Even before I got into medical school, I was locked onto orthopedics - wouldn't even consider anything else throughout medical school & matched into a surgery internship in the Navy. My very last month of medical school was EM & I really enjoyed it, but I was still very set in my mind that I was going to do ortho.
During internship, I got the opportunity to do a month of trauma & another month of EM during which I discovered that there was a lot of medicine that I found interesting in addition to ortho. Fortunately in the Navy, I then had a 2-yr tour as a flight surgeon to get a real good feel for what my professional interests really were & how best I could pursue them.
EM has all the best elements of what I enjoyed from ortho (acute diagnosis & treatment of M/S injuries, opportunity for specialization in sports medicine) while also challenging me in many other areas of medicine that I find stimulating (trauma, cardio, pulm, GI, infectious disease).
I count myself fortunate that I've had the opportunity to take a couple years of practice to figure out what was the best fit for me.