Identifying predictive factors of pediatric septic arthritis of the knee in a lyme endemic area

Background: Septic arthritis of the knee in the pediatric patient is a diagnosis that requires prompt identification and treatment. The purpose of this study was to identify clinical and laboratory parameters that allow differential diagnosis of septic arthritis from non-septic arthritis in children. Methods: Fifty-four pediatric patients with atraumatic isolated knee pain were retrospectively identified at three institutions and diagnosed with septic arthritis (SA, N = 28), Lyme arthritis (LA, N = 11), or transient synovitis (TS, N = 15). Clinical and laboratory data were analyzed to identify which factors were most predictive of SA of the knee. Results: Fever at time of presentation, a negative anti-streptolysin-O (ASO), erythrocyte sedimentation rate (ESR) > 40 mm/hr, and C-reactive protein (CRP) > 20 mg/L were the most predictive factors for distinguishing between septic arthritis (SA) and non-septic arthritis (transient synovitis or Lyme arthritis). Elevated ESR and CRP were both significantly higher in patients with SA when compared to TS or LA. Conclusion: When evaluating children with atraumatic isolated knee pain, a combination of the above factors should be utilized when ruling out septic arthritis.