Hey Kathy, Unless the area they fused fractured it wouldn't be considered a failed fusion.If a fusion is succesful, it should be harder to break the fused area than the vertabrea above or below a fused area. However if you have screws and the fractures radiate away from the screws, this is a sure sign the fusion failed because the screws shouldn't be bearing weight once a fusion grows and becomes solid. I have fractured several vertabrea and my sacrum this way and all they can do is put me back in a brace or revise a 6 level fusion and extend it up and run a bar from hip to hip , not to mention remove a rib from each side. The last surgery took 11 hours and I'm not ready to sign up for that monster surgery and roll the dice with such horriable odds it will do anything more than stabalize things where I'm at.
I would certainly get a second opinion though. not because I think there is a potential for a law suite, because you would have to prove the neglected area that caused no pain at the time is some how the cause of all your pain and disabilty now. Millions of people walk around with DDD and never know it, walking around with a fracture that isn't causing any symptoms is really no different. so I understand the reaon not to emphasize a problem that really isn't causing any synptoms.
My concern would be, Why haven't the fractures he saw 20 months ago healed yet?. As far as strengthening the muscles and needing to keep them strong, that is going to take an effort the rest of your life to add stability to an unstable area. If nothing surgically can be done, the only thing you can do is strengthen the sourounding muscles.
There are minimalluy invasive procedures called Vertebroplasty and kyphoplasty , where compression fractures where more than 1/3 of the vertebral hight has been lost can be performed to repair the fractures and rebuild the vertebral height. Personally I would still want another opinion from a doc that's going to shoot straight and explain why something can or can't be done. I just read about the osteoP Kathy and that really changes everything. If it's the area above or below a fusion that fractures, there is no reason to think the fusion failed other than poor odds of sucess with osteo P.
If nothing else can be done surgically or your not willing to risk ending up worse, There really is truth to building the muscles around the injured area. As crazy as excersing when you hurt
that bad sounds, if you come to the conclusion, your going to hurt whether you excercise or not, and it will only help in the long run, why not benefit from all it does for you. It took me 7 months of excercising once a day and then twice a day to get to the point I went back to work part time. I started at 8 minutes with no weight in my hands and that kicked my butt, however by the end I was excercising twice a day for 30 minutes with 5 lb weights in each hand. That also kicks my butt, however the benefit is so worth it.
My wife thought I was a maniac, no PT or doc would have ever pushed me that hard but it seemed like the only thing I really had control over as far as making a change in my life. Weight training, even light wieghts along with the right protocol for OP can be effective and hopefuly resolve the fracture problem. Have you already had vertebroplasty done?
I've been able to rebuild strength, loose 35 lbs and haven't had a fracture in over 2 years. It's a little easier to stabalize and strengthen the core muscles,"abs and lower back" but high thoracic will be core and upper body. I use an elyptical machine and instead of using the hand rails I use 5 pound dumbels and do hundreds of curls, over head presses,tricep extensions, anything to keep my arms moving with the weight in my hands. Not heavy weight, I started with l lb sand bags from an old ankle weight, but hundreds of repititions with light weights is just as good as trying to push heavy weight and muh safer as far as injury..
When I started, just holding my hands out in front of me with no weight and keeping my balance was tough. I'm proof it can be done, I still have bad days, pay for working, pay for excercising, but I'm not the same person I was before I started excercising and decided I couldn't live the next 30 years loosing more strength and getting fatter and lazier. The difference it's made in so many areas makes it so worth while, I just can't name them all without getting edited.

Going from sedentary to excercising has so many health benefits including psychological, it makes the increase in pain from excercising worth while.
Definitely get another surgical opinion.The docs have to do their part to allow you to do your part. The doc should be able to tell you why he thinks it hasn't healed if it hasn't, he should be able to discuss the options and show you what he's looking at on the films that make him think he could or couldn't fix things. Docs aren't gods and taking them of the pedestal was one of the best things I could do when it came to dealing with docs. Every doc has their opinion, That's it, just an opinion. They should be willing to explain it and justify it and if they can't, something isn't right.
The patient does need to know why or how, not just that He could operate if you wanted. What would he operate on? what is there that he's not telling you that leads him to think there is a reason to cut you open again.
Sorry to hear things aren't going well, Hang in there, Dave