The quick and crucial answer to the question, ?What's the difference between flat and flaccid feet?? is that flat feet, though they have fallen arches, retain mobility whereas flaccid feet have lost the ability to move at all. Both conditions are long term consequences of the polio virus, which in its most severe form can lead to paralysis and deformity. Ninety-five percent of the time, the virus never makes it out of the intestinal tract, and so the infected person is spared the more serious symptoms and instead suffers from what feels like symptoms of a common flu or cold.

When the virus does make it outside of the intestinal tract and into the bloodstream, it attacks nerves, which can lead to muscular paralysis. The actual duration of the illness may only last two weeks, but the damage to the nerves and the muscles they support can be permanent. Foot and leg deformities, including different sized limbs, high arches, hammertoe, claw toe, flat foot and flaccid foot, are often associated with the virus.

Flat feet (pes planus or fallen arches) occurs when the posterior tibial muscle (part of the system of muscles that makes up the calf) is paralyzed. This paralysis causes the arches of the foot to sag or fall, and the foot becomes flat across the bottom so that the entire sole of the foot makes contact with the ground when standing upright. Some people are born with flat feet while others lose their arches due to injury or an illness such as polio.

When there is no pain, someone with flat feet can largely go untreated. Pain in the foot, knees or lower back is an indication that treatment may be necessary. Orthotics may be required and worn for life. If the condition is less severe, arch supports can be purchased at a local drugstore. Some doctors also recommend various foot exercises. In children, these exercises (sometimes as simple as going barefoot on a rocky beach) can strengthen the muscle and help to form or reform the arch so that overtime the feet become normal. This reformation of the arch is much more difficult to accomplish with adults who have fallen arches.

Flaccid feet occur when there is complete paralysis of the foot muscles. Sometimes surgery is able to restore the foot to its fully functioning state. Occasionally non-surgical treatment is recommended by a doctor that includes orthopedic inserts and foot exercises designed to regain foot mobility.