In a mild case, the excercise can over come the problems many times without having to do the surgery, but they must be IN SHAPE, with forced excercise. Our vet has recommended to those that have had the problem (an aquaintance has one) to get the horse in shape hard- not just mild stuff, but really in shape. Yes the muscle helps hold everything where it is supposed to be. However, there is no quick and easy fix. The surgery helps in cases where you have no other choice, but there are problems with the surgery too- like causing arthritis in those joints later on.
However, rather than live in misery, the surgery can certainly give them a more normal and usable life. I would never breed one with this problem. (Unfortunately the person I know has not done the excercise on the horse at all that was recommended by the vet and it's been a year now and it's getting worse. She has also refused to geld the horse and wants to use him for breeding and didnt want to notify the breeder either that he had the problem! Good grief!)