Analysis of foot skeletal structure by 3D foot scanner on smartphone

Abstract

Background: The influence of foot skeletal structure on hallux valgus (HV) is poorly understood, so its detailed understanding at an early stage is required for prevention. In this study, a system using a 3D foot scanner on smartphone was developed for the purpose of clarifying relationships between skeletal features and the degree of HV risk. Methods: This system analyzes the foot skeletal structure by sending 2D video images recorded on smartphone to a computer or cloud server, where the 3D foot skeleton model is constructed by the 2D images. This system was developed to identify 10 skeletal features that are expected to be associated with hallux valgus. The participants comprised 419 individuals (40–89 years), and they maintained a standing pose with their toes 12 cm apart and heels 8 cm apart during the video recording. The height and weight were additionally measured to calculate BMI.Results: The study results showed that age-based variations in the foot skeletal features were observed slightly for men whereas distinctively for women. It was observed for women that the great toe-first metatarsal head-heel (GFH) angle increases with age, so it suggests that the increase of the GFH angle characterizes the development of HV. The multiple regression analysis reveals that the features determining the GFH angle are the second toe-heel-navicular angle and the axis of the bone distance among the skeletal features related to the midfoot, and the transverse arch length and height among those related to the forefoot. Their adjusted coefficients of determination were 0.52 and 0.48 for men and women, respectively. Conclusion: Using a 3D foot scanner on smartphone, we developed a simple method to access the skeletal structure of the foot related to HV risk. Trial registration: University hospital Medical Information Network- Clinical Trials (UMIN-CTR) with the number: UMIN 000037694. Registration date: 20/08/2019.