For the most part, a gen surg residency (5-7 years) is good enough for trauma since the gen surg residency prepares you for trauma pretty well. For some surgeons, they continue on to a 1-2 year fellowship in trauma, trauma/burn, trauma/critical care. Some surgeons hate trauma because they don't get to operate enough, trauma has a tendency to do a lot of babysitting. Just to let you know, to do trauma, you don't have to do a fellowship, most "trauma" surgeons don't (a lot of gen surg will take a weekend here or there on trauma call depending on the hospital). A gen surg residency will suffise.