I am not a two-hander so don't quote me on this, as I am just relaying an experience I had.
Whenever I have had the aches or swelling on my middle finger and joint, it was because my span was too long, and as compensation for that length, I gripped the ball too tightly, thus placing a lot of the ball's weight on that one digit.
After a number of games being thrown......soreness and pain would set in.