Bone age assessment: comparative analysis of Greulich-Pyle and Tanner-Whitehouse 3 by pediatric radiologists and endocrinologists

Two widely used bone age assessment (BAA) methods—Greulich-Pyle (GP) and Tanner-Whitehouse 3 (TW3) methods—differ in complexity, accuracy, and clinical utility. To compare GP and TW3 bone age estimations and assess inter- and intra-observer agreement between pediatric radiologists and endocrinologists. This retrospective study analyzed 1,725 left-hand radiographs of children aged 0–19 years (2008–2022). Twelve experts (six radiologists, six endocrinologists) independently assessed bone age using GP and TW3 radius-ulnar-short bones (RUS) methods following standardized training. Assessment time and method preference were recorded. Statistical analyses included descriptive statistics, intra-class correlation coefficients (ICC), Bland–Altman analysis, and comparative tests (p < 0.05). GP estimates ranged from 6 to 228 months, whereas TW3-RUS estimates were slightly lower due to age-range limitations. Inter- and intra-observer reliability were excellent for both methods (ICC > 0.9). Mean bone age did not differ significantly between specialties using GP, whereas minor differences were observed with TW3-RUS for overall (p < 0.001) and when stratified by sex (males p = 0.016, female p = 0.005). Age-stratified analysis demonstrated low mean absolute differences (MAD) between specialties across most age groups, with slightly greater variability in 84.1–180 months. MAD between GP and TW3-RUS was modest in most age groups (approximately 2.5–3.3 months) but increased in older adolescents, particularly ≥ 180 months. GP assessments were significantly faster than TW3-RUS (p = 0.002). Experts preferred GP for routine use due to speed and ease, while TW3-RUS offered greater accuracy, specificity, and detail for complex and borderline cases. Both specialists demonstrated excellent agreement using both GP and TW3-RUS. We recommend GP as the primary method, reserving TW3-RUS for complex cases. Moreover, developing a GP-analog atlas with narrower, finely defined age intervals may improve clinical applicability.