Naturally, most of the posts here these days are in relation to internal lengthening methods, but I’m wondering what the comparative risk of the most serious complications is for fully external vs newer methods.

Infection risks aside as that has been well documented–and also putting aside the analysis of the pros and cons of each lengthening method as a whole as I don’t want the thread derailed–I’m interested in the following:

Fat embolism: I would assume the risk is very small. As far as I’m aware, the fat embolism risk comes with reaming the bone thus moving droplets of fat into the bloodstream, which wouldn’t be happening with externals.

Pulmonary embolism: I’m not sure I even fully understand what causes this in the first place, and to what extent the risks can be mitigated by medication. I’m guessing that most of the risk is post-operatively rather than intra-operatively? 
I think I read somewhere that tibial lengthening has a lesser risk than femoral naturally, regardless of internal vs external, because there's less of a propensity for a clot to travel dangerously to the heart or brain, but is there a difference in risk attributed to the external frames alone?

Non-Union: I think I'd say this is my biggest fear with limb lengthening, and I know the tibias come with a slightly higher risk with this as well. I've browsed some old posts here about non-union, and I know there is a list of known risk factors like smoking and lengthening rate, but what is the likelihood of this actually occurring when you don't have any of those factors at play?

I assume that a lot of the people who get it regardless have some sort of pre-existing bone-forming condition. I guess these same people would have a similar problem if they broke a bone naturally. I've heard scary stuff about potentially having to have the leg amputated/have a permanent disability, but if the worst came to the worst with external frames, couldn't you just reverse the frame so that the bones met again?

Thanks!