Anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) tears can result from a significant blow to the knee while it is bent, often during sports, exercise, or car accidents. ACL injuries, including partial or complete tears, can occur when an athlete quickly changes direction, twists without moving the feet, slows down abruptly, or misses a landing from a jump. PCL injuries are likely to occur to the front of the knee or from hyperextending the knee.