Yeah, you'll break your wrist instead..
No one here seems to have broken it down yet, so i will. It all comes back to the verticle fist vs horizontal, and which knuckles you should connect with.
I recommend verticle, and bottom 3 knuckles. Most structurally sound. Test it by pressing both styles against a wall and see which one feels stronger. When you have realized this, you will also realize that direct straight line punches(jabs/crosses) are much safer than hooks. The opponent can step into it and you will still be fine. With a hook, there's much more risk of damaging your fist/wrist.
Also, connecting a hook with the top 2 knuckles with a horizontal fist in a street fight is the dumbest thing you could ever do. You will break your wrist and it will be near impossible to connect with the top 2 knuckles at the same time. You will most likely connect with the index finger knuckle only vs a moving target. This is probably what happened to Mike Tyson in that story everyone's heard about. If you have restrained the target however, throwing punches to someone you have in a headlock is fine, since you have less chance to fuck up and miss or hit something that isn't worth hitting(top of the head), and you probably won't have enough body structure and power generated to break your hand. If you break your hand or hurt your wrist but you break the guys jaw and knock him out, i would think that's a pretty good tradeoff(not really, but let's assume it's a fight where you are in fear of your life, and getting knocked out is the equivalent of death). If you're THAT worried about damaging your hand/wrist, then go for palm strikes and grapple the guy. In a real fight, this will most likely happen anyway(in 1on1. If more, then you should just run). Close the gap with a low line toe poke to shin/groin then jab/cross etc. So it's like a 1,2,3.
Any other questions?