When you say joints mate do you mean the join to the body.Tails have no joints,they are made up of bones ,36 in all,which get progressively smaller towards the end.If the baldness is at the join to the body then it probably started off as a flea problem.Even when defleaed regular this is where they irritate the dog most .Some dogs lick or bite this area out of habit after a flea attack.I take it the area is not red and inflamed or you would have said.
i mean where the bones in the tail join each other (knuckles) there not red or imflamed just bald ?