Do a google search under "Avascular Necrosis" AVN is a disease(my husband has it) that causes the bones to die at the joints(hip replacements and core decompressions are common among sufferers) but from my research on the disease I have found that Perth's disease is what AVN is called in children. There is a site devoted exclusiveley to OVN/AVN and will answer all of your questions. My husband did not have Perth's as a child. He developed AVN after taking steroids for a hernated disc (prednisone). I know another 32 year old woman who took prednisone and developed AVN and just had both hips replaced. I remember reading about the Perths disease being linked with AVN on the site and being classified as the childhood version. There is a previous post on this board from a man who's was asking the same questions about a 10-11 year old boy about a month ago. Good luck to your son. OVN/AVN is a very painful,time consuming disease. He is lucky to have a good support system in place. My husband and I have been going thru this for 2 years and still face more surgery and numerous doctor visits. Watching him struggle in pain is hard because I can't help him there, I can only try to stay abreast of the latest info and be ready to quiz the doctor at every visit. I think that is what I have been able to do the best for him. I refuse to let him be blindly led down every path the doctor suggests without investigating everything about it and then making informed decisions about how it may affect us personally. It would be so easy to just trust in a doctor but I've learned that to them,we are just another name on a chart and another body on the operating table so its up to us to question and investigate EVERYTHING and ask people who have been there if this is what is really best and if it is as successful as we are led to believe.