BOSTON — For years, Dr. Michael J. Weaver, an orthopedic trauma surgeon, went to meetings of his professional society and heard surgeons from the military describe what they had learned treating blast injuries. Then he would return to his practice at Brigham and Women's Hospital in Boston, where he mostly treated people injured in auto accidents or falls. All that changed on Monday when victims of the bombings at the Boston Marathon arrived. "We've seen similar injuries, but never of this magnitude," Dr. Weaver said. "This is completely different." The military experience, he added, "has been phenomenally helpful."