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.