Transient synovitis of the hip: Development and validation of a new diagnostic algorithm

To develop and validate an algorithm to rapidly distinguish transient synovitis (TS) of the hip from differential diagnoses without additional tests. This retrospective cohort study included all children admitted for non-traumatic limping in the emergency department at Lille University-Hospital between 2016 and 2020. The gold standard was a definitive diagnosis at follow-up visit. All variables associated with acute limping in children were analysed in univariate and multivariable analyses. An algorithm was then developed using recursive partitioning and validated internally on a subset of patients. There were 995 patients included (mean age 5.3 years; males 63%); 337 had a TS including 210 confirmed at follow-up visit and 354 another diagnosis. After multivariable analysis, the relevant variables for distinguishing between TS and differential diagnoses were: age 3-10 years, absence of fever, absence of local inflammation, sudden onset of limping on awakening. An algorithm combining these variables was developed (n = 297) and validated internally (n = 175) for children >12 months with limping for ≤10 days, with a specificity of 98.2% and a positive likelihood ratio of 19.6. No serious differential diagnoses were missed. Use of this algorithm enables the diagnosis of TS without additional tests and without missing serious differential diagnoses.