Very sorry to hear of your friend's injury. I hope his prospect for a full recovery is excellent.
Back when I worked uniform I wore a handcuff case on my gun belt SOB for a while. It didn't take long to discover this was not something I cared to do. Just normal sitting, and getting in & out of the car for hours at a time, caused noticeable discomfort.
I wouldn't want to fall on my back onto a hard surface with something held directly against my lower spine, either. Just bumping up against something with much force was noticeable.
Again, I hope your friend experiences a full recovery.
Retired LE - firearms instructor & armorer