Accessory navicular bone incidence in Chinese patients: a retrospective analysis of X-rays following trauma or progressive pain onset.

Background: Optimal treatment of symptomatic accessory navicular bones, generally asymptomatic 'extra' ossicles in the front interior ankle, remains debated.

Objective: Incidence and type of accessory navicular bones in Chinese patients were examined as a basis for improving diagnostic and treatment standards.

Methods: Accessory navicular bones were retrospectively examined in 1,625 (790 men and 835 women) patients with trauma-induced or progressive symptomatic ankle pain grouped by gender and age from August 2011 to May 2012. Anterior-posterior/oblique X-ray images; presence; type; affected side; modified Coughlin's classification types 1, 2A, 2B, and 3; and subgroups a-c were recorded.

Results: Accessory navicular bones were found in 329 (20.2%) patients (143 men and 186 women; mean age, 47.24 ± 18.34, ranging 14-96 years). Patients aged 51-60 exhibited most accessory navicular bones (29.7%), with risk slightly higher in women and generally increasing from minimal 10.9% at ages 11-20 to age 51 and thereafter declining to 0.4% by age 90. The incidence was 41.6% for Type 1 (Type 1a: 9.1%, Type 1b: 15.5%, and Type 1c: 19.4%), 36.8% for Type 2 (Type 2Aa: 2.1%, Type 2Ab: 13.7%, Type 2Ac: 5.1%, Type 2Ba: 2.1%, 2Bb: 2.1%, and 2Bc: 11.6%), and 21.6% for Type 3 (Type 3a: 4.5%, Type 3b: 14%, and Type 3c: 3.0%).

Conclusions: Approximately one-fifth (20.3%) of ankle pain patients exhibited accessory navicular bones, with Type 2 most common and middle-aged patients most commonly affected. Thus, accessory navicular bones may be less rare than previously thought, underlying treatable symptomatic conditions of foot pain and deformity.