The human knee performs a very basic but essential function. It is simply required to bend or extend. However, without these two basic motions, the body would be unable to perform many activities such as walking, running, kicking, sitting and getting out of bed among other necessary motions. It would be hard to get up from a chair without bending your knees.

The knee serves as a junction for four bones but its only the thigh bone (femur) and the shin bone (tibia) that form the knee joint. The strut bone called the fibula gives the knee stability while patella or knee cap assists in the joint and muscle function. There are two types of muscles that aid in the functioning of the knee namely the quadriceps in the front of the thigh and the hamstring muscles on the back of the thigh. When the quadriceps muscles contract, the knee straightens and when hamstring muscles contract the knee bends.

An acute injury in any part of the knee anatomy can cause tears or inflammation characterized by pain, swelling or limitation of movement. The knee is always susceptible to direct blows, twisting or stretching injuries. Injuries can also occur when the joint is forced through a range of movement beyond its tolerance. This causes ligament tears and stretching called sprains. The knee can also suffer twisting injuries that stress the cartilage and can lead to tears. Muscles and tendons surrounding the knee can also be injured by acute hyper-flexion or hyper-extension mostly due to overuse. Such strains are referred to as strains. Knee injuries are categorized in two groups. The first involves injuries that cause swelling and inability to bend the knee and the second involves injuries that cause discomfort with minimal effects on movement. For each case it is important to seek for medical attention immediately after the injury occurs to avoid complications.