As Victor said, there are many factors that can cause back and leg pain. EMG's can show nerve deficits (poor conduction, etc) but they won't necessarily pick up "pain" from a nerve that is getting irritated by pressure, but not enough pressure to cause immediate damage. In other words an "irritated " nerve root won't necessarily show up as a "damaged" nerve on an EMG, which is a good thing.
The MRI should show the bigger picture and determine whether there is a disk bulge that is pressing too closely to the nerve root.
My history of surgery was a disk decompression (L4-L5) back in 1979 when I was around 21. My nerve root was irritated but not damaged. Unfortunately, back then they didn't even have CAT scans, so they didn't know that I had congenital spinal stenosis (too narrow a spinal canal), and that's what was really causing the constriction on my nerve roots, not the disk herniation. I then had a later operation to widen the narrow canal and fuse the bones. (Since then I've had a couple of injuries that were not caused by the surgeries).
Bottom line, my nerve hurt like heck, but fortunately it wasn't damaged. I hope the same prognosis is found in your case. I have great faith in the MRI as a diagnostic tool.
Good luck and keep us posted, okay?