import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Primary Indications:** - Aseptic loosening with AORI Type 2-3 bone loss - Polyethylene wear with femoral osteolysis - Component malposition (rotation, flexion, sizing) - Instability not correctable with poly exchange - Periprosthetic fracture with loose component - Staged revision for periprosthetic joint infection **AORI Femoral Classification:** - **Type 1**: Intact metaphysis - standard revision stems - **Type 2A**: Damaged single condyle - augments needed - **Type 2B**: Damaged both condyles - multiple augments - **Type 3**: Severe metaphyseal deficiency - sleeves, cones, or allograft **Constraint Selection Algorithm:** - **PS (Posterior Stabilized)**: PCL deficient but collaterals intact, balanced gaps - **CCK (Constrained Condylar Knee)**: MCL insufficiency, varus/valgus laxity greater than 10mm, moderate gap mismatch - **RHK (Rotating Hinge Knee)**: Severe instability, collateral deficiency, cannot balance gaps - **Fixed Hinge**: Salvage only, arthrodesis alternative **Stem Requirements by Constraint:** - PS: Short stem (50-75mm) acceptable - CCK: Stems required (75-100mm) for load transfer - RHK: Long stems mandatory (100-150mm) **Rotation Reference Methods:** 1. **Transepicondylar Axis**: Gold standard, 0 degrees rotation to this line - Difficult to identify in revision with bone loss 2. **Posterior Condylar Axis**: 3 degrees external rotation - Easiest but variable in valgus knees 3. **Whiteside Line (AP Axis)**: Perpendicular to this - Most reliable in revision with posterior bone loss 4. **Tibial Axis**: Match femoral to balanced tibial cut **Consequences of Malrotation:** - Internal rotation: Patellar maltracking, medial poly wear - External rotation: Lateral poly wear, PCL tightness **Location**: Posterior to distal femur in popliteal fossa. Separated from posterior capsule by fat pad. Risk during posterior cement removal and posterior capsule release. **Location**: Anterior to femur in Hunter canal, transitioning to popliteal vessels at adductor hiatus. Risk with anterior cortical perforation during reaming. **Location**: Wraps around fibular neck laterally, 1-2cm distal to fibular head. Risk with valgus correction, lateral release, or leg lengthening greater than 3cm. **Location**: Superficial and deep fibers from medial epicondyle to proximal tibia. Risk during medial dissection, epicondylar osteotomy, or aggressive cement removal. **Location**: Lateral epicondyle to fibular head. Risk during lateral releases, lateral condyle augment placement, or lateral approach extension. **Patient Position**: Supine on radiolucent table with leg holder or lateral post. Tourniquet applied to upper thigh. Regional or general anesthesia with DVT prophylaxis initiated pre-operatively. **Surgical Approach**: Medial parapatellar arthrotomy via previous incision, with extensile exposure options if needed (quadriceps snip, V-Y turndown, or tibial tubercle osteotomy for severe stiffness). **Pre-operative Planning Checklist:** - Review long-leg alignment films for mechanical axis - CT scan for component rotation assessment - Measure femoral canal diameter for stem sizing - AORI classification from radiographs - Have augments, stems, and constraint options available - Aspiration to exclude infection (CRP, ESR, synovial WBC) ### Step 1: Exposure and Arthrotomy Exposure and Arthrotomy: Identify and excise previous scar (use most lateral if multiple scars). Develop full-thickness medial and lateral skin flaps. Perform medial parapatellar arthrotomy extending 5-6cm proximal to superior pole of patella through quadriceps tendon. Excise hypertrophic synovium, scar tissue, and adhesions. Attempt patellar eversion with knee flexion. **Technical Tip**: EXAM KEY: In stiff knees with limited flexion (less than 70 degrees), start with lateral gutter release before attempting eversion. Score adhesions in suprapatellar pouch. If patella will not evert safely, perform quadriceps snip (45 degree angle from lateral border of VMO proximally) - adds 10-15 degrees flexion. V-Y turndown for severe stiffness (risk of avulsion). TTO is last resort for ankylosed knees. - Patellar tendon avulsion during forced eversion in stiff knee - Patella fracture through thin or osteopenic bone - Quadriceps tendon rupture with aggressive manipulation - MCL damage during medial dissection ### Step 2: Polyethylene Insert Removal