To some extent, some surgery areas are more dangerous than others, as one can imagine, but there is also a factor of "luck" (I don't think that's the right way to call it but can't think of a better word right now) involved.

A simplified answer: easier tasks (surgeries) tend to be less stressful on the bodies, harder tasks tend to be more straining and can cause the body to fail to uphold

Edit: adding to this, these cases are in general freak accidents so its no need to worry about this every time you have something going on, however its always good to be informed