Trends in the Prevalence of Adolescent Idiopathic Scoliosis in a Japanese Prefecture: A 25-Year Population-Based School Screening Study Using Moiré Topography

Study Design Retrospective analysis of a prospectively maintained school-based screening database. Objective To investigate long-term trends in the prevalence of adolescent idiopathic scoliosis (AIS) in a Japanese population over 25 years. Methods This study evaluated a screening program conducted from 1998 to 2022 in Ehime, Japan. All fifth- (ages 10-11) and seventh-grade (ages 12-13) students were included. Primary screening used moiré topography (Tsukidate criteria). Students with positive findings were referred for radiographic confirmation (AIS defined as Cobb angle ≥10°). Linear regression assessed temporal trends in positivity rate, positive predictive value (PPV), and estimated prevalence. Results Of 534 322 examinations performed, the overall positivity rate increased significantly from 2.24% in 1998 to 4.06% in 2022. In a sub-cohort with complete radiographic follow-up (n = 221 318), estimated AIS prevalence showed a significant linear increase from 0.85% (initial 5 years) to 2.14% (final year). Notably, PPV remained stable throughout the period (mean 47.3%) with no significant trend. Conclusions AIS prevalence increased substantially over 25 years in this cohort. The stability of the PPV suggests a true epidemiological increase rather than a diagnostic artifact. These findings highlight the importance of continued screening and suggest lifestyle or developmental factors may contribute to the rising incidence.