I actually partially tore the patellar tendon in my left knee 2 years ago when I stuck on an older wooden approach while I was sliding.  The good thing was that it wasn't severe enough to need surgery.  It hurt like hell though when it happened but was able to walk out of there.  I ended up being in a knee brace for about 8 weeks and had to do physical therapy.  I also couldn't bowl during this time.  At least it was during the summer though.

It forced me to change my approach.  Instead of using the full approach, I now only use between 1/2 and 3/4ths.  Plus, I lowered my backswing a little bit because of this and I've become more consistent.

As for the worst I've seen, I saw a guy who probably weighed closer to 300 with a huge beer gut not being able to clear the thumb at the line.  He went flying and did a face plant into the lane.  His forehead was split open and he was taken in an ambulance.  I never did see that guy again after that.

I was subbing one night, and it was a low carry kinda night, no matter how well you bury the pocket. After some alcohol, in the 10th frame,  3rd game, i found my first turkey.  I proceeded to do a jump and spin, not realizing how close to the ball return for the pair over.  I landed flush next to the return.  My foot no longer spun, but the rest of me did, turning my ankle a bit over 90°, giving me a nasty sprain and about two weeks off of bowling.

My first ball had some thumb hole issues, and stuck frequently.  Once, the ball did not come off my hand and caused a rib to pop out of place, causing my first visit to the chiropractor and never using that proshop again.

Saw a kid try to throw the ball between his legs, but it hung up on his thumb, took out his leg and he landed on his elbow. I think he broke it.
As for me, I had a porter attack me. He swung at me and I tried to block the shot with my left hand. What I didn't know at the time, was he had a screwdriver in it. Broke my ring finger. I kicked him in the gut and another bowler grab him and removed him from the area. I won the lawsuit.