Hypermobile or pronated feet are seen in 15% of adults. The child with flatfeet is usually asymptomatic and has no activity limitations. Newborn and toddler flatfoot is the result of ligamentous laxity and fat in the medial longitudinal arch. This is called developmental flatfoot and usually improves by 6 years of age. In older children, flatfoot is typically the result of generalized ligamentous laxity, and there is often a positive family history. Hypermobile flatfoot can be thought of as a normal variant.
In the non-weight bearing position, the older child with a flexible flatfoot will have a medial longitudinal arch. When weight bearing, the foot pronates (arch collapse) with varying degrees of hindfoot valgus. Subtalar motion (essentially all ankle motion except plantar and dorsiflexion) is normal. Any loss of subtalar motion may indicate a rigid flatfoot, which can be related to tarsal coalition, neuromuscular disorders (cerebral palsy), and heel cord contractures. Radiographs of hypermobile flatfeet are usually not indicated.
Hypermobile pes planus cannot be diagnosed until after 6 years of age; prior to that, it is developmental pes planus. Reassurance that this is a normal variant is very important. Patients who are symptomatic with activity may require education on proper, supportive footwear, orthotics/arch supports, and heel cord stretching.