The Peritubercle Lucency Sign as a Considerable Predictive Factor for Contralateral Hip Slippage in Unilateral Slipped Capital Femoral Epiphysis Cases.

To determine whether the radiographic parameter at the epiphyseal tubercle region (peritubercle lucency sign) on the unaffected side can predict slipped capital femoral epiphysis (SCFE).  We retrospectively reviewed patients who received an initial diagnosis of unilateral SCFE between 1995 and 2020 at a pediatric hospital in a Brazilian state's capital. The patients were monitored for at least 18 months. Two reviewers independently and blindly assessed the radiographs for the presence or absence of the sign. Disagreements were resolved by a third senior reviewer.  Out of the 115 cases reviewed, the peritubercle lucency sign was observed in 21 of the 30 patients who developed the disease in the contralateral hip. The sign was observed on an average of 21 days after the diagnosis on the initial side, and approximately 301 days prior to the condition affecting the contralateral hip. It was present in 95% and 85% of the cases on the lateral (frog-leg) and anteroposterior (AP) views, respectively. Interobserver reliability was measured using the Kappa test (k = 0.0801). There was a significant relationship between the presence of the sign and SCFE (  < 0.001).  We propose that the peritubercle lucency sign can be used as a supplementary tool in early diagnosis, for it is beneficial in the therapeutic planning.  Level III - Diagnostic Study In Nonconsecutive Patients (Without Consistently Applied 'Gold Standard' As Reference).