A popular form of treatment for people with disc pain in the low back is the lumbar extension exercise. The basic principle is to bend the spine backwards to try and ease low back pain. Some people get nearly immediate relief. However, the treatment is not a magic bullet for people with disc pain. Sometimes, the pain doesn’t go away. The pain may even become worse. This study may shed some light on why some patients get relief and others don’t.
One theory behind this treatment is that bending the spine backwards squeezes the disc material forward, away from pain-sensitive soft tissues like the nerves and ligaments. A second theory has to do with pain from pressure on the back part of the disc. The disc is made up of a central nucleus pulposus, surrounded by rings of ligament-like material known as the annulus. The outer rings of the annulus are richly supplied with pain sensors, so injury or pressure on this part of the disc can hurt. If pain comes from the annulus on the back part of the disc, it makes sense that getting pressure off these sore tissues would feel better.
To measure disc pressure in various positions of the spine, a team of researchers tested the discs of 19 cadaver spines. To make the tests more life-like, the discs were altered to behave as though they were degenerated. Backward bending works differently when the discs are degenerated because the spine tends to pivot on the joints along the back of the spine. This shifts the forces onto the bony ring of the vertebra and can take pressure off the back part of the disc.
A key discovery is that backward bending didn’t always take pressure off annular rings near the back of the disc. In fact, when the spines were bent back two degrees, only seven out of nine spines showed less pressure. Discs that registered lower pressures in a neutral position tended to have less pressure on the annular rings near the back of the disc when the spine was bent backward.
These differences might explain why some people get better with extension exercises and others don’t. “The results,” say the authors, “caution against making predictive rules based on anatomic or pathologic assumptions.” In other words, patients are unique, and their symptoms may react differently to lumbar extension exercises.