Ligaments are elastic bands of tissue that connect bones to each other to provide stability and strength to the knee joint. Ligament injuries in the knee are fairly common, especially injury to the anterior cruciate ligament, or ACL. There are four main ligaments in the knee that connect the femur or thighbone to the tibia or shin bone:
- Anterior cruciate ligament or ACL – located in the center of the knee, controls the rotation and forward motion of the shin bone
- Posterior cruciate ligament or PCL – located at the back of the knee, controls backward movement of the shin bone
- Medial collateral ligament or MCL – connects the thigh bone to the shin bone on the inside of the knee—MCL stabilizes the inner knee
- Lateral collateral ligament or LCL – connects the thigh bone to the fibula, the smaller bone of the lower leg on the outer side of the knee—LCL stabilizes the outer knee
Injuries to these ligaments are common in many sports such as soccer, football, basketball, skiing and gymnastics where the knee may twist with the foot planted, when the knee gets hit, when it is extended too far, when jumping and landing on a flexed knee, stopping suddenly when running, or when suddenly shifting weight from one leg to another. Many people who have tears to the ligaments, particularly ACL tears, opt to have surgical treatment to repair the tear.