import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Location**: Posterior to knee joint, exits popliteal fossa distally at soleus arch, intimately related to posterior capsule especially with flexion **Protection**: Avoid aggressive posterior capsule release or osteophyte removal. Knee flexion during posterior work brings vessels anteriorly. Retract gently, use finger palpation to locate pulse **Location**: Wraps around fibular neck laterally, 2-3cm distal to fibular head. Tethered at fibular tunnel. At highest risk with valgus correction greater than 20 degrees or limb lengthening greater than 2cm **Protection**: Limit lateral release to necessary structures only. Pie crust technique preserves integrity. If lengthening greater than 2cm anticipated, consider prophylactic fibular tunnel release **Location**: Medial femoral epicondyle to proximal medial tibia 6-8cm distal to joint line. Superficial layer (mobile) and deep layer (meniscotibial ligaments) **Protection**: Stage releases for varus deformity: Pes anserinus, superficial MCL, posteromedial capsule, deep MCL (last resort - avoid if possible as creates instability requiring CCK) **Location**: Lateral femoral epicondyle to fibular head. LCL is primary restraint. PLC includes popliteus, popliteofibular ligament, arcuate complex **Protection**: Pie crust technique for valgus knee - multiple small stabs with 15-blade through tight structures rather than formal release. Preserves some structural integrity and vascular supply **Location**: Quadriceps tendon inserts on superior pole patella. Patellar tendon inserts on tibial tubercle. At risk during eversion, especially in revision setting with scarring **Protection**: Gentle eversion with knee flexed. If tight, lateral release first, then quadriceps snip (45 degree oblique in vastus lateralis). Avoid forceful eversion - avulsion is catastrophic requiring reconstruction ## Comprehensive Workup and Planning ### Mandatory Infection Workup **Critical First Step**: RULE OUT INFECTION before any instability revision **Laboratory Studies**: - ESR (erythrocyte sedimentation rate) - greater than 30mm/hr suspicious - CRP (C-reactive protein) - greater than 10mg/L suspicious - Joint aspiration with cell count (greater than 3000 WBC suspicious), differential (greater than 80% PMNs suspicious), culture (hold 14 days for slow-growing organisms) - Alpha-defensin if equivocal (high sensitivity and specificity for infection) **Key Point**: Infection is a contraindication to instability revision. If infected, perform 2-stage revision protocol (resection, antibiotic spacer, reimplantation after eradication) ### Imaging Assessment **Standing Radiographs**: - **AP and lateral knee**: Component position, fixation (radiolucent lines), bone loss, joint space - **Long-leg alignment film** (hip-knee-ankle): Mechanical axis (normal 0° ± 3°), varus or valgus deformity, component alignment relative to mechanical axis - **Flexion weight-bearing PA**: True joint space, polyethylene wear, posterior femoral condyles - **Merchant view**: Patellar tracking, tilt, subluxation **CT Scan** (if available): - Component rotation assessment (femoral rotation relative to epicondylar axis, tibial rotation relative to tubercle and transmalleolar axis) - Bone loss quantification (Aori classification) - Useful for preoperative planning ### Alignment Assessment **Mechanical Axis**: - Normal: 0° ± 3° (line from femoral head center to ankle center passes through knee center) - Varus: mechanical axis medial to knee center (common in post-traumatic, osteoarthritis) - Valgus: mechanical axis lateral to knee center (inflammatory arthritis, bone loss) **Component Alignment**: - **Femoral coronal**: 5-7° valgus to anatomic axis, perpendicular to mechanical axis - **Femoral sagittal**: 0-3° flexion acceptable, extension causes tight flexion gap - **Femoral rotation**: Parallel to surgical epicondylar axis (gold standard), Whiteside's