A number of factors would influence average salary. Orthopedic surgery is probably the most competitive medical field there is. There's also a very high amount of schooling you have to do beforehand - 4 year BA degree in bio or pre-med, additional 4 years of med school, another 4 years residency in a hospital on top of that. Then if you want to be a specialist like an Ilizarov surgeon you would need to do a fellowship or something, and maybe additional years of specialty training. That's a ton of debt once you're done with everything, and many years that you aren't going to be making any money at all. Orthopedic surgery is also very complex and requires long hours in the OR, I imagine you're on call at ridiculous hours. Plus there's a big demand for orthopedic doctors and it's just going to get higher with an aging population. Orthopedic problems also often require many repeat visits and follow up surgeries, and they get paid for each visit.
There's probably other factors involved but that's what I'd guess contributes to the high salaries they can start out with