[Differentiation between transient synovitis and septic arthritis of the hip with clinical and ultrasound criteria]

Introduction: Ultrasound does not distinguish between different types of synovitis. The aim of this study was to evaluate its contribution, together with several clinical data, in the diagnosis of septic arthritis (SA) and transient synovitis (TS) of the hip.

Methods: Prospective study of patients diagnosed with unilateral SA or TS of the hip carried out between December 2006 and July 2009. A set of clinical variables and ultrasound measurements were analysed. The ultrasound examinations were performed using a standardised procedure.

Results: The sample included 26 children, 22 diagnosed with TS and 4 with SA. A difference was found in the history of fever (P=0.002). On the other hand, no differences were detected in the age of the children, although mean and median in the TS group were 6 years vs a mean of 4.3 with a median of 2.3 years in the SA group. There were no differences in the ultrasound measurements either. The positive predictive value of the criterion "older than 4 years of age and no history of fever" for the diagnosis of transient synovitis was 100%, while "younger than 4 years and history of fever" for the diagnosis of septic arthritis was 75%, once radiology had excluded orthopaedic processes and ultrasound showed an effusion.

Conclusions: In spite of the study limitations (sample size and low prevalence) the combination of age and history of fever appears to be useful in distinguishing transient synovitis from septic arthritis. The contribution of ultrasound was to confirm the presence of joint effusion.