[TrineDaely]

Ah, gotcha. I'd also wager that it's something I'm guilty of myself in my own writings.

jbcohen has some good advice there. Rather than explaining the injury in the second book, you could do something simple like "caused by an incident in a previous adventure/case/whatever." They can either check to see if you have books out where it might have happened, or figure that it's part of the history of the character that hasn't been explained yet.