Flat foot (pes planus) is extremely common. Most babies are born with flat feet and approximately 10% of adults are flat footed. It is important to distinguish between physiological (normal) flat foot and more serious ‘pathologic’ causes.
Physiological flat foot is by far the commonest variety and is due to laxity of the ligaments that hold up the arch of the foot.
Pathological causes of flat foot include tarsal coalition (abnormal connection between the bone in the foot), vertical talus, accessory navicular bone and tight Achilles tendon.
Generally, if the deformity affects both feet, is supple and painless then it is probably physiological. An easy way of determining whether the deformity is supple is to get the patient to stand on tip toe. If the arch of the foot becomes apparent then the foot is supple.