Update on stage IV acquired adult flatfoot disorder: when the deltoid ligament becomes dysfunctional.

Deltoid ligament complex insufficiency is a fundamental pathologic component of stage IV AAFD. Failure of the deltoid ligament allows the talus to tilt into valgus within the ankle mortise. If left untreated, ankle joint biomechanics are altered and may lead to debilitating tibiotalar arthritis. All surgical treatments that address the valgus talar tilt seen with stage IV AAFD require accompanying procedures to properly realign the hindfoot. Stage IV AAFD can be subdivided into two groups. Patients with a flexible ankle deformity without advanced tibiotalar arthritis (stage IV-A) can be considered for a joint-sparing procedure. A variety of procedures have been described, but longterm follow-up studies have yet to determine which of these techniques is optimal. Patients with a rigid valgus ankle deformity or a flexible deformity accompanied by advanced tibiotalar arthritis (stage IV-B) should be considered for a joint-sacrificing procedure. To date, the most reliable results for stage IV-B AAFD have been reported with either tibiotalocalcaneal or pan-talar arthrodesis.