I know this is an OLD post, but I'm posting anyway:
Jen... this is EXACTLY what is going on with Condi. She hurt herself last week, and I took her for x-ray's. Turns out she fractured her femur.
As the bone has been weakened from the cancer (osteosarcoma), it's not repairable.
I'm having her right-hind leg amputated as we speak (at about 10:00am today), and I get to take her home tomorrow (Wednesday). The amputation will rid of her severe leg pain (from the fracture), but unfortunately, it doesn't slow the cancer down.
Her prognosis isn't great: 3-6 months to live, although the vet at Gulf Coast said that some dogs have been known to go 1 year+.
I'm in shock at the moment. I walked into the vet yesterday at 1:30 in the afternoon thinking they were going to tell me she had ligament or tendon damage, and that it could be repaired with surgery. By 3:00pm, my life had been turned up side down.
At least she'll be pain-free for the remainder of her life, however short a time'period that is.
Oh how awful! I know from experience how expensive TPLO surgery is. It was very succesful with my dog and I can't imagine going through that twice and then having to deal with cancer at the surgery site.
We have two veterinarians here at Med Help, and I think you should post your question to them. If nothing else, you will have educated two vets as to the possibility of cancer developing as a result of this surgery. Go to the Ask a Vet forum and post your story. I'll be interested myself in hearing if they've heard of this happening in other dogs.
You have my sympathy. You went over and above what most people would do to keep their dog healthy, and it just went south. There's nothing else you could have done though. :-(