ACL injuries are one of the most common knee injuries in any high intensity sport. Injuries to the ACL can range from mild to severe. However, it is more common to have a complete rupture then just a sprain. More commonly the injury is sustained in a non-contact movement, rather than a direct contact blow to the knee. Below is an overview of what you should know about ACL injuries.


The anterior cruciate ligament is one of four ligaments that helps hold the three bones of the knee joint together. The ACL in located on the inside of the knee joints and runs from the back where it attaches to the femur to the front where it attaches to the tibia. It crosses in front of the posterior cruciate ligament and together these two ligaments control the forward and backward motion of the knee. Specifically, the ACL prevents the tibia from sliding to far forward and help maintain rotational control.

Normal and torn ACL

Risk Factors

There are five main risk factors that can put someone at a higher risk for an ACL injury. Due to anatomical and hormonal differences between men and women, studies have shown that females are at a higher risk for ACL injuries. Different muscle strength and weakness can also contribute to an ACL injury. A strong quad dominance and weak posterior muscles like your hamstrings which ends up pulling the tibia forward and placing more stress on the ACL. Weak core muscles is another risk factor, a strong core is essential for supporting your trunk and executing smooth and correct movements of the body. Shoe type and playing surface all play a role in increasing the risk of an injury.

Mechanism/Cause of Injury

ACL injuries can happen on contact and in noncontact movements. Non-contact is actually more common, meaning it occurs simply through body position/body movement. A combination of these movements often leads to an injury: inward force on the knee, quad contraction, the knee is near full extension, and there is some sort of internal or external rotation. This can be achieved in several ways:

  • ​Cutting and changing direction
  • Stopping suddenly
  • Landing on one leg
  • Slowing down while running
  • Direct contact or collision

Cause of ACL Injury

There are three different types of ACL injuries, Grades 1, 2, and 3. Grade one is when there is only a partial tear of few fibers in the ACL ligament and the knee can still function. Grade 2 involves more pain and a greater percentage of torn fibers. The ligament will be loose and lose a lot of function. A grade 3 tear will be a complete tear of the ACL ligament and will leave the knee very unstable. A grade 3 tear almost always requires surgery if the athlete plans to return to the same level of play


Athletes will often say they felt a shift in their knee or heard a pop followed by immediate pain. Swelling will be large and occur very quickly after the injury as well as decreased range of motion. Pain can be hard to pin point sometimes, often feeling like the whole knee is painful, but pain in the anterior (front) aspect of the knee is common. If the ACL injury is not diagnosed and the athlete returns to play, they will often have moments where the knee feels very unstable and shifts. This will be followed by pain and swelling.


Treatment will depend on the severity of the injury. After the injury occurs the athlete should focus on decreasing swelling and maintaining range of motion. There are two paths to take, surgical and nonsurgical. Grades 1 and 2 will most likely not require surgery. Working with a physiotherapist they will often recommend pain free stretching and strengthening of the muscles surrounding the knee. Bracing is also a great idea if the athlete is going to be participating in high risk activities. For information on the best braces for an ACL injury click here.


If surgery is a possibility, there is a little controversy around it. The recovery time after surgery can be about 8-12 months and very limiting on your daily movement to begin. If you are a recreational athlete that doesn’t plan to return back to high intensity and high risk sport then non-surgical rehab and bracing may be a better option. However most professionals would recommend a ACL reconstruction surgery if elite performance is your goal.