I'd say that getting into an MD ortho residency is much much harder than getting into a DO ortho residency (as a DO applicant, obviously), hands down. BUT, it is possible...and it looks like many more DOs landed MD ortho spots this year.
In my opinion, the keys to a successful DO to MD ortho match are:
1) Do very well on USMLE Step I
2) Do very well on COMLEX Step I/II (take it early)...I think this helps
3) Have a high class rank
4) Have at least some research experience, publications are better
5) Befriend as many attendings/residents as you can so they can go to bat for you.
6) Apply very broadly (I'd say >60 programs)
7) Get some high powered letters of recs
8) Most importantly, ROTATE at the programs that have taken DOs or are open to taking DOs...and do very well on your rotation.
It can be done, I think more and more DO applicants are taking the risk. But then again, it's hard to give up a sweet "pre-match" DO spot to risk it all for an MD ortho spot...and for what reason.