The most common cause of an adult acquired flat foot deformity (AAFFD) is posterior tibial tendon dysfunction. As AAFFD progress, the midfoot and forefoot abduct, and the hindfoot moves into a valgus position. The deltoid ligament becomes incompetent late in the condition as the hindfoot moves further into a valgus position. A tight Achilles tendon can develop and worsen the deformity. Treatment largely depends on whether the flat foot deformity is rigid or flexible. A rigid flatfoot deformity cannot be corrected passively beyond neutral, which is a distinguishable feature from a flexible deformity. On exam of a rigid deformity forefoot pronation cannot be corrected passively with the heel in valgus. The rigidity of the talonavicular, subtalar, and calcaneocuboid joints leads to fixed hindfoot valgus and midfoot abduction.
Patients with posterior tibial tendon dysfunction, a flat foot deformity, and a flexible hindfoot are candidates for tendon transfers, including posterior tibial tendon debridement and flexor digitorum longus (FDL) tendon transfer or FDL tendon transfer to the navicular, spring ligament repair, calcaneal osteotomy, and Achilles lengthening. Patients with rigid hindfoot valgus and forefoot abduction deformities require a fusion procedure, most commonly a triple arthrodesis. A triple arthrodesis involves fusion of the talonavicular, subtalar, and calcaneocuboid joints. The goal of fusion is to create a neutral hindfoot and forefoot.
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
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