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Two-Stage Revision TKA - Stage 1: Antibiotic Cement Spacer Insertion

Comprehensive surgical technique for stage 1 two-stage revision TKA with an antibiotic cement spacer for periprosthetic knee infection and FRCS exam preparation

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By OrthoVellum Medical Education Team

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High Yield Overview

TWO-STAGE REVISION TKA - STAGE 1: ANTIBIOTIC SPACER

Arthroplasty | Advanced | Knee PJI Management

Mnemonic

KNEEKNEE PJI Diagnosis (MSIS Criteria)

Memory Hook:1 major criterion = definite PJI. 4/6 minor criteria = definite PJI. Alpha-defensin helpful adjunct.

Mnemonic

SPACERSPACER Knee Construction Principles

Memory Hook:Articulating spacer is STANDARD for knee. Static spacer = permanent stiffness in many cases.

Critical Danger Structures

Popliteal Vessels

Posterior to knee joint 1-2cm. At risk during posterior capsule debridement and cement removal. STAY ON BONE during posterior work. Cement extrusion posteriorly can lacerate vessels - monitor during polymerization.

Common Peroneal Nerve

Wraps around fibular neck laterally. At risk with lateral dissection, retraction, leg lengthening. Post-op palsy = foot drop. Avoid excessive lateral exposure below joint line.

Extensor Mechanism

Patella, patellar tendon, quadriceps. Disruption = functional disaster. Avoid forced eversion - use TTO if needed. Maintain patellar thickness >10mm for stage 2. Protect from burr heat.

MCL and LCL

Essential for knee stability. Preserve during synovectomy. Injury = spacer instability. If disrupted, consider static spacer or hinged brace. Test stability before closure.

Definite Indications

  • Chronic PJI (>4 weeks symptoms) confirmed by MSIS criteria
  • Failed DAIR for acute PJI
  • Difficult organisms: MRSA, resistant Gram-negatives, fungi, mycobacteria
  • Culture-negative PJI - two-stage safest approach when organism unknown
  • Significant bone loss requiring staged reconstruction

Consider One-Stage Instead

  • Known sensitive organism pre-operatively
  • Healthy soft tissue envelope
  • Good bone stock
  • Non-immunocompromised patient
  • Experienced high-volume centre (strict protocols)

DAIR May Be Appropriate If

  • Acute infection (<3-4 weeks symptoms or <6 weeks post-op)
  • Stable, well-fixed implants
  • Healthy patient
  • Known sensitive organism
  • Intact soft tissues

Equipment

Spacer Materials

  • Antibiotic cement: 2-3 × 40g packs (80-120g total)
  • Vancomycin powder: 6-8g (Gram-positive, MRSA coverage)
  • Tobramycin powder: 4.8g or Gentamicin 4g (Gram-negative, biofilm)
  • Commercial spacer moulds: Prostalac, Spacer-K, or femoral/tibial moulds
  • Reinforcement: Steinmann pins if hand-moulding

Extraction Equipment

  • Universal extraction set: Curved osteotomes, slap hammers
  • High-speed burr: For cement removal
  • Oscillating saw: For TTO if needed
  • Screw/post extractors: For constrained or stemmed components

Exposure Equipment

  • TTO set: Oscillating saw, drill, screws/cables for fixation
  • Retractors: Hohmann, Army-Navy, lamina spreaders
  • Self-retaining retractor: Restore visibility in deep wound

General Equipment

  • Pulsatile lavage: 9L minimum
  • Tissue sampling supplies: 5+ sterile containers
  • Drains: 2 deep drains
  • Hinged knee brace: For post-operative stability

Operative Technique

Step 1: Anaesthesia and Positioning - NO TOURNIQUET

CRITICAL: Do NOT use tourniquet in infected knee.

  • Tourniquet increases bacteremia during manipulation
  • Compromises local tissue antibiotic delivery
  • Accept higher blood loss (have blood available)

Position: Supine with bump under ipsilateral hip.

  • Foot of bed flexed to allow knee flexion
  • Thigh support for stability
  • All bony prominences padded

Exam Pearl

FRCS KEY: NO TOURNIQUET in infected knee. Examiners will test this. Tourniquet increases systemic bacteremia and reduces antibiotic penetration to infected tissue.

Step 2: Intraoperative Tissue Sampling (BEFORE Antibiotics)

HOLD prophylactic antibiotics until 5+ tissue samples obtained.

Take minimum 5 separate tissue samples from:

  1. Suprapatellar pouch/synovium
  2. Medial gutter synovium
  3. Lateral gutter synovium
  4. Interface tissue around tibial component
  5. Interface tissue around femoral component
  6. Any obvious purulent collections

Each sample in separate sterile container. Send for aerobic, anaerobic, fungal, AFB with prolonged 14-day culture. NOW give antibiotics.

