Flat-foot is, possibly with the exception of slight scoliosis, the most common deformity.

In most cases the deformity is due to the fact that the weight of the body falls on the feet, and it arises owing to a faulty relation between the ligaments and other articular parts which hold up the arch of the foot. It therefore arises as the result of corpulence or of work involving much standing or walking. Rickets also, with its lack of hardness in the bones, is thought to be of aetiological significance.

Fatigue and pain easily produced by standing or walking are the subjective symptoms. The pain is felt chiefly in the astragalo-calcaneo-navicular ligament, sometimes also in the os calcis and even at the external malleolus, when there is marked valgus position.

Simple flat-foot (pes planus) is often combined with a permanent position of eversion, and is then more correctly pes valgo-planus.

"An inflammatory contracture," distinct eversion with no power of inversion, may arise through reflex muscle cramp if the foot has been overworked. This yields quickly to an injection of cocaine in the astragalo-navicular joint, slowly to rest. Such a condition may become permanent owing to the contraction of the soft tissues if not treated.

The symptoms of flat-foot may arise owing to strain on the ligaments before the arch has had time to flatten out or even to sink. It is this condition which many modern orthopaedists call weak foot. It is treated in the same way as flat-foot (except for surgical treatment in severe cases of pes planus or valgo-planus).

We find infiltrations along the inner part of the arch, and part of our treatment consists of massage of this region.

But massage alone can never effect a cure. It is of the first importance to correct the abnormal position of eversion and to support the arch of the foot. This is done by putting suitably-formed cork or metal soles into the patient's shoes, or, best of all, by using the so-called "Lange's valgus pads." Slanting heels (higher on the inner than on the outer side) are more rarely used. Gymnastic exercises to produce inversion are best performed by making the patient walk on tiptoe with the feet directed straightforward.