Corey Hill is a giant in the UFC. He is 6'4" and fights at a mere 155 lbs according to Sherdog. Some may say that this is understandable because he is a professional athlete and probably has only 1% body fat. However, Barack Obama is 6'1" and weighs 180 lbs! Now, unless you think Obama is stacked like a body builder or you think he is obese (either conclusion would make me question your ideas about body image), you will agree that Corey Hill is REALLY light for his height.
Being so light probably suggests that his bone density is relatively low. I really have not learned anything about bone density, so I don't have any science to back this conclusion up...but it makes sense considering his BMI is 18.9 (probably not entirely true because I'm sure Corey Hill, like most UFC fighters cuts weight to fight in his weight division, however, I doubt that he cuts more than 10-15 lbs). Keep in mind, Hill IS an athlete, so he has a fair amount of lean muscle mass, which is relatively dense, i.e. heavy.
So, if his bone density IS relatively low, that would explain this:
I'm sure I'll eventually learn more about measuring bone density and in the future I'll be able to understand if my hypothesis about Corey Hill really explains his leg break. For now, I'm just going to drink a lot of milk.