Hrmm..

Trauma is one of those specialities that is evolving. To answer your question without getting into economic specifics..

You can either work at an institution that sees a heavy amount of trauma, or be the 'trauma guy' at a private group. That is, you don't take call all of the time, but you take care of the injuries that come in overnight (that your partners triage at night)during the day, while the rest of the practice takes care of their elective stuff.

As far as doing joints or whatever.. yes, you can tailor your practice however you want. especially with the demand for us to joints in the future.. that will most likely occur.. unless you work in a trauma center.