This document discusses posterior tibial tendon dysfunction (PTTD). It begins with the anatomy of the tibialis posterior tendon, including its location in the calf compartment, origin, insertion points, nerve and blood supply. It then discusses the causes of PTTD, including overuse, degeneration, trauma and congenital factors. The document presents Johnson and Strom's classification system for PTTD in 4 stages based on tendon integrity and foot deformity. Treatment options are outlined for each stage, including bracing, medial arch supports, surgery like medial displacement calcaneal osteotomy or flexor digitorum longus transfer. More advanced stages may require triple arthrodesis or ankle fusion to correct deform