Other traumatic causes include crushing injuries, frostbite, and electrical accidents. In these cases, a prosthesis provides more function to the patient than does the disabled limb. Congenital limb deficiency is different in that no amputation is involved even though the patient wears a prosthesis. A variety of reasons for this anomaly may exist, but the cause is a constriction of growth bands or a disruption of skeletal growth. These patients suffer no associative anomalies, and it is not a hereditary trait.
Most patients are women needing below-elbow prostheses.
In some cases underdeveloped distal limbs are still present. In the lower limb, proximal femoral focal deficiency results in an undeveveloped femur, hip joint, and knee and fully developed ankle and foot. In some cases the ankle is turned, creating a pseudo-knee and this is amputated later as the child grows into adulthood. In most developed countries the amputee population is about 1.55 amputees per 1,000. Based on a population of about 250 million in the U.S., the number of amputees in the U.S. would be about 387,500.