The routine cutoff displacement of 2 mm may not reliably reflect the stability of paediatric lateral humeral condyle fractures.

INTRODUCTION: Lateral humeral condyle fracture is one of the most common fractures in children. However, the prediction of the stability of the fracture with a cutoff displacement of 2 mm remains controversial. The aim of this study was to evaluate the reliability of the routine cutoff displacement of 2 mm in predicting the stability of paediatric lateral humeral condyle fractures. METHODS: A cohort of 79 children with imaging results for lateral humeral condyle fractures from 2013 to 2019 was evaluated. The displacement on the radiographs was measured by three surgeons at different levels, and ultrasound images were obtained by two senior surgeons. The interobserver and intraobserver reliability was assessed by the intraclass correlation coefficient (ICC). A binary logistic regression model and receiver operating characteristic (ROC) curves were used to evaluate the association between the measurement and the integrity of cartilage hinges. RESULTS: The ICC for the interobserver reliability was 0.85, and the intraobserver reliability was 0.93. For each additional millimetre of displacement, the odds of cartilage hinge disruption increased by 70%. The ROC curve determined that the Youden index was only 0.07 (sensitivity, 97.8%; specificity, 8.8%) with a cutoff displacement of 2 mm. CONCLUSIONS: The routine cutoff displacement of 2 mm may not reliably reflect the stability of paediatric lateral humeral condyle fractures. The cutoff value is sensitive but not specific for predicting whether the cartilage hinge is intact.