Analysis of foot shape variation based on the medial axis of foot outline

The variations in foot outline forms are analyzed by using flexion angles of the medial axis of foot outline. Foot outline and 12 conventional measurements taken on the right foot of 443 male and 297 female subjects with no visible pathological deformation of the foot were used for analyses. The results indicate that the foot is outflared in most of the subjects. Medial bulge and lateral concavity of foot outline are responsible for the foot outflare, and they are not correlated with each other. Medial bulge is due to the overhang of navicular bone that is caused by the pronation of the foot. Its intensity is negatively correlated with dorsal arch height. Lateral concavity is partly due to the abduction of talus and calcaneus relative to the tarsometatarsal bones anterior to them. These three-dimensional morphological characteristics of outflared feet intimately relate to the fit and comfort of the shoe. The flexion angles of medial axis of foot outline provide a useful tool in morphological analysis of the foot for the following reasons; (1) they carry the information on the three-dimensional foot shape that cannot be represented by conventional measurements; and (2) the data is easily obtained and calculations are easily made with minimum expense.