抄録
The disorder in which the medial longitudinal arch becomes lower is called flatfoot. It is inferred that the flatfoot condition is associated with a certain stress while walking.
The purpose of this study was to compare the changes of medial longitudinal arch and floor reaction force during gait between two groups : low arch and normal arch, and to make a conjecture about the cause of flatfoot stress while walking.
The subjects were 6 men and 6 women. The subjects, average age, average body height, and average weight were 23.5±2.5 years old, 165.6±8.2cm, and 56.5±10.8kg, respectively.
We used medial longitudinal arch ratio, which is the value obtained by dividing the height from the floor surface to navicular bone by actual foot length. The lower arch group showed less than 16.4% of medial longitudinal arch ratio for men, 14.6% for women, among 6 subjects. The normal group showed larger values, among the 6 subjects.
We measured configuration of arch and floor reaction force during gait movement at the times of heel strike, foot-flat, mid-stance, heel-off, and toe-off and compared them. We recorded the medial longitudinal arch, the changes of the medial arch angle between the line connecting medial heel area and the navicular bone, and the line connecting navicular bone and the first metatarsal head. Two units of high-speed cameras were used to measure this angle. Also measured, with two force plates, were the floor reaction force applied to the hind foot and the floor reaction force applied to the forefoot.
At HC, FF, and HO phase, the arch angles were significantly larger in the low arch group than in the normal group. The low arch group had larger medial force than the normal group at MS and had smaller posterior force than the normal group at TO phase.
As for the force components measured by force plates, from these results it appears that the low arch group, having lost the spring stiffness of the foot, is unable to make forward movement smoothly.
