Flat feet (also called pes planus or fallen arches) is a postural deformity in which the arches of the foot collapse, with the entire sole of the foot coming into complete or near-complete contact with the ground. Sometimes children are born with flat feet (congenital). There is a functional relationship between the structure of the arch of the foot and the biomechanics of the lower leg. The arch provides an elastic, springy connection between the forefoot and the hind foot so that a majority of the forces incurred during weight bearing on the foot can be dissipated before the force reaches the long bones of the leg and thigh.In pes planus, the head of the talus bone is displaced medially and distal from the navicular bone. As a result, the Plantar calcaneonavicular ligament (spring ligament) and the tendon of the tibialis posterior muscle are stretched to the extent that the individual with pes planus loses the function of the medial longitudinal arch (MLA). If the MLA is absent or nonfunctional in both the seated and standing positions, the individual has "rigid" flatfoot. If the MLA is present and functional while the individual is sitting or standing up on their toes, but this arch disappears when assuming a foot-flat stance, the individual has "supple" flatfoot. This latter condition is often treated with arch supports. However, a recent randomized controlled trial found no evidence for the efficacy of treatment of flat feet in children either from expensive prescribed orthotics (i.e., shoe inserts) or less expensive over-the-counter orthotics.
However, some also assert that persons with flat feet may have an underpronating if they are not a neutral gait. With standard running shoes, these professionals claim, a person who overpronates in his or her running form may be more susceptible to shin splints, back problems, and tendonitis in the knee. Running in shoes with extra medial support or using special shoe inserts, orthoses, may help correct ones running form by reducing pronation and may reduce risk of injury. Military performance
Studies analyzing the correlation between flat feet and physical injuries in soldiers have been inconclusive, but none suggest that flat feet are an impediment, at least in soldiers who reached the age of military recruitment without prior foot problems. A 2005 study of Royal Australian Air Force recruits that tracked the recruits over the course of their basic training found that neither flat feet nor high arched feet had any impact on physical capability, injury rates or bipedal aptitude. Although there have been results rendered from military trials that have shown those with flat feet to have fewer injuries. No current studies have been successful in fully ascertaining the chronic, long-term detriments to health that are caused by the overexertion (of which is necessary for athletes/soldiers performing with flat feet) and other compensating measures commonly enacted by the body during bipedal movement. Another divergent study of 295 Israel Defense Forces recruits found that those with high arches had almost four times as many stress fractures as those with the lowest arches.