Honestly, I have never seen a situation in ortho where being huge was a disadvantage, and many situations where being huge was an advantage (this from the perspective of a small guy).
That said, many great orthopods out there are not huge guys. Being huge helps with many of the tasks of daily living in ortho, but not being huge is not a great disadvantage either.
sounds like a reasonable compromise
big and strong helps with trauma and total joints. on a 250+lb total hip patient, you need to be able to range the hip with one arm, and feel in the joint for impingement/etc. with the other.
small and nimble is probably better for hand surgery, foot and ankle, etc.
either way, the career seems physically demanding when it comes to general stamina. if you're 400+lbs and way out of shape, you better have good help