After prophylactic knee braces were successfully tested in the National Football League, many athletes wanted access to similar products for use during contact activities.According to the American Academy of Orthopaedic Surgeons, knee braces fit into several categories: (1) prophylactic--braces intended to prevent or reduce the severity of knee injuries in contact sports; (2) functional--braces designed to provide stability for unstable knees; and (3) rehabilitative--braces designed to allow protected and controlled motion during the rehabilitation of injured knees. A fourth category includes patellofemoral braces, which are designed to improve patellar tracking and relieve anterior knee pain.