Septic arthritis

Investigations:

• Blood cultures recommended (positive in 60%). If positive, repeat blood cultures to ensure clearance of bacteremia.
• Synovial fluid for cell count, C&S, and crystal analysis.
  • Typical findings of septic arthritis: purulence, variable viscosity, WBC > 50 x 10⁹/L with > 75% neutrophils. Protein and glucose levels are not diagnostically useful.
  • Gram stain lacks sensitivity (only positive in 1/3); whereas culture is positive in 90%.
  • Tailor antibiotics according to C&S results.
• CBC and differential, serum creatinine.
• ESR, CRP - low sensitivity for diagnosis but if initially elevated, may be useful to monitor response.
• Plain x-ray +/- MRI
  • MRI superior to x-ray and bone scan for early diagnosis of bone/joint infections

- Drainage and/or debridement of the joint space recommended.