my school has had an outside med student doing research. it's not the norm, but i think it's possible. a connection at a particular place would probably facilitate that.
don't feel like you'll be too far behind though if you don't do ortho research between M1 and M2. i went to central america for the summer and still put together a competitive application. i'd recommend getting involved in some projects during 2nd, 3rd, or early 4th year. and make sure whatever you get involved in, you work hard to finish and produce. anyone can sign up, but people like to see results.