What Is It? A fallen arch or flatfoot is known medically as pes
planus. The foot loses the gently curving arch on the inner side
of the sole, just in front of the heel. If this arch is
flattened only when standing and returns when the foot is lifted
off the ground, the condition is called flexible pes planus or
flexible flatfoot. If the arch disappears in both foot positions
-- standing and elevated -- the condition is called rigid pes
planus or rigid flatfoot. Flexible flatfeet are considered
normal in young children because babies are not born with a
normal arch. The arch may not form fully until sometime between
ages 7 and 10. Even in adulthood, 15% to 25% of people have
flexible flatfeet. Most of these people never develop symptoms.
In many adults who have had flexible flatfeet since childhood,
the missing arch is an inherited condition related to a general
looseness of ligaments. These people usually have extremely
flexible, very mobile joints throughout the body, not only in
the feet. Flatfeet also can