Polyethylene Insert Removal: Remove polyethylene insert first to gain access to femoral component. Flex knee to 90 degrees and use curved osteotomes or dedicated extraction instruments to disengage locking mechanism. Deliver insert anteriorly. Inspect for wear patterns (anterior, posterior, medial, lateral), backside wear (micromotion), and delamination. **Technical Tip**: EXAM KEY: Document wear pattern systematically - asymmetric wear suggests instability or malalignment. Anterior wear in PS design suggests cam-post impingement or excessive posterior slope. Medial wear suggests varus malalignment or MCL insufficiency. Send explanted components for analysis. Photograph for medicolegal documentation and analysis. - Damaging femoral component surfaces if planning selective revision - Losing locking mechanism fragments into joint - Scratching well-fixed components during extraction ### Step 3: Assessment of Femoral Component Fixation Assessment of Femoral Component Fixation: Use thin flexible osteotomes to gently test femoral component stability around periphery (distal, anterior, posterior chamfers). Assess for micromotion, tilting, or gross loosening. Compare to pre-operative radiographs showing radiolucent lines, osteolysis, or subsidence. If well-fixed and well-positioned, may consider retaining and revising only tibial side. **Technical Tip**: EXAM KEY: Indications to revise well-fixed femoral component: malalignment (greater than 3 degrees varus/valgus, greater than 10 degrees rotation), flexion/extension mismatch, osteolysis requiring access, polyethylene wear into component, need for higher constraint, or instability not correctable with tibial revision alone. If retaining: clean surfaces thoroughly, check for damage or metallosis. - Creating iatrogenic bone defects while assessing stable component - Propagating occult fracture lines during manipulation - Missing subtle loosening on clinical exam ### Step 4: Femoral Component Removal Femoral Component Removal: Use thin flexible osteotomes to disrupt cement-bone or bone-implant interface. Work systematically: anterior flange first, then medial and lateral condyles, then posterior condyles. Use Gigli saws for well-fixed cementless components. Apply slap hammer to extraction device attached to femoral component. Remove in flexion with controlled force. **Technical Tip**: EXAM KEY: This is the most challenging step - well-fixed cemented components may take 30-45 minutes to remove safely. For ingrown cementless components, oscillating saw or Gigli saws under component are safer than osteotomes (less bone loss). Create small windows in anterior flange if needed to access cement. Preserve bone stock - patience is critical. Consider ultrasonic cement removal for well-fixed cement mantles. - Supracondylar or condylar fracture (most common intraoperative complication) - Posterior cortex perforation with vascular injury - MCL or LCL avulsion from epicondyle during extraction - Excessive bone loss from aggressive osteotome use - Fracture propagation in osteopenic or osteolytic bone ### Step 5: Cement and Membrane Removal Cement and Membrane Removal: Remove all cement, fibrous membrane, and debris down to viable bleeding bone. Use narrow osteotomes, curettes, rongeurs, high-speed burr, and ultrasonic cement removal devices. Work from distal to proximal, anterior to posterior. Preserve cortical shell and condylar bone stock. Remove cement from intercondylar notch and posterior condyles. **Technical Tip**: EXAM KEY: Complete cement removal is essential to assess true bone defects and achieve fixation of revision component. Use headlight and magnification. Pulsatile lavage after gross cement removal to clear debris. Cement restrictor deep in femoral canal may require flexible drill or osteotome. Send 5-6 tissue samples for culture and histology (even in presumed aseptic cases - occult infection in 7-10% of aseptic revisions). - Posterior cortex perforation during posterior cement removal - Condylar fracture through weakened or osteolytic bone - Thermal injury from high-speed burr (continuous irrigation essential) - Creating contained defects into uncontained by aggressive curettage ### Step 6: Bone Defect Assessment and Classification Bone Defect Assessment and Classification: Systematically assess femoral bone defects using AORI classification after all cement removed. Type 1: Intact metaphyseal bone (use