The peripheral joint most commonly involved in osteoarthritis is the knee, primarily due to knee function. The knee joint carries almost the greatest amount of weight of any joint in the body and is used almost as often as any other. The knee joint is inevitably subjected to all the gravitational compression during walking, and more seriously, the knee joint is subjected to compression forces during flexion and extension, stair climbing and descending, and deep squatting, not just by the body’s gravity, but by several times the body’s gravity. For example, when walking up and down stairs, the pressure on the knee joint can be 4-6 times the body weight, so osteoarthritis is particularly likely to occur in the knee joint.