import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Primary Indications:** - Symptomatic patellar component loosening with adequate bone stock - Polyethylene wear with metallosis or synovitis - Patellar fracture with component loosening - Component malposition causing maltracking - Secondary resurfacing of unresurfaced painful patella - Failed metal-backed patellar component **Bone Stock Classification:** - **Adequate (≥10mm)**: Standard revision component - **Compromised (5-10mm)**: Thin button, trabecular metal augment, or patelloplasty - **Deficient (<5mm)**: Patelloplasty, allograft, or patellectomy (last resort) **Surgical Exposure Options:** - **Standard medial parapatellar**: Most common, use previous incision - **Quadriceps snip**: Extension of medial parapatellar into quadriceps tendon at 45 degrees - improves exposure in stiff knee - **V-Y quadricepsplasty**: For severe stiffness, extends exposure but weakens extensor mechanism - **Tibial tubercle osteotomy**: Best exposure, preserves extensor mechanism, useful when concurrent tibial revision needed **Patellar Access Without Eversion:** - Flex knee 90-110 degrees - Work on patella in situ - Useful for thin bone or stiff knees where eversion risky **Patellar Component Types:** - **All-polyethylene dome**: Standard revision choice, various thicknesses (8-12mm) - **Anatomic all-polyethylene**: Matches native patellar shape - **Trabecular metal button**: Enhanced fixation in compromised bone - **Cemented vs cementless**: Cemented standard in revision **Fixation Configurations:** - **Central peg dome**: Lower stress concentration (preferred) - **Multi-peg peripheral**: Higher stress concentration (older designs) - **Trabecular metal ingrowth**: Enhanced initial stability **Location**: Inferior pole of patella to tibial tubercle. Risk of avulsion during eversion especially in stiff knees or with osteopenic bone. **Location**: Superior pole of patella extending proximally. Risk of rupture during forced flexion or aggressive exposure techniques. **Location**: Within patella substance. Measure from anterior cortex to articular surface. Minimum 10mm needed for safe resurfacing. **Location**: Anterior aspect of distal femur. Risk of notching during femoral preparation causing stress riser and potential fracture. **Location**: Courses over lateral femoral condyle deep to iliotibial band. Risk during lateral retinacular release causing bleeding, hematoma, and patellar AVN. **Patient Position**: Supine on radiolucent table with leg holder or bump under thigh. Tourniquet applied to upper thigh. Regional or general anesthesia with appropriate DVT prophylaxis initiated. **Surgical Approach**: Medial parapatellar arthrotomy via previous incision, with careful patellar eversion to prevent fracture or extensor mechanism injury. Use most lateral previous incision if multiple scars present. **Pre-operative Planning Checklist:** - Review skyline and lateral radiographs for patellar bone stock - CT scan if bone thickness uncertain - Note previous implant type (metal-backed vs all-poly) - Plan alternative strategies based on bone stock - Have cerclage wire, bone graft, and patellectomy options available ### Step 1: Exposure and Patellar Assessment Exposure and Patellar Assessment: Use previous scar (most lateral if multiple). Develop skin flaps carefully to avoid ischemia. Perform medial parapatellar arthrotomy. Assess patella: measure bone thickness with calipers, check for fracture lines, osteolysis, component loosening, polyethylene wear, metal backing failure. Assess tracking with trial components or existing prosthesis. **Technical Tip**: EXAM KEY: Pre-operative imaging crucial - skyline view shows patellar bone stock, tilt, subluxation. CT can assess bone thickness accurately. Intraoperatively, patellar thickness measured from articular surface to anterior cortex should be documented. Normal patella 24-26mm thick, post-primary TKR 14-18mm. Minimum 10mm needed for safe revision. Mark fracture lines with methylene blue if present. - Skin flap necrosis from thin or multiple previous incisions - Completing fracture line during manipulation - Avulsing patellar tendon during exposure in stiff knee ### Step 2: Patellar Eversion (if necessary) Patellar Eversion (if necessary): For failed patellar component requiring removal, must evert patella for access. Flex knee progressively to 30 degrees, 60 degrees, then 90 degrees while applying gentle lateral pressure on patella. Release adhesions in lateral gutter if