In general, chances for getting into ortho at all are low. I don't know a particular number, but if I had to guess, I'd say 1/4 at best, probably lower. Transferring to a PGY-2 spot depends on the number of spots that open up, which is about 0-5 per year. Factor in the number of unmatched applicants in prelim surgery spots and the percentages drop quickly.
Trying to match again (ie, as a PGY-1) may be a better option statistically, but you'll automatically be stigmatized a bit.
Nonetheless, if you really want to do ortho, it's worth a shot.