By Jonathan Chu, MD
Interventional Pain Medicine
PM&R

So you may have heard from your doctor that you have a herniated or bulging disc on your MRI. And if it’s the first time you’ve heard the term, it’s very common to be a little confused about what the disc actually is, how it fits into the rest of your spine, and why it can cause you so much pain.

So in this video, I’m going to explain exactly what the intervertebral disc is, what you, as a patient, need to know about it, and why it can potentially cause problems, as well as a few ways to keep your discs healthy in the long-term.

To start, it’s important to talk about the anatomy and the structure of the disc, and how it relates to other structures in your spine.

Now, a lot of people actually confuse the disc with the vertebral body, which is a different structure that is made of bone. And while the 33 vertebrae of your spine give it its bony structure, the discs are actually made out of cartilage, and fit in-between each of the vertebral bodies.

Let’s take a closer look at the structure of each disc.

I would often tell my patients that the intervertebral discs are quite similar to car tires, in that they are round, tough, flexible, and shock-absorbing.

The car-tire analogy applies mostly to the outer part of the disc, which is known as the annulus fibrosus.

If you break down the medical terminology, the name actually tells you a lot of information about what it is. Annulus means “little ring” in Latin, and Fibrosus means “made of threads or fibers.”

Thus, the annulus fibrosus is the tough outer ring of fibrocartilage of the disc. This ring is made up of many layers of concentric lamellae, which are composed of really tough collagen fibers. These collagen fibers are actually arranged in a criss-cross pattern, which helps your discs withstand twisting and tensile forces as you go about your activities throughout the day.

The inner part of the disc is known as the nucleus pulposus, and is actually quite different, in that it is full of a gel-like substance. This gel is made up of a combination of water, collagen fibers, and proteoglycans, which are a special type of protein. The nucleus pulposus of the disc is just as important as the annulus, in that it allows the disc to act as a shock absorber, every time you run, jump, or even go for a normal walk.

It is important to note that the discs, just like other cartilage in your body, do not have a direct blood supply. The medical term for this is that they are avascular. Thus, they have to get their nutrition via osmosis from the surrounding vertebral bodies, which are vascular.

It’s also important to note that, because the discs are made of cartilage, and not bone, they won’t show up directly on an x-ray, which is primarily for assessing bony structures. However, you can use an X-ray to indirectly get information about the discs, by looking at the spacing between the vertebrae, as well as their alignment. Overall, the best two imaging modalities for assessing the health and structure of the intervertebral discs would be CT scan and MRI. If an x-ray isn’t enough, the next step of spinal imaging is usually an MRI, and is definitely my preferred method for visualizing the soft tissues of the spine.

Lastly, as far as disc structure goes, the last thing I want to mention are the ligaments, which are dense bands of tough connective tissue. There are two main ligaments that border the intervertebral disc. In the front, there is the anterior longitudinal ligament, which is broad and strong, and prevents the disc and surrounding vertebrae from sliding forward. In the back, there is the posterior longitudinal ligament, which is actually quite a bit narrower, and helps to prevent the disc from herniating or sliding backwards. Of course, unfortunately, while this posterior ligament is quite tough, it sometimes just isn’t enough, and thus disc bulges and herniations can occur.

Now, let’s talk about function.

As we’ve established earlier, one of the main functions of the discs is that they act as nature’s shock absorber. However, it is important to note that the discs also perform two other major functions.

One of these is that the disc also allows your spine to bend and twist. The special structure of the disc makes it strong, flexible and elastic, which really helps to facilitate all the various spinal movements of your neck and low back throughout the day.

The last main function of the disc is that allows for proper spacing of the vertebrae. When the discs are healthy, their height allows for the spinal nerves to pass through the gaps in the vertebral bones, which are known as foramen.

This is actually a segway into the first major problem that can potentially happen to the disc, and that is, degenerative disc disease.

Now, as a person ages, over the years and decades, there is going to be repeated stresses and load bearing on these discs, which will cause age-related degeneration, as a natural consequence of the wear and tear. When this happens, the disc will tend to lose water content and elasticity, and just get thinner and shrink. Interestingly, since this happens throughout the entire spine, this is actually why people tend to get shorter as they get older. Furthermore, it is important to note that, as discs degenerate, they also tend to become less effective at shock absorption.

