#1
 
Hi, I just have a question: Can guitar playing change the shape of your fingers?. I have been playing guitar for about 16 years. My left hand pinky finger has grown a bit at the proximal interphalangeal joint over the years. I checked pictures today of 8 years ago and my joint was smaller but I also checked pictures from 2 years ago and the joint is a bit bigger than before but has stayed the same till today. I have no pain or stiffness and my finger flexibility is great. Is this normal?. Has anyone experienced this?. Thanks!
#2
Anything you do with your hands, including guitar playing, has the potential for causing change. But potential isn't the same as a sure thing. One contributing factor could be your personal DNA. Some folks are more prone to joint damage than others. 
#3
I think it's very unlikely that an activity like guitar playing could change bone structure significantly; though that's not to say that you're wrong about what you can see. What guitar players do experience is for the fingers on their fretting hand to spread wider than the picking; for obvious reasons.
#4
As a longtime amateur bodybuilder I'm going to point you to this video:



Yes, were talking about a major joint and lifting heavy weight but this might only happen for a grand total of maybe two hours a week of exercises that use the elbow when lifting weights even at a high level. When playing guitar you might be playing 2+ hours a DAY. It is IMHO completely conceivable that you could see something similar in your fingers from 1000's of hours of playing guitar.
#5
Just to add to this my ex gf was a hardcore runner that would run 10-17 km almost every day. It completely changed her toes. We used to joke that she has feet like a cat. The knuckles of her toes moved up so toes would arch up sharply and than down. Of course we're talking about much bigger forces than playing guitar but again I think it's possible. People underestimate the forces you're applying to your hand when playing. I stopped playing for years and recently went back to playing 2+ hours a day almost every day. After about two weeks my left wrist was sore as hell and I had to ease off a little bit for about a week. The small muscles in the top of my lower wrist were fried and I lift weights for 5-8 hours a week!
#6
This is what i mean with my hands
https://ibb.co/iNvDBQ
As you can see the left hand pinky joint is more prominent than the right one. The doctor told me that my body enlarged the joint with fibrous tissue to protect it when playing guitar and avoid injury. Something similar happens to climbers hands, their joints and fingers get bigger.