I'm a professional pianist and have been playing for eight years now. I recently noticed a problem in my left hand: if we enumerate the fingers consecutively, 1 beeing the thumb, my fourth finger is very weak compared to the fourth finger of my right hand, and if I position my left hand completely open and try to bend only the third and fourth fingers, I can't manage to keep them together while doing this. Could I have injured myself from practicing too hard?
I'm especially worried, since when I was little I used to bend my fingers backwards really hard, to the point that some of my knuckles got bigger and stayed this way even after I stopped. What kind of injuries could this cause, and what type of doctor should I visit to get my hand checked?