you are tough and brave to work with such pain. I, also have back problems 3 disc herniations and some arthrose. It's been 2 years now (8 with chronic pain altogether, just 2 with the back), by far the worse of my life.
Coincidentally, Oxycontin is the only med that has work for me too so far and believe me, I have tried a whole slew of them so far (Meth, fentanyl etc.).
I am no expert, but from what I can gather from my own experience, all these meds come from the same component: Codeine (hence the CO in all of them). So having the same molecule, if you take one of them for breakthru pain and the dose of the latter happens to be much less than your long acting one (oxy), you are not likely to feel the difference.
It is funny though how we go through almost the same process with meds. I, also, used to take oxy just occasionally, so I would not become tolerant to it, just like you. However, both ways have trade-offs.
The upside of this is that like I just said, you can take it longer since it's on and off, your body will not get used to it, but on the other hand you subject yourself to mini withdrawal symptom stints wich can mess with your mind and body. Some day you are fine and some day some you feel sick and in excruciable pain. Not to good for the spirits.
you take it round the clock, chances are, you will be less likely to suffer useless breakthru episodes in between and for a while, you'll be okay. The downside is that you are most likely to become tolerant and having therefore to increase your dose eventually. At some point in the future, you will reach a dosage which will be the limit for that very drug and then you will have to swich to another one. How long will it take for you to become tolerant? That a million dollard question. Everybody reacts differently. All I know is that, from my experience again, Oxy is a nasty one to come off of. Worse than anything I have experienced.
You have to weigh in the pros and cons of it and choose which one is most convenient for you. Unfortunately, with CP and meds, there are no miracle recipes. Just a lesser of two evils.
For breakthrus, Have you tried Hydromorphone, or hydrocodone (more potent plain codeine).
Let me know.