Will do my best - I don't currently have a character with an arm that badly damaged. Things heal.
Basically it's this: I have had two characters starting with the "Hurt, Helpless and Afraid" scenario with severe damage to one of their arms (it's possible one was a hand injury). The damage was bad enough to deny the character the ability to do tasks which required 2 hands and other tasks were "this task will be extremely awkward".
So, having picked up several rocks, I equipped one into the primary weapon slot. I then tried to throw at a bird (not that there was much chance of hitting with IIRC 67 in total injury, but luck sometimes happens). This did in fact open the inventory. I selected the rock I had wielded. I forget the exact message but it was something like "you must have two hands to do this."
I'll try making a random test character to see what happens.
- Shane