import { ComparisonTable, ContentSection, EvidenceCard, ExamCheatSheet, ExamPearl, ExamWarning, InfoCard, InfoCardGrid, MedicalImage, MnemonicCard, OnePagerSummary, SafetyAlert, Tab, Tabs, Timeline, TimelineItem, VivaScenario, VivaScenarioSection } from '@/components/mdx' {/* SECTION 1: ONE-PAGER SUMMARY */} {/* SECTION 2: EXAM WARNING */} **Only hip approach** with true internervous plane: gluteus maximus (inferior gluteal nerve) and gluteus medius (superior gluteal nerve). No muscle denervation occurs with proper technique. The **sciatic nerve** runs 1cm medial to the greater trochanter and posterior to the acetabulum. At highest risk during: posterior retractor placement, acetabular exposure, and leg lengthening. Injury causes foot drop and severe disability. **Capsular repair** with or without short external repair **reduces dislocation** from 7% to 2-3%. This is now standard of care. Use non-absorbable suture to reattach capsule and piriformis to femur. Post-op dislocation occurs with **combined flexion, adduction, internal rotation**. Highest risk: getting out of low chair, tying shoes, picking up objects. Patient education is critical for first 6-12 weeks. {/* SECTION 2.5: QUICK DECISION GUIDE */} {/* SECTION 3: MNEMONICS */} {/* SECTION 4: OVERVIEW AND BACKGROUND */} The posterior (Moore/Southern) approach to the hip is a **workhorse surgical approach** for total hip arthroplasty, hip fracture surgery, and revision procedures. First described by Austin Moore in 1957 and modified by Southern in 1980, it remains one of the most commonly used approaches worldwide. **Historical Context:** - **1957**: Austin Moore - original posterior approach with piriformis division - **1980**: Southern modification - piriformis preservation technique - **1990s-2000s**: Recognition of capsular repair importance for dislocation prevention - **2010s-present**: Enhanced recovery protocols with routine capsular repair **Australian Epidemiology (AOANJRR 2023):** - Posterior approach used in **35% of primary THAs** in Australia - Second most common approach (lateral 40%, anterior 20%) - No difference in long-term revision rates between approaches - Dislocation rates declining with routine capsular repair protocols **Key Advantages:** - **True internervous plane** - the only hip approach with no muscle denervation risk - Excellent acetabular exposure (especially posterior wall) - Extensile - can extend proximally or distally without neurovascular risk - Familiar to most orthopaedic surgeons worldwide **Key Disadvantages:** - Higher native dislocation rate (5-7%) if capsule not repaired - Sciatic nerve at risk (0.5-2% transient injury) - Posterior soft tissue disruption - Post-operative position restrictions (flexion + adduction + internal rotation) {/* SECTION 5: ANATOMY AND BIOMECHANICS */} ### The True Internervous Plane The posterior approach exploits the **only true internervous plane** to the hip joint: - **Gluteus maximus** (supplied by inferior gluteal nerve L5-S2) - **Gluteus medius** (supplied by superior gluteal nerve L4-S1) No muscle denervation occurs when the approach is performed correctly, as both muscles remain fully innervated. ### Short External Rotators (Superficial to Deep) 1. **Piriformis** - Key landmark; sciatic nerve runs below this muscle 2. **Superior gemellus** 3. **Obturator internus tendon** 4. **Inferior gemellus** 5. **Quadratus femoris** - Most inferior; sciatic nerve lies on its anterior surface ### Sciatic Nerve Anatomy The sciatic nerve is the **primary structure at risk**: - Exits pelvis through **greater sciatic foramen** (below piriformis in 85%) - Runs **1cm medial to greater trochanter** - Lies posterior to **acetabular posterior column** - Contains both **common peroneal** (lateral) and **tibial** (medial) divisions - Most at risk during: posterior retractor placement, acetabular reaming, leg lengthening ### Posterior Capsule and Stability The **posterior capsule** is the primary restraint to posterior dislocation: - Thickest at the posterior-superior quadrant - Iliofemoral ligament provides anterior restraint (not at risk posteriorly) - Capsular repair restores 60-70% of