Management in Stage IV Adult-acquired Flatfoot Deformity

Adult-acquired flatfoot deformity (AAFD) is one of the most common degenerative tendinosis problems of the foot and ankle in the aging population. Tendon dysfunction, which typically occurs in the tibialis posterior tendon, leads to secondary damage of surrounding ligaments. Degeneration of the posterior tibial tendon (PTT) induces a change in this complex, resulting in further deformity of the talonavicular joint. In addition to this deformity, the interosseous ligament of the subtalar joint is also affected, resulting in subtalar subluxation. The advanced stage of the posterior tibialis tendon and deltoid ligament insufficiency with a concurrent valgus deformity results in an abnormal deforming force to the ankle, disruption of the foot, and ankle biomechanics, and the increase in the peak pressure loads. If left untreated, this abnormal condition ultimately leads to arthritic changes of the midfoot, hindfoot, and ankle joints. Adult-acquired flatfoot deformity stage IV is the foot deformity that involved lateral talar tilt deformity of the ankle, which can be subclassified into flexible type (IVA) and fixed type (IVB). This chapter will provide a state-of-the-art understanding of how to deal with patients suffering from the Stage IV AAFD and the outcomes of each treatment method.