standard PS or CCK). Type 2: Damaged metaphysis (use distal or posterior augments 5-15mm). Type 3: Severe deficiency (use large augments, sleeves, allograft, or custom implants). Map defects on distal and posterior condyles, measuring depth and extent. **Technical Tip**: EXAM KEY: Common femoral defects - Distal: uncontained defects from loosening or osteolysis. Posterior: notching from malpositioned components or osteolysis. Uncontained defects greater than 5mm need metal augments (screw-fixed if possible). Contained defects less than 5mm can use cement or impaction grafting. Check posterior condyles carefully - often underestimated. Categorize as cavitary (contained) vs segmental (uncontained). - Underestimating defect depth leading to component undersizing - Missing posterior condyle defects (difficult to visualize) - Misclassifying uncontained defects as contained ### Step 7: Femoral Canal Preparation for Stem (if needed) Femoral Canal Preparation for Stem (if needed): If using stemmed revision component, prepare femoral canal with flexible reamers starting 1-2mm larger than canal diameter. Ream in 1mm increments to cortical chatter. For press-fit stems, ream to exact stem diameter. For cemented stems, over-ream 2mm. Aim for 4-6cm diaphyseal contact (press-fit) or 8-10cm (cemented). Check alignment with intramedullary rod. **Technical Tip**: EXAM KEY: Short stems (50-75mm) for AORI 1-2 provide rotational control and stress shielding reduction. Long stems (100-150mm) for AORI 3 or deficient metaphysis provide fixation and load transfer. Press-fit preferred (better long-term fixation). Offset stems available if canal deformity or malunion. Start small - can always ream larger but cannot make canal smaller. Fluoroscopy helpful to confirm alignment. - Anterior cortical perforation (femur has anterior bow in sagittal plane) - Spiral fracture propagation in osteopenic bone - Creating false passage in deformed or sclerotic canals - Weakening supracondylar region (fracture risk) ### Step 8: Distal Femoral Resection Distal Femoral Resection: Use intramedullary alignment rod (via stem trial) or extramedullary guide. Set resection perpendicular to mechanical axis in coronal plane (5-7 degrees valgus to anatomic axis). Set 3 degrees external rotation and 0 degrees flexion in sagittal plane. Resect minimum bone necessary to achieve flat surface - typically 2-4mm beyond primary resection. Use distal femoral cutting guide. **Technical Tip**: EXAM KEY: Goals of distal cut: perpendicular to mechanical axis (coronal), neutral flexion-extension (sagittal), minimal bone resection. Use intact condyle as reference (usually lateral in varus knees, medial in valgus knees). If massive asymmetric bone loss, may need asymmetric resection or augments. Avoid notching anterior cortex (supracondylar fracture risk). Resection level determines extension gap - balance against flexion gap later. - Excessive resection compromising metaphyseal bone stock - Creating varus or valgus malalignment - Anterior cortex notching (supracondylar fracture risk) - Resecting into uncontained defect (losing peripheral support) ### Step 9: Anterior, Posterior and Chamfer Cuts Anterior, Posterior and Chamfer Cuts: Set femoral component rotation using posterior condylar axis (3 degrees external rotation), transepicondylar axis (gold standard), or Whiteside line (AP axis). Make anterior, posterior and chamfer cuts with appropriate cutting guides. Size femoral component to avoid anterior notching and optimize posterior condylar offset. Remove posterior osteophytes. **Technical Tip**: EXAM KEY: Femoral rotation is critical - internal rotation causes patellar maltracking and medial polyethylene wear. Use transepicondylar axis if landmarks visible, otherwise 3 degrees external to posterior condylar axis. In revision with bone loss, Whiteside line (AP axis) most reliable. Avoid oversizing (notching, overstuffing) and undersizing (instability, poor coverage). Posterior condylar offset affects flexion gap - restore to maintain flexion. - Anterior cortex notching (stress riser for supracondylar fracture) - Malrotation causing patellar maltracking and instability - Asymmetric posterior resection creating flexion gap imbalance - Damage to collateral ligament origins during chamfer cuts ### Step 10: Defect Reconstruction with Augments Defect Reconstruction with Augments: Based on AORI classification, reconstruct