The ACL, or anterior cruciate ligament, runs diagonally through the knee, keeping the tibia (shin bone) from sliding forward. This tear usually occurs with a quick sudden movement such as rapid deceleration while the knee is bending, collision, pivoting quickly, or awkward landings. Immediately after the ACL is torn, the knee feels unstable and pain and swelling occurs. After a few hours, knee swelling is massive, there is ample pain and tenderness, and a full range of motion is lost.
The majority of the time, treatment requires surgery. Progressive physical therapy can attempt to restore the knee to its original function and strength and prevention exercises will also be taught so the patient knows how to keep the knee stablized.