Looking at the picture I can imagine the joy you feel. It's been a terrifying journey, but you made it. Hopefully his love of music will make him fight to regain full use of his arms.
Last week, we went to see a movie about Black Sabbath and my daughter told me the story of their lead guitar player, Toni Iommi, who lost the tips of the middle and ring finger of his right hand in an industrial accident at age 17. Obviously, the accident changed his playing style, but 50 years later he is still one of the best guitar players in the world. I assume your son knows this story!