needed. If patella will not evert safely, perform lateral release (outside-in or inside-out) or proceed with knee flexed without eversion. **Technical Tip**: EXAM KEY: Patellar eversion is dangerous in stiff knees, thin patellae, or osteopenic bone. Alternative: flex knee 90-110 degrees and work on patella in situ without eversion. Quadriceps snip can help but increases extensor mechanism complication risk. Document pre-operative extensor lag (indicates tenuous mechanism). Consider leaving well-fixed, well-positioned components if patellar access too risky. - Patellar fracture during forced eversion (most common complication) - Patellar tendon avulsion from tibial tubercle or inferior pole - Completing pre-existing stress fracture - Quadriceps tendon rupture in stiff knee with forced flexion ### Step 3: Patellar Component Removal Patellar Component Removal: Use thin flexible osteotomes to disrupt cement-bone or bone-implant interface. Work circumferentially around component starting from most accessible edge. For metal-backed components, remove metal shell first, then polyethylene and cement. For all-poly cemented components, use osteotome and gentle mallet or slap hammer attached to component. Remove slowly to avoid fracture. **Technical Tip**: EXAM KEY: Metal-backed patellar components (largely abandoned) have higher failure rate - metallosis, osteolysis, dissociation. Modern components are all-polyethylene (dome-shaped or anatomic). For well-fixed ingrown cementless components, may need Gigli saw underneath. Ultrasonic cement removal helpful for well-fixed cemented components. Take your time - rushing causes fracture. Have patellar cerclage wire available for intraoperative fracture. - Patellar fracture (comminuted, transverse, or vertical) - Excessive bone loss from aggressive osteotome use - Perforation through thin remaining bone into joint - Avulsion of quadriceps or patellar tendon during component extraction ### Step 4: Cement and Fibrous Membrane Removal Cement and Fibrous Membrane Removal: Remove all cement, fibrous interface membrane, and necrotic bone down to viable bleeding bone. Use curettes, rongeurs, and small osteotomes carefully. Avoid excessive force or high-speed burr on thin bone. Pulsatile lavage to remove cement particles and debris. Measure remaining bone thickness with calipers from anterior cortex to prepared surface. **Technical Tip**: EXAM KEY: Complete cement removal essential to assess true remaining bone stock and achieve revision component fixation. Gentle technique critical - thin patellar bone fractures easily. Small curettes and hand instruments safer than power tools. After cement removal, bleeding bone should be visible (viability indicator). Measure thickness in multiple locations - often asymmetric bone loss. Send tissue samples for culture (occult infection). - Fracture through attenuated bone during cement removal - Perforation into articular surface - Excessive bone removal reducing remaining stock - Thermal injury from burr (avoid if possible) ### Step 5: Bone Stock Assessment and Decision Making Bone Stock Assessment and Decision Making: Measure patellar bone thickness (anterior cortex to prepared surface). Assess bone quality and defects. Categorize: Adequate (10mm or more) - standard revision component. Compromised (5-10mm) - thin revision component, bone graft augmentation, or patelloplasty. Deficient (less than 5mm) - consider alternatives: trabecular metal augmentation, patellar allograft, or patellectomy (last resort). **Technical Tip**: EXAM KEY: Decision algorithm based on bone stock. 10mm or more: proceed with revision component (all-poly dome or anatomic design, 8-12mm thick). 5-10mm: options include thin revision button (8mm), trabecular metal button, morsellized bone graft augmentation, or patelloplasty (denude remaining cartilage, smooth bone, no resurfacing). Less than 5mm: patellar allograft reconstruction with component, patelloplasty alone, or patellectomy. Patellectomy causes extensor lag, weakness, pain - avoid if possible. - Oversizing component on thin bone (perforation, fracture) - Undertreating with patelloplasty when resurfacing possible - Proceeding with resurfacing when bone stock inadequate ### Step 6: Patellar Tracking Assessment Patellar Tracking Assessment: With trial femoral and tibial components in place, assess patellar tracking through ROM. Normal tracking: patella centers in trochlear groove by 30 degrees flexion, tracks centrally through full flexion. Assess for lateral