The Discs of the Spine: An Overview
The bones of the spine are separated by tough cartilage pads called intervertebral discs (inter = “between”; vertebral = “bones of the spine”). Healthy discs are thick and flexible (like a wet sponge) allowing a wide range of bending and twisting motions. An unhealthy disc is stiff and hard (like a dry sponge) and prone to injuries such as bulging or herniation. Over time gravity, spinal joint dysfunction and accumulated trauma cause the discs to compress, flatten and degenerate. This constant compression prevents much-needed oxygen and nutrients from entering the disc. This ongoing starvation causes the once-tough outer layers of the disc to soften allowing the disc to become injured or diseased. Disc damage can occur anywhere in the spine. However, the discs of the neck (cervical spine) and low back (lumbar spine) are the most commonly injured.
Disk Bulge Herniated Disk Ruptured Disk
Disease of the spinal discs can take many forms. Significant disc damage can lead to a Disc Bulge, become a tear called a Disc Herniation or the inner gelatinous material of the disc can leak out in the case of a Ruptured Disc. The “jelly center” of the disc can also dry out over time which is referred to as Degenerative Disk Disease. All forms of disc injury can eventually impinge on the nerves exiting the spine (“Pinched Nerve”) which can create numbness, tingling, burning or sharp pain down the arms or legs. Sharp pain originating from the back and “shooting” down the legs is often referred to as Sciatica.
Introduction to Degenerative Disc Disease
In order to understand the condition of Degenerative Disc Disease one must know two main facts about discs.
- Spinal discs do NOT have a direct blood supply. There are no arteries that feed the disc with oxygen and nutrients. Therefore, discs of the spine must receive their oxygen and nutrients from a different source. Normal, healthy discs are “fed” and oxygenated by the constant recycling of the disc fluid that occurs with spinal joint movement. This joint motion “sucks” in fluid filled with oxygen and nutrients and “pumps out” waste fluid. This process of fluid diffusion is greatly affected by internal disc pressure (intradiscal pressure) which brings us to key point #2.
- The discs of the spine are under constant pressure. The spinal discs are designed to absorb shock and maintain spinal flexibility by acting as cushions during body movement. The discs act similar to shock absorbers in a car. Car shock absorbers maintain a constant pressure to “push back” against the weight and movement of the car. Spinal discs act in a similar fashion. The pressure within the discs pushes the bones of the spine apart preventing them from crashing into one another during activities like running and jumping. Unfortunately, this constant internal disc pressure also pushes the fluid out of the disc consistently every day. This makes it difficult for the body to “suck” in new, healthy disc fluid with its much-needed oxygen and nutrients.
These two factors make it difficult for the body to maintain thick, plump, healthy discs making Degenerative Disk Disease one of the more common spinal ailments.
Degenerative Disc Disease: As the disc degenerates it loses height (Disc Height Reduction) allowing the bones above and below to “sandwich” the nerve between them.
Degenerative Disc Disease, as the name implies, is caused by the progressive degeneration of the intervertebral disc. Nearly every physical activity (no matter how simple) places strain upon these discs. Over time, repeated daily stress and minor traumas begin to weaken the discs of the spine. This process of accumulated wear and tear will eventually lead to disc degeneration commonly referred to as Degenerative Disk Disease.
The process of disc degeneration often begins with a chronic lack of oxygen and nutrients. This can occur because of 1) greater than normal compression of the disc or 2) as a result of decreased hydration. Greater compression comes from repetitive harmful activities such as bending, lifting or twisting – even prolonged sitting can create abnormally high levels of disc compression. Decreased hydration occurs when less fluid is pulled into the disc than is “pressed” out of the disc. This slowly creates a deflated or dehydrated disc. The medical term for this lack of disc fluid is Disc Desiccation and is the MRI finding most commonly used to identify Degenerative Disc Disease.
Symptoms of Degenerative Disk Disease
The symptoms of Degenerative Disc Disease can vary widely depending on the location and severity of the condition. In general the degenerated disc itself causes little to no pain. If it does cause symptoms; it often creates stiffness around the affected joints or a deep ache that is often increased with movement of the joint. However, as the joint “warms up” the pain often decreases with this same body movement.
Although the degenerated disc often causes only mild symptoms, Degenerative Disc Disease can still cause severe pain and disability in other ways. The most serious problem related to Degenerative Disk Disease is direct nerve compression. This occurs when the spinal disc becomes thinner as part of the degenerative process. This thinning, also called Disc Height Reduction, causes the space between the bones to narrow. This narrowing also makes the hole between the nerves, the foramen, smaller, as well. Neural Foraminal Narrowing causes direct bone-on-nerve compression which can create such severe and debilitating symptoms as sharp pain, burning, numbness, tingling and muscle weakness. Over time this degenerative process can compromise the integrity of the nerve to the point that the organs controlled by these nerves can become diseased. Therefore, the most disconcerting problems associated Degenerative Disk Disease are not due to the disc itself, but how the disc degeneration causes the nerves to become injured as a result.