Medical Library: Knee – ACL, PCL, MCL, LCL Tear

There are four main ligaments in the knee: Anterior Cruciate LigamentPosterior Cruciate LigamentMedial Collateral Ligament, and Lateral Collateral Ligament. Tears to any of these ligaments are serious conditions, and may require surgery, or rest and rehabilitation.


An anterior cruciate ligament (ACL) tear is an injury to the knee commonly affecting soccer players, basketball players, skiers, gymnasts, and other athletes. About 70% of ACL tears are the result of non-contact injuries; 30% are the result of direct contact (player-to-player, player-to-object). Women are 4-6 times more likely than men to experience an ACL tear.

Usually, you will be examined by a physical therapist or an orthopedic surgeon immediately following injury. Most people who sustain an ACL tear will undergo surgery to repair the tear; however, some people may avoid surgery by modifying their physical activity so that they don’t put a lot of stress on the knee. A select group can actually return to vigorous physical activity following rehabilitation without having surgery.

Your physical therapist, together with your surgeon, can help you determine if non-operative treatment (rehabilitation without surgery) is a reasonable option for you. If you elect to have surgery, your physical therapist will help you both prepare for surgery and recover your strength and movement following surgery.

The ACL is one of the major ligaments (bands of tissue) connecting the thighbone to the shin bone. It can tear if you:

  • Twist your knee while keeping your foot planted on the ground
  • Stop suddenly while running
  • Suddenly shift your weight from one leg to the other
  • Jump and land on an extended (straightened) knee
  • Stretch the knee farther than you should
  • Experience a direct hit to the knee


The PCL one of the four ligaments in the knee, and is the ligament that prevents the tibia (shin bone) from sliding too far backwards. Along with the ACL which keeps the tibia from sliding too far forward, the PCL helps to maintain the tibia in position below the femur (thigh bone). PCL injuries account for about 20% of knee ligament injuries.

The most common PCL injury is often referred to as a “dashboard injury.” This injury is often seen in car accidents when the shin forcefully strikes the dashboard. The knee is in the bent position, and an impact forcefully strikes the shin backwards. This injury can also occur when an athlete falls on the front of their knee which hyperflexes the knee (bends all the way back), with the foot held pointing downwards. Both scenarios stress the PCL, and if the force is high enough, a PCL tear will result.

Symptoms of a PCL tear are knee pain, swelling, and decreased motion, and some people will say that their knee “popped” or gave out. After a PCL injury, many patients believe that they can’t “trust” their knee, or that it feels as though the knee may give out which may be an indicator that surgery is needed.


The MCL is another one of the four ligaments in the knee. The MCL is on the inside of the knee joint. and spans the distance from the end of the femur (thigh bone) to the top of the tibia (shin bone). The MCL resists widening of the inside of the joint, or prevents “opening-up” of the knee.

The MCL is usually injured when the outside of the knee joint is struck, causing the outside of the knee to buckle, and the inside to widen. When the MCL is stretched too far, it may tear. A MCL injury may be an isolated injury, or it may be part of a complex injury to the knee. Other ligaments, most commonly the ACL or the meniscus may be torn along with a MCL injury.

MCL injury pain is usually focused directly over the ligament. Swelling may appear, and bruising and generalized joint swelling are common a few days after the injury. In some cases, patients may feel as though their knee may ‘give out’ or buckle. Symptoms of a MCL injury tend to correlate with the extent of the injury.


The LCL is another one of the four ligaments in the knee. The LCL is on the outside of the knee, and connects the end of the thigh bone (the femur) to the top of the smaller shin bone (fibula). The LCL helps to prevent excessive side-to-side movement of the knee joint. When the LCL is torn, the knee joint may move too far side-to-side when stressed.

The LCL is most commonly torn during sports activities or traumatic injuries (falls, etc.). The LCL is torn when the knee bends inwards excessively, and the LCL is stretched too far.