One of the more serious knee injuries an athlete can sustain is a tear of the anterior cruciate ligament, more commonly known as the ACL. Tearing of the ACL is usually seen in athletes playing high-contact or collision sports—however this is not a requirement for the injury. An ACL tear usually occurs when an athlete plants their foot, and twists, usually hearing a popping sound in their knee at the time of injury.
When the ACL is torn, another injury may be present, such as a torn meniscus and/or medical collateral ligament (MCL), a torn lateral collateral ligament (LCL), or a torn posterior cruciate ligament (PCL).
An ACL is: A cruciate ligament of the knee that attaches the front of the tibia with the back of the femur and functions especially to prevent hyper-extension of the knee.
An MCL is: A collateral ligament on the inside of the knee that serves as a stabilizer for the joint and supports the function of the knee.