Guys used to blow out their arms or knees and that was about as specific as sports medicine got for fans.
Now that we're all getting practice in saying "ulnar collateral ligament," I figured the most useful thing I could do right now is offer up a couple of links about what it is.
Here's background from the Web MD web site.
And here's a video about Tommy John surgery.
I'll be hosting a live chat from 11 to 11:30 this morning, if you want to talk surgery and bullpen and all of the issues that have come to the surface because of the Joe Nathan injury.