The biomechanics and functionality of the mid-foot of the foot is critical to normal walking and running gait and biomechanics. The support of the mid-foot ( arch ) of the foot is maintained by a number of elements, including the alignment of the bones, the ligaments, the muscles as well as the plantar fascia. One of the essential muscles in the functional support of the arch of the foot is the posterior tibial muscle. This is a strong muscle that is in the leg. The tendon of this muscle passes down the inside of the ankle joint and attaches below the bones that comprise the mid-part of the arch of the feet, so this particular muscle is really important for supporting the arch. In some individuals, the posterior tibial muscle seems to lose it capability to stabilize the foot, resulting in a disorder referred to as posterior tibial tendon dysfunction or adult acquired flat foot.

This disorder usually commences with a mild discomfort in the midfoot or medial side of the ankle joint and the longitudinal arch of the feet progressively collapses and the rearfoot rolls inwards (pronates). This is all due to the muscle being unable to do its job adequately. If therapy is not implemented, then the pain and disability of posterior tibial tendon dysfunction progresses. In its end stages it usually is very disabling and painful. It eventually has a significant effect on total well being and also the ability to walk. It is very exhausting because a lot of energy is necessary to walk with this condition.

Since the long term consequences of this disorder may be so debilitating, it is important that it must be detected as quickly as possible and therapy begun. The longer the delay the harder it is to manage. During the early stages, the only real satisfactory treatment are usually very hard or stiff foot supports. They have to be firm as the forces that are flattening the feet are so high that they have to be resisted. A softer orthoses will be flattened. A high top trekking or basketball type shoe or boot can be helpful at stabilising the rearfoot. If this isn't sufficient then more complex ankle braces are often the next step. If this does not work or the treatment is started too late, then surgery is actually the only suitable treatment at this late stage.