The slim bone thing that runs down the centre of the knuckle is a tendon which connects your finger to a muscle in your forearm. If you were to snap it you wouldn't be able to pull the finger up i.e. from the closed fist position. Never heard anyone snapping it through boxing, it's pretty tough but can get sore if you don't wrap the hands.

As long as your big knuckle is tough, I wouldn't worry too much about it breaking. A big knuckle might be a bit more susceptible than smaller ones because it is more likely to hit a target by itself, and thus absorbing all of the impact, rather than the impact being spread over the rest of the hand.



This could be why my hand hurts! never thought about that! I should make all my knuckles the same size.