What happened to my knuckle?

Today I got upset which resulted in me punching a brick wall a few times. I know it was stupid, you don't have to tell me, but now my middle finger knuckle is swollen. It was really large earlier, but it's gone down a bit now. It still hurts to touch and move though, and I can't make a fist with my hand. What have I done to it?
What happened to my knuckle?
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