I think it's a fracture. An avulsion can be either. All avulsion means is that something was torn away. I thought I heard KP say last night that his bone was torn away. If that's the case he has small fractures, like I had. It can also mean the ligament was torn away, which would actually be a little worse. It took me 2 weeks to be able to resume football, but missed no time in hockey (it hurt like hell though) I was better in about 4 weeks.
Avulsion is just a term though. Every time you rip a scab off of a sore you have an avulsion.