Usually, we mean by “flatfoot” which has a decreased height of longitudinal arch (also called plantar arch).
In fact, it is a set of disorders of alignment when the child is standing and supports its weight on the plantar arch.
In this situation, the heel deviates outward (what we call “valgus to”), the area of the plantar arch in the mid foot hits the ground giving an appearance standing “sunk” and the ball of the foot placed in supination, i.e., with greater support from the inside.
The flexible term refers to the mobility of foot joints and their ability to correct these disorders alignment. It’s recommended that people with this should get the best insoles for flat feet
How is the longitudinal arch formed?
The longitudinal arch progressively develops early in life, reaching its maximum height to adolescence.
During the first 2-3 years of life, the child’s foot has an appearance of flatfoot. This is conditioned by its high elasticity and the accumulation of adipose tissue in the inner area of the sole.