This usually includes a history of trauma, swelling and pain, restricted movement, and joint instability 1. There must be a relatively clear history of trauma, such as a sprain in basketball or soccer, or a car accident injury. 2, There is often significant swelling and pain in the knee joint within a few hours after the first injury. 3, Acute injuries often do not fully straighten the knee 4, chronic ACL injury, the most common manifestation is the inability to run fast, can not stop sharply, sharp turns, and therefore repeated sprains in sports.