A bruise on the knuckles should be treated with ice for 24 to 48 hours after it occurs to minimize pain and swelling, states WebMD. The ice should be applied for 15 minutes at a time with a towel creating a barrier between the ice and the skin. Elevating and resting the affected hand also helps promote healing.
To manage pain, acetaminophen can be taken as needed. Once 48 hours have passed, warm wash cloths or heating pads may be used on the bruise to help it heal.
If the swelling of the bruise does not improve after a few days or if a lump develops, a trip to the doctor is warranted.