import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' ### Indications for Two-Stage Exchange - **Chronic periprosthetic joint infection** (greater than 3-4 weeks duration) - Failed DAIR (debridement, antibiotics, implant retention) - Unknown organism or culture-negative infection - Resistant organisms (MRSA, VRE, multi-drug resistant) - Sinus tract present - Poor soft tissue envelope requiring staged approach - Severely immunocompromised patient ### MSIS Criteria for PJI Diagnosis (2018 Updated) **Major Criteria** (one = definite PJI): - Two positive cultures with same organism - Sinus tract communicating with joint **Minor Criteria** (total greater than or equal to 6 = PJI): - CRP greater than 10 mg/L (2 points) - ESR greater than 30 mm/hr (1 point) - Synovial WBC greater than 3000 cells/uL (3 points) - Synovial PMN greater than 80% (2 points) - Alpha-defensin positive (3 points) - Single positive culture (2 points) - Positive histology (3 points) **Examiner Question**: "How do you distinguish acute from chronic periprosthetic joint infection? Why does this matter?" **Model Answer**: "The distinction is based on **duration of symptoms**: Acute PJI is less than 3-4 weeks from symptom onset (or within 4 weeks of primary surgery for early postoperative infection). Chronic PJI is greater than 3-4 weeks duration. This distinction is CRITICAL because it determines treatment: **Acute PJI** may be treated with DAIR (debridement, antibiotics, and implant retention) if the implant is well-fixed, soft tissues are viable, and the organism is susceptible. **Chronic PJI** requires two-stage exchange because the mature biofilm cannot be eradicated with debridement alone - the entire implant and cement must be removed. The biofilm takes 2-4 weeks to mature and become resistant to antibiotic penetration and host immune response." - **Attempting DAIR for chronic infection** = high failure rate (50-80%) - use two-stage - **Missing the diagnosis** - culture-negative PJI is still PJI if MSIS criteria met - **Sinus tract = definite PJI** regardless of culture result - do not delay treatment - **Proceeding with one-stage in resistant organism** - high reinfection rate with MRSA, VRE ### Contraindications to Two-Stage Exchange - Patient medically unfit for staged surgical procedures - Unable to comply with antibiotic regimen - Severe immunosuppression (may consider suppression only) - Life expectancy too short to complete both stages ### Consider Alternative Procedures - **DAIR**: Early infection (less than 3-4 weeks), susceptible organism, stable implant - **One-stage exchange**: Selected cases with susceptible organism, good soft tissue - **Arthrodesis**: Failed two-stage, severe bone loss, extensor mechanism loss - **Amputation**: Life-threatening sepsis, non-reconstructable limb - **Antibiotic suppression**: Unfit for surgery, limited life expectancy **Examiner Question**: "When would you consider one-stage exchange instead of two-stage?" **Model Answer**: "One-stage exchange may be considered in **highly selected patients** who meet ALL the following criteria: (1) **Known organism** that is susceptible to available antibiotics, (2) **Not highly virulent** - exclude MRSA, VRE, resistant gram-negatives, (3) **Good soft tissue envelope** - no sinus tract, no extensive skin necrosis, (4) **No significant bone loss** requiring structural grafting, (5) **Patient factors** - fit for prolonged single surgery, motivated, reliable for follow-up. Success rates of 85-90% are reported in selected series, but patient selection is CRITICAL. If any doubt, two-stage is safer. In Australia, two-stage remains the gold standard for chronic PJI." - **Pushing for one-stage in unsuitable patient** - high failure rate with resistant organisms - **Underestimating frailty** - two-stage has significant morbidity; ensure patient can survive both surgeries - **Proceeding without ID input** - complex antibiotic regimens require infectious diseases consultation - **Ignoring patient compliance** - failed antibiotic course means failed treatment ### Preoperative Workup **Confirm PJI Diagnosis** 1. Serology: CRP, ESR (D-dimer adjunct) 2. Knee aspiration (stop antibiotics 2 weeks before if on treatment) - Cell count and differential - Alpha-defensin - Culture (aerobic, anaerobic, fungal if indicated) 3. Nuclear medicine: If diagnosis unclear (WBC scan) **Organism Identification** - Critical for antibiotic selection - Culture-negative: use broad-spectrum (vancomycin + gram-negative coverage) - Request sensitivities including aminoglycoside for cement **Imaging** - AP/Lateral knee radiographs: component position, bone loss - Long leg standing films if malalignment suspected - CT if bone loss quantification needed for Stage 2 planning ### Antibiotic Cement Planning - Vancomycin 2-4g per 40g PMMA (gram-positive coverage) - Tobramycin or gentamicin 2-4g per 40g PMMA (gram-negative coverage) - Organism-specific if known (e.g., add fluconazole for fungal) - Higher antibiotic load acceptable for spacers (sacrifice mechanical strength) **Examiner Question**: "How do you manage culture-negative PJI?" **Model Answer**: "Culture-negative PJI accounts for 10-25% of cases and presents a significant challenge. If the MSIS criteria confirm PJI despite negative cultures, I would: (1) **Ensure adequate sampling** - minimum 5-6 tissue samples at Stage 1, hold for 14 days for slow-growing organisms, (2) **Consider sonication** of explanted components to disrupt biofilm, (3) **Request extended cultures** for atypical organisms (mycobacteria, fungi), (4) **Use empiric broad-spectrum antibiotics** in the spacer - vancomycin 4g + tobramycin 4g per 40g cement covers most organisms, (5) **IV antibiotic regimen** would typically be vancomycin (gram-positive) + ciprofloxacin or ceftazidime (gram-negative) for 6 weeks, (6) **ID consultation is essential** - they may recommend adding rifampicin or other agents. Culture-negative cases may have slightly lower success rates but are still treatable with two-stage exchange." - **Aspirating while on antibiotics** = false-negative cultures; stop for 2 weeks - **Not requesting sensitivities to cement antibiotics** - aminoglycoside resistance increasingly common - **Underestimating bone loss** - CT helps plan for Stage 2 reconstruction needs - **Operating without ID consultation** - suboptimal antibiotic regimens lead to treatment failure ### Stage 1 Equipment - **Extraction instruments**: Osteotomes, saws, cement removal tools - **Antibiotic cement**: Multiple packs (typically 6-10 packs of 40g) - **Antibiotic powder**: Vancomycin, tobramycin - **Spacer molds**: For articulating spacer (metal femoral trial, cement tibia) - **Reinforcement**: K-wires or metal rods for static spacer core - **Tissue sampling**: Multiple specimen containers, hold for cultures ### Stage 2 Equipment - Full revision TKA system - Stems, augments, sleeves/cones - Constraint options (PS, VVC, hinge) - Bone graft (autograft/allograft) - Fresh specimen containers for intraop cultures ### Spacer Types | Type | Advantages | Disadvantages | |------|------------|---------------| | Static block | Better antibiotic elution, easier removal, cheaper | ROM loss, stiffness, bone loss | | Articulating | Preserves ROM, easier Stage 2, patient function | More complex, dislocation risk, fracture | **Examiner Question**: "How do you fabricate an articulating antibiotic spacer?" **Model Answer**: "For an articulating spacer, I mix **high-dose antibiotics** (vancomycin 4g + tobramycin 4g per 40g cement) into PMMA. For the **femoral component**, I use a **metal trial component** sized to the patient and cement it into the femur - this provides a smooth articulating surface and reduces cement wear. For the **tibial component**, I form a cement baseplate with a flat or slightly dished articular surface using a mold or hand-shaping. Key points: (1) Ensure adequate soft tissue tension to prevent dislocation, (2) The metal femoral trial is reusable at Stage 2, (3) Some surgeons use commercial spacer molds for consistency, (4) The spacer should be stable through a functional ROM. Alternative: all-cement spacers using molds, but these have higher wear and dislocation rates." - **Insufficient cement** - need 6-10 packs; running out mid-case is catastrophic - **Wrong antibiotic dose** - too low = inadequate elution; review sensitivities - **No reinforcement for static spacer** - risk of fragmentation and migration - **Stage 2: No backup implants** - expect more bone loss than at Stage 1; have sleeves/cones ready **Behind posterior capsule**. At risk during aggressive cement removal posteriorly. Maintain posterior retractor on bone. Catastrophic if injured - vascular surgery backup essential. **Around fibular neck**. May be encased in scar tissue in chronic infection. At risk during lateral releases and