According to the National Limb Loss Information Center (NLLIC), approximately 130,000 people in the United States require an amputation each year. Although the majority of these procedures are lower limb amputations due to vascular diseases, amputations may also be needed to treat birth
defects, cancer, or severe injuries from accidents or military action. Many different types of prosthetic legs, which are classified based on the complexity of the artificial knee, have been developed to partially restore capacity to walk. The simplest type is the polycentric knee that the user swings during walking. Hydraulic knees are more complex and incorporate adjustable hydraulic pumps to improve the motion of walking. The third type of knee is the electronic knee, which combines microprocessor control with the mechanical and hydraulic elements in other types of prosthetic knees. Electronic knees provide the highest degree of function but require more maintenance due to their complexity.