The knee is the largest joint in the human anatomy. It forms the movable connection between femur and tibia, and its primary function is to enable the flexion and extension of the lower leg. In addition, it also allows for limited rotation of the lower leg relative to the thigh. Due to its complex anatomy, it is particularly vulnerable to injury, wear, and arthritic deformation. Many recreational activities and types of occupational stress can cause acute or chronic knee problems. Younger individuals more frequently experience ligament injury (often to the cruciate ligaments) or injury to the meniscus. The elderly are more likely to experience naturally occurring degenerative changes caused by cartilage wear.