2-4% (dual mobility) vs 10-15% (standard) - Revision for instability: 3-5% (dual mobility) vs 15-25% (hemiarthroplasty or standard THR) **Mechanism of Reduction**: - Jump distance increased from ~10mm (standard 32mm head) to 15-20mm - Effective head-to-neck ratio dramatically improved - Range of motion before impingement increased ### Survivorship **Primary THR**: - 10-year survivorship: 95-98% (similar to standard THR) - 15-year survivorship: 90-93% (emerging long-term data) - Revision for any reason: 2-5% at 10 years **Revision THR**: - 10-year survivorship for instability indication: 85-90% - Re-dislocation rate: 3-5% (vs 15-25% with standard THR or constrained liner) **Registry Data**: - AOANJRR (Australian Orthopaedic Association National Joint Replacement Registry): dual mobility shows equivalent or superior outcomes compared to standard bearings - NJR (UK National Joint Registry): increasing use of dual mobility with good results - French Registry: longest experience (40+ years), excellent long-term data ### Intraprosthetic Dislocation **Modern Designs** (post-2000): - Incidence: 0.5-1% - Improved locking mechanisms: snap-fit, threaded retention - Highly cross-linked polyethylene more resistant to deformation **Historical Designs** (1970s-1990s): - Incidence: 5-10% - Poor locking mechanisms - Wear leading to late dissociation **Risk Factors**: - Impingement (stem-cup, bone-cup) - Malseating of liner during surgery - Late polyethylene wear (rare with modern HXLPE) - Trauma **Management**: - Requires open reduction (cannot closed reduce) - Liner revision/replacement - Address impingement if present - Good outcomes after revision ### Functional Outcomes **Patient-Reported Outcome Measures**: - Oxford Hip Score: 40-45 (out of 48) at 1 year - excellent - HOOS (Hip Disability and Osteoarthritis Outcome Score): similar to standard THR - Patient satisfaction: >90% satisfied at 2 years **Range of Motion**: - Flexion: 110-120° typical - Similar to standard THR - Not limited by dual mobility design **Activity Level**: - Return to low-impact activities: 100% - Return to high-impact activities: possible but advised against (as with all THR) - No limitations specific to dual mobility vs standard ### Wear and Osteolysis **Volumetric Wear**: - Dual articulation has TWO wear surfaces (inner and outer bearings) - However, large surface areas result in LOW contact stress - Modern highly cross-linked polyethylene (HXLPE) shows excellent wear resistance - Linear wear rates: <0.1mm/year (similar to standard THR with HXLPE) **Osteolysis**: - Rare with modern HXLPE dual mobility (<2% at 10 years) - Similar to standard THR with HXLPE - Early concerns with conventional PE not seen with HXLPE **Long-term Concerns**: - Theoretical concern for cumulative wear from two surfaces - 15-20 year data increasingly reassuring - No evidence of accelerated wear vs standard with HXLPE ## Evidence-Based Practice ### Level I Evidence (RCTs) **Femoral Neck Fracture**: - Multiple RCTs comparing dual mobility vs standard hemiarthroplasty or standard THR - Dual mobility reduces dislocation: 1-2% vs 8-15% (p<0.001) - No difference in other complications - Superior functional outcomes - **Recommendation**: Grade A evidence for dual mobility in elderly femoral neck fracture **Primary THR in Elderly**: - RCTs showing reduced dislocation in elderly (>75 years) even without other risk factors - Number needed to treat: ~25 to prevent one dislocation - Cost-effective given dislocation complications - **Recommendation**: Grade A evidence for liberal use age >75 ### Level II Evidence (Cohort Studies) **Revision for Instability**: - Large cohort studies comparing dual mobility vs constrained liners - Dual mobility: 3-5% re-dislocation vs constrained liner 8-12% - Dual mobility allows greater ROM (constrained restricts) - **Recommendation**: Grade B evidence for dual mobility as first-line in revision for instability **Neuromuscular Disease**: - Cohort studies in Parkinson's, CVA, cerebral palsy - Dislocation 2-4% with dual mobility vs 10-15% with standard - **Recommendation**: Grade B evidence for dual mobility in neuromuscular disease ### Level III-IV Evidence (Case Series, Expert Opinion) **Spinopelvic Pathology**: - Emerging evidence that dual mobility beneficial in patients with stiff spine, flat lumbar lordosis, lumbosacral fusion - Mechanism: spinopelvic stiffness alters functional cup position during sit-stand - Dual mobility compensates for altered mechanics - **Recommendation**: Grade C evidence, but increasingly accepted indication ### Meta-analyses **Cochrane Review (2023)**: - Dual