Epidemiology and bone-related comorbidities of ingrown nail: A nationwide population-based study.

Although ingrown nail (IN) is common, there is no large-scale study regarding its epidemiology and risk factors, such as foot deformity. The purpose of this study is to determine the demographics of IN and clarify its association with bone-related comorbidities of the ankle, foot and toe. Patients in a representative sample cohort of the National Health Information Database of South Korea from 2004 to 2013 who had IN were compared with a control group without IN. Ten-year overall incidence was 307.5/100 000 person-years (95% confidence interval, 304.1-310.9). IN incidence and prevalence showed an increasing trend, and IN was more common in women than in men. Incidence showed bimodal peaks, among teenagers and among participants in their 50s. The IN group showed more common valgus deformity (64.3%) than did the control group (61.6%), and flat foot was also a significant risk factor of IN. There were increasing tendencies of IN incidence and prevalence among females. Confirmed bone deformity, especially acquired valgus or varus deformity, and flat foot were associated with IN.