line, or 3° external rotation to posterior condylar axis - **Tibial coronal**: Perpendicular to mechanical axis (0° varus-valgus) - **Tibial sagittal**: 0-7° posterior slope (3-5° typical), matches femoral component - **Tibial rotation**: Centered on tibial tubercle, parallel to transmalleolar axis ### Clinical Stability Assessment **Examination Under Anesthesia**: - **Varus stress at 0° and 30° flexion**: MCL competence (greater than 5mm opening = incompetent) - **Valgus stress at 0° and 30° flexion**: LCL competence (greater than 5mm opening = incompetent) - **Lachman test**: Anterior translation (PCL assessment if CR design, cam-post function if PS) - **Posterior drawer**: Posterior translation (PCL if CR, post height if PS) - **Recurvatum test**: Hyperextension instability (posterolateral corner insufficiency) ### Gap Analysis (Inferred from Imaging and Exam) **Four Common Patterns**: 1. **Tight extension + loose flexion**: Femoral component flexed OR tibial slope excessive 2. **Tight flexion + loose extension**: Femoral component extended or undersized OR malrotation 3. **Balanced gaps**: Components well-positioned, polyethylene wear or ligament attenuation 4. **Global laxity**: Ligament insufficiency (MCL/LCL), requires constraint ### Etiology of Instability **Component Malposition** (most common correctable): - Rotation (femoral internal rotation, tibial external rotation) - Varus-valgus alignment - Flexion-extension position - Tibial slope (excessive or reverse) **Ligament Insufficiency**: - MCL (most critical for stability) - LCL and posterolateral corner - Global ligamentous laxity (Ehlers-Danlos, inflammatory arthritis) **Flexion-Extension Gap Mismatch**: - Component sizing errors - Soft tissue imbalance **Polyethylene Wear**: - Insert too thin from wear - Progressive instability **Extensor Mechanism Weakness**: - Quadriceps atrophy - Patellar maltracking - Giving way sensation ## Decision-Making Algorithm for Implant Selection ### Level 1: Posterior Stabilized (PS) **Indications**: - Intact MCL and LCL (competent collaterals) - Standard primary TKR - Stable revision cases - Minimal bone loss (Aori 1, 2A) **Mechanism**: - Cam-post substitutes for PCL - Post height 12-18mm (standard) - Relies on collateral ligaments for varus-valgus stability - Allows flexion-extension and rotation **Outcomes**: - 10-year survival: 90-95% - Best long-term results - Lowest loosening rate (2-5% at 5 years) ### Level 2: Posterior Stabilized with Lipped Insert **Indications**: - Intact MCL/LCL but mild laxity - Concern for anterior translation - Extensor mechanism weakness **Mechanism**: - Elevated anterior lip (6-8mm) provides anterior translation resistance - Standard cam-post mechanism - Minimal additional constraint **Outcomes**: - Similar to standard PS - Slightly increased contact stress on anterior lip ### Level 3: Constrained Condylar Knee (CCK) / Varus-Valgus Constrained **Indications**: - **ONE collateral incompetent** (MCL OR LCL, not both) - Global mild-moderate ligamentous laxity - Recurvatum deformity - Moderate bone loss (Aori 2B) **Mechanism**: - Taller post (15-20mm) - provides varus-valgus constraint - Deeper femoral box cut (add 3-5mm to standard PS box depth) - Wider intercondylar box - Thicker post resists varus-valgus and rotational stress - **NOT linked** - still relies on remaining competent collateral - Allows flexion-extension and rotation **Technical Requirements**: - Deeper box cut on femur (3-5mm additional resection) - May require stems for fixation (short stem 50-75mm) - Competent collateral on one side mandatory **Outcomes**: - 5-year survival: 85-90% - 10-year survival: 75-85% - Loosening rate: 5-10% at 5 years (higher than PS) - Reoperation: 10-15% ### Level 4: Rotating Hinge **Indications**: - **BOTH MCL and LCL incompetent** (no collateral support) - Massive bone loss (Aori 3) - Salvage situations (multiple failed revisions, infection, tumor