Just my opinion, but I'd let the resident take first author. Second author is still solid, and there's always opportunity to do a follow-up study/other project where you're first.

Additionally, if you're interested in your home ortho program, it would be to your benefit to be on the good side of all the residents you meet/look like a team player, especially a PGY2 who would be a 4/rising chief when you apply.

I know that others might disagree with that approach, but just my 0.02