Septic Arthritis

Description

Microbiologic infection and inflammation of the usually sterile joint space

Epidemiology

• 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)

Pathophysiology

• 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

Etiology

• 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)

Commonly Associated Conditions

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