resection) - Neuromuscular disorders (polio, muscular dystrophy) - Arthrodesis conversion **Mechanism**: - **LINKED articulation** via central axle connecting femur and tibia - Allows flexion-extension and rotation (15-20° typical) - Constrains varus-valgus and AP translation completely - Transfers all load to bone-implant interface (high stress) **Technical Requirements**: - **MANDATORY stems greater than 100mm** (usually 150mm) to handle torque - Stems press-fit (cementless) for load transfer - Bypass bone defects to diaphyseal fixation - Often requires metaphyseal cones or sleeves for bone loss **Outcomes**: - 5-year survival: 75-85% - 10-year survival: 60-75% - Loosening rate: 10-20% at 5 years, 20-30% at 10 years (highest of all) - Limited ROM: 0-90° typical (versus 0-115° for PS) - High infection risk: 5-10% - Reoperation: 20-30% - **Salvage procedure, not ideal solution** ### Level 5: Fixed Hinge (Obsolete) **Historical**: - Linked, NO rotation allowed - Extremely high loosening rate (greater than 50% at 5 years) - Catastrophic failures common **Current Use**: - Palliative only (elderly, non-ambulatory, limited life expectancy) - Fused knee conversion (consider rotating hinge instead) - **Generally avoided** - rotating hinge superior in all situations ### Constraint Decision Tree ``` Competent MCL + LCL → PS (standard) or PS-lipped (if mild laxity) ↓ Incompetent MCL OR LCL (one side) → CCK (taller post, NOT linked) ↓ Incompetent MCL AND LCL (both sides) → Rotating hinge (linked, stems >100mm) ↓ Massive bone loss (Aori 3) → Rotating hinge with long stems + cones/sleeves ``` ### Golden Rule of Constraint **Use MINIMUM constraint necessary**: - Higher constraint = higher stress at bone-implant interface - Higher stress = accelerated loosening and failure - Stepwise escalation: PS → CCK → Rotating hinge - Reassess intraoperatively - do not over-constrain based on preoperative plan alone ## Surgical Exposure and Revision Technique ### Positioning and Preparation **Patient Position**: - Supine on standard OR table - Tourniquet on thigh (inflate to 100mmHg above systolic, maximum 2 hours) - Leg holder or foot post for knee flexion/extension assessment - Ability to flex knee 90° and achieve full extension essential for gap assessment - Contralateral leg abducted for long-leg alignment assessment if needed **Surgical Approach**: - Medial parapatellar (95% of cases) - Extensile approaches if needed: tibial tubercle osteotomy, quadriceps snip, V-Y quadricepsplasty - Subvastus or midvastus rarely used in revision **Incision**: - Midline skin incision over previous scar (minimize skin necrosis risk) - 15-20cm depending on revision extent - Extend proximally to mid-patella, distally to tibial tubercle - If multiple previous scars, use most lateral (preserves medial blood supply) ### Surgical Exposure and Component Evaluation **Arthrotomy**: - Medial parapatellar through retinaculum and capsule - From quadriceps tendon to proximal tibia along medial border patella - Extend proximally into vastus medialis obliquus (VMO) fibers if needed **Patellar Eversion**: - Gentle eversion laterally with knee flexed - If tight, perform lateral retinacular release (careful - common peroneal nerve, lateral genicular vessels) - If still cannot evert: quadriceps snip (45° oblique cut in vastus lateralis 2-3cm above patella) OR V-Y quadricepsplasty (rare) - **AVOID patellar tendon avulsion** - devastating complication **Synovectomy and Scar Release**: - Extensive synovectomy (instability cases often thick scarring) - Release adhesions around components - Identify and protect neurovascular structures **Remove Polyethylene Insert**: - Extract insert (may need specialized extraction tools if locked mechanism) - Inspect wear pattern: anterior (tight extension), posterior (tight flexion), medial (varus), lateral (valgus) - Indicates maltracking or instability **Component Assessment**: **Femoral Component**: - Rotation (parallel to epicondylar axis? Whiteside's line? 3° ER to posterior condyles?) - Flexion-extension position (flexed causes tight extension, extended causes tight flexion) - Varus-valgus alignment - Fixation (stable or loose - radiolucent lines, subsidence, migration) - Bone quality and bone loss (Aori F1/F2/F3) **Tibial Component**: - Rotation (centered on tubercle? parallel to transmalleolar axis?) - Slope (0-7° posterior? excessive or reverse?) - Varus-valgus alignment - Fixation - Bone loss (Aori T1/T2A/T2B/T3) **Patella**: - Tracking, tilt, subluxation - Resurfaced or not - Component position if resurfaced - Bone stock ### Flexion-Extension Gap Assessment **Trial Stability Testing**: Insert trial polyethylene inserts of varying thickness (8mm, 10mm, 12mm, 15mm, 18mm) **Extension Gap** (knee at full extension): - Apply varus and valgus stress - Measure with spacer blocks or trial insert - Normal: 1-2mm opening bilaterally with firm endpoint - Tight: less than 1mm or no opening - Loose: greater than 3mm opening **Flexion Gap** (knee at 90° flexion): - Apply varus/valgus stress and anterior-posterior drawer - Measure gap - Normal: 1-2mm laxity with firm endpoint - Tight: less than 1mm or cannot flex 90° comfortably - Loose: greater than 3mm laxity or excessive AP translation **Goal**: EQUAL and BALANCED flexion-extension gaps with RECTANGULAR configuration (medial = lateral in both extension and flexion) ### Gap Balancing Scenarios and Solutions **Scenario 1: Balanced Gaps** (extension = flexion, medial = lateral) - Ideal situation - Retain components if well-fixed and positioned - Exchange insert to appropriate thickness for stability - Consider PS or CCK if mild asymmetry **Scenario 2: Tight Extension, Balanced/Loose Flexion** - **Causes**: Femoral component flexed, tibial slope excessive, extension space not released - **Solutions**: - Remove more distal femur (if femoral flexed or undersized) - Reduce tibial slope (revise tibial component) - Release posterior capsule and remove osteophytes **Scenario 3: Balanced/Loose Extension, Tight Flexion** - **Causes**: Femoral component extended or undersized, femoral rotation internal, tight posterior capsule - **Solutions**: - Downsize femoral component or revise to smaller size - Correct femoral rotation (revise femoral component) - Remove posterior femoral osteophytes - Release posterior capsule **Scenario 4: Global Laxity** (both flexion and extension loose) - **Causes**: Ligament insufficiency (MCL/LCL attenuated), bone loss, component undersizing - **Solutions**: - Thicker insert (up to 18-20mm if components well-positioned) - CONSTRAINED insert (CCK if one collateral intact, rotating hinge if both gone) - Revise components if malpositioned causing undersizing **Asymmetric Gaps** (medial ≠ lateral): **Varus Knee** (medial tight): - Stage releases: Pes anserinus → Superficial MCL → Deep MCL → Posteromedial capsule - Reassess after each stage - AVOID complete MCL release (creates instability requiring CCK) **Valgus Knee** (lateral tight): - Release LCL, popliteus, ITB, posterolateral capsule, lateral head gastrocnemius - **PIE CRUST technique**: Multiple small stabs with 15-blade rather than formal release - Preserves some stability and vascular supply - Release in extension with knee reduced ## Femoral and Tibial Component Revision ### Femoral Component Revision **Indications**: - Malposition (rotation, varus/valgus, flexion/extension) - Loosening - Undersized causing laxity - Bone loss requiring augments/stems **Component Removal**: - **Loose**: Levers out with osteotomes or extraction devices - **Well-fixed cementless**: Gigli saw cuts, reciprocating saw around ingrown areas, careful osteotomes - **Cemented**: High-speed burr to disrupt cement, osteotomes, ultrasonic cement removal - **Preserve bone**: Every millimeter counts for reconstruction **Bone Loss Assessment**: - **F1**: Intact metaphyseal bone - standard