Alper DUNKI
Musculoskeletal Infections and Microbiology
Spot Knowledge
Staphylococcus aureus is the leading cause of MSK infections.
MRSA strains (community vs hospital) differ in virulence.
Children 6 mo–4 yrs: Kingella kingae is most common.
Sickle cell disease: Salmonella is typical pathogen.
Implant infections: Biofilm formation → requires debridement.
MRI is nearly 100% sensitive in early osteomyelitis.
Epidemiology & Microbiology
Main pathogens: S. aureus, S. epidermidis, coagulase-negative staphylococci.
Gram-negative: E. coli, Proteus, Klebsiella, Enterobacter.
IV drug users: Pseudomonas, Serratia, fungi.
Gonococcal arthritis: Neisseria gonorrhoeae in young adults.
Post-shoulder surgery: Propionibacterium acnes.
Pathogenesis
Synovium lacks basement membrane → easy microbial entry.
S. aureus virulence factors: Protein A, polysaccharide capsule, biofilm, PVL toxin.
Biofilms protect bacteria in prosthetic joint infection → need surgery + antibiotics .
Clinical Findings
Septic arthritis: monoarticular, knee most common.
Kocher criteria (peds): fever, non-weight bearing, ESR >40, WBC >12,000.
Osteomyelitis (peds, MRSA risk): fever >38°C, Hct <34%, WBC >12,000, CRP >13.
Diagnosis
Radiology: joint space narrowing, periosteal reaction, Codman’s triangle.
MRI: gold standard, early detection.
Lab: CRP, ESR monitoring.
Synovial fluid: WBC >50,000, >90% PMN highly suggestive.
Treatment
Osteomyelitis: 4–6 wks (≥6 for MRSA).
Septic arthritis: 3–4 wks.
Adults empiric: Vancomycin + Ceftriaxone.
Children (MRSA): IV Vancomycin (15 mg/kg q6h).
Implant infection: add Rifampin (synergy vs biofilm).
C. difficile must be considered in prolonged antibiotic use .
Antibiotic Prophylaxis in Orthopaedics
Not routine in elective surgery without implants.
Give ≤1 h before incision (Vanco: 2 h prior).
1st line: cephalosporins.
Clinda/Vanco for β-lactam allergy.
Duration: ≤24 h.
Prevention of Surgical Site Infection
Risk factors: DM, obesity, malnutrition, smoking, RA, MRSA colonization.
Measures: chlorhexidine prep, double gloving, monofilament sutures, drains <24h, normothermia, glycemic control.
Periprosthetic Joint Infection
Knee arthroplasty: Synovial WBC >2,500/mm³ or >90% PMN → chronic infection.
Gram stain not useful.
Atypical & Rare Infections
Necrotizing fasciitis: S. pyogenes, CA-MRSA; urgent surgery.
Gas gangrene: Clostridium spp., surgery + high-dose PCN/Clinda.
TB: spine most common, 4-drug ≥6 months.
NTM: M. marinum (hand infections post-water exposure).
Vibrio vulnificus: severe necrotic infection after seawater.
Candida albicans: rare prosthetic infection.
Lyme (Borrelia): late monoarthritis.
HIV/AIDS: optimize immunity pre-surgery .
References
Masters EA, et al. Nat Rev Microbiol. 2022.
Touaitia R, et al. Antibiotics. 2025.
Sanpera I, et al. Current Concepts in Septic Arthritis. 2024 .