Um yep, that's an interesting one, I myself an accordion player, suffer now and again with, what i would describe as tennis elbow in my left elbow, usually when playing a lot, but it takes a few weeks of heavy playing (5-6 nights a week) before it kicks in, just repetative strain really i suppose, as for the knuckles????

Mind you one thing did cross my mind, I knew a banjo player once who suffered terrible joint problems with his fingers, just came on over a period, having tried everything, just as the music world was preparing to celebrate the departure of a banjo player, some smartass sugested, "Your fingers is ruined with rheumatism boy, Go git yerself a copper bracelet!!" which he did, and i'm sorry to say that it cured the problem in about 3 to 4 weeks, and last i heard he was still playing the F***ING thing.

However if this tragic story has a silver lining with wich to rescue a box player, I believe in passing it on
:o)