The vet said it was an ACL tear, and would require surgery to fix - $3000.
Now: if you live in Nevada, you can take any number the vet gives you and double it to get the actual cost. I called vets who performed the surgery, and sure enough - $6000.
Of course, every vet these days is a woman.
I did my own research on the internets. I found that there are shots that when combined with rest and a temporarily forced sedintary lifestyle are more effective than $6000 surgery.
The shots cost me a total of $700 (bi-weekly injections for 2 months). During this time, I discouraged my dog from play or rough-housing with my other dog.
She is much better now, and can run again!
And trust me, she was limping so bad, I thought she'd never run again.
All this said, I have realized that the veterinary field has become infected with a grossly disproportionate number of females, whose only goal is to exploit the compassion pet owners have for their animals.
There was another incident when I lived in Reno - long story short, I paid $900 to have my dogs rabies vaccinated. If I had went to the pound - it would have been $24. The excuse from the vet was: new patient fee + general physical fee + normal appointment fee + vaccination - all that times two. Bullshit.
I don't know how these vets get away with these kinds of charges and flagrant deception and exploitation, but they do.
As a pet owner, there is little you can do about it.