The surgeons I've seen for my fusion could tell that my fusion was solid by X-ray. I'm not sure why your dr had to go back in to check this. Even if your fusion is successful you can still have pain. There is only about a 50/50 chance that you will have pain relief from the surgery. Were you given a bone growth stimulator to wear? It's supposed to be worn 4 hrs a day. Did they use your bone or donor bone? If you are concerned you have another non union I would definetly look into getting a second opinion. I don't think that your back should of been opened just to see if there was a problem or not. Yes if you had a non union you would need an additional surgery but again the doctor should of been able to tell you this by looking at your x ray films.
A couple of things, when had my 1st Cervical fusion, they X- rayed me like 3 or 4 times. I think it was @ 2, 6 and 12 weeks but I'm not positive.The first time, I actually fused @ 12 weeks, it's not that common but it can happen.
If they suspect there is a non- union they will generally do a CT scan, which is much better than an MRI due to the artifact distortion.
Did someone tell you that if you have a solid fusion you won't have any pain? Because nothing could be further from the truth. When fully fused, the Surgeon will generally consider the surgery a success and release you, regardless of your pain level. I was in horrible pain months after I fused with both of my ACDF's, particularly the 1st one, there's a lot of other factors involved.
I agree about the pain thing. It did not relieve my pain, it made it worse and now I'm disabled in my 30's.