Step 1: Remove the retaining clip, which holds the crank handle in place.
Step 2: Using a #8 screw about 1/2″ long, secure the knob to the crank, from the back of the handle. This expands the knob, causing it not to pop off.
Step 3: Reinstall the retaining clip to it’s proper location.
Step 4: Pop the handle back on the door. No more busted knuckles!