Septic Arthritis in Adults

Background

• Septic arthritis refers to an infection of 1 or more joints, most commonly of bacterial origin, but may include fungal, mycobacterial, and viral infections.
• Infection of the joint may be due to hematogenous spread, direct inoculation, or contiguous spread.
• Risk factors include older age, IV drug use, diabetes, immunosuppressed patients, an underlying joint injury or damage, and presence of a prosthetic joint.
• Skin flora such as Staphylococcus aureus, including methicillin-resistant strains, and streptococcal species are the most common infecting organisms; gram-negative bacteria (including gonococcus), fungi, and atypical organism are less common.

Evaluation

• Suspect septic arthritis in any patient with an acute onset of a hot, painful, red, tender, swollen joint with restricted movement especially with history of prior joint surgery.
• Diagnostic evaluation:
  • obtain synovial fluid cell counts, Gram stain and culture, and microscopy for crystals (Strong recommendation)
    • synovial white blood cell count typically elevated, but this is not specific for infection
  • obtain blood cultures, which may be positive even when synovial fluid culture is negative (Strong recommendation)
  • obtain serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
• Imaging is not diagnostic for septic arthritis. Consider plain x-ray to define any underlying joint damage and magnetic resonance imaging (MRI) if osteomyelitis is suspected.

Management

• Initial management consists of drainage and antibiotic therapy.
  • Consider aspiration for small joints.
  • Consider arthroscopy and arthrotomy for large joints or if aspiration is ineffective.
  • Empiric antibiotics should be started as soon as Gram stain and culture material are obtained.
    • Antibiotic selection is based on the clinical presentation, host risk factors, local epidemiology, and Gram stain.
    • Common options based on Gram stain include:
      • for gram-positive cocci, vancomycin 15-20 mg/kg IV every 8-12 hours
      • for gram-negative rods, ceftazidime 2 g IV every 8 hours, cefepime 2 g IV every 8 hours, or ceftriaxone 1-2 g IV every 24 hours (if pseudomonas is not a concern)
    • When Gram stain is negative, vancomycin plus either ceftriaxone or cefepime is a reasonable option.
    • For suspected sexually transmitted infection, give ceftriaxone 1 g intramuscularly or IV daily plus doxycycline 100 mg orally twice daily for 7 days if chlamydial infection not excluded.
• The optimal duration of treatment has not been determined.
  • Gonococcal arthritis is usually treated for at least 7 days.
  • Nongonococcal arthritis usually requires 2-4 weeks of IV antibiotics.
  • Additional considerations in determining duration and route of therapy include; infecting pathogen, bioavailability of chosen antibiotic, and clinical response.