What is happening to my little fingers?

I bought a rechargable mosquito bat weeks ago to combat pest problem. After using it frequently for several days, my right little finger (I am right-handed) began to feel funny. Then I realized the bat handle is too large and that has "overstressed" my little finger when it and other fingers are holding the bat.

Specifically, something is wrong at the joint between the lower part (proximal phalange?) and the middle part (intermediate phalange?) of the little finger. Starting from the completely curled position and slowly letting the finger become flat, I discovered at about one-quarter of the way, there is a "spring action" or "bounce action". (This is abnormal. I did the same thing with the left little finger and the whole movement was smooth.) I used to be able to make a knuckle sound at that joint, but now I can't.

(To my chagrin, I started to use my left hand to hold the bat and now my left little finger has the same problem, but not as much. Now I avoid using the little fingers to hold the bat, though they still touch the bat handle.)

I haven't talked to a doctor and haven't had a X-ray of the little fingers.

I am worried. What is happening to the little fingers? Are the bones there growing because of the "demand" I put on them. Would this problem just go away gradually if I let the little fingers rest?
Tweet