I came across an interesting theory the other day. The gist of it is this:
If a fist is improperly formed it will have a space within it. At the instant of punching with that fist energy will be wasted compressing this space. More importantly, this space will break the continuity of between the fingers and the larger bones of forearm, so more of the energy that the fist absorbs will remain in the hand, increasing the chance of injury. If you are holding something within your fist, such as a roll of quarters, a flashlight, a kongo or even a rolled magazine this airspace is eliminated and energy can more freely be transmitted from arm to hand and back.
I can’t see any majorly obvious flaws in this theory. The same source advocated that properly designed knuckledusters transmitted force directly from the palm of the hand to the target, the fingers only serving to keep the weapon in position.