The ACL is one of four ligaments in the knee that connect the upper and lower leg bones. An ACL injury is almost always related to sports such as soccer or football. After your doctor diagnoses an ACL injury with tests such as an arthroscopy or an MRI, he or she will prescribe treatments. These may include rest, rehabilitation, or surgery. As with any injury, the goal is prevention. Doing strengthening exercises can help reduce your risk of an ACL injury. Follow the links below to find WebMD's comprehensive coverage about how an ACL injury is contracted, what it looks like, how to treat it, and much more.