I love a challenge so I've been working windshield wipers! Works just about every muscle in your body. I did a total of 12, 6 on each side but working towards 20. They're really hard, but give them a try!
The shoulder makes the arm I always say, so in order to get that nice round shape, you have to hit all three head of the shoulder. Shoot for 15 reps and pick a weight where you begin to struggle around 12 reps. If you need to rest a moment to finish them, that's ok.
You CAN stay in shape while recovering from injury. As long as you're cleared with by your doctor and the moves have been approved, there's no reason you can't work the other pieces of your body that are ok.