Step 3: Incision and Exposure

Use previous incision (most common: midline or medial parapatellar).

Medial Parapatellar Arthrotomy (standard):

  • Incise 3cm above superior pole of patella
  • Curve around medial patella, 1cm from tendon
  • Extend distally to tibial tubercle
  • Careful dissection through scar tissue

Decision point: Can patella evert and flex knee without excessive tension?

  • YES: Proceed with exposure
  • NO: Proceed to Tibial Tubercle Osteotomy

Forced Eversion = Extensor Mechanism Rupture

NEVER force patellar eversion against resistance. Patella fracture, patellar tendon avulsion, or quadriceps rupture will occur. Use TTO for difficult exposure.

Step 4: Tibial Tubercle Osteotomy (TTO) - If Required

Indications:

  • Patella baja (patella-tendon ratio <0.8)
  • Severe scarring preventing eversion
  • Stiff knee (<70° flexion)
  • Previous quad snip or V-Y turndown

Technique:

  1. Mark osteotomy: 6-8cm long, 1cm wide, start at patellar tendon insertion
  2. Use oscillating saw for medial and distal cuts
  3. Lateral cut: osteotome to create hinge (protects lateral periosteum)
  4. Elevate tubercle fragment with attached patellar tendon
  5. Patella can now flip laterally without tension
  6. At closure: Fix with screws (bicortical) or cables

Exam Pearl

FRCS KEY: TTO protects extensor mechanism, allows excellent exposure, and heals reliably (95%+) when fixed with screws. Far better than forced eversion or muscle-damaging approaches.

Step 5: Radical Synovectomy and Debridement

Remove ALL infected tissue - this is the single most important step.

Synovectomy:

  • Complete excision of synovium from suprapatellar pouch to posterior capsule
  • Debride gutters medially and laterally
  • Remove all granulation tissue

Debridement:

  • Excise necrotic tissue to healthy bleeding margins
  • Debride bone surfaces to fresh bleeding bone
  • Remove all foreign material (sutures, cement debris)
  • Preserve MCL and LCL attachments

Step 6: Tibial Component Removal

Cemented tibial tray:

  • Identify cement-bone interface
  • Use curved osteotomes to disrupt interface
  • Thin flexible osteotomes for underneath tray
  • Remove tray, then meticulously remove ALL cement
  • High-speed burr for retained cement

Cementless tibial tray:

  • Curved osteotomes around periphery
  • Disrupt bone ingrowth progressively
  • Avoid aggressive levering (fracture risk)

Remove polyethylene insert and tibial stem if modular.

Step 7: Femoral Component Removal

Cemented femoral component:

  • Use thin osteotomes at cement-bone interface
  • Start anteriorly, work posteriorly
  • Curved osteotomes for posterior condyles
  • Remove ALL cement (critical for infection eradication)

Cementless femoral component:

  • Disruption osteotomes around periphery
  • Specialized extraction equipment may be needed
  • Protect posterior cortex (avoid notching)

Posterior Condyle Cement

Cement behind posterior condyles is difficult to remove but MUST be removed. Residual cement harbors bacteria. Use curved curettes, burrs, and visualization. Protect popliteal vessels.

Step 8: Complete Cement Removal

Remove ALL cement - any residual cement = potential treatment failure.

  • High-speed burr for adherent cement
  • Long curettes for intramedullary cement
  • Thin flexible osteotomes
  • Direct visualization from all angles

Debride canal to healthy bleeding bone:

  • Sequential reaming if needed
  • Remove all interface membrane

Step 9: Copious Pulsatile Lavage

Minimum 9 litres pulsatile lavage:

  • 3-6L during debridement
  • 3L final lavage before spacer insertion
  • Ensure lavage reaches all recesses (posterior capsule, gutters)

Exam Pearl

FRCS KEY: "Dilution is the solution to pollution." High-volume pulsatile lavage mechanically removes bacteria and debris. Essential complement to debridement.

Step 10: Antibiotic Cement Spacer Fabrication

Standard Knee Formulation (80g cement):

  • 80g cement (2 × 40g) - Palacos preferred for elution
  • Vancomycin 6-8g (Gram-positive, MRSA)
  • Tobramycin 4.8g OR Gentamicin 4g (Gram-negative, biofilm)
  • Maximum 10% antibiotic by weight

Mixing Technique:

  1. Combine antibiotic powders with cement powder FIRST
  2. Mix thoroughly for homogeneous distribution
  3. Add liquid monomer
  4. Mix to doughy consistency
  5. Mould into spacer components

Spacer Types:

  • Commercial articulating (Prostalac, Spacer-K): Standardized, reliable
  • Hand-moulded: Higher antibiotic dose possible, custom sizing
  • Static: ONLY if MCL/LCL disrupted, massive bone loss, or extreme instability

Step 11: Tibial Spacer Component Insertion

Technique:

  • Size to match tibial plateau dimensions
  • Create flat articular surface for stability
  • Insert in doughy phase
  • Cement interdigitates with cancellous bone for stability
  • Remove excess cement before polymerization

If hand-moulding:

  • Flatten posterior aspect for rotation control
  • Create slight posterior slope (3-5°)
  • May reinforce with Steinmann pin if large

Step 12: Femoral Spacer Component Insertion

Commercial systems: Follow manufacturer technique.

