Prosthetic Joint Infection (PJI) — Diagnosis and Management

Prosthetic joint infection represents a microbial colonization of the implant-tissue interface, complicated by biofilm formation that protects pathogens from host immunity and antimicrobial agents. Classification by timing distinguishes early postoperative (<3 months, typically virulent pathogens like Staphylococcus aureus, gram-negative bacilli), delayed/low-grade chronic (3-24 months, often coagulase-negative staphylococci, Cutibacterium acnes), and late hematogenous (>24 months, originating from distant infection sites).

Common pathogens include Staphylococcus aureus (including MRSA), coagulase-negative staphylococci (especially Staphylococcus epidermidis), streptococci, enterococci, gram-negative bacilli, anaerobes (Cutibacterium acnes particularly in shoulder arthroplasty), and rarely fungi or mycobacteria. Polymicrobial infections occur in 15-20%. Increasing concern surrounds difficult-to-treat pathogens including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and multidrug-resistant gram-negatives.

Diagnostic evaluation integrates inflammatory markers (ESR, CRP, D-dimer), synovial fluid analysis (cell count >3000-4000/μL with neutrophil predominance, leukocyte esterase, alpha-defensin), and microbiologic studies (multiple cultures, sonication of explanted implants increasing yield). Validated diagnostic criteria (MSIS, EBJIS) categorize as definite, likely, or unlikely infection. Surgical management depends on chronicity and host factors: DAIR for early or acute hematogenous infection with stable implant, one-stage revision in selected cases with antibiotic-loaded cement, and two-stage revision (gold standard for chronic PJI) involving prosthesis removal, antibiotic spacer placement, prolonged antimicrobial therapy, and reimplantation.