Suddenly, you feel a pop in your knee, then immediate pain followed by swelling. You may have just injured or torn your anterior cruciate ligament, or ACL. How an ACL tear can happen. The ACL is a tough band of tissue that lies within your knee and provides front-to-back and rotational stability. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.