Hand-moulded technique:

  • Form femoral condyle shape
  • Ensure adequate anterior flange (for patella tracking)
  • Size to match native femur
  • Insert in doughy phase
  • Check alignment in extension and flexion

Step 13: Stability and ROM Assessment

Test stability:

  • Varus/valgus stress in extension and 30° flexion
  • Check for laxity or dislocation tendency

Test range of motion:

  • Goal: 0-90° minimum, ideally 0-120°
  • Check patella tracking
  • Assess for impingement

If unstable:

  • Thicker spacer construct
  • Hinged knee brace post-operatively
  • Consider static spacer if grossly unstable (MCL/LCL deficient)

Exam Pearl

FRCS KEY: Articulating spacer allows 90-120° ROM. This prevents stiffness, allows patient mobilization, and makes stage 2 exposure dramatically easier. Static spacer = often permanent stiffness.

Step 14: TTO Fixation (If Performed)

If TTO was performed, fix at closure:

  • Screw fixation (preferred): 2-3 bicortical screws (4.5mm)
  • Cable fixation: 2 cerclage cables
  • Ensure secure fixation - TTO non-union is rare but problematic

Step 15: Wound Closure

Layered closure:

  • Deep drains (2 minimum)
  • Capsule/retinaculum - strong absorbable suture
  • Subcutaneous - absorbable suture
  • Skin - staples or absorbable subcuticular

Critical: Tension-free closure. Skin necrosis = exposed spacer = treatment failure.

Step 16: Post-operative Immobilization

  • Hinged knee brace: Set for ROM 0-90° initially
  • Prevents hyperextension
  • Provides stability during mobilization
  • Gradually increase ROM as tolerated

Post-operative Protocol

Immediate Post-operative

  • Weight bearing: Protected with frame/crutches
  • DVT prophylaxis: LMWH or aspirin per protocol
  • Drains: Remove when <50mL/24hrs
  • IV antibiotics: Start post-operatively based on cultures

Rehabilitation During Spacer Period

  • ROM exercises: Start POD#1 - critical to prevent stiffness
  • Goal: 90-120° flexion, full extension
  • Physiotherapy: Daily exercises, CPM if available
  • Hinged brace: Worn during mobilization

Antibiotic Protocol

  • Duration: 6 weeks IV antibiotics minimum
  • PICC line: Insert before discharge
  • OPAT: Outpatient parenteral antibiotic therapy
  • Organism-specific: Adjust when sensitivities available
  • ID consultation: Essential for complex organisms

Monitoring

  • Weekly bloods: CRP, ESR (expect initial rise then normalization)
  • Clinical assessment: Wound, ROM, pain, systemic symptoms
  • Watch for: Spacer dislocation, wound dehiscence, stiffness

Criteria for Stage 2 (EXAM ESSENTIAL)

  1. 6 weeks IV antibiotics completed
  2. 2-6 week antibiotic holiday
  3. Normalized markers: CRP <10, ESR <30 for 2+ consecutive weeks
  4. Knee aspiration during holiday: WBC <3000, PMN <80%, negative culture
  5. Healed wound, no drainage
  6. Patient medically optimized

Exam Pearl

FRCS KEY: Do NOT rush to stage 2. Interval typically 8-12 weeks. Knee aspiration during antibiotic holiday only 50% sensitive - clinical judgment and markers equally important.

Complications

Complications: Recognition, Prevention, and Management

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 72-year-old presents 18 months after TKA with knee pain, swelling, and stiffness. CRP is 45, ESR is 68. How do you manage this patient?"

