Chronological Age Distribution Across Risser+ Stages: A Retrospective Study of 535 Radiographs

Background Accurate assessment of skeletal maturity is essential in pediatric orthopedics, particularly in the management of adolescent idiopathic scoliosis (AIS), where remaining growth potential strongly influences treatment decisions. The Risser sign remains a widely used radiographic indicator of skeletal maturity. Accurate assessment of skeletal maturity is essential in pediatric orthopedics, particularly in the management of adolescent idiopathic scoliosis (AIS), where remaining growth potential strongly influences treatment decisions. The Risser sign remains a widely used radiographic indicator of skeletal maturity. A modified staging system incorporating triradiate cartilage status and refined iliac crest ossification stages has been proposed to improve characterization of early skeletal maturation. However, data describing the relationship between chronological age and these stages remain limited. However, data describing the relationship between chronological age and Risser+ stages remain limited. Objective To evaluate the relationship between chronological age and Risser+ stages and to assess sex-related differences in skeletal maturation timing and progression. Methods This retrospective observational study included pelvic radiographs obtained at a single tertiary center between October 2024 and March 2025. A total of 588 radiographs were initially identified; after exclusion of studies with inadequate image quality or incomplete data, 535 radiographs from patients aged 8–20 years were included in the final analysis. Skeletal maturity was assessed using the Risser+ classification. Age distributions across stages were analyzed using descriptive statistics and independent-sample t-tests. Stage-to-stage progression was evaluated in a subset of 123 patients with serial radiographs. Inter- and intra-observer reliability of Risser+ staging were assessed using Cohen’s kappa coefficient. Results Chronological age increased progressively with advancing Risser+ stages, from a mean of 10.69 years at stage 0 (-) to 15.82 years at stage 5. Females reached stages 1–3 at significantly younger ages than males (p ≤ 0.05), with small to moderate effect sizes, whereas no significant sex differences were observed at stages 0+, 4, or 5. Among patients with serial radiographs, the mean stage-to-stage progression interval was 10.5 ± 9.1 months, with the longest transition occurring between stages 4 and 5 (13.96 months). No statistically significant differences in progression tempo were detected between sexes. Reliability analysis demonstrated excellent reproducibility of Risser+ staging (inter-observer κ = 0.907; intra-observer κ = 0.893). Conclusion Chronological age shows a consistent relationship with Risser+ stages, supporting the clinical utility of this classification in skeletal maturity assessment. Sex-related differences are most evident during early maturation stages, with females reaching equivalent stages earlier than males. Distinguishing between Risser 0(–) and 0(+) further refines early maturity assessment and may improve interpretation of pelvic radiographs in the management of AIS.