I figure if the underpadding can stop a 9mm round this punch is unlikely to be able to actually break Metz bones, as it's specifically designed to disperse impacts. Plus I can't help but feel that in terms of durability someone's entire chest would overcome someone's arm in this situation, if it were locked I'd assume your arm would probably outright snap. With the mass and momentum arguably on his side Metz is going to be able to power through.

It has knocked the wind out of Metz, and it might have bruised him pretty badly, but as Skallagrim noted it doesn't actually stop him from being able to use his knife.

We'll see anywho.