Fourth year is the time to do rotations in stuff that you're interested in, but may never get an opportunity to see again.

But to answer your question, most people do Rads, infectious dz, rheum, or an anatomy dissection course to prep them for ortho.

I did
2 home 1 away ortho
1 MSK rad
1 anatomy disection
1 ID
med sub I in MICU
RAD sub I
EM sub I
3 vacation
I did 1 month of research 3rd year to gain an extra vacation month.

I would recomend to do an away in every region/eschilon you want to apply. Many people asked why I only did one away or why there and not here.

I could have done some total blow of classes but all of these will help me and none have been painful time wise compared to ortho.
INtj