Septic arthritis


  • Blood cultures recommended. If positive, repeat blood cultures to ensure clearance of bacteremia.
  • Synovial fluid for cell count and C&S (fluid can be injected into paediatric blood culture bottle). NB: Gram stain lacks sensitivity; whereas culture is more sensitive. Tailor antibiotics according to Gram stain and subsequent C&S results. Typical findings of septic arthritis: purulence, variable viscosity, WBC > 50 x 109/L with > 75% neutrophils. NB: protein and glucose levels are not diagnostically useful.
  • CBC and differential, serum creatinine.
  • ESR, CRP - low sensitivity for diagnosis but if initially elevated, may be useful to monitor response.
  • Plain x-ray +/- ultrasound +/- bone scan/MRI
    • Ultrasound to confirm that there is fluid in the joint
    • MRI superior to x-ray and bone scan for early diagnosis of bone/joint infections
    • Bone scan may be falsely positive if recent trauma/aspiration of joint/superficial infection

- Drainage and/or debridement of the joint space recommended if practical, and mandatory for infected hip.

- If fever, lethargy, or poor feeding in the neonate, recommend lumbar puncture to rule out meningitis.

- Specialist consult is recommended.