Why is the spine so prone to injury?
Your spine must be both stable and flexible to support upright posture, allowing you to bend and twist. This is mechanically very challenging and makes your spine vulnerable to injury. The spine is made up of a chain of bones, called vertebrae, connected together by ligaments and muscles.
A disc separates each vertebrae and acts like a cushion, absorbing shock along the spine. The disc is made up of a jelly-like substance known as the nucleus, covered with many strong outer layers called the annulus. The discs do not have a supply of blood vessels to nourish and replenish them, rather they depend on a transfer of fluids, nutrients, and oxygen from the vertebrae above and below. This transfer of nutrients depends on the difference in pressure between the inside of the discs and the surrounding vertebrae and blood vessels. This is why most disc nutrition and regeneration takes place when we lie down and the pressure inside the discs is reduced. This process is not very efficient, and as we age, the disc is exposed to wear and tear greater than its ability to heal and regenerate.
The discs are prone to injury and degeneration as we use our backs each day, as they are compressed and torqued through sitting, bending and lifting. In the two lower levels of the lumbar spine, stress forces can equal 2,000 to 3,000 pounds of pressure per square inch. Repeated injury weakens and eventually tears the annulus. With increased pressure inside the discs, these tears allow the disc to bulge like an old tire with a broken casing. If all of the layers of the annulus break, the jelly-like nucleus will ooze out of the disc, causing a disc herniation. A bulging or herniated disc may press on spinal nerves, causing sciatica or radiculopathy.