Dynamic structure of the human foot.

1 Department of Anatomy, Columbia University, New York, N.Y. 10016 THE FOOT is one of the most dynamic structures in the human body. The lively interplay of forces which makes its function possible is easily forgotten and it is too often treated like the graven image of a static structure. The success of modern therapeutic measures in solving other problems has owed much to close cooperation between Nature working from within and assistive devices from without. The forces within the foot can be powerful allies in such a partnership. The human foot acts in concert with the rest of the body during standing and movement. It provides man with his most effective physical contact with the environment and is especially responsible for successful regulation of initial and final contact of the body with the ground. The foot must also provide adjustable support during the characteristic human occupations of manipulating the environment or of simply standing in line. Human bipedality was made possible by the redesign of an ancestral foot with five long toes used for the grasping of the limbs of trees. We still testify to our heritage by having a big toe larger than the rest but no longer opposable. The heel bone was brought down into contact with the ground to provide additional area of support. Each of these changes traded an old advantage for a new one and the barter is still going on.