The Validation of the Tanner–Whitehouse 3 Method for Radiological Bone Assessments in a Pediatric Population from the Canary Islands

Background/Objectives: Bone age assessments are essential for evaluating the growth and skeletal development of children and adolescents, influenced by factors such as genetics, ethnicity, culture, and nutrition. Clinical standards for these assessments must be adapted to the specific populations under study. This study validates the use of the Tanner–Whitehouse 3 method for determining bone age in pediatric and adolescent populations in the Canary Islands. Methods: This cross-sectional study analyzed 214 posteroanterior radiographs of the left hand and wrist from 80 females and 134 males, aged between 5 and 18 years. The radiographs were independently evaluated by three raters: a Radiologist Specialist (Rater 1), a General Practitioner (Rater 2), and a Medical Student (Rater 3). Intra- and inter-rater reliability were assessed using intraclass correlation coefficients (ICCs). Accuracy was evaluated by comparing estimated bone age with chronological age, stratified by sex and developmental stage. Results: Strong intra-rater reliability was observed across all raters. Raters 1 and 2 demonstrated excellent consistency (ICCs: 0.990–0.996), while Rater 3 exhibited slightly lower yet robust reliability (ICCs: 0.921–0.976). Inter-rater agreement was high between Raters 1 and 2 but decreased with Rater 3, reflecting the influence of experience (ICCs: 0.812–0.912). Bone age was underestimated in preschool children (mean difference: 3.712 mos.; 95% CI: 1.290–6.130; p = 0.199) and school-age males (mean difference: 3.978 mos.; 95% CI: −12.550 to 4.590; p = 0.926), with minimal discrepancies in females. In teenagers, the Tanner–Whitehouse 3 method slightly overestimated bone age (mean difference: −0.360 mos.; 95% CI: −0.770 to −0.954; p = 0.299). Conclusions: In conclusion, the Tanner–Whitehouse 3 method demonstrates overall precision and reliability but requires caution, as it underestimates bone age in preschool children and school-age males, while slightly overestimating it in adolescents.