Pes planus is a condition in which the arch or instep of the foot collapses and comes in contact with the ground. In some individuals, this arch never develops while they are growing.

Flat feet are a common condition. In infants and toddlers, the arch is not developed and flat feet are normal. The arch develops in childhood. By adulthood, most people have developed normal arches.

When flat feet persist, most are considered variations of normal. Most feet are flexible and an arch appears when the person stands on his or her toes. Stiff, inflexible, or painful flat feet may be associated with other conditions and require attention.

Painful flat feet in children may be caused by a condition called tarsal coalition. In tarsal coalition, two or more of the bones in the foot fuse together. This limits motion and often leads to a flat foot.

Most flat feet do not cause pain or other problems. Flat feet may be associated with pronation, in which the ankle bones lean inward toward the center line. When the shoes of children who pronate are placed side by side, they will lean toward each other (after they have been worn long enough for the foot position to remodel their sole).

Foot pain, ankle pain, or lower leg pain (especially in children) may be a result of flat feet and should be evaluated by a health care provider.

Adults can develop a flat foot when they are 60-70 years old. This type of flat foot is usually on one side.

• Absence of foot arch when standing
• Foot pain
• Heel tilts away from the midline of the body more than usual

An examination of the foot is enough for the health care provider to diagnose flat foot. However, the cause must be determined. If an arch develops when the patient stands on his or her toes, the flat foot is called flexible and no treatment or further work-up is necessary.

If there is pain associated with the foot or if the arch does not develop with toe-standing, x-rays are necessary. If a tarsal coalition is suspected, a CT scan is often ordered. If a posterior tibial tendon injury is suspected, your health care provider may recommend an MRI.

Flexible flat feet that are painless do not require treatment. If you have pain due to flexible flat feet, an orthotic (arch supporting insert in the shoe) can bring relief. With the increased interest in running, many shoe stores carry shoes for normal feet and pronated feet. The shoes designed for pronated feet make long distance running easier and less tiring because they correct for the abnormality.

Rigid or painful flat feet require evaluation by a health care provider. The treatment depends on the cause of the flat feet. For tarsal coalition, treatment starts with rest and possibly a cast. If this fails to improve the pain, surgery may be necessary.

For problems with the posterior tibial tendon, treatment may start with rest, anti-inflammatory medications, and shoe inserts or ankle braces.

In more advanced cases, surgery may be needed to clean or repair the tendon, or fuse some of the joints of the foot into a corrected position.

Flat feet in older adults can be treated with pain relievers, orthotics, and sometimes surgery.

Most cases of flat feet are painless and do not cause any problems. The outlook for painful flat feet depends on the cause of the condition. Usually treatment is successful, regardless of the cause. Some causes of flat feet can be successfully treated without surgery if caught early, but occasionally, surgery is the last option to relieve pain.

People with fusions will have some loss of ankle motion, especially when turning the foot inward and outward. Otherwise, these patients report tremendous improvement in pain and function.

Flat feet are not really associated with any complications except pain.

Although surgery is usually successful, it sometimes does not result in satisfactory results. Some patients have persistent pain. Other possible surgical complications include infection and failure of the fused bones to heal.

Call your health care provider if you experience persistent pain in your feet or your child complains of foot pain or lower leg pain.

Most cases are not preventable.

Hosalkar HS, Spiegel DA, Davidson RS. The Foot and Toes. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007; Chap. 673.

Wexler D, Kile TZ, Grosser DM. Posterior tibial tendon dysfunction. In: Frontera WR, Silver JK, eds. Essentials of Physical Medicine and Rehabilitation. 2nd ed. Philadelphia, Pa: Saunders Elsevier;2008:chap 87.