Yosef Karo

“ We are not versed in what flesh a surgeon would remove therefore any place that the flesh appearance has changed does not save it (H"M) . 11 If the flesh is cut by a knife in a ring around the fracture and the majority of its girth is covered, it's kosher, as long as the flesh is adhered to the bone around along the incision.
12 If the bone is broken at a place that makes it treif and then it mended but it's unknowable if the majority of it protruded out or not - it's kosher, so long as it mended at its original place and fracture joined fracture and they stick together. ”

“ And it's good to be stringent when there isn't a big loss. If the hip is not disconnected and the Nibs rotted then it's kosher (Mordekhai) . 3 If the end of the Qulit (femur) bone that connects to the Shok is dislocated from its place it's kosher even if its Nibs are rotted. (But some say this is specifically when the hide and flesh covers most of it) (Responsa Rosh 20:10)
4 If it has three legs it's treif, because an extra part counts like it's missing so it's like it's missing a leg. ”