When Can We Avoid Knee Arthrocentesis in Lyme-Endemic Areas?

The knee is a common location for arthritic presentation of Lyme disease, but the possibility of bacterial septic arthritis must be considered before choosing antibiotic treatment. Because Lyme diagnostics can take several days, arthrocentesis is often performed to help guide therapy. To identify predictors of septic arthritis, investigators retrospectively evaluated 474 children (age range, 1–18 years) with knee monoarthritis who presented to an emergency department in a Lyme-endemic area between 2000 and 2012. Half the children had Lyme arthritis, 3% had septic arthritis, and 47% had other types of inflammatory arthritis.

In multivariate analysis, absolute neutrophil count (ANC) >10,000 cells/mm³ and erythrocyte sedimentation rate (ESR) ≥4…