Infected Arthroplasty Management

Basics & Bugs - Infection Unmasked

• Periprosthetic Joint Infection (PJI): Infection involving prosthesis & adjacent tissues.
• Classification (Timing & Source):
  • Early (<3 months post-op): Exogenous (intraoperative contamination).
    • Pathogens: S. aureus (MSSA/MRSA), Gram-negatives.
  • Delayed (3-12 months post-op): Exogenous (low-virulence organisms).
    • Pathogens: CoNS (S. epidermidis), Cutibacterium acnes.
  • Late (>12 months post-op): Hematogenous spread.
    • Pathogens: S. aureus, Streptococci, Gram-negatives.
• Common Culprits:
  • Overall: Staphylococcus species (both S. aureus & CoNS).
  • Biofilm formation is key to chronicity.

⭐ Staphylococcus aureus is the most common pathogen in acute PJI, while Coagulase-Negative Staphylococci (CoNS) like S. epidermidis are more frequent in chronic PJI.

Spotting Trouble - Diagnosis Decoded

Suspect PJI: Persistent pain (esp. rest), fever, warmth, erythema, wound discharge, or sinus tract.

• Initial Workup:
  • Labs: ↑ ESR (>30 mm/hr), ↑ CRP (>10 mg/L). Serial monitoring vital.
  • Imaging: X-ray (loosening, osteolysis, periosteal reaction).
• Synovial Fluid Aspiration (CRUCIAL):
  • Cell Count: WBC >3000/µL (hip/knee PJI, chronic).
  • Differential: PMN% >80%.
  • Culture: Aerobic & anaerobic (hold antibiotics).
  • Biomarkers: Alpha-defensin, Leukocyte Esterase (++).
• MSIS Criteria (2018) for PJI Diagnosis:
  • 1 Major: Sinus tract OR ≥2 positive cultures (identical organism).
  • ≥3 Minor (of 6): ↑ESR/CRP, ↑Synovial WBC, ↑Synovial PMN%, +Histology (>5 PMNs/HPF), +Culture (single), +LE strip/Alpha-defensin.

⭐ Synovial fluid WBC count and PMN% are key components of MSIS criteria for PJI diagnosis.

Fixing the Mess - Surgical Fixes

• Goal: Eradicate infection, pain relief, function restoration.
• Factors: Infection timing, organism, implant stability, host, soft tissue.

• 1. DAIR: (Debridement, Antibiotics, Implant Retention)
  • Acute PJI (<4wks post-op / <3wks symptoms); stable implant; sensitive organism.
• 2. One-Stage Exchange:
  • Healthy host; known sensitive organism; good soft tissue/bone.
• 3. Two-Stage Exchange: (⭐ Gold Standard for Chronic PJI)
  • Stage 1: Removal, debridement, antibiotic spacer.
  • Interim: Systemic Abx (4-6wks).
  • Stage 2: Re-implantation post-clearance.

  ⭐ Two-stage exchange is preferred for chronic PJI, especially with resistant organisms or compromised hosts.

• 4. Resection Arthroplasty: (e.g., Girdlestone - hip)
  • Salvage; low demand; medically unfit; persistent infection.
• 5. Amputation:
  • Last resort: uncontrolled infection; severe tissue loss.

Drug Power & Defense - Germ Warfare

• Core Principles: Bactericidal, good penetration. IV then oral switch.
• Antibiotic Choice (Culture-guided):
  • MSSA: Nafcillin/Cloxacillin, Cefazolin.
  • MRSA/CoNS: Vancomycin, Linezolid, Daptomycin. + Rifampicin (combo).
  • Streptococci: Penicillin G, Ceftriaxone.
  • Gram-negatives: Piperacillin-tazobactam, Cefepime.
• Duration: 4-6 weeks IV/oral post-surgery. Lifelong suppression if retained.
• Antibiotic-Loaded Cement Spacers (ALCS): High local antibiotic delivery (Vancomycin, Gentamicin).
• PJI Prevention:
  • Pre-op: S. aureus decolonization, optimize comorbidities.
  • Intra-op: Prophylactic antibiotics (<60 min pre-incision), strict asepsis.

  ⭐ Rifampicin is key for Staphylococcal PJI (anti-biofilm), always use in combination to prevent resistance.

High‑Yield Points - ⚡ Biggest Takeaways

• MSIS criteria are key for diagnosing Periprosthetic Joint Infection (PJI).
• Two-stage exchange arthroplasty remains the gold standard for managing chronic PJI.
• DAIR (Debridement, Antibiotics, Implant Retention) is suitable for acute early PJI (<4 weeks) with a stable implant.
• Antibiotic-loaded cement spacers (e.g., Vancomycin, Tobramycin) are vital in two-stage procedures.
• Prolonged IV antibiotic therapy (typically 4-6 weeks) is essential after surgical intervention.
• Staphylococcus aureus is the most common causative pathogen in PJI.