Hi and Welcome.

What kind of dog is Emma?  How big is she?

My first pug Maggie had a luxating patellas, but they were not too bad.  Turns out the worst of the two was on the leg she lost to mast cell cancer.  Mag lived for almost 4 years after that but never had trouble with her remaining back leg.

My quad pug Obie has had both of his knees fixed.  His patellas would go out and stay out which cause his CCL to tear.  He had his surgeries 2 days short of two years apart.  The second knee he was a virtual tripawd before we could get the surgery done, he rarely put his foot on the ground.

If the patellas are as bad as my quad pug Obie then I would expect the knee to fail at some point.  Have you had them repaired? It doesn't sound like it.  What kind of tumor is in the soft tissue? Is it slow growing enough that you could get the other leg fixed before an amputation?  The recovery from knee surgery is pretty long- 8 weeks of crate rest and several more weeks of leashed, limited activity.

It is possible to do a surgery on a remaining back leg- Murphy is a great example.  It's not easy but can be done.

I'll be interested to see what the surgeon says.

Karen and the Spirit Pug Girls