Nice idea. If you wanted some ideas on how specifically lower leg external fixators look and attach to bone etc in real life you could have a look at (warning, some photos of actual ops in progress);

https://tristan.membrane.com/aona/tech/ortho/hybfix/

which has a specific guide to fitting their particular product with some decent shots of the construction. Might assist with the general look if you break the leg down to it's various layered components.

Very interesting figure and really well modelled. Look forward to seeing more.