靴着用を想定したときの足型3次元形状の変化

抄録

Three-dimensional shape and leg-heel alignment of the right foot were measured for 8 male subjects under the following two conditions: 1) standing on a flat plane and 2) standing on a wooden base whose surface simulates the lower surface of shoe last (20mm of heel height). The coordinates of 23 sections were calculated for the data obtained under the first condition. All the sections were vertical to the reference plane defined by MT (metatarsale tibiale), MH and LH (medial and lateral heel points: medial and lateral points 30mm forward from heel point at the height of MT), which is parallel to the horizontal plane. For the second condition, the coordinates of 5 sections were calculated vertical to the surface of the wooden base for the part anterior to and crossing MT, and those of 18 sections vertical to the reference plane for the part posterior to and crossing MT. The differences in shape between the two conditions were analysed by using geometrical properties of each cross-section. Also the shape of the foot represented as a set of 17 equidistant cross-sections (sections 6-22) was described by the Fourier descriptors, and the shape difference was evaluated by the pseudo-distance measures, which are defined corresponding to the 5 independent global features of the 3-D object: elongatedness, horizontal strain, section shape, displacement, and torsion. There was no significant difference in the breadth of each cross-section. The height (sections 7-11), direction angle of principal axis (sections 9-13 and 20-22), and flatness index (sections 7-10) in condition 2 were larger than those in condition 1. Cross-sections 7-13 showed a swollen lateral part of the lower border of the outline and a pronounced plantar arch. The differences in leg-heel alignment between the 2 conditions indicate foot supination in condition 2. The differences in 3-D shape between the 2 conditions were clear only in displacement. These differences were probably due to the obliquity of the ankle in the coronal plane; movement of the leg over a fixed foot produces lateral rotation of the lower leg on planter flexion, which in turn produces supination of the foot. Other possible causes are change in the weight distribution on the metatarsal heads and tension in ligaments of the sole such as plantar aponeurosis.