What Causes a Disc Bulge? (Video Guide)

The transcript follows the narration, with spelling corrected where the automatic captions misheard a term.

Some people experience neck or back pain as a fleeting problem, but for many the pain lingers, becoming almost impossible to bear. Neck and back pain are fast becoming an epidemic in which there is no immunity. Today the most common disorder presenting to spinal surgeons is a herniated or prolapsed intervertebral disc. In these cases, the disc bulges or ruptures, partially or totally, toward the back or the back and side, and presses on the nerve roots in the spinal canal or foramina.

However, research shows that a healthy disc does not herniate as easily as previously believed. In fact, mechanically induced herniations of a healthy disc can only be accomplished in a controlled laboratory setting, by mechanical forces larger than those ever normally encountered. In most experimental tests, the vertebral body failed rather than the disc. So how does a disc herniate? According to recent medical research, some degenerative changes must be present before a disc can herniate.

Disc degeneration occurs when there is increased intradiscal pressure, which results from increased or improper load-bearing activities, such as a poor sitting posture. When the intradiscal pressure increases, the disc loses its hydrostatic behavior. The disc's hydrostatic ability is derived from proteoglycan molecules, the disc's super sponge-like materials, capable of attracting and holding large amounts of water inside the disc. These molecules are the building blocks of the aggrecan molecules that form the major structural component of the disc. In a healthy disc, up to 100 proteoglycan aggrecan molecules combine on a long piece of hyaluronic acid to form the giant proteoglycan aggregate molecule.

The continued load-bearing activities that increase the intradiscal pressure have been shown to affect the disc in three ways. One, it forces nutrients such as amino acids, glucose, water and oxygen out of the disc and prevents new nutrients from entering the disc. As a result, the disc cells are malnourished and unable to continue the production of the proteoglycan molecules. Two, it breaks down the existing larger proteoglycan aggrecan molecules into much smaller proteoglycan molecules, which are then easily leached out, creating a proteoglycan deficiency within the disc. And three, it affects elastin production by decreasing the inward diffusion of nutrients, which in turn decreases proteoglycan production.

Elastin is the chemical binding that holds the annular fibers tightly together. Normal daily activities break this elastin bond, and if the disc does not have enough nutrients diffusing inward, the elastin cannot replenish, making the annular fibers susceptible to injury. To summarize, with the loss of proteoglycans, the osmotic pressure falls and the disc is less able to maintain hydration under load, leading to premature degeneration. A degenerated disc is a weak disc in which the annular fibers easily buckle or, worse, tear, allowing the nucleus to herniate or rupture through.