In the Fallout games they make your punches hit harder using gyroscopic thingamajigs and plutonium voodoo.
The physics of it seems to change every time you can get a decent look at the weapon itself - in the 2D games it looked like a glowing, spiked metal glove, in the 3D games it’s like a giant block of steel that’s been equipped with a crazy pneumatic ram on the back of the knuckles.
And it wouldn’t be a major thing to implement; I believe we already have a weapon tag that causes stuff to use the unarmed combat skill.