I'm currently recuperating from a dislocated shoulder I had just last week. Doc told me no biking because that would put extra stress on my shoulder and the fact that my arm is pointing forward could possibly put it at risk of being dislocated again.
My arm is in a sling but I am allowed to move my forearm forward so long as my bicep is along my side. Now I look at this picture:
And considering they also make a one handed kit, I could even keep my left arm completly in the sling. When I look at the guy in the terratrike in the above picture I notice that his left shoulder is in the same position as mine currently is in.
You have to understand that I really want to go biking but at the same time I really want to prevent another dislocation. It hurts like hell and I really don't want to do it again. I go through extra precautions to protect my left shoulder these days.