Re: Severe low back pain and slight leg pain/emg?
Do you have sciatic-type pain running down your leg? Is most of your pain located in your back or in your leg, or both?
The EMG is another piece of the puzzle that your doctor can use to try to figure out what is causing your pain. The nerves that innervate the muscles in your legs come out from the spinal column. The nerve conduction part of the test is used to determine if there is any damage to the peripheral nervous system. This takes in all the nerves that lead away from the spinal cord and the smaller nerves that branch out from those nerves.
If you search for a dermatome map, you will see the the spinal nerves that lead out from L4, L5 and S1 run down the leg and into the feet. If the EMG test shows some interference in one of the nerves, it will tell the doctor which level may be causing your pain.
Remember that all these tests are just pieces of a puzzle that when all put together can (hopefully) reveal where the doctor should start looking for an issue. Not all nerve compression is easily seen on imaging. If the disc is pretty-well shot at L5-S1 from the collapsed vertebrae, there may be a tear in the annulus fibrosis which is allowing the center of the disc (nucleus) to leak out. This in itself can cause nerve pain as it contains a substance that is VERY irritating to the nerves.
Even though this event is happening in your lower lumbar spine, the nerves carry signals to your legs, and the pain you feel may be radiating from this. Or there may be compression that is not easily visible.
In any case, if you are looking to resolve the pain, and other testing has not revealed anything, the EMG would be the next step.
Good luck. I hope they will soon find out the nature of your issues.