Age associations, sex differences, and interrelationships of five skeletal maturity indicators: a cross-sectional study in a Korean clinical sample

Abstract Skeletal maturity indicators are widely used to time orthopedic intervention, but the extent to which they convey overlapping information is unclear. In an age-balanced sample of 203 Korean subjects (100 males, 103 females) aged 6.0–20.8 years, five indicators—cervical vertebral maturation (CVM), spheno-occipital synchondrosis (SOS) fusion, and midpalatal (MPS), zygomaticotemporal (ZTS), and zygomaticomaxillary (ZMS) suture maturation—were evaluated concurrently. Age–maturation associations were assessed with Spearman correlations and Somers’ D yx , age-adjusted sex differences with the van Elteren test, and between-sex differences in these associations with age × sex interaction tests; inter-indicator relationships were examined using bootstrapped age-adjusted partial Spearman correlations. All indicators were associated with age ( P < 0.001), most strongly CVM (r s = 0.90) and SOS (r s = 0.87), whereas the intermediate stages of MPS, ZTS, and ZMS spanned broad age ranges. After age adjustment, females showed more advanced SOS and CVM stages, whereas ZTS and ZMS showed significant age × sex interactions, with stronger age–maturation associations in males. Age-adjusted inter-indicator associations were generally weak to moderate (partial r s = 0.31–0.49), except between ZTS and ZMS (partial r s = 0.76). These represent residual associations conditional on age; correlation analyses alone cannot establish interchangeability or clinical complementarity.