Nails were driven through the wrist. The tissue of the hand would rip.
I had read that and wondered if it was true. I also read that the feet were placed on either side of the upright post and the nail driven into the side of the foot so the pain was extreme when the victim pushed up to breath.
Articles on the Shroud of Turin do a good job of describing what we know about the art of crucifixion. Check out the site: