In more extreme cases, known as a kinked flatfoot, the entire inner edge of the footprint may actually bulge outward, where in a normal to high arch this part of the sole of the foot does not make contact with the ground at all. On plain radiography, flat feet can be diagnosed and graded by several measures, the most important in adults being the talonavicular coverage angle, the calcaneal pitch, and the talar-1st metatarsal angle (Mearys angle). The talonavicular coverage angle is abnormally laterally rotated in flat feet. It is normally up to 7 degrees laterally rotated, so a greater rotation indicates flat feet. Radiographies generally need to be taken on weightbearing feet in order to detect misalignment. Treatment
Most flexible flat feet are asymptomatic, and do not cause pain. In these cases, there is usually no cause for concern. Flat feet were formerly a physical-health reason for service-rejection in many militaries. However, three military studies on asymptomatic adults (see section below), suggest that persons with asymptomatic flat feet are at least as tolerant of foot stress as the population with various grades of arch. In a study performed to analyze the activation of the tibialis posterior muscle in adults with pes planus, it was noted that the tendon of this muscle may be dysfunctional and lead to disabling weightbearing symptoms associated with acquired flat foot deformity. The results of the study indicated that while barefoot, subjects activated additional lower-leg muscles to complete an exercise that resisted foot adduction.
A later study of 449 U.S. Navy special warfare trainees found no significant difference in the incidence of stress fractures among sailors and Marines with different arch heights. See also
Planovalgus deformity
Marfan syndrome
Ehlers-Danlos syndrome
Comparison of orthotics
Rocker-bottom feet

References
External links
Can minimalist shoes help flat feet
Best flat feet shoes solution
Natural flat feet solution the details