How to move back bone, without move the hand

[Vincenzo_Casillo]

Hello, I have a seated character, and I want to move the back position, but I want the hand position to remain fixed, obviously as long as the lenght of the arms allow it.
This is the start position:

I want to rotate the back in another position, keeping the hand in the same position of the image

[Geospinelsulfid (Jonas März)]

Hello vincenzo, does your character have a rig to control it, or is it a fixed mesh? Is this gonna be for a still image or do you want this action to be animatable? The more infomation you can give us, the better we can help