Amazingly, this doesn't seem to have ended his ball-playing days...
"Coach Corbin Quote: Corey has made great strides after suffering a devastating mid-season injury. He rehabilitated his knee over the summer and ended up pitching very well for us this fall. Corey will be a very important part of our bullpen - he can be utilized in many roles because of his pitchability. He could eventually end up starting some ball games for us as well."
I've never quite understood the reason for a kneecap (other than to shield the rest of the leg from a ball) so why can't he just remove his kneecap and call it good?
It adds a point of leverage, IIRC. It's actually fairly integral. A missing kneecap means you can't really extend your leg with any force at all. No kicks, jumps, or pedaling.