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Did You Know?
In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.

A common ailment stemming from bipedalism is flatfoot, also known as fallen arches or pes planus. It occurs when the lengthwise arch of the foot has not developed properly, causing the entire sole of the foot to come in contact with the ground. When feet lack the arches that help support the body's weight, it causes structural changes that lead to a whole list of other problems, such as knee, leg, shoulder, and neck pain. Hyper-pronation of the feet is also associated with flatfoot and occurs when the ankle bones lean inward. This can be identified when the worn shoes of an individual slant toward each other when placed side-by-side.

All babies are born with flat feet; their arches don't fully develop until they are a few years older. However, 15 to 20 percent of people never develop normal arches. In this case, the condition is usually inherited, but flatfoot that occurs suddenly in adulthood is often caused by injury or disease.

There are two types of flatfoot: flexible and rigid. In the first, the arch returns when standing on one's toes and is typically painless and symptom-free, requiring no treatment. If bothersome, arch supports, arch taping, or orthotics can be helpful. Some running shoes are designed for people with feet that over-pronate.

Rigid flatfoot is usually painful, and the arch is never present, whether the foot is on the ground or elevated. There are different types of surgery for this condition, including a relatively new surgery called the sinus tarsi implant procedure, which involves inserting a titanium implant into the foot to restore the arch. It's a five-minute outpatient procedure that requires the individual to be on crutches or use a cane for about two weeks.

Short-term problem solvers for both kinds of flatfoot include calf and foot stretches and exercises, as well as toe curls (picking up marbles, coins or a towel with the toes). Other recommendations: lose weight, stop wearing worn-out shoes, stay away from high-impact sports, and avoid exercising on hard surfaces.

—Emily MacDowell