The so called rigid orthotic devise, designed to control function, may be made of a firm material such as plastic or carbon fiber, and is used primarily for walking or dress shoes. It is usually fabricated from a plaster of paris mold of the individual foot or a digital foot scanner. The finished device normally extends along the sole of the heel to the ball or toes of the foot. It is worn mostly in closed shoes with a heel height under two inches. Because of the nature of the materials involved, very little alteration in shoe size is necessary.
Rigid orthotics are chiefly designed to control motion in two major foot joints, which lie directly below the ankle joint. These devises are long lasting, do not change shape, and are difficult to break. Strains, aches, and pains in the legs, thighs, and lower back may be due to abnormal function of the foot, or a slight difference in the length of the legs. In such cases, orthotics may improve or eliminate these symptoms, which may seem only remotely connected to foot function.