My 2nd public service announcement for all models built on the elbow bone TDA style technique.
Miku V4X doesn't use SDEF weighting on the elbow. Instead she uses a elbow bone that makes it look more pointed and natural. To help bring awareness of how your elbow works it actually bends in only one axis. It is your upper arm and shoulder that allow your arm to twist to move your lower arm where it needs to be. Miku V4X is based on real anatomy.
This is how your arm actually works and arm twist bone models are designed to work! Happy MMDing!