# A practical tip for estimating skeletal maturation in children aged < 3 years using humeral ossification on chest radiographs: A retrospective study

## TL;DR

This study introduces a new method to estimate bone age in children under 3 years old using chest X-rays, avoiding the need for extra imaging.

## Contribution

The study demonstrates a strong linear relationship between humeral ossification and age, and provides sex-specific formulas for rapid skeletal maturation assessment.

## Key findings

- A strong positive correlation (r > 0.88) was found between humeral ossification center diameter and chronological age.
- Sex-specific formulas (0.5 × age + 4 for males, 0.6 × age + 3 for females) were proposed for practical clinical use.
- Reference ranges (±2 SD) were established for six 6-month age groups to identify deviations in skeletal maturation.

## Abstract

Bone age assessment in children aged < 3 years is difficult owing to the limited visibility of carpal ossification centres. We aimed to evaluate skeletal maturation patterns in relation to chronological age using humeral ossification on chest radiographs. We retrospectively reviewed the chest radiographs of 187 children aged 0– < 3 years. Three readers independently measured the longitudinal diameter of the humeral head epiphyseal ossification centre. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC). Pearson’s correlation and linear regression analyses were performed. Reference ranges (± 1 standard deviation [SD] and ± 2 SD) were established for six 6-month age groups. A strong positive correlation was observed between ossification centre diameter and age (r > 0.88 for all observers). The ICC was 0.96 (p < 0.001), indicating excellent interobserver agreement. Moreover, ± 2 SD reference ranges enabled the identification of deviations in skeletal maturation. A comparison by arm position (raised vs. lowered) revealed no significant difference (p = 0.454), supporting the robustness of the measurement. Additionally, simplified estimation formulas were proposed for practical clinical reference: the longitudinal diameter of the humeral head epiphyseal ossification centre (mm) = 0.5 × age in months + 4 for males and = 0.6 × age in months + 3 for females.

Conclusion: This study presents a simple, reproducible method using routine chest radiographs as a supplementary tool to assess skeletal maturation and to approximate chronological age in children aged < 3 years.
What is Known:• Assessment of skeletal maturity and bone age in children aged < 3 years is difficult owing to immature carpal ossification.• Traditional hand-based methods are often unreliable and require extra imaging.What is New:• A strong linear association between the longitudinal diameter of the humeral head ossification centre and chronological age was demonstrated in children aged < 3 years.• Sex-specific simplified estimation formulas and ± 2 SD reference ranges were established, allowing rapid assessment of skeletal maturation without additional imaging.

What is Known:

• Assessment of skeletal maturity and bone age in children aged < 3 years is difficult owing to immature carpal ossification.

• Traditional hand-based methods are often unreliable and require extra imaging.

What is New:

• A strong linear association between the longitudinal diameter of the humeral head ossification centre and chronological age was demonstrated in children aged < 3 years.

• Sex-specific simplified estimation formulas and ± 2 SD reference ranges were established, allowing rapid assessment of skeletal maturation without additional imaging.

The online version contains supplementary material available at 10.1007/s00431-026-06760-6.