I use MSM for long term pain in my long ago broken ankle.
It also seems to help allergies..it is a form of Sulfur. Think about all those famous Sulphur Springs that people have flocked to for ages even in spite of the stinking water. They sit in it so it will be absorbed through the skin and even drink it.
Now we can get it in capsules or powder, even though it's bitter I can take it in juice.
Won't hurt, might help him a lot.