What is my dogs condition please help?

hi my father has a king german sheperd he is 8 years old and hes about 250 pounds , ever since he was a puppy he's had bad skin at his ancles and knee caps have big blochy bumps about 1 inch thick and they also sweat blood and puss recently Taz bit his ancle almost down to the bone and we have been putting peroxide and polysporn and raping his leg so my question is: would you know what his condition is? and is there a way that i can take care of this my self ?