Anterior Cruciate Ligament (ACL)

ACL tear knee anatomy
The ACL is one of four major knee ligaments.. Credit: Photo © A.D.A.M.

What is the Anterior Cruciate Ligament - ACL?

The anterior cruciate ligament (ACL) is one of four ligaments critical to stabilizing the knee joint. A ligament is made of tough fibrous material and functions to control excessive motion by limiting joint mobility. Of the four major ligaments of the knee, the ACL is the most frequently injured. When you have an injury to your ACL it often feels like the knee is "giving out."

What does the ACL do?

The anterior cruciate ligament provides the primary restraint to forward motion of the shin bone (tibia). The anatomy of the knee joint is critical to understanding this relationship. The femur (thigh bone) sits on top of the tibia (shin bone), and the knee joint allows movement at the junction of these bones. Without ligaments to stabilize the knee, the joint would be unstable and prone to dislocation. The ACL prevents the tibia from sliding too far forward.

The ACL also contributes stability to other movements at the joint including the angulation and rotation at the knee joint. The ACL performs these functions by attaching to the femur on one end, and to the tibia on the other. The other major ligaments of the knee are the posterior cruciate ligament (PCL), and the medial and lateral collateral ligaments (MCL and LCL, respectively).

Cruciate - What's in a Name?

Cruciate means cross.

The anterior cruciate ligament crosses the posterior cruciate ligament (PCL) to form an X or cross. The ACL is in front of the PCL, which is why it is named anterior while the PCL is posterior, or behind it.

Grades of ACL Sprains

When a ligament is injured, it is called a sprain. For the ACL, it is graded from 1 to 3.

A grade 1 sprain has mild damage and the knee joint is still stable. A grade 2 sprain is a partial tear with the ligament stretched and damaged. A grade 3 sprain is a complete tear of the ligament and it is the most common. 

ACL Tears - How to Treat a Torn Anterior Cruciate Ligament

Tears of the ACL can happen when you land a jump or make a sudden pivot, as is typical in sports such as basketball, soccer, football, and skiing. But you can also have a tear in a fall or work-related injury. Learn about causes, symptoms, treatment and prevention for ACL tears.

Source:

Anterior Cruciate Ligament (ACL) Injuries, American Orthopaedic Society for Sports Medicine, March, 2014.

Continue Reading