native posterior stability - Short external rotator repair adds additional posterior restraint {/* SECTION 5b: INTERNERVOUS PLANE */} ### The True Internervous Plane of the Posterior Approach The posterior approach to the hip is the **only hip approach with a true internervous plane**. This fundamental anatomical advantage distinguishes it from all other hip approaches. **Superficial Internervous Plane:** - **Laterally**: Gluteus maximus (inferior gluteal nerve, L5-S2) - **Medially**: Gluteus medius (superior gluteal nerve, L4-S1) These muscles are separated without denervating either. Gluteus maximus is split in the line of its fibers (not across), preserving its innervation. **Deep Internervous Plane:** There is no true deep internervous plane. The short external rotators share innervation from sacral plexus branches: - Piriformis: S1-S2 - Gemelli and obturator internus: L5-S1 - Quadratus femoris: L4-S1 These muscles are divided (Moore) or partially divided (Southern), not split along an internervous plane. **Clinical Significance:** - No abductor denervation (unlike lateral approaches) - Gluteus maximus function preserved - Lower risk of Trendelenburg gait than lateral approaches - Main limitation: posterior instability from capsular disruption (addressed by repair) **Examination Pearl:** When asked "What is the internervous plane of the posterior approach?" the answer is: "Gluteus maximus (inferior gluteal nerve) and gluteus medius (superior gluteal nerve). This is the ONLY true internervous plane to the hip." {/* SECTION 5c: PATIENT POSITIONING */} ### Lateral Decubitus Position for Posterior Approach **Standard Position:** The patient is placed in lateral decubitus with the operative hip uppermost. **Key Positioning Elements:** 1. **Pelvis Perpendicular to Floor** - Most critical positioning factor - Use pelvic positioner or sandbags anteriorly and posteriorly - Check with C-arm: obturator foramina symmetric, coccyx midline - Any pelvic tilt causes equivalent error in cup anteversion 2. **Lower Leg Positioning** - Knee flexed 90 degrees for comfort - Padded between legs (axillary roll and knee) - Secured to table 3. **Operative Leg Free** - Must move through full range during surgery - Needs to achieve flexion, adduction, and internal rotation for dislocation - Needs to be positioned for trial reduction and stability testing 4. **C-arm Access** - Position allows true AP and lateral fluoroscopy - Verify landmarks before draping **Common Positioning Errors:** | Error | Consequence | |-------|-------------| | Pelvis tilted forward | Cup appears more anteverted than actual (false security) | | Pelvis tilted backward | Cup appears more retroverted than actual (may overcorrect) | | Patient rolling backward | Makes posterior exposure easier but causes anteversion error | | Inadequate padding | Pressure injuries, nerve compression | **Examination Tip:** Always mention pelvic position when describing the posterior approach. Examiners expect you to recognize that pelvic tilt is the most common cause of cup malposition. {/* SECTION 5d: PATHOPHYSIOLOGY */} ### Biomechanical Rationale for Posterior Approach **Native Hip Stability Mechanism:** The hip joint relies on several stabilizers that must be understood when selecting and performing surgical approaches: 1. **Bony containment**: Deep acetabulum with 170° arc of coverage 2. **Labrum**: Increases acetabular depth by 21%, adds suction seal 3. **Capsule**: Posterior capsule is thickest and most critical for stability after posterior approach 4. **Ligamentum teres**: Minor stabilizer, typically sacrificed in arthroplasty 5. **Muscular stabilizers**: Short external rotators provide dynamic posterior stability **Pathophysiology of Posterior Dislocation:** After posterior approach THA, instability occurs through a specific mechanism: - **Combined motion vector**: Flexion + adduction + internal rotation brings femoral head toward posterior-inferior capsular defect - **Critical angle**: Risk increases dramatically when hip flexed beyond 90° with adduction and IR - **Capsular deficiency**: Untreated posterior capsulotomy creates path of least resistance - **Loss of short external rotators**: These muscles provide dynamic posterior restraint when intact **Why Capsular Repair Works:** The posterior capsule contributes approximately 60-70% of posterior hip stability. Repair addresses: - Recreates mechanical barrier to posterior translation - Restores proprioceptive feedback from capsular receptors - Allows early mobilization without strict hip precautions - Reduces dislocation rate from 5-7% to 2-3% **Sciatic Nerve Vulnerability:** The sciatic nerve is at risk due to its anatomical course: - Exits pelvis through greater sciatic foramen below piriformis - Runs 1cm medial to greater trochanter tip - Courses posterior to short external rotators and posterior capsule - Vulnerable to direct injury, retractor compression, and leg lengthening stretch {/* SECTION 6: CLASSIFICATION SYSTEMS */} ### Moore vs Southern Approach Variants | Feature | Moore Approach | Southern Approach | |---------|----------------|-------------------| | Piriformis | **Divided** | **Preserved** | | Short externals | All divided | Gemelli + obturator only | | Exposure | Slightly better | Slightly less | | Theoretical stability | Less (piriformis divided) | More (piriformis intact) | | Evidence | Extensive | Limited | | Current practice | Common | Less common | **Current consensus**: Capsular repair is **more important** than piriformis preservation for preventing dislocation. Either approach acceptable if capsule repaired. ### Lewinnek Safe Zone for Cup Position The **Lewinnek safe zone** defines optimal cup position to minimize dislocation: | Parameter | Safe Range | Optimal | |-----------|------------|---------| | Inclination | 30-50° | 40° | | Anteversion | 5-25° | 15-20° | ### Combined Anteversion Concept **Combined anteversion** = Femoral anteversion + Acetabular anteversion | Combined Anteversion | Risk | |---------------------|------| | 25-40° | **Safe range** | | Under 25° | Increased **anterior dislocation** risk | | Over 40° | Increased **posterior dislocation** risk | For posterior approach, target **combined anteversion 30-40°** to reduce posterior dislocation risk. ### Sciatic Nerve Injury Patterns | Injury Type | Mechanism | Prognosis | |-------------|-----------|-----------| | Neuropraxia | Retractor pressure, traction | **Good** (60-80% recovery) | | Axonotmesis | Stretch, compression | **Variable** (months-years) | | Neurotmesis | Laceration, transection | **Poor** (permanent deficit) | ### Division Affected | Pattern | Clinical Finding | Significance | |---------|------------------|--------------| | Common peroneal | Foot drop, lateral numbness | **Most common** (lateral division) | | Tibial | Ankle plantarflexion weakness | Less common | | Complete | Both above | Severe injury | {/* SECTION 7: CLINICAL ASSESSMENT */} ### Pre-operative Assessment **History:** - Primary complaint: Hip pain (groin, lateral, posterior), stiffness, limp - Duration and progression of symptoms - Previous hip surgery or injections - **Dislocation risk factors**: Age over 70, female, neurological disorder, cognitive impairment, prior hip surgery - Medical comorbidities affecting anesthesia and rehabilitation **Physical Examination:** - **Gait**: Antalgic, Trendelenburg (abductor weakness) - **Range of motion**: Flexion, extension, abduction, adduction, internal and external rotation - **Limb length**: Measure from ASIS to medial malleolus - **Neurovascular status**: Document pre-operative nerve function (especially if revision) - **Skin quality**: Previous incisions, skin condition **Pre-operative Nerve Documentation:** Critical for posterior approach given sciatic nerve risk: - Ankle dorsiflexion (L4-L5, deep peroneal) - Great toe extension (L5) - Ankle plantarflexion (S1-S2, tibial) - Sensation in sciatic distribution **Always document pre-operative nerve function** before posterior approach THA. If patient has pre-existing foot drop or numbness, this must be noted. Post-operative neuropraxia rate is 0.5-2% even with perfect technique - defending against medicolegal claims requires thorough pre-operative documentation. {/* SECTION 8: INVESTIGATIONS */} ### Pre-operative Imaging **Radiographs (mandatory):** - **AP pelvis**: Assess acetabular morphology, femoral offset, leg length, osteophytes - **Lateral hip**: Femoral version, anterior osteophytes, femoral bow - **Templating**: Pre-operative planning for implant size and positioning **CT Scan (selective indications):** - Significant bony deformity (DDH, previous trauma) - Revision surgery - assess bone stock - Complex acetabular morphology - 3D assessment of version and bone loss ### Pre-operative Templating | Parameter | Measurement | Goal | |-----------|-------------|------| | Cup size | Acetabular diameter | 2mm larger than native | | Cup position | Inclination/anteversion | 40° / 15-20° | | Stem size | Femoral canal diameter | Fill canal metaphyseally | | Femoral offset | Contralateral comparison | Restore to native | | Leg length | Contralateral comparison | Equal or slightly longer (under 10mm) | | Neck osteotomy | Lesser trochanter reference | Match template level | ### Laboratory Investigations Standard pre-operative workup: - FBC, U&E, coagulation studies - Group and hold (or crossmatch for revision) - ECG (if indicated by age/comorbidity) - Infection markers if concern (ESR, CRP, joint aspiration if indicated) {/* SECTION 9: MANAGEMENT ALGORITHM */} **Posterior dislocation:** - **Incidence**: 2-3% (with repair), 5-7% (without repair) - **Direction**: Posterior (flexion + adduction + internal rotation) - **Timing**: 80% in first 3 months, risk persists lifelong - **Prevention**: Capsular repair, patient education, avoid risk positions - **Treatment**: Closed reduction (first time), revision surgery if recurrent (2+ dislocations) **Sciatic nerve palsy:** - **Incidence**: 0.5-2% (transient), 0.1-0.5% (permanent) - **Presentation**: Foot drop (common peroneal division), numbness lateral leg - **Risk factors**: Revision surgery, DDH, excessive lengthening (over 4cm), direct trauma - **Recovery**: 60% recover by 1 year if neuropraxia, poor if neurotmesis - **Management**: Ankle-foot orthosis (AFO), physiotherapy, nerve exploration if progressive **Heterotopic ossification:** - **Incidence**: 20-40% (radiographic), 5-10% (symptomatic) - **Risk factors**: Male gender, DISH, hypertrophic osteoarthritis, previous HO - **Prevention**: Indomethacin 25mg TDS × 6 weeks OR single-dose radiation (7 Gy) - **Treatment**: Excision if symptomatic after maturation (12+ months) The **risk position** after posterior approach THA is: **Flexion beyond 90° + Adduction + Internal Rotation**. Common scenarios: getting out of low chair, tying shoes, picking object off floor, sitting on toilet. Patient education to avoid this position for 6-12 weeks is critical. {/* SECTION 14: POSTOPERATIVE CARE */} ### Immediate Post-operative Period (Day 0-2) **Day of Surgery:** - Weight bearing as tolerated with walking frame - DVT prophylaxis: Rivaroxaban 10mg daily × 5 weeks OR enoxaparin OR aspirin - Pain management: Multimodal (paracetamol + NSAID + opioid PRN) - Ice to surgical site **Mobilization Protocol:** | With Capsular Repair (Modern) | Without Capsular Repair (Historical) | |-------------------------------|--------------------------------------| | No hip precautions | Strict hip precautions | | Sit on normal chair | Raised toilet seat, cushion | | Bend to floor if able | Avoid flexion over 90° | | Cross legs if comfortable | No leg crossing | | Enhanced recovery | Traditional pathway | **DVT Prophylaxis (Australian Guidelines):** - Chemical: Rivaroxaban 10mg daily × 35 days OR Enoxaparin 40mg daily OR Aspirin 100-150mg daily - Mechanical: TED stockings, intermittent calf compression intra-operatively - Early mobilization: Most important factor ### Week 1-6 - Progressive gait training: Frame → crutches → single stick → unaided - Hip strengthening exercises (abductors, flexors, extensors) - Range of motion exercises (within precautions if applicable) - Wound review at 2 weeks - Follow-up radiographs ### Week 6-12 - Increase activity level - Driving typically allowed at 6 weeks - Return to low-impact activities (swimming, cycling, golf) - If capsule repaired: No restrictions - If capsule not repaired: Continue precautions until 12 weeks {/* SECTION 