I'm a violin player for about 10 years. Since I was a kid all my fingers are double jointed (hypermobility) and makes it hard to play violin :) Now I'm trying to learn arm and hand vibrato and wanted to know if anyone had the same problem in fingers like me and if so what did you do to overcome this problem and learn vibrato?
This is advice I give all musicians but it should come especially in handy for your particular problem. You must attempt to play with as little tension in your fingers as possible. Let gravity and mechanics do its job rather than your hand squeezing the string.
I want you to pick up your violin and go into playing stance. Play an A on your G string like you normally do, then observe how your hand is positioned and the tension you use on it. Play long tones like this.
Next you'll want to release tension very slowly until the note sounds only as a whisper. Once you're there, lift your thumb off while moving your fingers over the top of the string. Your wrist should be straight and your fingers should come almost straight down on top of the strings. If your fingers are flat they're more likely to collapse. A nice C shape is what you want for your hand, not a < shape. Feel gravity pulling your hand down on top of the string with your body adding only just enough extra tension to let the note speak properly. Not only does a straight wrist and arm prevent injury but it also lets your tendons work as efficiently as they can.
For vibrato there are 3 main ways you can do so; sliding up and down the string, rocking your wrist back and forth, and rocking with the arm. It depends how wide you want the vibrato, but wrist rocking is considered the normal way, where your finger tip rolls up and down the string. Practice slowly with a metronome to be sure you're not adding any unnecessary tension.