I'm having some pain in my low back (just on one side). Usually I can put my finger right on the spot. But sometimes it seems to move up or down a little. A few times, I could feel the pain clear to my knee. Is this a sign that the nerve is getting pinched or what?

Identifying the exact mechanism of low back pain (LBP) can be quite a challenge. The discs don't generate pain directly but they can put pressure on the nearby nerves and set up a pain pattern in that way.

The spinal (facet) joints make spinal motion possible. Forward bending, side bending, twisting, and straightening are movements that all take place at the facet joint. Anything that can reduce the joint space or alter the joint biomechanics can produce LBP.

If more than one joint or disc is affected, you could have pain at more than one level. Pain from the joint can be referred to the knee but does not go below the knee. Pain caused by nerve impingement from disc herniation can travel from the low back to the buttock and down the leg all the way to the foot.

Palpation and position are also used to help sort out the source of painful symptoms. Some positions are known to make the symptoms better or worse in each case. Palpation to reproduce the symptoms is possible when a facet joint is the source of the symptoms. Palpating the painful area will not increase the pain when the disc is involved.

Your doctor will be able to help make the correct diagnosis related to your LBP. It's important to rule out a more serious cause of pain. Once it's confirmed that there isn't a medical problem, then treatment can be applied to help improve motion, function, and reduce symptoms.

Victoria E. Wilde, et al. Indicators of Lumbar Zygapophyseal Joint Pain: Survey of an Expert Panel with the Delphi Technique. In Physical Therapy. October 2007. Vol. 87. No. 10. Pp. 1348-1361.