Herniated Disc in the Lumbar Spine Overview
If you have ever experienced lower back pain, then you are certainly not alone. The lumbar spine (which is the technical term for the lower back) represents an area where many injuries and disorders can occur. One of the most common problems we treat in our practice are herniated discs that are associated with the lower back. Herniated discs in the lumbar spine can cause a great deal of lower back pain and leg pain.
The Lumbar (Lower) Spine
Between each vertebra in the spine is a disc. These discs are the main stabilizers in the spine. They function like restricting shock absorbers. Each disc is in place to absorb impact and still allow motion of the spine, but it has to restrict this motion to prevent damage to the spine. This is a great deal to ask of a tissue and is the reason why the lower spine is so susceptible to injury.
Each disc in the lower back surround an element known as the nucleus pulposus which is a gel-like substance within the spine. The easiest way to describe these discs is to compare them to a jelly-filled donut. The inside jelly (nucleus) is made of sugar attached to protein and acts like a giant sponge. This material pulls in water from the body of the vertebra to create a high-pressure interior mass. The outside of this donut (annulus) is made up of about sixty rings of collagen. These rings are quite tough. The endplates of the vertebra separate the bone from the disc. These endplates are made of cartilage – the same cartilage that lines the hip and knee joints. This material creates a barrier to nutrients and oxygen flowing into and out of the disc.
Problems Associated with the Lumbar Spine
After the age of eight the blood flow to these discs naturally begins to disappear. This leaves the interior of the disc in the adult with no blood supply. Therefore, the only fluids that can be exchanged are under pressure. This effect is evident in our height differences throughout a typical day. When we get up in the morning, we are actually one-half inch taller than we are in the evening. The pressure inside the disc with prolonged standing squeezes water out, making the disc less thick. Therefore, the spine has less height at the end of the day. Motion of the disc exchanges fluids similarly to squeezing a sponge under water. Fluid is forced out and then reabsorbs. This barrier significantly restricts nutrient and waste exchange.
Without oxygen, the cells inside the disc that manufacture the shock-absorbing protein that make up the jelly become senile. Without the production of these proteins, the pressure in the disc drops. When the pressure drops, the walls of the disc (the annulus) take more of the strain and are at more risk to tear. Therefore, a degenerative disc is much less resistant to abnormal movements and these motions can create injury.
Another problem with the disc is the type of collagen that makes up the outside of the donut. Not all collagen is created equal. Some types of collagen can be bent and stretched continuously and they will continue to function as though they were new, while other types of collagen are somewhat brittle, like coat hangers. You can bend them only a limited amount of times before they fail. The genetics of the discs go a long way in predetermining the health of your back. This gives you a good reason to shift responsibility for your back pain to your parents.
Herniated Discs in the Lumbar Spine
You can see that the disc is mechanically and biologically at risk. The disc is the largest structure in the body that has no blood supply. Without a blood supply, the disc can’t heal after an injury. All injuries to the disc therefore are cumulative. To say it another way, any injury to the disc is, essentially, a permanent injury. A tear of the collagen in the donut won’t repair itself. If you were born with brittle or weak collagen, there is a greater risk of injury to the disc.
What happens if you develop an annular tear? If one of these discs, or outer bands breaks or cracks open, the gel-like substance inside can spill and leak out causing a herniated disc. This leakage ultimately puts pressure on nearby nerve roots and on the spinal cord itself. In addition, the substance that makes up the nucleus also contains elements that can cause inflammation within the nerve, which can lead to a dull aching pain in the lower back once released into the spinal chord.
When there is a tear of the outer disc wall, a very weak supply of blood is available to assist in the healing process. Tears will attempt to heal, but the scar tissue laid down is not nearly as strong as the collagen fibers it attempts to replace. In addition, blood vessels that grow into the torn fibers of the disc carry new pain fibers in with them. This is another cause of pain for the disc.
This is ultimately an extension of degenerative disc disease. The tear in the disc (which itself causes back pain) can finally rip through and through and the jelly inside (nucleus) can be forced out just like squeezing a toothpaste tube with the cap off. The resultant herniation material pushes against the nerve root and leg pain ensues.
One of the more interesting scenarios associated with a herniated disc in the lumbar spine is that in some cases, the patient may have had low back pain for months to years. When the patient lifts or twists, a “pop” occurs in the lower back resulting in a complete through and through disc tear. Patients will have immediate relief of their ongoing back pain. This is because the scant remaining intact fibers of the disc were under significant tension. When these fibers rupture, the back pain disappears. This tear of the remaining fibers however allows the nucleus to herniate, which compresses the nerve root. Leg pain sometimes takes 1-2 days to occur after the herniation, so there is a short period of total relief
Stages of a Herniated Disc
There are several stages of a herniated disc in the lumbar spine. Over time, due to wear and tear of the spine and due to age, the discs will naturally weaken. During this stage, very minimal symptoms may be present such as periodic slight back pain. The next stage usually results in a prolapsed disc whereas the shape or form of the disc may have a bulge resulting from a slight impingement into the spinal canal. If the gel-like nucleus pulposus actually breaks through the outer later but remains inside the disc, an extrusion will occur. The final and most serious stage is a sequestered disc which will occur when the nucleus ruptures and breaks essentially spilling the substance into the spinal canal.