An ACL injury occurs when the anterior cruciate ligament becomes damaged through either a pull, twist, tear or other disruption of the knee. ACL injuries usually occur during athletic activities and are common in running, jumping or during sudden twisting, turning or stopping movements. An injured ACL reduces stability in the knee and decreases support of the knee joint during athletic activity.
Injuries can vary in severity, ranging from a minor sprain to a complete tear or rupture of the ligament. Less serious injuries are frequently treatable with physical therapy alone, while a torn ligament will usually require surgery, as a completely torn ligament cannot repair or reattach itself.