An ankle-foot orthosis (AFO) is an orthosis or brace that encumbers the ankle and foot. AFOs are externally applied and intended to control position and motion of the ankle, compensate for weakness, or correct deformities. AFOs can be used to support weak limbs, or to position a limb with contracted muscles into a more normal position. They are also used to immobilize the ankle and lower leg in the presence of arthritis or fracture, and to correct foot drop; an AFO is also known as a foot-drop brace. An AFO is generally constructed of lightweight polypropylene-based plastic in the shape of an “L”, with the upright portion behind the calf and the lower portion running under the foot.