Adult Acquired Flatfoot

Adult acquired flatfoot (AAFD), first described as posterior tibial tendon dysfunction (PTTD), is a complex pathology defined by the collapse of the medial longitudinal arch of the foot with continued progressive deformity of the foot and ankle. Adult acquired flatfoot is a debilitating condition that affects up to 5 million people within the US.The anatomy of the foot and ankle are complex, with multiple structures involved in the stability and function needed to walk and bear weight. A structure principally involved in the development of adult acquired flatfoot is the posterior tibial tendon. In addition to plantar flexion, the posterior tibial tendon is the primary inverter of the foot. The posterior tibial tendon inserts principally on the navicular tuberosity, but also has lesser insertions on to other tarsal and metatarsal structures. The spring and deltoid ligaments are crucial to the stability of the foot and ankle. The spring ligament, which is the ligament most frequently involved in adult-acquired flatfoot, supports the ankle by connections from the sustentaculum tali of the calcaneus to the navicular. The primary role of the spring ligament is to support the head of the talus. The deltoid ligament is usually affected later in the progression of the adult acquired flatfoot. The superficial deltoid ligament has a wide insertion on the navicular to the posterior tibiotalar capsule. It is the primary support against tibiotalar valgus angulation. The deep deltoid ligament prevents axial rotation of the talus, where it inserts, from its origin on the intercollicular groove and posterior colliculus. The deltoid ligament as a whole is critical in supporting the articulating surfaces of the ankle and the spring ligament. Acquired flatfoot grading is by the Johnson and Strom classification system, which has classification grades of I to III. Myerson added a fourth grade in 1997. The classification system aids practitioners in identifying AAFD severity and also can guide treatment plans. Stage I disease characteristically presents with posterior tibial tendon tenosynovitis with no arch collapse. Patients with stage II adult acquired flatfoot will have foot collapse and will be unable to perform a single-leg heel rise. This stage further subcategorizes into stage IIa and IIb. Stage IIa is foot collapse with valgus deformity of the hindfoot but no midfoot abduction, while in stage IIb midfoot abduction is present. Patients with stage III adult-acquired flatfoot will have fixed deformity with hindfoot valgus and forefoot abduction. Patients with stage IV deformity will have ankle valgus secondary to deltoid ligament attenuation.