There are four major ligaments in the knee joint. The Medial Collateral Ligament, the Lateral Collateral Ligament and two ligaments which cross in the middle of the knee, the Anterior Cruciate Ligament and the Posterior Cruciate Ligament. Of these, the most commonly injured are the Medial Collateral Ligament and the Anterior Cruciate Ligament. These ligaments stabilize and secure an otherwise inherently unstable knee joint. They provide stability as we run and twist our knees into various positions with sports. When they are injured they can cause significant disability, giving way, swelling, loss of motion and can lead to early arthritis. Of these, the Anterior Cruciate Ligament is often, but not always, treated with surgery.