Hi, I really feel for your grandson as I went through much of the same thing. My IV also ended up infected and they had to remove it. I then had to tke the Antibiotics by mouth. They really tore up my digestive system. I contracted my infection in the hospital when I had knee surgery. They tried to clean out the infection 3 times. Be really carefull to monitor his fevers. You don't want the IV to remain if it also gets infected.
Good luck and do everything you can to keep him comfortable. This is no treat to go through. My knee pain was almost unbearable even with high powered pain killers.
Thats also a concern if he is on pain killers for a long time, he may have trouble getting off of them.