septic arthritis

Causes

Septic arthritis is an infection of the synovial joint space.

Septic arthritis can occur through hematogenous spread, local extension, or direct inoculation (trauma).

  • S. aureus: most common, more than 50% of cases
    • children > 2
    • invasive procedures
  • Streptococci
  • S. epidermidis: foreign bodies, prosthetic joints
  • N. gonorrhoeae: In young, sexually active patients who are otherwise healthy
  • Salmonella: sickle cell disease
  • P. aeruginosa and GNR: in IV drug users and diabetics
  • fungal and candida infections: immunocompromised patients

Symptoms

  • Acute onset, monoarticular
  • Joints affected: knee > hip > wrists > shoulder > ankles
  • triad: fever, joint pain, decreased ROM

Physical exam findings in septic arthritis include a warm, red, and tender joint with possible skin lesions over the affected area.

Diagnosis

  • Serum:
    • WBC count > 10,000
    • ESR > 30
    • CRP > 5
  • Joint aspirate:
    • Definitive: positive gm stain or culture
    • Presumptive: WBC count > 50,000 with purulent fluid
    • also shows a high neutrophil count and low glucose.
  • Imaging: Ultrasound and MRI can help confirm joint effusion in septic arthritis.

Treatment

  • 2 sets of blood cultures to assess origin
  • surgical irrigation and drainage of the affected joint.
  • Empiric abx:
    • GPC: vancomycin
    • GNC: ceftriaxone or fluoroquinolone
    • GNR: 3rd/4th generation cephalosporins: ceftazidime, cefepime, pip-tazo, carbapenem
    • Penicillinase-resistant penicillins: oxacillin, naficillin, cefazolin
    • suspected pseudomonas: IV ceftazidime + IV aminoglycoside
    • N gonorrhea: rocephin and azithromycin or doxy (for chlamydia), surgical drainage usually not necessary
  • Tailor abx for 2 weeks
    • concomitant bacteremia: at least IV 4 weeks
    • endocarditis: tailor duration to endocarditis duration

Monitoring CRP is the best measure of treatment efficacy in cases of septic arthritis.