My bitch did both of hers, 1st the right leg, when she was 3 years old (on the track) rested her for 6 months, she had a few good runs, then she did her left one.(AT 4 YEARS OLD)
After 12 months rest she started running again, but unfortunately her right one has gone again, she's nearly 6 now so she will just be used for a bit of mooching
Just to add, she did both hers while racing, working never seemed to bother her.
Good luck with your dog