To be honest, publications mean the most... the more publications, the more excited the programs get.
this usually means clinical research which is far less time consuming. id find a project with anyone that frequently publishes... be that the cardiology department, plastic surgery, whatever. just find someone that wants you to be published or presenting at meetings--have something to show for your work. the real value for research outside of ortho is in its novelty... its something to talk about in the interview that might make the program actually remember you... with ortho research you may get bombarded with difficult questions.
also, its silly to work on something you don't care about just because it might help you get a interview/residency. it doesn't seem genuine to me. working on something youre actually interested in will take you much farther.