exposure. Identify and protect - decompress if needed. **Tibial tubercle insertion**. High risk of avulsion in revision setting with scarring. Use extensile exposures (TTO) if tendon at risk. Catastrophic if avulsed. **Medial and lateral joint line**. May be weakened by infection/debridement. Assess carefully - plan constraint level accordingly. MCL at risk during medial exposure. **Compromised in chronic infection**. Multiple incisions, sinus tracts, poor vascularity. May need plastic surgery involvement. Tension-free closure essential. ### Positioning and Preparation **Patient Position**: Supine on radiolucent table. Thigh tourniquet. Leg holder or foot positioner. **Prep and Drape**: Prep entire limb including sinus tracts if present. Use antimicrobial-impregnated drapes. Consider wound retraction system for infected cases. **Pre-incision**: Stop prophylactic antibiotics until tissue samples obtained (if organism unknown). Have multiple specimen containers ready. ### Step 1: Exposure Use previous surgical incision (most lateral if multiple). Raise full-thickness skin flaps. Medial parapatellar arthrotomy. Excise any sinus tracts completely back to healthy tissue. May require extensile exposure for stiff or scarred knee. **Technical Pearl**: "I use the previous incision and raise full-thickness flaps. Before giving any antibiotics, I take 5-6 tissue samples from different areas for culture and hold them for 14 days. I excise all sinus tracts back to healthy bleeding tissue. If the knee is stiff, I may need a quadriceps snip or TTO for adequate exposure." - Take tissue samples BEFORE antibiotics if organism unknown - Minimum 5-6 tissue samples from different locations - Hold cultures for 14 days (slow-growing organisms) - Frozen section if available (greater than 5 PMN/HPF = infection) ### Step 2: Component Removal Remove all implants including polyethylene, femoral component, tibial baseplate, and patellar component if present. Use thin osteotomes at implant-bone interface. Remove all cement meticulously using burrs, chisels, or ultrasonic device. Remove any remaining fixation screws or wires. **Technical Pearl**: "I must remove ALL foreign material - any residual cement or debris harbors biofilm and will cause persistence of infection. I carefully inspect the entire joint, including the posterior recesses. I debride all necrotic and infected tissue until I reach healthy bleeding bone and soft tissue." - Remove ALL cement - residual cement harbors biofilm - Protect posterior structures during cement removal - Preserve bone stock where possible (for Stage 2) - Debride to healthy bleeding tissue ### Step 3: Thorough Debridement Perform radical debridement of all infected and necrotic tissue. Curette any bone cavities. Irrigate copiously (6-9L pulsatile lavage). Consider Betadine solution soak. The joint should appear clean with healthy bleeding surfaces. **Technical Pearl**: "I debride aggressively - the adequacy of debridement is the most important factor in infection eradication. I irrigate with at least 6-9 liters of normal saline using pulsatile lavage. Some surgeons add dilute Betadine for 3-minute soak, then lavage out." - **Inadequate debridement = treatment failure** - the most important surgical factor - **Posterior capsule debridement** - popliteal artery is 5-10mm behind; use posterior retractor on bone - **Do not compromise bone stock excessively** - need some bone for Stage 2 fixation - **If tissue quality poor** - consider adding local antibiotic beads for additional elution ### Step 4: Antibiotic Spacer Fabrication Prepare antibiotic-loaded cement spacer: **Static Spacer**: Mix antibiotics into cement (vancomycin 2-4g + tobramycin 2-4g per 40g PMMA). Form into block that fills the joint space. May use K-wires or rods for reinforcement. **Articulating Spacer**: Use metal femoral trial or mold cemented femoral component. Create cement tibial component. Allows range of motion and easier second-stage surgery. **Technical Pearl**: "I typically use an articulating spacer because it maintains ROM and makes the second stage easier. I mix vancomycin 4g and tobramycin 4g into each 40g pack of cement - this high-dose elutes therapeutic antibiotic levels locally. I ensure the spacer is stable and will not dislocate." - High antibiotic load acceptable for spacers (4g per 40g cement) - Cement becomes more brittle with high antibiotic load - reinforce if needed - Ensure