acl tear

This can happen in a number of contexts, including something as simple as landing on it wrong or pushing off of it wrong. For example, in sports, when you plant your foot and suddenly change direction, the ACL can sustain damage. This is fairly common in a lot of sports, including soccer and football and basketball. Of course, this can even happen in other environments, such as falling off a ladder or missing a step on the stairs. When it happens you may hear a loud pop, and swelling will likely occur within the first few hours. The pain and swelling will limit your further movement.