Septic Arthritis



Microbiologic infection and inflammation of the usually sterile joint space


  • Most common age: toddler and school age (2 to 6 years)
  • Predominant sex: male (2:1 female)
  • Most common location: lower extremities (hip, knee, and ankle) and large joints (hip, shoulder, elbow)


  • Entry of bacteria into joint space
    • Hematogenous spread (seeding during transient bacteremia) most common
    • Direct inoculation (penetrating trauma or during surgery)
    • Extension from bone infection (mainly in children <1 year old when vessels cross from metaphysis to epiphysis)
  • In response to cytokines, influx of inflammatory cells and release of proteolytic enzymes
  • Leads to destruction of synovium and cartilaginous structures


  • Most common causes by age:
    • Neonates: group B Streptococcus, Staphylococcus aureus, Escherichia coli, and Candida albicans
    • Older children: S. aureus, group A Streptococcus, Kingella kingae in toddlers, Haemophilus influenzae
  • Also consider
    • Salmonella: in patients with sickle cell
    • Neisseria gonorrhoeae: in sexually active adolescents and in neonates
    • Neisseria meningitidis
    • Mycobacterium tuberculosis
    • Anaerobes (rare)
    • Rubella
    • Parvovirus
    • Hepatitis B or C
    • Mumps
    • Herpesviruses (Epstein-Barr virus, cytomegalovirus, herpes simplex virus, varicella-zoster virus)
    • Fungal etiologies (e.g., coccidioidomycosis, rarely candida)


  • Sickle cell disease: Salmonella
  • Immunocompromised patients: Mycoplasma, Ureaplasma, Klebsiella, or Aspergillus infection

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