OMG< that's horrible about your neighbors dog killing them. OMG...I have had it develop once in a couple of young black swans. Did not jump on it immediately, and ended up with my vet in surgery....cleaned the condyles out, realigned the tendon, a couple of stitches to help hold it in place, wrapped and kept off leg. Things were looking good, but neighbors dog killed them when I moved them to a small outside brooder to limit activity.
Perosis starts by gradually having the tendon slip. I would increase the cholinr, folic acid, and B12. I would hesitate adding too much of a multi-vitamen to avoid hypervitaminosis of the fat-soluble vitamins. I would manually churck the tendon and keep putting it in place if it moves.
Clint