What is the difference between a bulge and a herniation?

A herniation is a focal protrusion.

A bulge is a diffused protrusion.

It depends on the character of the ANNULAR TEAR.  The same way the characters of the hole in a tire determines whether you have a slow leak or a blowout.

Slow leak = Bulge

Blowout = Herniation

Don’t be confused by the terminology! The implication is, that a herniation is worse than a bulge; or that if bulge or herniation is not touching a nerve, that it will not be painful. These are common misconceptions that are held by doctors, as well as lay-people! THE KEY ISSUE IS THE ANNULAR TEAR!! The annular tear is, in and of itself, painful. And, it is the character of the annular tear, (i.e., how big it is, and whether it is longitudinal or radial), that determines whether the disc will bulge or herniate. The annular tear is analogous to a hole in a tire. The size of the hole determines if the tire will have a blow-out, or a slow-leak.

Why are discs painful if they are not pinching a nerve?

The truth is, in the vast majority of cases of low back pain, the bulge or herniation does NOT touch the nerve. And, when the bulge or herniation does touch the nerve, it causes LEG pain, not BACK pain! As our knowledge of low back pain has grown over the years, we have had to adjust our thinking. This misconception, however, seems to persist, despite what we have learned.

We now know that the disc is innervated, (has a nerve supply), similar the nerve supply found in the finger tips. It is called the sinuvertebral nerve. This tiny nerve’s only function is to perceive pain.

It monitors mechanical and chemical stimuli.

Mechanical stimuli are generated when the disc is injured, and the shock-absorbing function is lost, as in the case of an annular tear.

Chemical stimuli are generated when the body tries to “clean up” the tear, in the same way it does when other areas of the body are injured, (for example: a cut on the fingertip), by sending in white cells, evoking inflammation. This process, actually, changes the chemical composition of the nucleus, resulting in a loss of water in the nucleus, which, in turn, further compromises the disc’s shock-absorbing capacity.

This is best illustrated by the MRI, specifically the T2, sagittal, images. Sagittal simply refers to the orientation of the MRI image. It a slice taken lengthwise, from front-to-back, (as opposed to side-to-side). On T2 images, water appears as white, (as opposed to T1 images where fat is white). When we look at a T2, sagittal image, the spinal cord, or more specifically, the water surrounding it, should appear white. If we look at a normal disc, we see that the center, the nucleus, is white.

It is white because it is composed of large molecules called proteoglycans that hold water. As we age, the proteoglycan content of the nucleus decreases. This process is hastened when an annular tear occurs, and the entire disc becomes black. Note that an annular tear can occur in a disc that has already begun to degenerate.

A black disc is also, often, referred to as a degenerated, or desiccated, or dehydrated disc. The annular tear can often be seen in the posterior annulus as a white dot.

The next big misconception is that a bulge or a herniation, (annular tear), will get better. While it is true that it may become less painful over time, the disc has lost it’s capacity to dampen motion at the facet joints. The disc has little capacity to repair itself. It’s like expecting a worn-out, shock-absorber to suddenly start working again. In fact, the opposite is true. Once injured, the disc will continue to degenerate. The annular tear is the inciting event that triggers an entire cascade of degenerative events, that culminates in a condition called spinal stenosis.