defects with metal augments. Distal femoral defects: use distal augment blocks (5-15mm thickness) secured with screws if possible, fully supported peripherally by host bone. Posterior condyle defects: use posterior augment wedges. Size augments to fill defect completely. Trial to ensure stability and appropriate joint line restoration. **Technical Tip**: EXAM KEY: Metal augments are modular blocks or wedges that fill specific defects. Must be fully supported by host bone at periphery (no cantilever). Screw fixation into host bone preferred when possible (improves stability). Cemented to both bone and prosthesis at final implantation. Alternative: modular component systems with built-in augmentation. Avoid structural allograft for femoral defects if possible (high resorption rate). - Undersizing augments leading to subsidence or collapse - Screw penetration into neurovascular structures - Incomplete seating creating interface gaps - Augment not fully supported leading to failure ### Step 11: Trial Reduction and Gap Assessment Trial Reduction and Gap Assessment: Insert femoral trial with stem (if used) and augments. Insert tibial trial and select polyethylene thickness. Reduce knee and assess through full ROM. Check: extension gap (0 degrees) vs flexion gap (90 degrees) - should be equal plus or minus 2mm. Assess medial-lateral stability with varus/valgus stress (maximum 5mm opening). Check patellar tracking. Test ROM (target 0-110 degrees minimum). **Technical Tip**: EXAM KEY: Gap balancing philosophy - Extension gap set by tibial and distal femoral cuts. Flexion gap set by posterior femoral cuts and condylar offset. If extension gap tight: recut tibia or downsize femoral component. If flexion gap tight: add posterior augment or increase tibial slope. If gaps unequal by greater than 2mm, consider revision of cuts or use of constraint (CCK). Assess joint line - should be 2-3cm distal to medial epicondyle. - Overstuffing extension gap (limited extension, anterior knee pain) - Overstuffing flexion gap (limited flexion, PCL impingement if retained) - Accepting instability (early failure and dislocation) - Joint line elevation greater than 8mm (extensor mechanism dysfunction, instability) ### Step 12: Constraint Selection Constraint Selection: Based on trial assessment, select appropriate constraint level. Posterior Stabilized (PS): if PCL deficient but collaterals intact, good bone stock, balanced gaps. Constrained Condylar Knee (CCK): if MCL or LCL incompetent, flexion-extension gap imbalance, moderate instability. Rotating Hinge Knee (RHK): if severe instability, collateral deficiency, inability to balance gaps. Fixed hinge: salvage only. **Technical Tip**: EXAM KEY: Constraint ladder in revision TKR - CR (rarely used in revision) to PS (most revisions) to CCK (varus/valgus laxity greater than 10mm, MCL insufficiency) to RHK (severe instability, cannot balance) to Fixed hinge (salvage, arthrodesis alternative). CCK has taller post and wider box than PS, provides 3-7 degrees varus/valgus constraint. RHK allows axial rotation but prevents varus/valgus tilting. Higher constraint needs longer stems (load transfer). - Under-constraining (early instability and failure) - Over-constraining (interface stress, loosening, reduced ROM) - Using RHK without stem (high failure rate from metaphyseal stress) - Missing indication for constraint (recurrent instability) ### Step 13: Final Implant Preparation and Cementation Final Implant Preparation and Cementation: Prepare bone surfaces with pulsatile lavage (6-9L) and dry thoroughly with suction and swabs. Mix high-viscosity antibiotic-loaded bone cement (1g vancomycin plus 3.6g tobramycin per 40g cement). Apply cement to bone surfaces and implant using cement gun. For hybrid fixation: press-fit stem, then cement metaphyseal component. For fully cemented: cement stem and component as single construct. **Technical Tip**: EXAM KEY: Third generation cementing technique - clean dry bone, pressurization, cement gun application, component insertion during dough phase, removal of excess before polymerization. Hybrid fixation (press-fit stem, cemented metaphyseal component) is popular - combines biological fixation with immediate stability. Use antibiotic cement in all revisions (even aseptic) - reduces infection risk. Apply cement to augments and bone-augment interface. - Cement extrusion posteriorly into neurovascular