Septic arthritis
Investigations:
- 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.