septic arthritis

• related: MSK, ID, pediatric septic arthritis, osteomyelitis, prosthetic joint infection, notes, arthrocentesis

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.