歩行における足機能の動的評価

Measurement of dynamic force distribution under the foot is discussed for the purpose of dynamic analysis of foot function in walking. This method is expected to bring various beneficial information about foot function because the foot is always exposed to great pressure in standing or walking, and foot deformities or pain can be assumed to be the result of this great force. Some basic problems are studied here concerning the dynamic force distribution pattern drawn by the foot in walking, the production mechanism of this pattern, and the relation between this pattern and the skeletal structure of the foot. The first finding was that in all 17 subjects the pressure moved constantly from the heel to the medial part of the forefoot and the great toe through the lateral part of the forefoot. This constant moving pattern can be thought to be the clinical standard for the functional estimation of foot disorders. An example of functional estimation of postoperative club foot disease is shown to point out the effectiveness of this estimation. Moreover, the peak pressure on the second metatarsal head is the greatest in the forefoot, and the so-called anterior arch is thought not to exist at least when great pressure is loaded on the forefoot. The second finding was that the phenomenon of the pressure once going round from the lateral to the medial part of the forefoot is caused not by the skeletal structure but is the result of the control involved in walking. In other words, this phenomenon can be explained by the movement of the center of body weight from one foot to the other during the propelling period. This finding can be utilized for the estimation of walking control abililty, and a case of Charcot-Marie-Tooth disease is discussed. The last finding was that the great toe does not actively push off the floor, because even if the great toe is fixed in a fully dorsal flexing position, the pushing off force obtained by the force plate does not change. The greatest pressure is seen on the great toe in the propelling period. These two opposite results can be explained by the "windlas mechanism." Namely, the tension of the plantar fascia according to the dorsal flextion of the MP joint firms the medial longitudinal arch and simultaneously extends the MP joint by the reaction force of the plantar fascia. A simple model is proposed to calculate the plantar fascia reaction force, and this force is proved to attain up to 67% of the body weight. This great force is thought to be the mechanical cause of hallux valgus.