spacer is stable - dislocation is common complication - Size appropriately to maintain soft tissue tension ### Step 5: Closure Irrigate final time. Achieve meticulous hemostasis. Close in layers - deep capsular closure is critical. Consider negative pressure wound therapy if soft tissue concerning. Apply bulky dressing and knee immobilizer. **Technical Pearl**: "I close the capsule and retinaculum securely over the spacer. If I'm concerned about the soft tissue envelope, I use negative pressure wound therapy. The patient is kept in a knee immobilizer, especially if I used a static spacer or there's any instability concern." - **Tension-free closure is essential** - excessive tension leads to wound breakdown - **Consider gastrocnemius flap** if soft tissue deficient - plastic surgery referral - **Drain placement controversial** - some surgeons avoid to prevent colonization track - **NPWT (negative pressure wound therapy)** - consider for high-risk wounds (previous sinus, diabetes, obesity) ### Antibiotic Regimen - Begin IV antibiotics after cultures obtained (may be empiric until sensitivities available) - **Duration**: Minimum 6 weeks IV organism-specific antibiotics - Infectious diseases consultation for regimen guidance - Monitor for antibiotic toxicity (renal function, levels for aminoglycosides/vancomycin) ### Monitoring - Weekly CRP and ESR initially, then every 2 weeks - Clinical wound inspection - Inflammatory markers should trend down and normalize ### Antibiotic Holiday - Stop antibiotics 2 weeks before reimplantation aspiration - Critical to avoid false-negative cultures - Reaspirate at 2-3 weeks off antibiotics ### Eradication Criteria for Stage 2 - CRP normalized (less than 10 mg/L) - ESR trending down or normalized - Knee aspiration negative (WBC less than 2000, culture negative) - No clinical signs of infection (wound healed, no erythema, no fever) - If any doubt, delay Stage 2 or repeat cultures ### Timing - Minimum 6-8 weeks after Stage 1 (longer if difficult organism or slow response) - Some surgeons use 8-12 week interval - ONLY proceed if eradication criteria met ### Step 1: Exposure and Spacer Removal Use previous incision. May require extensile exposure as knee often stiff. Remove antibiotic spacer carefully - articulating spacers may be well-fixed. Take fresh tissue cultures (5-6 samples). **Technical Pearl**: "At Stage 2, I take 5-6 fresh tissue cultures before giving antibiotics. If frozen section is available, I send tissue - greater than 5 PMN per high-power field suggests persistent infection and I would consider aborting reimplantation and repeating debridement/spacer exchange." - **Take cultures BEFORE antibiotics** - just like Stage 1; don't give prophylactic antibiotics until samples obtained - **Frozen section >5 PMN/HPF = abort reimplantation** - consider repeat debridement and spacer exchange - **Articulating spacer may be well-fixed** - careful extraction to avoid bone loss - **Extensile exposure may be needed** - knee often very stiff, especially after static spacer ### Step 2: Bone Assessment Assess bone loss using AORI classification after spacer removal: - Type 1: Intact metaphysis - standard revision - Type 2A/2B: Damaged metaphysis - augments, sleeves/cones, stems - Type 3: Deficient metaphysis - structural allograft, megaprosthesis **Technical Pearl**: "After spacer removal, I assess bone stock. There is often more bone loss than at Stage 1 due to disuse and the explantation process. I need to plan for stems to bypass the deficient metaphysis and achieve diaphyseal fixation." - **Expect MORE bone loss than at Stage 1** - disuse osteopenia, spacer erosion, debridement - **AORI Type 3 defects may need megaprosthesis** - have backup plan and equipment - **Assess ligament integrity** - MCL/LCL may be compromised; plan constraint accordingly - **Extensor mechanism assessment** - if damaged, may need reconstruction or consider alternative (arthrodesis) ### Step 3: Revision TKA Reconstruction Perform revision TKA using standard principles: - Establish tibial and femoral platforms on healthy bone - Address bone defects with augments, sleeves/cones - Add stems for diaphyseal fixation - Select constraint based on ligament competency - May use antibiotic cement for fixation (some surgeons add low-dose) **Technical Pearl**: "I approach Stage 2 as a complex revision TKA. I expect significant bone loss and plan for stems and augments. I