What Causes Swollen And Painful Knee With History Of Knee Surgery?

I had knee surgery in the fall to remove all of my plica after a rock climbing accident. This week I was a leader at a camp. Monday I fell hard during an activity. It hurts to breathe so I think I may have bruised my ribs on my right side. My knee took the worst injury. It is still swollen and painful. What could I have injured? It isn't locked so I know it isn't an ACL injury.