On my left-hand, the pinkie's last knuckle won't bend all the way when I curl my fingers. It partially curls, but all the grip strength comes from the middle phalanx. The only thing I can think that may of happened in that I broke my middle fingers growth plate and had my hand in a cast. Afterwards, I wasn't told to do anything with my fingers for therapy and, as a kid, thought nothing of it. Now I can't hold on to the bar very long when doing pull-ups. Is there anything I can do to help it?