The intervertebral disc is often linked to low back disorders. Conditions like degenerative disc disease (DDD), disc bulge/herniation, sciatica, radiculopathy and myelopathy all can be causes by the break down of the disc. So we will discuss the roll of the disc and how it gets injured.
The disc is made up of two main sections. The first outer section is mostly fibrocartilage. It consists of strong fibers that are angled at approximately 30 degrees. [i] The layers alternate directions to increase structural strength. This helps the disc resist the twisting and tensile forces placed upon it. The second is the centre of the disc, which is called the nucleus pulposus. It is more of a gel-like structure, which makes it resistant to compressive forces.
The disc is important in providing force transfer from one vertebrae to the next and resisting twisting and bending forces. Many believed that it had a role in shock absorption of the spine; much like a sponge. But due to its liquid centre, which I previously mentioned resists compression; it is actually a poor shock absorber. The vertebral bodies better serve that job. Even though they are made of bone, the internal structure is a dense a network of flexible beams called trabeculae. They bend like bamboo to absorb the forces transmitting through the spine.
So based on the structure and nerve supply, it seems that the outer fibrocartilage section of the disc is to blame for disc pain. When there is a radial tear of the inner layers of the disc, it allows the nucleus material to exit.[i] This places more stress on the next layer, leading to subsequent tears and the nucleus moving further away from center, causing the discs radius to increase. The disc itself has some nerve supply around the outer layers of the disc but not the nucleus pulposus. The process can continue until the nucleus material eventually makes its way to the outer most layers and extrudes into the spinal canal. (See fig.1)
Once in the spinal canal, an inflammatory process occurs that can sensitize local nerves, leading to increased pain and sciatica symptoms.
The disc itself has some nerve supply around the outer layers of the disc but not the nucleus pulposus. These nerves can perceive pain when the outer layers of the disc are damaged or when the disc has; enlarged as mentioned above.
Most of the issues leading to disc bulges and herniations are due to repeated forward bending and twisting. These movements place stress on the posterior aspect of the disc fibers and encourage the nucleus to move toward the spinal canal.
So how can you know if your discs are a problem?
Here is a quick exercise you can try to see if you have discogenic low back pain.
1)Lie face down on the ground
2)Lift your head up and place your elbows on the ground directly under your shoulders. Support your head by placing your hands under your chin. You should look like you are watching TV at this point. This is the called the sphinx position.
3)Hold this position for 1 minute. Your low back should be totally relaxed.
4)Rest for 10 seconds by lying flat again.
5)Repeat this 2 more times
After this, stand up and bend forward and see if your symptoms have improved or moved centrally towards the spine. If so, your low back discs are likely a source of pain for you and should consult your local chiropractor. In the mean time, this is a good drill to perform first thing in the morning to encourage better disc health.
Next post we will go over another disc condition: degenerative disc disease (DDD).
Dr. Mike Rumeo is chiropractor with a passion for improving the health of his community and pain management. He primarily utilizes chiropractic, medical acupuncture and rehabilitation to help his patients. He is the owner of the Oakville Optihealth Clinic, a multidisciplinary clinic located at Fourth Line and South Service Rd W, in Oavkville ON. To contact Dr. Rumeo, please email him at email@example.com or call at 905.465.0202.
[i] Adams MA & Roughley PJ. What is intervertebral disc degeneration, and what causes it? Spine 2006; 31(18): 2151-2161.