tilt, subluxation, or maltracking. Identify causes: femoral component malrotation (internal rotation), lateral retinacular tightness, patella alta/baja, trochlear dysplasia. **Technical Tip**: EXAM KEY: Patellar tracking crucial for success - maltracking causes pain, wear, loosening, fracture. No-thumb test: reduce patella without thumb pressure, flex knee - patella should stay centered. If lateral subluxation: check femoral rotation (internal rotation causes maltracking), check Q-angle, consider lateral release. If medial subluxation: check for over-released lateral retinaculum, femoral external malrotation. Intraoperative tracking with trial components predicts post-op outcome. - Missing femoral malrotation as cause of maltracking - Performing unnecessary lateral release (creates instability) - Over-releasing lateral structures causing medial instability ### Step 7: Lateral Retinacular Release (if indicated) Lateral Retinacular Release (if indicated): Indications: lateral patellar tilt greater than 10 degrees, lateral subluxation, tight lateral retinaculum preventing central tracking. Technique: inside-out approach preferred (safer for vessels). Release lateral retinaculum from lateral border of patella extending from superior to inferior pole. Use cautery for hemostasis. Check tracking after release - should improve to central tracking. **Technical Tip**: EXAM KEY: Lateral release performed in 10-20% of revisions, less common in primary. Inside-out technique: from medial arthrotomy, insert scissors or blade underneath lateral retinaculum, divide under direct vision, reduces risk to lateral superior genicular vessels. Outside-in technique: direct visualization laterally, but higher vascular injury risk. Modern trend: avoid lateral release if possible (use optimal femoral rotation, proper component sizing). If needed, partial release may suffice. - Lateral superior genicular artery injury (bleeding, hematoma) - Over-release causing medial subluxation and instability - Hematoma formation (use drain if extensive release) - Skin necrosis if combined with lateral incision ### Step 8: Patellar Preparation for Component (if adequate bone stock) Patellar Preparation for Component (if adequate bone stock): If bone stock 10mm or more, proceed with patellar preparation. Use patellar cutting guide or freehand technique to create flat surface parallel to anterior cortex. Resect minimum bone necessary (typically 2-3mm more than primary to achieve flat surface). Goal: composite thickness (remaining bone plus component) equals pre-operative patellar thickness (24-26mm, plus or minus 2mm acceptable). **Technical Tip**: EXAM KEY: Patellar resection principles - Preserve maximum bone stock while achieving flat surface. Resect parallel to anterior cortex (avoid oblique cuts). Composite thickness (bone plus component) equals native thickness plus or minus 2mm. Thickening more than 2mm causes overstuffing (limited flexion, pain, fracture). Thinning more than 2mm causes patella baja effect, potential instability. Measure with calipers before and after. Central peg holes minimize stress concentration vs peripheral pegs. - Excessive resection leaving inadequate bone for fixation - Oblique resection creating asymmetric component seating - Perforation into anterior cortex or joint surface - Lateral or medial perforation losing peg fixation ### Step 9: Peg Hole Preparation Peg Hole Preparation: Use drill bit to create peg holes matching revision component design. Most modern components have 3-4 pegs (1 central dome, 2-4 peripheral) or single central peg. Drill perpendicular to prepared surface. Depth: 8-12mm depending on remaining bone thickness. Avoid perforation. Trial component to ensure proper seating without rocking. **Technical Tip**: EXAM KEY: Peg configuration varies by manufacturer. Central peg designs reduce stress concentration vs all-peripheral pegs (early metal-backed designs). Drill perpendicular to surface - oblique drilling weakens bone. Depth gauge critical to avoid perforation. Remaining bone between peg holes and articular surface should be 5mm or more for strength. Trial component must seat fully without gaps or rocking - redo holes if needed. - Perforation through remaining bone into joint - Fracture during drilling (especially if thin bone or osteopenic) - Peg holes too close to periphery (fracture during impaction) - Asymmetric hole depth causing component tilt ### Step 10: Cementation and Component Insertion Cementation and Component Insertion: Prepare bone surface