Low back pain

Low back pain, the pain that sits in the lower back, has many possible causes, but one dominates the picture: mechanical pain, which accounts for 90% of back pain cases. It is called mechanical because it arises from the way the spine itself works and bears load.

It shows up when the nociceptive elements of the spinal segment or of the soft tissues next to it, meaning the nerve endings that detect damage, are overloaded or torn. A spinal segment is the block made up of two vertebrae and everything that joins them.

There are two different stories. The acute episode is usually a sprain or a strain of the paraspinal muscles, the ones that run along either side of the spine, and of their ligaments, after a loaded segment is pushed past what it can take while bending, straightening or twisting. That leaves microscopic tears, edema, meaning swelling from fluid, the release of inflammatory mediators and a reflex spasm that limits movement. It is a hinge forced past its range of motion: first it stretches, then it jams. Chronic pain, by contrast, usually comes from degenerative changes in the intervertebral disc, the cushion that separates one vertebra from the next.