The Incidence and Anatomic Variation of Os Naviculare in a Multiethinic Asian Population

The incidence of asymptomatic os naviculare ranges from 4% to 21%, varying between different ethnicities, with majority of studies performed in Caucasians. The aim of this study was to document the incidence of asymptomatic os naviculare in an Asian population stratified by ethnicity, and to characterize the features of each type. The records of all patients who underwent dorsoplantar and oblique foot radiographs between July and December 2017 were reviewed. We excluded patients with medial-sided foot pain. The radiographs of the remaining patients were reviewed and the incidence and type of os naviculare according to Coughlin's classification were recorded. About 439 patients were included. The overall incidence of asymptomatic os naviculare was 46.0%, of which 76.7% were bilateral. The prevalence of type Ia, Ib, and Ic os was 7.5%, 6.2%, and 5.9%, respectively. The prevalence of type IIAa, IIAb, IIAc, IIBa, IIBb, and IIBc was 2.7%, 0.7%, 0.2%, 16.6%, 5.9%, and 2.1%, respectively. The prevalence of type IIIa, IIIb, and IIIc was 1.1%, 8.4%, and 0.2%. Type IIBa had the highest prevalence of 16.6% out of 439 patients. The highest incidence of os naviculare was in the Chinese population (n = 145, p = .034) at 50.2%. There was no significant gender difference in the incidence of asymptomatic os naviculare. The incidence of asymptomatic os naviculare in a multiethnic Asian population is higher than that reported in other populations, and particularly in the Chinese. Type IIBa was the most prevalent type, which differs from previous reports. When treating patients of Chinse ethnicity who present with pain over the medial aspect of the foot, the diagnosis of a symptomatic os naviculare should be considered.