Flat feet (also called pes planus or fallen arches) is an informal reference to a medical condition in which the arch of the foot collapses, with the entire sole of the foot coming into complete or near-complete contact with the ground. In some individuals (an estimated 20-30% of the general population) the arch simply never develops in one foot (unilaterally) or both feet (bilaterally). It should be noted that being flatfooted does not decrease footspeed; having flat feet does not affect one's response to the Plantar reflex test; and horses also develop flat feet.
Flat arches in children usually become proper arches and high arches while the child progresses through adolescence and into adulthood.
Because young children are unlikely to suspect or identify flat feet on their own, it is a good idea for parents or other adult caregivers to check on this themselves. Besides visual inspection, parents should notice whether a child begins to walk oddly, for example on the outer edges of the feet, or to limp, during long walks, and to ask the child whether he or she feels foot pain or fatigue during such walks. Children who complain about calf muscle pains or any other pains around the foot area, may be developing or have flat feet. A recent randomized controlled trial found no evidence for the treatment of flat feet in children either for expensive prescribed orthoses (shoe inserts) or less expensive over-the-counter orthoses.
There is little debate, however, that going barefoot, particularly over terrain such as a beach where muscles are given a good workout, is good for all but the most extremely flatfooted, or those with certain related conditions such as plantar fasciitis. One medical study in India with a large sample size of children who had grown up wearing shoes and others going barefoot, found that the longitudinal arches of the barefooters were generally strongest and highest as a group, and that flat feet were less common in children who had grown up wearing sandals or slippers than among those who had worn closed-toe shoes. Flat feet can be treated by insoles.
Flat feet can also develop as an adult ("adult acquired flatfoot") due to injury, illness, unusual or prolonged stress to the foot, faulty biomechanics, or as part of the normal aging process. Flat feet can also occur in pregnant women as a result of temporary changes, due to increased elastin (elasticity) during pregnancy. However, if developed by adulthood, flat feet generally remain flat permanently.
If a youth or adult appears flatfooted while standing in a full weight bearing position, but an arch appears when the person dorsiflexes (stands on tip-toe or pulls the toes back with the rest of the foot flat on the floor), this condition is called flexible flatfoot. Muscular training of the feet, while generally helpful, will usually not result in increased arch height in adults, because the muscles in the human foot are so short that exercise will generally not make much difference, regardless of the variety or amount of exercise. However, as long as the foot is still growing, it may be possible that a lasting arch can be created.
Most flexible flat feet are asymptomatic, not painful. In these cases there is usually no real cause for concern. Rigid flatfoot, a condition where the sole of the foot is rigidly flat even when a person is not standing, often indicates a significant problem in the bones of the affected feet, and can cause pain in about 1/4 of those affected. Other flatfoot-related conditions, such as various forms of tarsal coalition (two or more bones in the midfoot or hindfoot abnormally joined) or an accessory navicular (extra bone on the inner side of the foot) should be treated promptly, usually by the very early teen years, before a child's bone structure firms up permanently as a young adult. Both tarsal coalition and an accessory navicular can be confirmed by x-ray.
Treatment of flat feet may also be appropriate if there is associated foot or lower leg pain, or if the condition affects the knees or the back. Treatment may include using arch supports, orthotics, foot gymnastics or other exercises as recommended by a podiatrist or other physician. Surgery can provide lasting relief, and even create an arch where none existed before, but should be considered a last resort, as it is usually very time consuming and costly.
A recent study of Royal Australian Air Force recruits which followed up the recruits over their basic training, found that neither flat feet or high arched feet had any impact on physical functioning, injury rates or foot health. If anything, there was a tendency for those with flat feet to have fewer injuries. Several studies of soldiers explored the link between arch height and stress fractures. One study of 287 Israel Defense Forces recruits found that those with high arches suffered almost four times as many stress fractures as those with the lowest arches. One later study of 449 U.S. Navy special warfare trainees found no significant difference in the incidence of stress fractures among soldiers with different arch heights and another was inconclusive.