i completely blew out my ACL. when you completely blow it out, there is not that much pain, and you could ski with it, it would just be more unstable. in my case, i also tore my lateral and medial meniscuses, which is what causes most of the pain and the not being able to ski. when you dont have an ACL though, every other ligament in your knee is weakened, so if you fall, the chances of tearing more shit are high.