with physical ability. but i like the physical side better. the goal is to reach as far forward with your arm. 4 million will have brachial plex plexus palsy. they typically have trouble moving around. >> it's difficult for me to throw with my right hand because i can't detect the motion. my name is mason and i'm 11. >> when he was born, tendons were torn in his shoulder. his muscles have extreme irritation. >> it's been a very challenging problem to analyze, and the reason is because of the way the upper extremity is structured. the only real good way they have of measuring that is through ct scan, which provides a significant amount of radiation. that's usually not a decision that they will migrate towards medically. there is not much work going on