Arm Twist Rig:

The purpose to this file is to show how to simulate the twisting of the forarm and upper arm in a human or bipedel character. It is nessesary to twist the arm along the length so that the mesh can be skinned to several bones. This will help prevent the mesh collapsing in on its self durring animation.

The basic principal is to add a bone in the forarm and upper arm and have them lookat the elbow. Then use the upvector of the lookat to control the twist.