The underlying cause of adult acquired flatfoot disorder is uncertain.
One of the more common causes is posterior tibial tendon dysfunction (PTTD). This condition affects one of the most important tendons in the foot, the posterior tibial tendon whose main job is to support the arch of your foot as you walk.If this tendon is injured or becomes swollen, it can eventually lead the arch to collapse.
Arthritis also causes AAF, it that attacks and inflames the cartilage in the joints of the foot can cause the foot to lose its arch and flatten.
In some cases, adult acquired flatfoot can also be caused by an injury or tear to the ligaments of the foot. An injury to the middle of the foot called a Lisfranc injury can cause the foot to become flat.