MECHANISM OF THE NORMAL FOOT AND OF FLAT FOOT

PART II.

In the analysis of Flat Foot and its allied disorders, the following points stand out as the most important ones:

1. The disorder is essentially and primarily a faulty posture of the os calcis, by which an improper distribution of body-weight and muscle force is transmitted to the fore part of the foot through its two channels, the scaphoid and cuboid bones; in the fore part of the foot, functional derangement and subsequent deformity is purely secondary to the improper distribution of forces thrown upon it from the posterior half.

2. The nature of the disorder is a loss of the normal balance of the forces passing through the foot so that the unbalanced structure is caused to roll inward (pronate). This movement increasingly exaggerates the faulty distribution of pressure and at the same time breaks down the resistance of the tissues which attempt to oppose the abnormal movement. Hence a vicious circle is formed.

3. The plantar ligaments are the only real weight-supporting soft structures of the foot; the lateral muscles and ligaments are merely controlling in their actions and incapable of sustaining any considerable amount of body-weight.

4. The early movement of the faulty posture is almost directly lateral; the resulting progressive slant, however, of the calcaneal facets causes an inward shifting of body-weight and the creation of a strong lateral thrust, which together constitute an overpowering burden upon the relatively weak lateral structures.

5. This burden is termed a "false load" because it is a new and abnormal element of strain thrown upon lateral structures and by them is merely transmitted back again upon the leg and foot. This "false load" constitutes the pernicious element of this type of foot disorder and should be viewed as a vicious development that is comparable to a neoplastic growth; it has no useful purpose, and is solely destructive in its effects.

6. Bone changes ultimately occur which accord with the disordered movements of force and the uneven contact of joint surfaces. The changes are widely scattered to all the bones of the foot, each bone presenting a relatively small share of the total deformity.

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