Henkel,
I'm so terribly sorry to hear about your son. For someone so young to be thus afflicted is exceedingly saddening – joint issues so severe usually affect only the very old.
There's one remedy that comes to mind – but I'm afraid the key component is bear fat. Should you manage to obtain some, come see me at St. Tyna's and we shall do our utmost to produce an ointment to relieve the pain your little one is experiencing.
May God watch over you,
Mother Bernice