They actually reshot part of the scene with another actor back at ILM because George decided he didn’t want Vader’s wrists bound up to the sides of his head as seen in the EP3 teaser. In the other trailers and the movies his wrists are strapped at near waist level at his sides.
Its actually the same footage, but they used a digital replacement for the arms etc. If you look closely you can see parts where the tracking & blending doesn’t quite work. The part where he breaks from his restraints is a good example.