EXCEPTIONAL ANSWER
This clinical presentation with elevated inflammatory markers strongly suggests periprosthetic joint infection. My workup would begin with aspiration - the patient must be off antibiotics for minimum 2 weeks for accurate culture results. I would send aspirate for cell count and differential (WBC >3000 and PMN >80% supports PJI), culture (aerobic, anaerobic, fungal, AFB with 14-day prolonged culture), and consider alpha-defensin which has 97% sensitivity and specificity for knee PJI. I would obtain plain radiographs to assess component position and loosening. With chronic infection (18 months), I would plan two-stage revision as the gold standard. Stage 1 would involve: no tourniquet (increases bacteremia), 5+ tissue samples before antibiotics, radical synovectomy and debridement (single most important factor), component removal with complete cement extraction, 9L+ pulsatile lavage, and articulating antibiotic spacer insertion (80g cement + 6-8g vancomycin + 4.8g tobramycin). Post-operatively: 6 weeks IV antibiotics via PICC line, ROM exercises from POD#1 targeting 90-120°, then antibiotic holiday. Stage 2 criteria: normalized CRP (<10) for 2+ weeks, negative aspiration during holiday. Expected success rate 90%.
VIVA SCENARIOStandard

EXAMINER

"During stage 1 revision for knee PJI, you cannot evert the patella safely. How do you proceed?"

EXCEPTIONAL ANSWER
If the patella cannot be everted safely without excessive tension, I would perform a Tibial Tubercle Osteotomy (TTO). Forced eversion risks extensor mechanism disruption - patella fracture, patellar tendon avulsion, or quadriceps rupture - which is a devastating complication with poor functional outcome. TTO technique: I mark the osteotomy 6-8cm long and 1cm wide, starting at the patellar tendon insertion and extending distally. I use an oscillating saw for the medial and distal cuts, preserving a lateral periosteal hinge. Using an osteotome, I create a controlled crack to elevate the tubercle with attached patellar tendon. The patella can now flip laterally without tension, providing excellent exposure. At closure, I fix the TTO with 2-3 bicortical screws (preferred) or cables. TTO heals reliably in 95%+ of cases when properly fixed. The key is recognizing when TTO is needed - patella baja (ratio <0.8), previous surgery with scarring, stiff knee with <70° pre-operative flexion. TTO is far superior to muscle-damaging alternatives like quadriceps snip or V-Y turndown.
VIVA SCENARIOStandard

EXAMINER

"Why do you choose an articulating spacer rather than a static spacer for knee PJI, and when might you use a static spacer?"

EXCEPTIONAL ANSWER
Articulating spacer is the STANDARD of care for knee PJI for several critical reasons. First, knee stiffness after static spacer is often permanent and devastating - patients may lose 60-80° of motion that never recovers, even after stage 2. Second, articulating spacers allow ROM exercises between stages, typically achieving 90-120° flexion, which maintains soft tissue pliability and makes stage 2 exposure dramatically easier. Third, patient quality of life is much better - they can mobilize, participate in rehabilitation, and maintain muscle strength. Fourth, evidence shows equivalent infection eradication rates between static and articulating spacers, so there is no infection control advantage to static. I would only use a static spacer in specific situations: gross collateral ligament insufficiency (MCL or LCL disrupted) making articulating spacer unstable, massive bone loss preventing creation of stable articulating surfaces, severe extensor mechanism disruption, or a patient who is medically unfit and won't mobilize anyway. Even then, I would strongly consider a constrained spacer design rather than completely static. The 10-15% dislocation rate with articulating spacers is accepted as the trade-off for preserving motion.

Two-Stage Revision TKA - Stage 1 - Exam Summary

High-Yield Exam Summary

References

  1. Parvizi J, 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. Deirmengian C, et al. Diagnosing periprosthetic joint infection: has the era of the biomarker arrived? Clin Orthop Relat Res. 2014;472(11):3254-3262.

  3. Hofmann AA, et al. Two-stage reimplantation for infected total knee replacement. Knee. 2005;12(1):9-18.

  4. Fehring TK, et al. Articulating versus static spacers in revision total knee arthroplasty for sepsis. Clin Orthop Relat Res. 2000;(380):9-16.

  5. Freeman MG, et al. Articulating antibiotic spacers in two-stage exchange for prosthetic knee infection. Clin Orthop Relat Res. 2007;464:65-72.

  6. Emerson RH, et al. Comparison of a static with a mobile spacer in total knee infection. Clin Orthop Relat Res. 2002;(404):132-138.

  7. Whiteside LA. Exposure in difficult total knee arthroplasty using tibial tubercle osteotomy. Clin Orthop Relat Res. 1995;(321):32-35.

  8. Osmon DR, et al. Diagnosis and management of prosthetic joint infection: clinical practice guidelines by IDSA. Clin Infect Dis. 2013;56(1):e1-e25.

  9. Kurtz SM, et al. Economic burden of periprosthetic joint infection in the United States. J Arthroplasty. 2012;27(8 Suppl):61-65.

  10. Diaz-Ledezma C, et al. Revision total knee arthroplasty for periprosthetic joint infection: the positive predictive value of the preoperative workup. J Arthroplasty. 2014;29(9):1802-1806.