Almost all children develop some degree of pronation during the early stages of weight bearing. Most infants have flexible flatfeet. Typically, the condition is transient, resolving with normal growth and development in 97% of children, usually before 2½ years of age. A family history may be found in children with flat foot that persists beyond the usual time of physiological resolution.

Symptoms, including aching of the feet and legs, muscle cramps in the calves at night, easy fatigability, and reluctance to participate in strenuous activity, are uncommon but may occur. Symptoms result from the strain caused by the child's continual attempt to shift weight bearing laterally toward the center of the foot, bringing about some degree of toeing-in. Persistent pronation without symptoms occurs in some children who may have a family history of pronation and often demonstrates ligamentous laxity or hyperextensibility of other joints, including the knees, elbows, wrists, and thumbs.

The incidence of pes planovalgus is unknown. Vertical talus is very rare. Accessory tarsonavicular is fairly common; 14% of adolescents experience symptoms according to 1 study. Tarsal coalitions are bilateral in 50% of patients, probably occur in 1% of the population, and are usually hereditary. They may be found in other family members who are asymptomatic but have no hindfoot motion.[6]

The Achilles tendon is seen to curve inward, and the medial longitudinal arch of the foot, observed without weight bearing, disappears on standing. These changes occur because a wide-based stance is assumed for balance (accentuated by bulky diapers), causing the weight to be borne on the medial aspect of the feet (Figure 183-9). Laxity of the ligaments supporting the feet contributes to pronation. When symptoms do occur, the clinician should look for associated conditions, such as obesity, neuromuscular disorders, and structural abnormalities above the level of the ankle.

Vertical talus and accessory tarsonavicular can usually be detected in the newborn by the presence of a bony prominence on the medial and plantar aspects of the foot, with limitation of plantar flexion and inversion of the forefoot.

Tarsal coalitions are not usually detected until late childhood or adolescence, when the initially fibrous or cartilaginous bar connecting the hindfoot bones becomes ossified, producing pain with walking and an inability to invert the foot. The foot is held in a pronated position with eversion of the forefoot. The peroneal tendons stand out prominently when attempts are made to invert the foot. Calcaneonavicular coalition tends to develop between 9 and 13 years of age, whereas talocalcaneal coalition develops later, typically 13 to 16 years of age. The foot is held in a pronated position, with eversion of the forefoot. This condition, commonly called spastic flatfoot, is not related etiologically to simple pronation.

Figure 183-9 Pronation. A, Viewed from behind, the hindfoot is everted. B, Viewed from in front, the forefoot is everted and abducted. (Sharrard WJW. Paediatric Orthopaedics and Factures, 2nd ed. Oxford, NY: Blackwell Scientific; 1979. Reprinted by permission of Blackwell Publishing Ltd.)

Flexible flatfoot (pes planus) does not require any imaging in most cases. If pronation is persistent beyond 2½ years of age, if symptoms are present, if flexibility is limited, or if a suspicion of planovalgus exists, then radiographic examination may be necessary.