Just anecdotal, of course, but my horse seemed to be injured more often when she was kept in a stall than when she was pastured or at least in a large paddock.

The only major injury she's incurred while pastured was when she tore open the back of her leg. I still don't know how or where, even though blood was oozing down her leg and hair was missing, I couldn't find what she'd done it on.

Some of her injuries while stall kept were due to her playing too hard when did she get turnout. The broken splint bone is the prime example of this. I doubt she would have done that if she'd been out 24/7.