Loop a rope over a high pole or pulley. Have the rope in both hands to the short end is in the non-affected arm and the long end in the injured / surgical arm. Try to stand under the rope vertically as much as able. Slowly pull down on the rope with the good hand, and lightly gripping the rope with the other - let it move upwards. Go to pain only, don't go into the pain. Slowlyl let the tension off again so the injured arm returns down again.