Good question, and I don't know myself. However, some things that may help you estimate the answer. I think the NRMP results said that about 14% of people who applied for ortho didn't match. This is a falsely low number, since probably many people who applied for ortho also ranked general surgery (prelim or categorical) or other specialties. The better question would be who didn't match in ortho who ranked an ortho program No. 1 in their list. Following this website for a while I don't think anyone has the numbers but some people put their guesses. I would guess the number is somewhere between 20-40%, but I really don't know.