You could in theory have three (or more) sets of arm geometry, optimize for diffrent zRotations. One set to be used from -45° to +45°, one set for over +45°, and one set for under -45°. The different geometries would be switched automatically via ERC as 'alternateGeom' (as in the genital switch). I suspect this would work very well at reducing deformation for those doing static posing, but it would probably require some very skilful JCMs to get a smooth transition between geometries in an animation.

P.S.
Sam, you should make an urgent appointment to see a physiotherapist! :scared:

P.P.S
3doutlaw, I can rub my girlfriend's tummy whilst patting her head. Does that count? :blink: