Here, HMGB1 protein levels were significantly higher in the synovial fluid of patients with LCPD by threefold compared with controls (p < 0.05), and were highly correlated with IL‐6 levels (Pearson correlation coefficient 0.94, p < 0.001, R2 = 0.87). This evidence concerns the gene HMGB1 and Legg-Calve-Perthes disease.