Relationship between the presence of abnormal hallux interphalangeal angle and risk of ingrown hallux nail: a case control study

BACKGROUND Many risk factors have been identified to be associated with ingrown toenail. Internal pressure by the distal phalanx of the hallux and the second toe and external compression from the shoes has been proposed as a reason for the pathology. The main objective of the study was to analyze the existence of a correlation between the presence of pathological hallux interphalangeal angle (HIA) and risk of ingrown hallux nail. METHODS One hundred and sixty-five subjects (312 ft) were enrolled in a cross-sectional, analytical and observational case-control study. A radiographic computerized system was used to measure HIA in both groups. The angle was considered as the sum of three angles, obliquity, asymmetry and joint deviation. RESULTS The mean HIA in case group subjects (patients with hallux ingrown nail) was significantly higher than that obtained in control group subjects (17.39 ± 6.0° versus 13.47 ± 4.6°, p = .036). A total of 73.71 and 46.79 % of feet presented an angle equal or greater than 13.47° in the onychocryptosis and control group, respectively. CONCLUSIONS The results show a correlation between the variables analysed. The presence of an HIA greater or equal than 14.5° may be a predisposing factor for developing onychocryptosis of the hallux. Clinicians treating individuals with pathology in hallux might use a baseline cutoff of HIA equal than 13.5°.