structures - Air entrapment creating weak spots in cement mantle - Premature cement polymerization before component seated - Inadequate cement penetration into cancellous bone ### Step 14: Femoral Component Insertion and Polyethylene Selection Femoral Component Insertion and Polyethylene Selection: Insert stem first if hybrid technique. Apply cement to femoral bone surfaces and undersurface of component. Insert femoral component with firm steady pressure, ensuring proper rotation (aligned with transepicondylar axis), AP position (no anterior notching, adequate posterior coverage), and seating. Pressurize cement. Remove excess. Hold until polymerized. Select and insert final polyethylene after cement set. **Technical Tip**: EXAM KEY: Femoral component position checks - Rotation: 3 degrees external to posterior condylar axis or parallel to transepicondylar axis. Flexion: neutral (0 degrees or slight flexion acceptable, avoid extension). Sizing: maximize coverage without notching, restore condylar offset. Poly thickness: 10mm minimum for PS, 12-15mm for CCK (taller post), 15-20mm for RHK. Lock poly securely and confirm cannot be removed by traction. - Malrotation (internal rotation causes patellar problems and wear) - Anterior notching (supracondylar fracture risk) - Incomplete seating leaving gaps under component - Polyethylene insert not fully locked (catastrophic failure) ### Step 15: Final Assessment, Closure and Post-Operative Protocol Final Assessment, Closure and Post-Operative Protocol: Final check: ROM 0-110 degrees minimum, stable throughout arc, no lift-off with varus/valgus stress, patellar tracking central. Remove all cement, debris with lavage. Achieve hemostasis. Insert drain if significant dead space. Close capsule and extensor mechanism with strong interrupted sutures (No.2 or No.5) in flexion. Close layers and skin. Apply compression dressing with knee in extension. **Technical Tip**: EXAM KEY: Post-operative protocol - Tranexamic acid 1g IV at induction and closure. Ice and elevation. TED stockings and chemical thromboprophylaxis (LMWH or DOAC) for 35 days. IV antibiotics 24h. Early mobilization day 1 with physiotherapy - WBAT with walking frame. CPM if available (0-60 degrees advancing to 0-90 degrees by week 2). Remove drain 24-48h. Radiographs: AP, lateral, skyline check alignment, component position, no fracture. Discharge day 4-7 to rehabilitation. Follow-up 6 weeks, 3 months, 1 year, then annually. - Wound dehiscence (higher risk with extensile exposures) - Deep infection (5-10% risk in revision surgery) - Supracondylar fracture during early mobilization - Extensor mechanism failure or rupture - Persistent instability or stiffness requiring re-revision - Neurovascular complications (DVT, PE, nerve palsy) 1. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Hip, Knee & Shoulder Arthroplasty Annual Report 2023. Adelaide: AOA; 2023. Available from: https://aoanjrr.sahmri.com 2. Engh GA, Ammeen DJ. Bone loss with revision total knee arthroplasty: defect classification and alternatives for reconstruction. Instr Course Lect. 1999;48:167-175. 3. Fehring TK, Odum S, Griffin WL, Mason JB, Nadaud M. Early failures in total knee arthroplasty. Clin Orthop Relat Res. 2001;(392):315-318. 4. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res. 1998;(356):144-153. 5. Haddad FS, Bentley G. Total knee arthroplasty after intra-articular fractures of the tibial plateau. J Bone Joint Surg Br. 2003;85(4):584-587. 6. Barrack RL, Nakamura SJ, Hopkins SG, Rosenzweig S. Winner of the 2003 James A. Rand Young Investigator Award. Early failure of cementless mobile-bearing total knee arthroplasty. J Arthroplasty. 2004;19(7 Suppl 2):101-106. 7. Morgan HD, Battista V, Leopold SS. Constraint in primary total knee arthroplasty. J Am Acad Orthop Surg. 2005;13(8):515-524. 8. Parvizi J, Zmistowski B, Berbari EF, et al. New definition for periprosthetic joint infection: from the Workgroup of the Musculoskeletal Infection Society. Clin Orthop Relat Res. 2011;469(11):2992-2994. 9. Whiteside LA, Arima J. The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty. Clin Orthop Relat Res. 1995;(321):168-172. 10. Rorabeck CH, Taylor JW. Classification of periprosthetic fractures complicating total knee arthroplasty. Orthop Clin North Am. 1999;30(2):209-214.

Revision Total Knee Replacement - Femoral Component

Revision Total Knee Replacement - Femoral Component