There have been a few, no hospitaliztions, but I have MCL tear in my knee that still nags me 3 years later. But none as frustratingly memorable as:

It's springtime and the studded have tires been prematurely removed by some total idiot (me). A big thaw one day then freeze over night, that I didn't realize happened. Ice everywhere, I'm on the ground three times in a 5 mile stretch and almost down about 20 more times. No injuries but a painful lesson learned.