Flatfoot deformity is a general term used to describe a person whose arches are slowly dropping to the ground, aka “fallen arches.” Adult-acquired flatfoot deformity can be caused by several factors, but the most common is abnormal functioning of the posterior tibial tendon in the foot and ankle.
The posterior tibial tendon is the primary tendon that supports the arch. If this tendon begins to elongate from a sustained, gradual stretch over a long period of time, then the arch will progressively decrease until full collapse of the arch is noted on standing. What makes this tendon elongated? Biomechanical instability of the foot such as over-pronation or an accessory bone at the insertion site of the tendon are the primary causes for posterior tibial tendon dysfunction.