I bet most were AOA trained, since there are a lot of AOA orthopedic surgery residencies. However, if you look at the NRMP match, it is extremely difficult for DO students to match. To top it all off the amount of audition rotations on the DO side can limit ones chances in match, since most DO residencies take students who rotate with them. I also remember places looking for people with rather good level I scores as well. You could put in the border of practical, but it isn't practical though.
This is what I found from the NMS:
https://natmatch.com/aoairp/stats/AACOM-NMS-Apr4-14.pdf
Can't really make heads or tails of the data, but it shows pg. 20 that ortho is on the higher end of competitiveness. I wish they gave a percentage though of how many match.