The four major ligaments in the knee are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL).

Injuries to the ACL, the ligament that controls forward movement and rotation of the shin bone, are the most common type of ligament injury in the knee. The ACL can easily be torn or stretched during physical activities that require sudden twisting motions, such as skiing. Injuries to the PCL are also common and they usually occur during a direct impact incident, such as a car accident.

An injury to any of the knee ligaments is usually accompanied by the following symptoms: sudden and severe pain, swelling, an audible pop or snapping sound at the time of injury, and difficulty applying weight or pressure to the joint.