An Overview of a Herniated Disc of the Thoracic Spine
The thoracic spine is a series of building blocks called vertebra stacked one on top of another, separated in the front by the discs and in the back by the facets. When an injury or condition occurs to one of these discs, pain in the middle of the back can result. From the front view, normal spinal alignment should be straight with the center of the head sitting on a plumb line directly over the pelvis. The side view of the thoracic spine has a curve that is “C” shaped.
Anatomy of the Disc
In appearance, the disc looks like a jelly donut. The jelly (called the nucleus) is made of sugars attached to a protein backbone called a proteoglycan. This structure allows it to act like a giant sponge. The jelly pulls in water from the body of the vertebra to create a high-pressure interior matrix (think of the jelly as the air pressure in a tire). The outside of the donut is made up of about twenty to thirty rings of collagen, called the annulus, just like the plies of a tire. These rings are normally quite tough. Each layer of these rings alternates in angulation in their attachment to the bone of the vertebra. The endplates of the disc separate the bone of the vertebral body from the interior of the disc. They are made of hyaline cartilage – the same cartilage that lines the hip and knee joints. This material creates a barrier to nutrients and oxygen entering and exiting the disc.
Blood Supply and Imbibition
Problems exist with the design of the disc that causes the “disease” we know today as degenerative disc disease or DDD. This can be a source of pain in the middle of the back and can also lead to arthritis of the spine. The first problem is that the blood supply, for all intensive purposes, disappears from the disc by about the age of three. This means that collectively, the discs are the largest structures in the body that have no blood supply.
Without a blood supply, there is very poor oxygen penetration into the interior of the disc. The only fluids that can be exchanged are under hydrostatic and osmotic pressure. This means that motion of the disc exchanges fluids similarly to a squeezing a sponge under water and releasing it. The water and nutrients that this material absorbs and releases, transfers through the endplate of the vertebra under a process called imbibition.
The fluids that are transferred into the disc are poor in oxygen and limited in nutrients. This creates a problem for the living cells inside the disc. These cells produce the glycoproteins, which make up the nucleus, (the gel or sponge) and they need oxygen to function well. Without oxygen, these cells become much less effective keeping up with maintaining the jelly. Without the production and maintenance of these gel proteins, the pressure in the disc drops with age. This causes middle back pain and can lead to a herniated disc of the thoracic spine, slipped disc, or bulging disc.
If the back wall of the disc tears through and through, the jelly inside can push out. When patients ask, what causes a herniation of the spine, this is often the culprit. If a herniated disc of the thoracic spine pushes into the spinal canal, compression of the spine of the nerve root, and even the spinal cord can occur.