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Causes of Ligament Tears

Learn what causes ligament tears in this Howcast video about physical therapy exercises for the knees.


The cause of ligament tears is pretty simple. It's almost always going to involve some sort of a traumatic event. The ligaments in your knee are fairly strong by nature. They're thick. There are two ligaments that run on the outside of your knee called your medial collateral ligament and your lateral collateral ligament. Then you have two ligaments on the inside of your knee called your ACL and PCL, or anterior cruciate ligament and your posterior cruciate ligament. So you have four ligaments that are there to support you knee.

The medial and lateral collateral ligaments, they're going to require you to either experience what's called a varus or a valgus force to the knee. That's basically a blow to the side of your knee, the inner side or the outer side, and like a rubber band, if you take a blow to the inside of your knee, it's going to create what's called a varus force, and then the outer ligament is susceptible to a tear. A blow to the outside of the knee is going to create a valgus force, and that's going to create a problem with the medial collateral on the inside of your knee. Based on that, the medial collateral ligament is much more susceptible to injury as we typically take our blows from the outside and creating a tear to the medial ligament.

The LCL is often spared from trauma and often stays intact. On the inside of your knee, you have your PCL and your ACL. The posterior or PCL is in a nicer place inside your knee. So it's going to require more of a blunt force to the front, like in a football game or something, to create that tear.

And lastly is the ACL. I saved the ACL for last because that is the most susceptible ligament that gets injured. You may know one or two people that have had ACL injuries and ACL tears before. The reason why it's such a common one is its location inside the knee, and therefore it's so susceptible to both blows to the outer and inner, blows to the front, but it's also very susceptible to other traumatic events like landing long on your feet or simply twisting your knee when you're playing sports, or if you're running really fast and you have to decelerate on a dime, that might actually literally tear the ACL. So it's in a weird place. It's in a tricky spot inside your knee. It's much more susceptible to tears, and we deal with that the most in the clinic. LCLs being the least common and ACLs being the most common.

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