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 to 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.

The authors have declared no competing interest.

Yes

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Not Applicable

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

This study was approved by Ethics Committee of Wakayama Medical University (No.3594).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Not Applicable

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Not Applicable

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Not Applicable

Data cannot be shared publicly because they contain personal information of the research participants. Data are available from the Ethics Committee contact via the Department of Orthopedic Surgery, Wakayama Medical University for researchers who meet the criteria for access to confidential data.