by pulsatile lavage and thorough drying (critical for cement interdigitation). Mix antibiotic-loaded bone cement. Apply cement to prepared patellar surface and undersurface of component. Insert component while cement doughy, ensuring proper orientation (matched to trochlear groove). Press firmly and hold with patellar clamp or manual pressure until polymerized. Remove excess cement. **Technical Tip**: EXAM KEY: Patellar cementation technique crucial - thin cement mantle (1-2mm) provides secure fixation without heat necrosis. Dry bone essential - use suction, swabs, thrombin-soaked gauze. Apply cement to both bone and component. Orient component to match femoral trochlea (usually slight lateral offset). Maintain pressure during polymerization - prevents gaps. Cement exotherm can cause thermal necrosis in thin bone - thin cement mantle and avoid excessive cement. Remove excess cement before polymerization. - Thermal necrosis from thick cement mantle or excessive cement - Incomplete seating leaving gaps (early loosening) - Cement extrusion into joint (third-body wear, impingement) - Malorientation causing edge loading and accelerated wear - Fracture during component impaction ### Step 11: Alternative: Patelloplasty (if inadequate bone stock) Alternative: Patelloplasty (if inadequate bone stock): If bone stock 5-10mm and component not feasible, perform patelloplasty. Denude remaining articular cartilage and fibrous tissue. Use rongeurs, curettes, and burr to create smooth patellar surface. Contour to match trochlear shape. Preserve anterior cortex. This leaves unresurfaced but smoothed patellar surface to articulate with femoral component. **Technical Tip**: EXAM KEY: Patelloplasty indications: insufficient bone stock for safe component (less than 10mm), elderly low-demand patient, significant comorbidities. Technique: remove all cartilage and necrotic bone, create smooth contoured surface, preserve anterior cortex. Outcomes: moderate improvement in pain (60-70% satisfaction), inferior to successful resurfacing but better than patellectomy. Counsel patients regarding residual anterior knee pain and crepitus. Still requires optimal patellar tracking. - Excessive bone removal compromising structural integrity - Incomplete cartilage removal leaving irregular surface - Fracture during contouring - Anterior cortex violation ### Step 12: Management of Intraoperative Patellar Fracture Management of Intraoperative Patellar Fracture: If fracture occurs: assess pattern (transverse, vertical, comminuted). Transverse: tension band fixation (two parallel 1.6mm K-wires plus 18-gauge cerclage wire figure-8). Vertical: if non-displaced, consider component fixation alone; if displaced, lag screw plus or minus cerclage. Comminuted: attempt reconstruction if possible, or consider partial patellectomy of fragments, or total patellectomy (last resort). **Technical Tip**: EXAM KEY: Intraoperative patellar fracture occurs in 1-3% of revisions (higher than primary). Transverse fracture most common - managed with tension band fixation plus component if bone stock adequate. Bury K-wire ends subcortically to prevent migration. Vertical fracture: often stable with component fixation alone if non-displaced. Comminuted: very difficult - may need patellectomy. Post-op: protected weight-bearing 6 weeks, limited ROM until healing, brace in extension between therapy sessions. - Missing fracture and proceeding without fixation - K-wire migration causing soft tissue irritation - Wire prominence causing skin breakdown - Inadequate fixation leading to fracture displacement - Avascular necrosis of patellar fragments ### Step 13: Final Tracking Assessment and ROM Check Final Tracking Assessment and ROM Check: After patellar component insertion (or patelloplasty), perform final tracking assessment with all components in place. Reduce patella and flex knee from full extension to maximum flexion. Patella should track centrally in trochlear groove without tilt, subluxation, or clunk. Assess ROM - should achieve 0 degrees extension and 110-130 degrees flexion without restriction. Check for patellofemoral crepitus or impingement. **Technical Tip**: EXAM KEY: Final checks before closure: 1) Patellar tracking central throughout arc, 2) No patellar clunk (impingement on femoral component), 3) ROM matches trial assessment, 4) Composite patellar thickness appropriate (not overstuffed), 5) No extensor lag when extending passively. Document ROM and tracking for medicolegal record. If maltracking persists, identify