Hope its not the arm you wipe your bum with 
Good luck with the op.
reminds me of this...

Two old age pensioners having oral sex. The old man says, "I can't stay down here much longer, it stinks." The old woman replies, "That'll be my arthritis."
"Arthritis in your fanny ?" asks the old man. "No", says the old woman, "The arthritis means I can’t wipe my arse.