When ligaments are damaged, the knee joint may become unstable. Ligament damage often occurs from a sports injury. A torn ligament severely limits knee movement, resulting in the inability to pivot, turn, or twist the leg. Surgery is an option to repair a torn ligament if other medical treatment is not effective. There are 4 major ligaments in the knee. The ligaments in the knee connect the femur (thighbone) to the tibia (shin bone), and include the following: Anterior cruciate ligament (ACL).