Foot fatigue is a symptom of flatfoot.

When the entire sole of the foot is in contact or near contact with the ground while standing, it is considered a flat foot. The result is that there is little to no arch to the foot. Flatfoot is a common disorder. It is a complex deformity, and some types and stages vary in degree of symptoms and disability.

Flatfeet are also referred to as the following:

• pes planus,
• posterior tibial tendon dysfunction, and
• fallen arches.

There are two general types of flatfoot:

1. Flexible flatfoot
2. Rigid flatfoot

In flexible flatfoot, the foot has a normal arch at rest (not standing or walking) but disappears once it comes in contact with the ground. If there is no arch, whether sitting or standing, they have a "rigid" or "true" flatfoot.

Flexible flatfoot is sometimes called "pediatric flatfoot" because it is first apparent in childhood. Congenital or rigid "true flatfoot" (talipes planovalgus) is much less common in children. Of note, almost all infants appear to have a flatfoot due to the fat pad on the sole of their feet, and the arch does not develop until 5 or 6 years of age.

When a rigid flatfoot develops in adults, it is called "adult acquired flatfoot" or "posterior tibial tendon dysfunction." This type of flatfoot develops because of the weakening of the tibialis posterior muscle tendon, a major supporting structure of the foot arch. It is a condition that leads to flattening the arch and rolling in of the ankle. It is a progressive deformity with early symptoms of pain and swelling at the inside arch of the foot and ankle. It eventually may lead to arthritis of the foot and ankle joints.

Flexible flatfoot is usually in both feet whereas posterior tibial tendon dysfunction or adult-acquired flatfoot can occur in one or both feet.

As described above, a person may be born with a flatfoot, pediatric flexible flatfoot, or develop it as an adult (adult acquired flatfoot).

Less common causes of flatfoot include the following:

• Tarsal coalitions: A condition where foot joints bridge or grow together restricting or prohibiting the movement of that joint.
• Accessory navicular bone (os tibiale externum): a small extra bone in the posterior tibial tendon that causes a weakening of tendinous support to the arch
• Ligament laxity in congenital diseases such as Marfan syndrome or Ehlers-Danlos syndrome
• Charcot arthropathy
• Trauma
• Obesity
• Diabetes
• Neuropathy
• Age
• Pregnancy, due to hormonal changes such as increases in elastin
• Osteoporosis
• Overuse

A flatfoot may cause no symptoms; however, when they are present, symptoms may include pain in the inside arch, heel, or ankle and on the outside of the foot just below the ankle. Patients often complain of generalized foot fatigue as a first sign of flatfoot. Younger patients may complain about their inability to keep up with their peers during physical activity.

Over time, the flattening of the arch can lead to rolling in of the foot and ankle and tilting outward of the heel. Flatfoot can also cause shin pain (shin splints) and aching of the knee, hip, and/or lower back. Excessive inner heel wear patterns may be seen on shoes.

For a general assessment, one may look at their feet to see if they have an arch when standing barefoot. A foot specialist will provide an in-depth evaluation usually including X-rays to determine the precise type of flatfoot, its cause, and potential treatments. A doctor may perform a thorough study of walking patterns, called gait analysis, to determine the severity of the flatfoot.

Treatment depends on the type of flatfoot, its stage of progression, and the symptoms. Early treatment is advised whether one's condition is a flexible, rigid, or adult-acquired flatfoot.

Treatments include the following:

• Proper shoe gear
• Over-the-counter inserts
• Custom functional orthotics
• Bracing
• Casting/immobilization
• Physical therapy
• NSAIDs
• Weight loss
• Changes in activities
• Surgery

The prognosis depends on the type and severity of the flatfoot. Many people with pediatric or flexible flatfoot function without any signs or symptoms and are unrestricted in their levels of activity. These people do perfectly well without any treatments. If there are symptoms, however, they are often successfully managed with conservative care.

Adult-acquired flatfoot or true rigid flatfoot tends to be progressive, leading to functional disability and progression of symptoms that interfere with normal daily activities. Therefore, proper diagnosis and early treatment are vital to having a good prognosis.