the problem is that the twist and side to side change the orientation of the joint center such that the 'pin' no longer rotates on the same axis as the 'sleeve'

I had hoped that by weight mapping the whole knee to area to the exact same weight it would let the bend work right even when twist or SS was applied to the joint.  It doesnt work that way however as even though the geometry doesnt distort, the bend still goes off on a different angle.  

I've tried using other bones to control just the twist/SS or just the Bend but it always causes joints further down the chain to move out of sinc, or breaks conforming.

I even tried adding a completely alternate rig from the thigh down as ghost bones, but that didnt work either

maybe i need to make the 'regular' joints the ghost bones and have their rotations just control an alternate rig/group structure via dependancies...

That might allow me to re-group/rig the lower leg to move the way I want while still letting it conform...

I'll play with that after breakfast...

 

 

Quote - In my various experiments with joints, I've found that sometimes allowing twists in bones that normally wouldn't twist on a real human actually achieves the result I'm looking for. 

So using that theory, maybe try allowing for twist in the shin, but set the end points much higher than they would be for the figure's actual shin. 

Or maybe you've tried that already. 

 

~Shane