An MRI seems like a great idea. Let's look under the covers, and then we'll know what's what. Right? We get injured... we get an MRI... we look at the image and say, "There! That's what's causing the pain". The problem is we're only looking at the "after" pic. What if we had taken a "before" pic... and it looked the same as the "after" pic? Now it's not so conclusive.
They did a study once. They took MRI's of people who had no current nor previous back pain. What they found is that a significant amount of them had what would be classified as a herniated disc. 30% of the people in their 30's had one. 40% in their 40's, 50% in their 50's. See a pattern? So if disc herniation is the source of back pain, how come these people had no symptoms? And now you can see the folly of the typical scenario of feeling back pain, getting an MRI, and coming to the conclusion that the disc herniation is the source of pain.
Knowing all of this, I went for an MRI anyways. My rationale was that maybe it would show my back had no disc herniations so I could rule that out, plus then I would have a "before" pic in the event that I had some future issue. So into the white cave with the ominous hum I went. The results... Richy has an L4/L5 disc herniation. Crap! Stay tuned...
Update (1/1/2018) - If you're interested in delving further into the science of how chronic back pain is likely more mental than structural check out this article.