15: OUTCOMES AND PROGNOSIS */} {/* MISSING IMAGE: /images/topics/hip-posterior-approach-moore-southern/web-sourced/1-fig-3-probability-of-dislocation-and-revision-afte.png {/* MISSING IMAGE: /images/topics/hip-posterior-approach-moore-southern/web-sourced/1-fig-3-probability-of-dislocation-and-revision-afte.png */} */} ### Short-term Outcomes (under 2 years) **Dislocation:** - With capsular repair: 2-3% - Without capsular repair: 5-7% - 80% occur in first 3 months - Most can be managed with closed reduction **Functional Recovery:** - 90% satisfied with pain relief by 3 months - Full recovery of function: 6-12 months - Return to driving: 4-6 weeks - Return to golf/swimming: 3-6 months ### Long-term Outcomes (AOANJRR Data) **Revision Rates:** - 5-year revision rate: 5% (similar across approaches) - 10-year revision rate: 7-8% - 15-year revision rate: 10-12% - No difference between posterior, lateral, or anterior approaches **Causes of Revision:** | Cause | Percentage | |-------|------------| | Loosening | 25% | | Infection | 20% | | Dislocation/instability | 18% | | Fracture | 12% | | Other | 25% | ### Prognostic Factors **Good Prognosis:** - Primary OA indication - Age 60-80 - BMI under 30 - No cognitive impairment - Good soft tissue quality - Experienced surgeon with capsular repair **Poorer Prognosis:** - Revision surgery - Neuromuscular disorder - Cognitive impairment - Age over 80 or under 50 - BMI over 35 - AVN or DDH {/* SECTION 16: EVIDENCE BASE */} {/* REMOVED: 3-statistical-analysis-of-dislocation-between-ha-hem.png */} {/* SECTION 9: VIVA SCENARIOS */} {/* SECTION 10: MCQ PRACTICE */} **Q: What is the internervous plane for the posterior approach to the hip?** A: Between **gluteus maximus (inferior gluteal nerve)** and **gluteus medius (superior gluteal nerve)**. This is the only hip approach with a true internervous plane. **Q: Where does the sciatic nerve run in relation to the greater trochanter?** A: Approximately **1cm medial to the greater trochanter** and posterior to the acetabulum. It exits the pelvis below the piriformis muscle (85% of patients). **Q: What is the effect of capsular repair on dislocation rate after posterior approach THA?** A: Capsular repair **reduces dislocation rate** from approximately **7% to 2-3%**. This is now considered standard of care for posterior approach. **Q: What combination of hip positions causes posterior dislocation after posterior approach THA?** A: **Flexion (over 90 degrees) + Adduction + Internal Rotation**. Common scenarios: getting out of low chair, tying shoes, picking up objects from floor. **Q: What is the difference between the Moore and Southern modifications of the posterior approach?** A: **Moore approach**: Divides piriformis and all short external rotators. **Southern approach**: Preserves piriformis, divides only obturator internus and gemelli. Both require capsular repair - more important than piriformis preservation. {/* SECTION 11: AUSTRALIAN CONTEXT */} **AOANJRR Data:** - Posterior approach: **35% of primary THAs** in Australia - Second most common approach (lateral is 40%, anterior 20%) - Dislocation rates declining with routine capsular repair protocols - No difference in long-term revision rates between approaches **Training implications:** - Essential skill for Orthopaedic exam and practice - Most Australian fellowship programs teach posterior as one of two primary approaches - Understanding of both posterior and lateral approaches expected **Enhanced Recovery Protocols:** - Australian units increasingly adopting enhanced recovery (ERAS) - Posterior approach with capsular repair compatible with ERAS - Reduced or no hip precautions if capsule repaired For Orthopaedic clinical and viva exam, you must know: (1) True internervous plane (Gmax vs GM), (2) Sciatic nerve location and protection, (3) Moore vs Southern modifications, (4) **Mandatory capsular repair** to reduce dislocation, (5) Dislocation risk position (flexion + adduction + IR), (6) Management of sciatic nerve palsy and recurrent dislocation. {/* SECTION 12: EXAM CHEAT SHEET */}

Hip Posterior Approach (Moore/Southern)

Hip Posterior Approach (Moore/Southern)