component - **F2A**: Damaged metaphyseal bone one condyle - small augment or cement - **F2B**: Defect greater than 5mm one condyle - modular augment + screws - **F3**: Severe damage both condyles - metaphyseal cone or sleeve + long stem **Femoral Preparation**: - Remove posterior osteophytes completely - Confirm rotation landmarks: - **Surgical epicondylar axis** (most reliable - medial sulcus to lateral epicondyle) - Whiteside's line (AP axis) - 3° external rotation to posterior condylar axis (if condyles intact) - Size femoral component (avoid undersizing or oversizing) **Femoral Rotation**: - **0° to surgical epicondylar axis** (gold standard, independent of bone loss) - Parallel to Whiteside's line (AP axis from trochlear groove to intercondylar notch) - 3° ER to posterior condylar axis (only if condyles symmetric and intact) **Femoral Augments**: - **Posterior** (most common - for flexion contracture release or bone loss) - **Distal** (for extension gap if excessive distal cut) - **Offset** (medial or lateral for varus/valgus deformity correction) - Screw fixation, then cement component onto augment **Femoral Stems**: - **Short stem** (50-75mm): F2B or rotational stability needed, cemented or press-fit - **Long stem** (100-150mm): F3, rotating hinge (greater than 100mm mandatory), press-fit, bypass defects - Intramedullary alignment guide ### Tibial Component Revision **Indications**: - Malposition (rotation, slope, varus/valgus) - Loosening - Bone loss - Undersized **Component Removal**: - **Loose**: Levers out - **Well-fixed cementless**: Oscillating saw, osteotomes - **Cemented**: Disrupt cement with burr/osteotomes, remove all cement - **Preserve bone** **Bone Loss Assessment** (Aori - most critical): - **T1**: Intact metaphyseal bone - standard tibial baseplate - **T2A**: One condyle or rim defect less than 5mm - cement or small augment - **T2B**: One condyle greater than 5mm - modular metal augments + screws + short stem - **T3**: Severe defect both condyles greater than 10mm OR damage below metaphysis - metaphyseal cones/sleeves + long stem **Tibial Preparation**: - Confirm rotation landmarks: - Tibial tubercle (component centered or slightly medial) - Medial 1/3 of tibial tubercle - Transmalleolar axis - Cut perpendicular to mechanical axis (coronal) - Posterior slope 0-7° (typically 3-5°) matching femoral component **Managing Tibial Bone Loss**: **T2A** (less than 5mm): - Cement fill or small metal augment - No stem required **T2B** (greater than 5mm one condyle): - Modular metal augments (blocks) - Screw fixation - Short stem (50-75mm) for rotational stability **T3** (severe, both condyles): - **Metaphyseal cones** (tantalum or titanium, press-fit into meta-diaphyseal bone, tibial component cemented onto cone) - **Metaphyseal sleeves** (metal cylinder in tibia, component cemented onto sleeve) - **Long stem** (100-150mm) press-fit for load transfer - Structural allograft (rare, for massive defects in young patients) **Tibial Stems**: - **Short stem** (50-75mm): T2B, cemented or press-fit, rotational stability - **Long stem** (100-150mm): T3 or rotating hinge, press-fit, bypass defects, load transfer to diaphysis **Tibial Slope**: - **0-7° posterior slope** (3-5° typical, match femoral) - **Excessive slope** (greater than 7°): tight extension, cam-jump in PS, patellar tracking issues - **Reverse slope**: recurvatum, posterior instability ### Insert Selection - Constraint and Thickness **Constraint Level Decision**: Test MCL and LCL with trial components in place: - **Varus stress** in extension and 30° flexion - if opens greater than 5mm medially → MCL incompetent - **Valgus stress** in extension and 30° flexion - if opens greater than 5mm laterally → LCL incompetent **Decision**: - **BOTH competent** (less than 5mm opening, firm endpoint) → PS insert (standard 12-18mm post) - **ONE incompetent** → CCK insert (taller 15-20mm post, wider box, deeper box