Im willing to bet you could still manage bdsm from a wheel chair (or rather he could). It would rely a lot more of mind rather than then boday though.

Self bondage if the other person is totally confined- or at least be extra sure that you can get out if they cant help you.

Toys that are easy to latch/tie/whatever. Especially if the fingers are numb, some things like velcro can become *very* hard to undo. Find toys with handles that are really easy to grip and lightweight...nothing too slippery, skinny, or akward since they just end up getting dropped (wrist guards can help hold the wrist steady though so the wrist wont collapse when its numb).

Also watching the positions you are in- especially if you are worried about the arms. make sure he is not bending the wrist at an angle, try not to put too much pressue on the arm, and try to find a way is which he wont have to do any lifting (i see something cool with pulleys that would be fun)