The stability of your knee depends on the ligaments surrounding your knee. There are several ligaments found within your knee joint and their function is to connect the tibia (shin bone) and femur (thigh bone) together.
The four stabilizing ligaments of the knee are:
1. Medial Collateral Ligament (MCL) - located medially (on the inside of your knee) from the end of the femur to the top of the tibia

2. Lateral Collateral Ligament (LCL) - located laterally (on the outside of your knee) from the end of the femur to the top of the tibia

3. Anterior Cruciate Ligament (ACL) - located within the center of your knee joint, from the back of the femur to the front of the tibia

4. Posterior Cruciate Ligament (PCL) - located within the center of your knee joint, from the front of the femur to the back of the tibia

Your collateral ligaments limit side to side motion of the knee. The cruciate ligaments limit front to back motion as well as rotation of the knee. The specific function of your MCL is to prevent instability on the medial side of your knee joint. An MCL tear is more common than an LCL Tear.

If stretched too far, your ligament can tear. Your ligament can tear in the middle or on either end where it attaches to bone. An MCL tear can occur as an isolated injury or as part of a more complex injury to your knee. A complex injury to the MCL means you can also have tears to the PCL, ACL, or Mensicus.

Keep in mind that MCL tear and MCL sprain are terms that are often used interchangeably. The term "sprain" is more commonly used when only a few of the ligament fibers are torn. The term "tear" is more commonly used when all the ligament fibers are torn.