Extensor deficiency: first cause of childhood flexible flat foot.

Childhood flexible flat foot is the most common paramorphism of the lower limb. The cause is not a bony malformation of the foot but a functional deficiency of the anatomic structures supporting the plantar arch. These structures, working as active tie rods (the tibialis anterior and posterior muscles) or passive factors of support (flexor hallucis longus and flexor digitorum longus muscles) act together to maintain the plantar arch. Their deficiency is responsible for childhood flexible flat foot, characterized by a flattening of the plantar arch and calcaneus pronation (heel valgus) and manifested in the characteristic "duck walking" in children. Hypothesizing poor extensor activity of the tibialis anterior, extensor digitorum longus, and extensor hallucis longus muscles during the heel contact phase of the gait cycle, we began a preliminary study to evaluate, through superficial electromyography (sEMG), the activation of muscle groups involved in the pathogenesis of childhood flexible flat foot, in particular the tibialis anterior and extensor hallucis longus muscles, to plan a rehabilitative program addressing the strengthening of insufficient muscles. The therapeutic program should also include the use of a medial elastic push orthosis. Data obtained by sEMG highlight a reduced activation of muscles related to the grade of flat foot, emphasizing the concept that a reduced activation of extensor muscles may be involved in determining flexible flat foot.