typically use cemented components with consideration of adding low-dose antibiotics to the cement (1g vancomycin per 40g) - though this is controversial." - **Use longer stems to bypass metaphyseal defects** - achieve diaphyseal fixation and protect deficient bone - **Do not undersize constraint** - if ligaments compromised, VVC or hinge may be needed - **Cement technique** - antibiotic-loaded cement for reimplantation is controversial; lower dose (1g/40g) if used - **Intraoperative fracture risk** - osteopenic bone; handle gently, especially during impaction ### Step 4: Closure and Post-op Irrigate thoroughly. Layered closure. Consider drains. Extended antibiotic prophylaxis (some surgeons give 24-48 hours IV, others extend to 5 days). DVT prophylaxis. Early mobilization. **Technical Pearl**: "I irrigate copiously, achieve meticulous hemostasis, and close in layers. Some surgeons advocate for extended oral antibiotic suppression after Stage 2 (3-6 months), particularly for resistant organisms or immunocompromised patients. DVT prophylaxis for 35 days per Australian guidelines. Early mobilization with weight bearing as bone stock allows - typically WBAT unless significant bone loss or reconstruction concerns." - **Extended antibiotic prophylaxis** - controversial; 24-48hrs IV minimum, some extend to 5 days or add oral suppression - **DVT risk is HIGH** - prolonged immobility between stages; rivaroxaban 35 days post Stage 2 (Australian guidelines) - **Wound surveillance** - any drainage beyond 5-7 days is concerning for persistent infection - **Monitor cultures** - Stage 2 cultures may take 14 days; if positive, reinfection or persistence must be addressed ### Stage 1 Post-op - **Weight bearing**: Toe-touch or protected WB with walker (depends on spacer stability) - **Immobilization**: Knee immobilizer if static spacer or unstable - **ROM**: Early gentle ROM if articulating spacer, restricted if static - **Antibiotics**: 6 weeks IV organism-specific - **Monitoring**: Weekly CRP/ESR, clinical assessment, antibiotic levels ### Between Stages - Continue ROM exercises (if articulating spacer) - Optimize nutrition (albumin greater than 3.5, total protein greater than 6) - Stop smoking - Optimize glucose control (HbA1c less than 8) - Address any other infections (dental, urinary) - 2-week antibiotic holiday before reimplantation aspiration ### Stage 2 Post-op - **Weight bearing**: Per revision TKA protocol (WBAT unless TTO or bone loss concerns) - **ROM**: CPM or early passive ROM, target 0-90° by 2 weeks - **Antibiotics**: Variable - some give extended oral suppression (3-6 months) - **DVT prophylaxis**: 35 days per Australian guidelines - **Follow-up**: 2 weeks wound check, 6 weeks X-ray, then 3/6/12 months, annual ### Long-term Surveillance - Lifelong risk of reinfection - any dental procedures need antibiotic prophylaxis - Monitor for signs of recurrent infection - Annual review with CRP 1. 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. 2. Parvizi J, Tan TL, Goswami K, et al. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty. 2018;33(5):1309-1314.e2. 3. Insall JN, Thompson FM, Brause BD. Two-stage reimplantation for the salvage of infected total knee arthroplasty. J Bone Joint Surg Am. 1983;65(8):1087-1098. 4. Hofmann AA, Kane KR, Tkach TK, Plaster RL, Camargo MP. Treatment of infected total knee arthroplasty using an articulating spacer. Clin Orthop Relat Res. 1995;321:45-54. 5. Fehring TK, Odum S, Calton TF, Mason JB. Articulating versus static spacers in revision total knee arthroplasty for sepsis. Clin Orthop Relat Res. 2000;380:9-16. 6. Zimmerli W, Trampuz A, Ochsner PE. Prosthetic-joint infections. N Engl J Med. 2004;351(16):1645-1654. 7. Osmon DR, Berbari EF, Berendt AR, et al. Diagnosis and management of prosthetic joint infection: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2013;56(1):e1-e25. 8. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Annual Report 2023. Hip, Knee and Shoulder Arthroplasty. 9. Gomez MM, Tan TL, Manrique J, Deirmengian GK, Parvizi J. The Fate of Spacers in the Treatment of Periprosthetic Joint Infection. J Bone Joint Surg Am. 2015;97(18):1495-1502. 10. Tan TL, Kheir MM, Tan DD, Parvizi J. Polymicrobial Periprosthetic Joint Infections: Outcome of Treatment and Identification of Risk Factors. J Bone Joint Surg Am. 2016;98(24):2082-2088.

Two-Stage Exchange for Infected TKA

Two-Stage Exchange for Infected TKA