They tell us that Joe McLinebacker is out "with a knee."
I hope Joe McLinebacker has a knee. In fact, if he only had one knee, I would be concerned, and on that level it would make sense that he couldn't play, except that if Joe only had one knee his NFL career would probably be short-lived and lacking in incident.
I mean, you can mix it up. You don't have to say "injury" every time. You can say "pulled hamstring." Or "torn Achilles." (I'm not saying you have these various options to describe the same injury.) You could also say "terminal idiocy," if you happened to be talking about Ricky Williams.
But my immediate reaction to "So-and-so is out with a knee" is to see an abstracted knee, possibly accompanying So-and-so to a movie. Which is kind of alarming.