The index finger on my left hand was injured when I was about 15. A mis-lick with my Boker knife almost cut the end off. Never have had much feeling in this finger.
Problem. This makes it very hard to properly note guitar or banjo strings. (No its not a recent problem. I started 50 years ago.)
When I play a C chord or F or anything needing that finger, it is very difficult to play and sound properly.
I seem to remember a product that was used by folks learning to pick that would harden the fingers like a callous. Something like that might help. Jeep