I had an ACL reconstruction as a consequence of a football injury. The surgery isn't that bad ( muscle is taken from the thigh to construct a new ligament ) but the real issue is potential muscle wastage due to the initial bed rest. The physio is intense to say the least and the new ligament is only well and truly good to go once it has developed its own new blood vessels. This is why it takes so long to come back from an injury of this nature. It can also cause cartilage issues later on.