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Anatomy of the Knee: An Introduction to the ACL

By Lisa Moore, ATC June 05, 2017 Posted in: Sports Medicine

By now anyone who has watched a sporting event has heard about the ACL, or specifically the ACL tear. Everyone knows it’s a devastating injury but few know what it actually does or is!

Where is Your ACL?


Our knee is comprised of four ligaments:

  1. Anterior cruciate ligament (ACL)
  2. Posterior cruciate ligament (PCL)
  3. Lateral collateral ligament (LCL)
  4. Medial collateral ligament (MCL)

Ligaments connect bone to bone and are responsible as a last stabilizer for a joint after the muscles - like the brakes on a car. The MCL and the LCL are both on the outside of the knee and are responsible for the knee moving side to side. In the knee, the ACL and PCL are in the center of the knee, deep under the knee cap, and form an X shape. These two work together to prevent the lower leg from slipping forwards or backwards from the upper part of the leg.

How Can the ACL be Injured?

The ACL can be injured two ways - contact and non-contact injuries. Contact injuries occur when the athlete gets hit from the outside of the knee, or from the front and the knee buckles in an awkward angle. Think of a football player getting tackled, or a soccer player making contact with another player. The other type of injury is a non-contact injury, or a plant and a twist. Usually the athlete will describe planting and twisting the knee and feeling an immediate pop. This can happen with jumping, or a start stop motion.

How Does an ACL Injury Affect You?

The ACL is extremely important in the stability of the knee, and unfortunately the tissue cannot repair itself so a significant injury does require surgery. If the patient has no interest in returning to sports or doesn’t have an active lifestyle it is possible to conservatively treat the ACL without surgery and with physical therapy.

With surgery an ACL repair can take 6-9 months to fully heal, sometimes up to 12 months. This can knock an athlete out of an entire season at times. Non-contact ACL injuries can be prevented through proper training and strengthening.

Lisa Moore, ATC
Lisa Moore, ATC

Lisa Moore, ATC is a sports medicine provider and athletic trainer for CHI Health.

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