Hi, I am sorry to hear about what sounds like a pretty nasty accident and the pain afterwards. I am concerned that he has pain all the way down his back and on one side of the buttock down to his legs. This could be from injury to the bones of the spine (vertebrae) or the cushions in between them (intervertebral discs). There are nerves that come out in between the bones of the spine and any displacement of the bone or the cushions between them can compress the nerves and cause pain that shoots down one or both legs. The swelling in the legs is concerning because it could be from several causes including a fracture, sprain, or less likely a blood clot. I would recommend that you see either a primary care doctor or an orthopedic surgeon at the earliest. I think he will need at the least an Xray of the spine and hips. He will need to be examined carefully to look for any nerve damage. If nothing serious is found, treatment usually comprises of medicines to decrease pain (tylenol, ibuprofen, naproxen) with physical therapy. Please let me know if that was helpful. If it was, please take a moment to provide a rating. Thanks!