Flat feet is a very common condition and is normal in infants and toddlers. However, most people have normal arches by the time they are adults. The arch, or instep, is the inside part of the foot that's usually raised off the ground when you stand, while the rest of the foot remains flat on the ground.
A significant number of people with flat feet or fallen arches experience no pain and have no problems. Some, however, may experience pain in their feet, especially when the connecting ligaments and muscles are strained. The leg joints may also be affected, resulting in pain. If the ankles turn inwards because of flat feet the most likely affected areas will be the feet, ankles and knees.
Having low or no arches is normal for some people. In these cases, flat feet are usually inherited and the feet are fairly flexible. Occasionally, flat feet can be caused by an abnormality that develops in the womb, such as a problem with a joint or where two or more bones are fused together. This is known as tarsal coalition and results in the feet being flat and stiff.
Flat feet also occur because the tissues holding the joints in the foot together (called tendons) are loose. The tissues should tighten and form an arch as children grow older. This will take place by the time the child is 2 or 3 years old. However, the arch may never form in some people resulting in flat feet.
Other cause of flat feet include aging, injuries, or illness that harm the tendons and cause fallen arches or flat feet to develop in a person who has already formed arches. This type of flat foot may occur only on one side. The feet of people with flat feet may roll over to the inner side when they are standing or walking, and the feet may point outwards as a result. This is called over pronation.