Flat feet (also called pes planus or drooping arches) are a postural deformity in which the arches of the foot collapse, with the entire sole of the foot coming into full or nearly full contact with the ground. Some individuals (20-30% of the general population) have an arch that simply never develops in one foot (unilateral) or in both feet (bilaterally).
There is a functional relationship between the arch structure of the foot and the biomechanics of the lower leg. The arch provides an elastic connection between the forefoot and the rear foot. This association protects so that most of the forces incurred during weight bearing of the foot can be dissipated before the force reaches the long bones of the leg and thigh.
In flatfoot, the head of the talus bone is displaced medial and distal to the navicular. As a result, the spring ligament and the tendon of the posterior tibial muscle are stretched, so much so that the individual with flat feet loses the function of the medial longitudinal arch (MLA). If the LMA is absent or does not function in both the sitting and standing positions, the individual has “stiff” flat feet. If the LMA is present and functional while the individual is sitting or standing on the toes, but this arch disappears when assuming a flat-foot posture, the individual has a "flexible" flatfoot. The latter condition can be corrected with well-adjusted arch supports.
Three studies of military recruits have shown no evidence of a subsequent increase in injuries or foot problems due to flat feet in a population of people reaching military service age with no prior foot problems. However, these studies cannot be used to judge possible future harm from this condition when diagnosed at a younger age. They also cannot apply to people whose flat feet are associated with foot symptoms or certain symptoms in other parts of the body (such as the leg or back) that may refer to the foot.
