Prosthetic Joint Infections

PJI Basics - Setting the Stage

• Prosthetic Joint Infection (PJI): A severe complication involving the artificial joint and adjacent tissues, often leading to implant failure.
• Significance: Major cause of morbidity, multiple surgeries, prolonged antibiotics, and ↑ healthcare costs.
• Temporal Classification (from index surgery):
  • Early Onset: <3 months. Often acquired intraoperatively.
  • Delayed Onset: 3-12 months (some use 3-24 months). Typically low-virulence organisms.
  • Late Onset: >12 months (some use >24 months). Usually due to hematogenous seeding.

⭐ PJI is a leading reason for revision arthroplasty, especially in knee replacements (TKA).

Bugs & Biofilms - The Culprit Crew

• Key Pathogens by Onset:
  • Early (<3 months): Staphylococcus aureus (most common overall, MSSA/MRSA), Gram-negative bacilli (e.g., Pseudomonas, Enterobacteriaceae).
  • Delayed (3-12 months): Coagulase-negative Staphylococci (CoNS) like S. epidermidis; Cutibacterium acnes (especially shoulder implants).
  • Late (>12 months): Hematogenous spread; S. aureus, Streptococci, Gram-negative bacilli.
• Biofilm - The Microbial Fortress:
  • Definition: Structured community of bacteria encased in a self-produced Extracellular Polymeric Substance (EPS), adherent to the prosthesis.
  • Pathogenesis: Attachment → Microcolony formation & EPS production → Maturation (3D structure) → Dispersion.
  • Significance: ↑ Antibiotic resistance (often 100-1000x), shields from host immunity, necessitates implant removal for cure.

⭐ Staphylococcus epidermidis, a CoNS, is notorious for its robust biofilm formation, leading to chronic, low-grade, delayed-onset PJIs that are difficult to treat without implant removal.

Diagnosis Dilemma - Cracking the Case

• Clinical Clues:
  • Persistent joint pain (new/worsening).
  • Local: Swelling, erythema, warmth.
  • Sinus tract (strong PJI indicator).
  • Fever (acute PJI).
• Lab Markers:
  • Serum: ↑ ESR (>30 mm/hr), ↑ CRP (>10 mg/L).
  • Synovial Fluid:
    • WBC >3000/µL, PMN% >80% (hip/knee).
    • Culture (aerobic/anaerobic): Min. 2 samples.
    • Leukocyte Esterase (++), Alpha-defensin.
• Diagnostic Standards:
  • MSIS or ICM 2018 criteria are key.

  ⭐ A sinus tract communicating with the prosthesis is a major criterion for PJI diagnosis.

Treatment Tactics - Battling the Bugs

• Core Goals: Eradicate infection, pain relief, restore function, prevent recurrence.

• Multidisciplinary Team: Ortho, ID, Microbiology.

• Surgical Strategies:

  • DAIR (Debridement, Antibiotics, and Implant Retention):
    • Early PJI (<4 wks post-op OR acute hematogenous <3 wks symptoms).
    • Stable implant, susceptible organism, good soft tissue.
  • One-Stage Exchange:
    • Select cases: known susceptible organism, good host & tissues.
    • Implant removal, debridement, immediate reimplantation.
  • Two-Stage Exchange (Gold Standard for Chronic PJI):
    • Stage 1: Implant removal, debridement, antibiotic spacer + IV Abx (4-6 wks).
    • Stage 2: Reimplantation after infection clearance (typically 2-8 wks post-Abx).
  • Resection Arthroplasty / Amputation: Salvage for severe/failed cases.

• Antibiotic Therapy:

  • Prolonged: IV then oral (weeks to months).
  • Biofilm-active agents (e.g., Rifampicin for Staph).
  • Guided by culture & sensitivity.

⭐ Rifampicin is crucial for treating Staphylococcal PJI due to its excellent biofilm penetration, but it should never be used as monotherapy to prevent resistance.

High‑Yield Points - ⚡ Biggest Takeaways

• Key organisms: Staphylococcus aureus and Coagulase-Negative Staphylococci (CoNS) are most common.
• Diagnosis: Synovial fluid culture is gold standard; ↑ ESR/CRP are sensitive inflammatory markers.
• Biofilm formation on implants makes eradication challenging, often requiring implant removal.
• Treatment for acute early PJI: DAIR (Debridement, Antibiotics, Implant Retention).
• Gold standard for chronic PJI: Two-stage revision arthroplasty.
• Antibiotic-loaded cement spacers are integral to two-stage revision success.
• Prolonged antibiotics (IV then oral) are essential post-operatively for 4-6 weeks or longer based on sensitivity and clinical response.