Validation of bone age methods by their ability to predict adult height

Aim: Several bone age (BA) methods are in use today. The aim of this study was to introduce a framework for assessing the validity of a BA method by its ability to predict adult height (H) and to apply it to manual ratings based on Greulich-Pyle (GP) and Tanner-Whitehouse 3 (TW) and to the fully automated BoneXpert method.

Material: The study used X-rays of 232 children from the First Zurich Longitudinal Study recorded close to each anniversary.

Method: For each height measurement (h), we calculated the growth potential (gp), defined as gp = (H-h)/H. The standard deviation of the gp prediction error for children of the same age was taken as a measure of the validity of the BA method and averaged over the age range 10-18 years for boys and 8-16 years for girls to obtain the overall gp prediction error (GPPE).

Results: Manual TW yielded GPPE = 1.32% [95% CI 1.28-1.36], and was significantly outperformed by manual GP with GPPE = 1.26% [1.22-1.30]. The automated rating obtained GPPE = 1.23%, and omitting radius and ulna yielded GPPE = 1.22%.

Conclusion: Manual GP rating is better than manual TW rating in predicting adult height, and the fully automated method works as well as manual GP rating.