I'm currently rehabbing a full thickness tear of the rotator cuff in my left shoulder. The tendon tore away completely from the bone and had to be surgically re-attached. It's been almost 12 weeks since my surgery and while I now have full range of motion again, I am only now starting to lift very light weights in the gym. So if he's out running full sprints at 4 months I'd say he's doing pretty well.