The rare exploding knee. Yet to see one in the wild.Are knee explosions common? If so, what are we doing about it? We need big knee to take responsiblity!
It all seriousness, probably has moderate to severe osteoarthritis, it swells up on him, he has waxing/waning symptoms, and it's destined to end his career early at some point.
Let's hope they can get 1-2 above average years out of him, though wonder if they already have some buyer's remorse.