I was told once that yonkyo came from a sword cut. If we look at the placement of our hands on our uke's wrist, then it is the same or should be similar.
More often than not we use the nerve technique, but we do sometimes practice it without.
I find the version that we do without the nerve alot more 'worrying'. it seems to be that we hold the wrist upright as if holding a sword and then step back with the font leg.
this brings uke back and twists the two bones in his arm against each other. as you step forward and cut you can use this twist to extra effect in controling the elbow and shoulder of your uke.
I think its easier to get to if you do an uchi movement on your partner and treat it kinda like sankyo, but instead on the wrist, twisting the bones against each other (not nice on myself, as I have very thin wrists and bones).
we do an alternative submission also when using this 'variation'.
the pin ends with us sitting on our uke's back with the arm entwined around one of our knees.
its very difficult to explain and describe, its a bit like ude garami, but using your legs. and its very painful, especially when you get a heavy nage and you cant breath.