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Validation of Septic Knee Monoarthritis Prediction Rule in a Lyme Disease Endemic Area. Pediatr Emerg Care 2022 Feb 01;38(2):e881-e885



Pubmed ID




Scopus ID

2-s2.0-85123969087 (requires institutional sign-in at Scopus site)   5 Citations


OBJECTIVE: In Lyme disease endemic areas, Lyme and septic arthritis often present similarly. A published septic knee arthritis clinical prediction rule includes 2 high-risk predictors: absolute neutrophil count of 10,000 cells/mm3 or greater and erythrocyte sedimentation rate of 40 mm/h or greater. The objective of the study was to externally validate this prediction rule in a multicenter prospective cohort.

METHODS: We enrolled a prospective cohort of children with knee monoarthritis undergoing evaluation for Lyme disease at 1 of 8 Pedi Lyme Net emergency departments located in endemic areas. We defined a case of septic arthritis with a positive synovial fluid culture or a synovial fluid white blood cell count of 50,000 or greater per high powered field with a positive blood culture and Lyme arthritis with a positive or equivocal C6 EIA, followed by a positive supplemental immunoblot. Other children were classified as having inflammatory arthritis. We report the performance of the septic arthritis clinical prediction rule in our study population.

RESULTS: Of the 543 eligible children, 13 had septic arthritis (2.4%), 234 Lyme arthritis (43.1%), and 296 inflammatory arthritis (54.5%). Of the 457 children (84.2%) with available laboratory predictors, all children with septic arthritis were classified as high risk (sensitivity, 100%; 95% confidence interval [CI], 77.2%-100%; specificity, 68.1%; 95% CI, 63.6-73.3; negative predictive value, 278/278 [100%]; 95% CI, 98.6%-100%). Of the 303 low-risk children, 52 (17.2%) underwent diagnostic arthrocentesis.

CONCLUSIONS: The septic knee arthritis clinical prediction rule accurately distinguished between septic and Lyme arthritis in an endemic area. Clinical application may reduce unnecessary invasive diagnostic procedures.

Author List

Grant DS, Neville DN, Levas M, Balamuth F, Garro AC, Bennett JE, Thompson AD, Kharbanda AB, Lyons TW, Nigrovic LE, for Pedi Lyme Net


Michael Levas MD Associate Professor in the Pediatrics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Arthritis, Infectious
Diagnosis, Differential
Knee Joint
Leukocyte Count
Lyme Disease
Prospective Studies
Synovial Fluid