Other causes are rickets; inflammation of the ankle joint, as in tuberculosis; or, as a result of a badly treated fracture of the ankle-joint; or, as a result of paralysis of the muscles of the inner side of the leg.
Pathology of Acquired Flat Foot. The pathologic condition is due to change in the relations of the bones rather than to any change in the bones themselves. The abnormal position is an exaggeration of the normal yielding of the foot under weight bearing. The front of the astragalus rotates inward, and with it the bones of the leg turn at the hip-joint.
The deformity is essentially a displacement of the astragalus on the bones of the tarsus. The scaphoid, cuneiform, and the base of the first metatarsal move downward and inward with the head of the astragalus; the outer border of the foot is made more concave and the inner border becomes convex in extreme cases. In the severest cases, the head of the astragalus, and scaphoid may be displaced below the plane of the other bones. The ligaments are respectively shortened and stretched in the severest cases and there is a loss of motion in certain of the tarsal articulations, due to faulty apposition of joint surfaces, and to constant strain.
Symptoms. The feet burn and tire easily and feel stiff and lame. They may swell, and the size of the shoe worn must be then increased. Later, a painful period generally begins in which walking is avoided and a dragging pain in the arch and behind the inner malleolus is noticed. This is increased by walking and standing and tender points may be found under the scaphoid and on the upper surface of the heel. The foot feels strained and irritated and is a constant source of discomfort. The inner malleolus is generally more prominent and the foot is displaced outward in relation to the leg. The height of the arch is somewhat diminished; it may be much lowered, or it may be flat on the ground.
When the foot is really flattened, it presents two types, one the flexible flat foot, in which the arch can be restored by gentle manipulation; the other, the rigid foot, which is held by structural changes in the position of deformity.
An intermediate type is sometimes seen, in which the peroneal spasm is so great that the foot is held abducted and everted as long as the spasm lasts (spastic flat foot.)
Some symptoms of flat foot that are less generally recognized, which are of great value in diagnosis are: corns, ingrowing nails, callosities on the sole of the front of the foot, enlargement of the great-toe joint, and pain (especially at night) in the calves of the legs and backbone, which is aggravated by standing and walking.
Diagnosis. The diagnosis of flat foot, whether flexible or rigid, is made chiefly by inspection. The difficulty comes in the milder cases, which form the bulk of those seen, and in which the changes in form are slight.
Symptoms. The symptoms, as described by the patient, are the most reliable and points of tenderness under the arch or heel would help to confirm the diagnosis. Some help may be obtained from a wet impression of the foot, on a piece of paper, but the slighter cases show but little changes in the imprint. In most normal feet, the outer border of the foot touches the paper, and in flat foot, only two areas bear the weight, one on the inner side of the front of the foot, and one under the inner part of the heel. An X-ray picture is often of great assistance.