eyrie

Pinning the wrist and pressing on the elbow with the other hand seems to be common way to immobilize uke. But that only has the effect of isolating the wrist, elbow and shoulder to some extent, leaving uke with the ability to move the rest of their body and wriggle out of the pin. The elbow compression also causes some pain and discomfort for uke if they attempt to struggle.

There is a way to pin the wrist without applying yonkyo, without the elbow compression, and using kokyu "extension" to control the whole body. It is hard to describe this in words, but it can be demonstrated through feel.

BTW, I've seen versions of shihonage which involve a knife hand strike to the throat as uke is going down, and others which involve dislocating the shoulder as uke drops under their own weight, obviating any need for a subsequent pin, so the point about pinning from shihonage is somewhat moot, since by definition, shihonage is a throw - not a pin or immobilization control.

FWIW