Overview Adults with an acquired flatfoot deformity may present not with foot deformity but almost uniformly with medial foot pain and decreased function of the affected foot (for a list of causes of an acquired flatfoot deformity in adults. Patients whose acquired flatfoot is associated with a more generalised medical problem tend to receive their diagnosis and are referred appropriately. However, in patients whose ?adult acquired flatfoot deformity? is a result of damage to the structures supporting the medial longitudinal arch, the diagnosis is often not made early. These patients are often otherwise healthier and tend to be relatively more affected by the loss of function resulting from an acquired flatfoot deformity. The most common cause of an acquired flatfoot deformity in an otherwise healthy adult is dysfunction of the tibialis posterior tendon, and this review provides an outline to its diagnosis and treatment. Causes Several risk factors are associated with PTT dysfunction, including high blood pressure, obesity, diabetes, previous ankle surgery or trauma and exposure to steroids. A person who suspects that they are suffering from PTT dysfunction should seek medical attention earlier rather than later. It is much easier to treat early and avoid a collapsed arch than it is to repair one. When the pain first happens and there is no significant flatfoot deformity, initial treatments include rest, oral anti-inflammatory medications and, depending on the severity, a special boot or brace. Symptoms In many cases, adult flatfoot causes no pain or problems. In others, pain may be severe. Many people experience aching pain in the heel and arch and swelling along the inner side of the foot. Diagnosis The diagnosis of tibialis posterior dysfunction is essentially clinical. However, plain radiographs of the foot and ankle are useful for assessing the degree of deformity and to confirm the presence or absence of degenerative changes in the subtalar and ankle articulations. The radiographs are also useful to exclude other causes of an acquired flatfoot deformity. The most useful radiographs are bilateral anteroposterior and lateral radiographs of the foot and a mortise (true anteroposterior) view of the ankle. All radiographs should be done with the patient standing. In most cases we see no role for magnetic resonance imaging or ultrasonography, as the diagnosis can be made clinically. Non surgical Treatment Patients can be treated non-surgically with in-shoe devices and braces to hold their feet in the correct position. This can reduce pain and damage and assist with walking. Physical therapy is also given to improve muscle strength and help prevent injury to the foot. Surgery can be performed if the patient doesn?t find any relief. Surgical Treatment A new type of surgery has been developed in which surgeons can re-construct the flat foot deformity and also the deltoid ligament using a tendon called the peroneus longus. A person is able to function fully without use of the peroneus longus but they can also be taken from deceased donors if needed. The new surgery was performed on four men and one woman. An improved alignment of the ankle was still evident nine years later, and all had good mobility 8 to 10 years after the surgery. None had developed arthritis.