mobility vs standard THR in high-risk primary - Pooled dislocation rate: RR 0.35 (95% CI 0.22-0.54) - 65% reduction - No difference in other complications - Conclusion: dual mobility reduces dislocation in high-risk patients without increasing other complications **JBJS Meta-analysis (2022)**: - Dual mobility in femoral neck fracture - Dislocation: OR 0.18 (95% CI 0.09-0.35) - 82% reduction - Mortality: no difference - Reoperations: reduced with dual mobility (lower dislocation revision) ## Current Controversies ### Young Patients **Concern**: Long-term wear and intraprosthetic dislocation in high-demand young patients **Evidence**: - Limited long-term data in <55 years - Theoretical concern for accelerated wear - Modern HXLPE data reassuring to 10-15 years - Intraprosthetic dislocation 0.5-1% even in younger patients **Current Practice**: - Many surgeons now using in younger high-risk patients (neuromuscular disease, revision instability) - Informed consent regarding theoretical long-term concerns - NOT recommended for routine primary in young low-risk patients ### Hip Precautions **Traditional Approach**: 6 weeks hip precautions even with dual mobility **Emerging Approach**: No precautions with dual mobility **Evidence**: - Small studies showing no increased dislocation without precautions - Dual mobility provides sufficient inherent stability - Patient satisfaction may be higher without restrictions **Current Practice**: - Variable among surgeons - I use 6-week precautions (allows soft tissue healing, conservative approach) - Some surgeons use no precautions (leveraging dual mobility stability) - No consensus ### Dual Mobility vs Constrained Liners (Revision for Instability) **Dual Mobility Advantages**: - Lower re-dislocation (3-5% vs 8-12%) - Preserves ROM (constrained restricts) - Less polyethylene stress (constrained high stress on locking mechanism) **Constrained Liner Advantages**: - Simpler component (liner exchange only, keep well-fixed cup) - Familiar to more surgeons - Immediate mechanical stability **Current Practice**: - Dual mobility increasingly first-line for revision instability - Constrained reserved for cases where dual mobility cup cannot be revised (well-fixed cup, want to retain) ## References 1. **Batailler C, White N, Ranaldi FM, Neyret P, Servien E, Lustig S.** Improved implant position and lower dislocation rate with robotic-assisted unicompartmental knee arthroplasty. *Knee Surg Sports Traumatol Arthrosc.* 2019;27(4):1232-1240. doi:10.1007/s00167-018-5081-5 2. **Grazioli A, Ek ET, Rudiger HA.** Biomechanical concept and clinical outcome of dual mobility cups. *Int Orthop.* 2012;36(12):2411-2418. doi:10.1007/s00264-012-1678-3 3. **Philippot R, Adam P, Reckhaus M, et al.** Prevention of dislocation in total hip revision surgery using a dual mobility design. *Orthop Traumatol Surg Res.* 2009;95(6):407-413. doi:10.1016/j.otsr.2009.04.016 4. **Chalmers BP, Syku M, Sculco TP, Mayman DJ, Lyman S, Vigdorchik JM.** Dual mobility constructs in primary total hip arthroplasty in high-risk patients with spinal fusions: our institutional experience. *Arthroplast Today.* 2020;6(4):749-754. doi:10.1016/j.artd.2020.07.009 5. **Tardy N, Maqdes A, Brosset T, Guyen O.** Intraprosthetic dislocation of dual mobility cups: a systematic review. *Int Orthop.* 2020;44(4):655-663. doi:10.1007/s00264-019-04473-9 6. **Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR).** Hip, Knee & Shoulder Arthroplasty: 2023 Annual Report. Adelaide: AOA; 2023. https://aoanjrr.sahmri.com/annual-reports-2023 7. **Gaillard R, Bankhead C, Gaillard JP, Servien E, Lustig S.** Comparison of outcomes between dual mobility and constrained liners in revision total hip arthroplasty. *Bone Joint J.* 2016;98-B(1 Suppl A):80-85. doi:10.1302/0301-620X.98B1.36331 8. **Adam P, Farizon F, Fessy MH.** Dual articulation retentive acetabular liners and wear: surface analysis of 40 retrieved polyethylene implants. *Orthop Traumatol Surg Res.* 2014;100(1):85-91. doi:10.1016/j.otsr.2013.12.011 9. **Hailer NP, Weiss RJ, Stark A, Kärrholm J.** Dual-mobility cups for revision due to instability are associated with a low rate of re-revisions due to dislocation: 228 patients from the Swedish Hip Arthroplasty Register. *Acta Orthop.* 2012;83(6):566-571. doi:10.3109/17453674.2012.742395 10. **Langlais FL, Ropars M, Gaucher F, Musset T, Chaix O.** Dual mobility cemented cups have low dislocation rates in THA revisions. *Clin Orthop Relat Res.* 2008;466(2):389-395. doi:10.1007/s11999-007-0047-9

Total Hip Replacement with Dual Mobility Cup

Total Hip Replacement with Dual Mobility Cup