We go camping in the mountains every year and by the time the week is over, most of us have swollen knuckle joints.
It must be something to do with the altitude that causes this. I don't usually have any trouble removing my rings, but am not able to do this for a few days after I return home from the mountains.
This is something that happens every year and happens to almost every one in our group. Many people not only have swollen knuckles, but ankles and feet as well.