L.,
It may be that this is the only way your son can deal with what is happening to him. But on the other hand, I would talk to his surgeon. In certain ages groups - the very young and very old - behavior changes are the only thing we have to tell us that there is a problem. He may have an infection in the leg of that appliance or have pain he doesn't understand. I am a physician assistant in internal medicine, so orthopedics and pediatrics are not my area, but still, I find his behavior change troubling. Have you spoken to his surgeon? If surgeon doesn't think it is because of a medical complication to the procedure, I bet they would have a list of other families who went through this procedure that would be willing to talk to you. Infections are not always obvious things, so don't eliminate that as a possibility if his skin around the insertion looks good and he doesn't have a fever. Good luck
M.