Ligament Tears – Anterior Cruciate Ligament (ACL)

The knee is the largest joint in the body and is vital to movement. The stability of the knee mostly depends on the ligaments and muscles around it. Therefore, injuries to knee ligaments are common. In 2006, more than 12 million people visited orthopaedic surgeons because of knee problems.

Two sets of ligaments in the knee give it stability: the cruciate ligaments and the collateral ligaments.

Cruciate Ligaments

The cruciate ligaments are located within the knee joint and connect the thighbone (femur) to the shinbone (tibia). They function like short ropes that hold the bones of the knee joint tightly together when the leg is bent or straight. This is needed for proper knee joint movement.

The cruciate ligaments are so named because they cross each other to form an “X.” The term cruciate comes from the Latin word crux, which means “cross.”

The cruciate ligament located toward the front of the knee is the anterior cruciate ligament (ACL). The cruciate ligament located toward the rear of the knee is the posterior cruciate ligament (PCL).

ACL Injuries

The ACL prevents the shinbone from sliding forward beneath the thighbone.
The ACL can be injured in several ways:

  • Changing direction rapidly
  • Stopping suddenly
  • Slowing down while running
  • Landing from a jump
  • Direct contact or collision, such as in a football tackle


If you injure your ACL, you may not feel any pain immediately. However, you might hear a popping noise, and you may feel your knee give out from under you.

Within 2 to 12 hours, the knee will swell, and you will feel pain when you try to stand. Apply ice to control the swelling, and elevate your knee until you can see an orthopaedic surgeon.