In every city I have heard several guards tell me this same story. What do you think is responsible for this apparent rash of arrow-related knee wounds? Are all bandits aiming for the knee? Might there be some reason why all adventurers take an arrow to the knee and then become guards? Do you feel safe when all of the people in charge of protecting you suffer from an old knee injury?
I feel like this phenomenon, above all others, bears research!