The ACL usually does not heal well on its own because it does not have a good blood supply. Dr Alan Cheung, an orthopaedic surgeon in Singapore liken it to a rope, and if completely torn in the middle, it is difficult for the rope ends to come together to heal, particularly as the knee is moving all the time. However some athletes are able to return to sports if they only have a partial ACL tear, minimal instability or play sports that do not involve sudden turning movements (e.g. baseball).