My son was a lot younger than yours when his Perthes was diagnosed, 3 years, and due to his being so severe and the hip being almost worn away to the growth plate, he was ordered to non weight bear immediately.
Our son was a bit unusual as his pain levels and inflammatory markers were sky high, which led to him being admitted to hospital for traction numerous times and eventually we took him home with the traction equipment to use ourselves. He had lots of tests including bone marrow biopsies as they were worried he may have cancer, but nothing extra was found. His Consultant, who had been in Orthopaedics for over 30 years, had never seen a case like ours.
Our son also suffered dreadful lower back pain. We were initially told he'd be in a wheelchair for a year, but his hip just kept disintegrating for the next 5 years, before we saw a tiny bit of new bone growth, it was another 9 months before he was allowed to begin a small amount of weightbearing and hydrotherapy.
He continued to suffer with awful back pain and in the end had multiple MRIs which didn't find a reason for the pain, but showed a Syrinx (cyst) in his spinal cord at the base of his neck which one day may start to damage his spinal cord, but isn't responsible for his back pain.
He is now 15 years old and suffers with constant back pain, hip pain and knee pain, and will sometimes walk on tip toe because it's too painful to put his heel to the floor.
He is also Autistic, Dyspraxic, ADHD, Hypermobility, Dyslexic.
The consultant we had had was one of the best in the country, and we learnt that it depends on who you see for how your child will be treated. Some will allow the child to continue to weightbear in the house and wheelchair in the house, others will allow weightbearing at all times as long as no running etc, others will immediately go to surgery before trying anything else, but what we learnt after speaking to the Perthes Association about getting a second opinion was that we had the best Surgeon with the best treatment method and success.
I know how hard this is on your son and your family, but now it is about controlling his pain and to not allow him to over do it. He needs to be on good regular pain relief, we found a combination of meds was best (anti inflammatories and something much better than paracetamol), anti inflammatory gel was quite good to rub into the really sore areas. Heat was also very important for pain relief, we used wheat bags warmed in the microwave, a electric heat pad and very warm baths.
The next thing will be for your son to use his wheelchair a lot more, it's horrible to have to but it will really help to reduce the pain and help to protect his hip more. If the pain really gets too much, take him to A&E as he may need a period of traction to calm it down.
I would also ask for a second opinion, if you haven't already, 15 years is an awful long time to leave him like this and a different surgeons point of view may be helpful.
I hope I haven't bombarded you with too much, but weve lived with this disease for 12 years now and learnt an awful lot, it's something that affects us every day but we've learnt to live with it along with all his other difficulties.
Xx