This is extremely common, especially in competitive fields like Ortho. As a matter of fact, I would wonder about someone who didn't have a Plan B if they didn't match in said competitive field.
Pretty much everyone I knew, including myself, applying for Integrated PRS also applied to Gen Surg and it continues on into fellowship as well, with people applying to Breast, Burns, Hand etc. if they don't match into Traditional PRS programs. This pattern is repeated in many other competitive fields as well.
In your case, however, I might wonder about someone who is "surgically minded" enough to apply for Ortho but is using fields like Medicine or EM as back-up.
A) could you *really* possibly be happy doing those, especially Medicine? For someone who likes surgery, these are not necessarily the fields to go into (and before the EM crew rushes over here to correct me, yes I realize you do procedures, but a surgeon wants to be in the OR)
B) Why wouldn't you choose general surgery as your back-up? I would question your commitment to a surgical field if you were not applying to something surgical other than Ortho or for that matter, sitting out a year and reapplying, perhaps after doing some Ortho research.
The two different fields won't necessarily find out that you applied to both unless you did so at the same hospital and they *happened* to find out...there is no centralized service that programs have available that tells them where people are applying to and for what. They may ask what your plans are if you don't match into Ortho (which is where my comments above might come in...I can't imagine an Ortho faculty not thinking it strange that you would do a Medicine residency. EM is more plausible but still not surgery). But unless you tell them or their best buddy is PD of the other program and your name just happens to come up, I wouldn't worry about it.
What I would worry about is interviewing for Ortho and teling them that if you don't match that you will be doing a Medicine residency. Right next to where it says "motivation for surgery" on your eval form, I would place a red "X" to mean questionable if not doubtful.
But that's just me...
