Investigation of accessory navicular in local pre-adolescence children: A longitudinal study with 2-year follow-up-KID Locomo Study.

INTRODUCTION: The accessory navicular (AN) is an accessory ossicle located on the medial side of the navicular bone and is often associated with sports-related overuse injuries during adolescence. However, little is known about the natural history of AN. This study aimed to clarify the natural course of AN, including symptomatic cases, in children through a longitudinal epidemiological investigation. METHODS: Data from the KID Locomo Study, a prospective cohort study aimed at elucidating musculoskeletal disorders in childhood, were used. Of the 834 children recruited in the 2022 baseline survey, 66 children (109 feet) aged 11-13 years with AN were enrolled in this 2-year longitudinal analysis. The presence of AN was assessed using ultrasonography. Data on sex, age, height, weight, presence of pain at the AN site, laterality, flatfoot (based on footprint analysis), and participation in athletic clubs were collected. The natural history of AN, including painful presentations, was evaluated. Multivariable logistic regression analysis was performed to identify risk factors for non-fusion of the AN with the navicular bone. RESULTS: Among the 109 feet with AN at baseline, 38 (34.9%) demonstrated fusion with the navicular bone at the 2-year follow-up. Of the 21 feet with painful AN at baseline, pain had resolved in 15 (71.4%) after 2 years. Multivariable logistic regression analysis revealed that female sex (odds ratio: 3.00; 95% confidence interval: 1.26-7.45; p = 0.01) and higher body mass index (BMI) (odds ratio: 1.20; 95% confidence interval: 1.02-1.43; p = 0.02) were significant risk factors for non-fusion. CONCLUSIONS: This study provides epidemiological data on the natural history of AN, including symptomatic cases, in children. To our knowledge, this is the first study to report the natural course of painful AN. These findings may offer fundamental insights into prevention and management strategies for painful AN in children.