cut) - **BOTH incompetent** → Rotating hinge (linked, stems greater than 100mm) **Insert Thickness**: - Trial inserts: 8mm, 10mm, 12mm, 15mm, 18mm, 20mm - Test stability in: extension (varus/valgus), flexion 90° (varus/valgus, AP), mid-flexion 30-60°, full ROM - **Goal**: Use thinnest insert that provides stability throughout ROM - **Avoid over-stuffing**: If need greater than 18-20mm, likely component malposition ### Final Implantation **Cement Preparation**: - Vacuum mix, pressurize, finger consistency - Most revisions use cement for tibial minimum **Sequence**: 1. **Augments/cones**: Position and fix first (screws for augments, press-fit for cones) 2. **Stems**: Insert stems (press-fit or cemented) 3. **Femoral component**: Cement onto augments/bone, confirm rotation (epicondylar axis) 4. **Tibial component**: Cement onto augments/cones/bone, confirm rotation (tubercle) and slope 5. **Polyethylene insert**: Lock into tibial baseplate (confirm audible click and visual seating) **Final Stability Testing**: - Extension (full? varus/valgus stable less than 2mm?) - Flexion 90-120° (stable?) - Mid-flexion 30-60° (often most unstable zone) - Patellar tracking (central through full ROM?) - ROM smooth 0-120° without binding? - Firm endpoint in all directions? - **DO NOT accept instability** - will fail **Fluoroscopy Confirmation**: - Component position - No fractures - Appropriate alignment ## Closure Technique and Post-operative Protocol ### Soft Tissue Balancing and Patellar Management **Final Soft Tissue Adjustments**: If asymmetric gaps persist despite component positioning: **Medial Release** (for varus knee): 1. Pes anserinus from proximal tibia 2. Superficial MCL from proximal tibia 3. Posterior capsule medially 4. Deep MCL (AVOID if possible - last resort) - Reassess after each stage **Lateral Release** (for valgus knee): - PIE CRUST technique - multiple small stabs with 15-blade - Through LCL, posterolateral capsule, ITB, popliteus - Preserves structural integrity versus formal release - Release lateral retinaculum if patellar tilt **Patellar Management**: **Tracking Assessment**: - "No thumbs" test - patella tracks centrally without manual guidance **Maltracking Causes**: - Component malrotation (femoral IR or tibial ER - most common) - Patella baja (joint line elevated) - Lateral retinacular tightness - Trochlear dysplasia **Treatments**: - Lateral release if tight (length-dependent, preserve superior lateral genicular) - Correct component malrotation (revise if needed) - Patellar resurfacing if not done and symptomatic (three-peg all-poly button, avoid overstuffing) ### Closure **Irrigation**: - Copious irrigation (remove debris, cement, bone particles) - 3-6 liters normal saline - Pulse lavage if available **Hemostasis**: - Meticulous hemostasis with electrocautery - Deflate tourniquet, identify and cauterize bleeders - Consider tranexamic acid (topical 1-2g in 100ml saline, 5 minutes dwell time) **Drain**: - Consider drain if large dead space or significant oozing - Remove 24-48 hours **Capsule**: - Repair medial parapatellar arthrotomy with interrupted absorbable sutures (0 or 1 Vicryl) - Ensure watertight closure to prevent extensor mechanism disruption - If quadriceps snip or V-Y performed, repair with non-absorbable sutures (Ethibond number 2 or number 5) **Subcutaneous**: - Close in layers with absorbable sutures - Reduce dead space **Skin**: - Monofilament suture or staples - Waterproof dressing **Dressing**: - Compressive dressing - Knee immobilizer for first 24-48 hours if concerned about extensor mechanism or instability ### Post-operative Protocol **Weight Bearing**: - **WBAT immediately** with walker/crutches for: - Standard revision with cement fixation - Well-fixed components retained - PS or CCK with good bone stock - **PWB (partial weight bearing) 6-12 weeks** for: - Bone grafts - Metaphyseal cones/sleeves (need ingrowth) - Moderate bone loss (Aori 2B/3) - **TDWB (toe-down weight bearing) 6-12 weeks** for: - Tibial tubercle osteotomy - Extensor mechanism repair - Severe bone loss with structural allograft **Range of Motion**: - Early passive ROM if stable construct - CPM machine 0-60° day 1, increase 10° daily to 0-90° by week 2 - Cautious ROM if rotating hinge or constrained (increased stress) - Active-assisted ROM week 2 - Avoid forced flexion or manipulation unless necessary **Physiotherapy**: - Day 1: Quad sets, straight leg raises, ankle pumps - Week 1-2: Passive ROM, gait training with assistive device - Week 2-6: Progressive strengthening (isometric → isotonic) - Week 6-12: Advanced strengthening, proprioception, balance - Wean assistive device by 6-12 weeks **Anticoagulation**: - Extended DVT prophylaxis (high-risk surgery) - LMWH (enoxaparin 40mg daily) or DOAC (rivaroxaban 10mg daily, apixaban 2.5mg BID) - Duration: 4-6 weeks minimum (versus 2 weeks for primary TKR) - Higher risk: revision, constrained implants, prolonged surgery, obesity **Antibiotics**: - 24-48 hours post-operatively - Institutional protocol (typically cefazolin or vancomycin) **Imaging**: - Post-operative AP and lateral knee X-rays (document component position, alignment) - Serves as baseline for surveillance **Surveillance Schedule**: - **6 weeks**: Wound check, X-ray (assess early stability, alignment) - **3 months**: X-ray, ROM assessment, function - **6 months**: X-ray, functional outcome scores - **1 year**: X-ray, comprehensive assessment - **Annually thereafter for life**: X-rays to monitor stability, alignment, radiolucent lines (greater than 2mm progressive concerning for loosening), osteolysis, polyethylene wear **Monitoring**: - Clinical: ROM, stability, pain, function (Oxford Knee Score, KOOS, WOMAC) - Radiographic: Component position, alignment, radiolucent lines, osteolysis, migration, subsidence, wear - **Constrained implants**: Closer surveillance (annual X-rays mandatory) due to higher loosening risk ## References 1. Vince KG, Abdeen A, Sugimori T. The unstable total knee arthroplasty: causes and cures. *J Arthroplasty*. 2006;21(4 Suppl 1):44-49. doi:10.1016/j.arth.2006.02.101 2. Lombardi AV Jr, Berend KR, Adams JB. A rational approach to treating the unstable total knee arthroplasty. *Instr Course Lect*. 2012;61:287-302. PMID: 22301240 3. Hossain F, Patel S, Haddad FS. Midflexion instability of the knee. *J Bone Joint Surg Br*. 2011;93-B(9):1165-1171. doi:10.1302/0301-620X.93B9.26482 4. Anderson JA, Baldini A, MacDonald JH, Pellicci PM, Sculco TP. Primary constrained condylar knee arthroplasty without stem extensions for the valgus knee. *Clin Orthop Relat Res*. 2006;442:199-203. doi:10.1097/01.blo.0000197771.41932.59 5. Barrack RL, Nakamura SJ, Hopkins SG, Rosenzweig S. Winner of the 2003 James A Rand Young Investigator's Award. Early failure of cementless mobile-bearing total knee arthroplasty. *J Arthroplasty*. 2004;19(7 Suppl 2):101-106. doi:10.1016/j.arth.2004.06.014 6. Whiteside LA. Soft tissue balancing: the knee. *J Arthroplasty*. 2002;17(4 Suppl 1):23-27. doi:10.1054/arth.2002.33264 7. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. *Clin Orthop Relat Res*. 1998;(356):144-153. doi:10.1097/00003086-199811000-00021 8. Mihalko WM, Whiteside LA, Krackow KA. Comparison of ligament-balancing techniques during total knee arthroplasty. *J Bone Joint Surg Am*. 2003;85-A Suppl 4:132-135. doi:10.2106/00004623-200300004-00016 9. Engh GA, Ammeen DJ. Bone loss with revision total knee arthroplasty: defect classification and alternatives for reconstruction. *Instr Course Lect*. 1999;48:167-175. PMID: 10098042 10. Gupta SK, Chu A, Ranawat AS, Slamin J, Ranawat CS. Osteolysis after total knee arthroplasty. *J Arthroplasty*. 2007;22(6):787-799. doi:10.1016/j.arth.2007.05.041

Total Knee Replacement Instability - Assessment and Constraint Ladder Management

Total Knee Replacement Instability - Assessment and Constraint Ladder Management