Posting a rigging tip for Blender, Robin Wilson shows how you can set up in IK pole vector in blender without breaking the bind pose. Often times Robin notes that setting an IK Pole vector on an elbow for a character will break the bind pose.
Yes, you can vary it by hand until the elbow is roughly in the binding pose, but if you do it this way, you won’t get it exactly right
Blender’s IK system let’s you assign targets which are called Pole Vectors that allow you to control the orientation of the bend in the IK chain. This will allow you to point the elbow or knee of a character to help with some degree of control over posing.
The issue is that if you have a bound character already in Blender, adding a pole vector will break the bind pose, which can lead to greater problems. Here, Robin shows how you can set the pole vector without ruining the original bind pose of the character.
Check out Robin’s post Blender Quick Tip: How to set up IK pole vectors without breaking the bind pose here.