cause: femoral rotation error, inappropriate component sizing, inadequate lateral release, or excessive lateral release. - Accepting maltracking (causes pain, wear, failure) - Overstuffing causing limited flexion - Missing patellar clunk syndrome (needs femoral notchplasty) - Inadequate ROM requiring manipulation ### Step 14: Closure and Hemostasis Closure and Hemostasis: Perform thorough lavage (6-9L pulsatile) to remove all cement particles, bone fragments, and debris. Achieve meticulous hemostasis - use cautery for bleeding points. Consider drain if extensive lateral release performed or large dead space. Close medial parapatellar arthrotomy with interrupted absorbable sutures (No.2 or No.5) in flexion. Close subcutaneous layers and skin. Apply compression dressing. **Technical Tip**: EXAM KEY: Patellar region highly vascular - hemostasis crucial to prevent hematoma (infection risk, adhesions). If lateral release performed, inspect lateral gutter for bleeding from lateral superior genicular vessels. Tranexamic acid (1g IV induction, 1g closure) reduces blood loss 30-40%. Close arthrotomy in 30-40 degrees flexion to avoid tension. Test closure by extending knee - should hold without gapping. Compression dressing over patella reduces swelling and hematoma formation. - Inadequate hemostasis causing hematoma - Retained cement particles (third-body wear) - Closure under tension (dehiscence risk) - Drain malposition causing pain or vessel injury ### Step 15: Post-Operative Rehabilitation Protocol Post-Operative Rehabilitation Protocol: Elevate leg, ice, compression. TED stockings and chemical thromboprophylaxis (LMWH or DOAC) for 35 days. IV antibiotics 24h. Day 1: begin quadriceps sets and ankle pumps. Day 2: mobilize WBAT with frame or crutches. CPM machine 0-60 degrees advancing to 0-90 degrees by week 2 if tolerated. If patellar fracture: protect with brace locked in extension for 6 weeks, limited ROM protocol (0-60 degrees weeks 2-6, advance after radiographic healing). **Technical Tip**: EXAM KEY: Early mobilization crucial for ROM and preventing arthrofibrosis. Quadriceps strengthening essential for patellar function and stability. If intraoperative fracture or compromised bone stock: more protected rehabilitation - brace in extension, limited ROM initially, progressive weight-bearing. Remove drain 24-48h. Wound check day 3. Radiographs: AP, lateral, skyline views confirm component position, patellar tracking, no fracture. Discharge day 3-5. Outpatient review 2 weeks (wound), 6 weeks (ROM, radiographs), 3 months, 1 year. Monitor for anterior knee pain, crepitus, instability. - Aggressive early ROM causing component loosening or fracture displacement - Inadequate quadriceps strengthening (extensor lag, instability) - Wound complications (dehiscence, necrosis in thin skin flaps) - Deep infection (higher risk in revision) - Persistent anterior knee pain (multifactorial) - Re-fracture during rehabilitation if inadequate healing 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. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res. 1998;(356):144-153. 3. 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. 4. Chalidis BE, Sachinis NC, Papadopoulos P, Petsatodis E, Christodoulou AG, Petsatodis G. Long-term results of posterior-cruciate-retaining Genesis I total knee arthroplasty. J Orthop Sci. 2011;16(6):726-731. 5. Pagnano MW, Scuderi GR. Patellar component resurfacing. In: Insall JN, Scott WN, eds. Surgery of the Knee. 4th ed. Philadelphia: Churchill Livingstone; 2006:1665-1676. 6. Berry DJ, Rand JA. Isolated patellar component revision of total knee arthroplasty. Clin Orthop Relat Res. 1993;(286):110-115. 7. Hanssen AD, Rand JA. A comparison of primary and revision total knee arthroplasty using the kinematic stabilizer prosthesis. J Bone Joint Surg Am. 1988;70(4):491-499. 8. Tria AJ Jr, Harwin SF. Patellar complications in total knee arthroplasty. In: Callaghan JJ, Rosenberg AG, Rubash HE, eds. The Adult Knee. Philadelphia: Lippincott Williams & Wilkins; 2003:1457-1476. 9. Keblish PA, Varma AK, Greenwald AS. Patellar resurfacing or retention in total knee arthroplasty. A prospective study of patients with bilateral replacements. J Bone Joint Surg Br. 1994;76(6):930-937. 10. Brick GW, Scott RD. The patellofemoral component of total knee arthroplasty. Clin Orthop Relat Res. 1988;(231):163-178.

Revision Total Knee Replacement - Patellar Component (Resurfacing/Revision)

Revision Total Knee Replacement - Patellar Component (Resurfacing/Revision)