I would like to re-emphasize what orthodoc said. It is more about your particular practice setup than your subspecialty. Many people think trauma has an inherently poor schedule/lifestyle. I know a trauma guy that is in private practice at a level one non-university hospital. He only does trauma, no scopes/joints/general. He takes 4 overnight calls a month and covers the ER M-F until 4pm. The majority of his cases are cases seen by others in the community while they are on call and refered to him the next morning. Emergent stuff is taken care of obviously (open fx, compartments, etc) but they have an agreement that he will take whatever they (about 12 other docs) want to refer to him, no questions asked. He has available OR times each day so he is not starting cases after 5pm usually. He rarely is in the hospital (when not on call) after 5 or 6. Basically the other people in the practice do not want to disrupt their clinics/elective cases during the day, so they are willing to basically do night triage and handle emergencies and dish of stuff than can wait so that their 5 ACL reconstructions are not cancelled the next day.
SO in my opinion its all about the setup you find.