Now, I actually had an attending when I was in residency who would always tell us that degenerative disc disease is really a misnomer, as it is really just a consequence of natural aging, and would say that degenerative disc disease is really no more of a disease than aging is a disease.

It is a fairly good analogy and way of thinking about it, because the truth is, after a certain age, no one is able to escape some degree of degeneration of their discs, just like with wrinkles or gray hairs.

However, just like with aging of the body in general, there are factors that either slow or accelerate that process for the disc. In the case of degenerative disc disease, the three big negative factors are repetitive stress, poor posture, and obesity, especially over the long-term.

In general, degenerative disc disease is asymptomatic, meaning it doesn’t really cause pain in most circumstances. As I said earlier, most people after middle age are walking around with discs that are just not as tall and fluffy as when they were 18, and that is just fine, as long as it isn’t causing you symptoms or interfering with your life.

The problems usually come if the degeneration becomes so severe that the thinning of the disc actually causes significant narrowing around the spinal nerves, which is known as stenosis. In that case, the narrowing can potentially cause irritation and inflammation of the nerves, which can cause pain, numbness, and weird sensations down the legs.

Now the other common problem that can occur with the discs is that they can potentially bulge or herniate. There’s a good chance that if you’re watching this video, you may have suffered from this. If the disc bulge is mild and not pushing on any nerves or the spinal cord, then there’s a good chance that it will be asymptomatic. In fact, there’s a large portion of the general population in middle age or their later years, who are just walking around with bulging discs and do not even know it.

However, depending on the size or the location of the bulge, it can press on one of the exiting spinal nerves, and can pinch and irritate that nerve, leading to inflammation and pain. This is a condition known as radiculopathy, or radiculitis, which is a common condition that most people simply refer to as pinched nerves, or sciatica; since it is such a prevalent problem, I will cover this topic in much more depth in a future video.

Now, with a bulging disc, the outer layers of the annulus remain intact. With a disc herniation, the nucleus pulposus actually breaks through a defect in the annulus, and thus is more likely to cause pain and symptoms.

It’s important to note that over 95% of lumbar disc bulges and herniations occur at the L4-5 and L5-S1 levels, which are the two lowest levels of the low back; this of course makes a lot of sense because this is where most of the motion occurs when people bend and twist.

It’s also important to note that sometimes disc injuries themselves can cause pain, even when the discs aren’t directly pressing on a nerve root. This is known as discogenic pain, when a tear or injury to the disc itself causes pain, without involvement of the spinal nerves.

This is unfortunately a very difficult condition to treat. With lumbar radiculopathy, or pinched nerves, there are multiple types of epidural steroid injections that are quite effective at quelling the inflammation and associated nerve pain symptoms. However, with strictly discogenic pain, there really aren’t any quick and simple procedures that can easily knock out the pain. Thus, the treatment for discogenic pain is usually just conservative, involving mainly physical therapy and strengthening while the disc heals. Of course, as I explained earlier, unfortunately the intervertebral discs have minimal blood supply, and thus they heal at a slower rate than most other structures in the body, which sadly can be quite frustrating for many patients. If you’d like to see a video that does a deep dive into discogenic pain, let me know in the comments, as it is a less common condition than the others I mentioned earlier.

Now, lastly, let’s talk about how to keep your discs healthy and pain-free, and how to slow their degeneration as much as possible.

1. The first is regular exercise, ideally low-impact. Walking, swimming, recumbent bicycle, and yoga are good ideas overall. These activities will increase circulation to your spine and improve nutrient supply to your discs and other spinal structures. In my opinion, if you have any issues with your discs, I recommend staying away from too much running and jumping, as they are high-impact activities, and as I explained earlier, the discs are shock absorbers, and so these activities can put a lot of excess stress on the discs.

2. The second is to maintain a healthy weight. It is just logical common sense that excessive weight from obesity will place a lot of unnecessary chronic load on the discs and is just not healthy for them, especially over the long term.

3. The third is to stay hydrated. As we discussed earlier, the discs are composed of mostly water, especially in the nucleus pulposus. Thus, if your discs are well hydrated, they’re going to be able to perform their function as shock absorbers much more effectively and easily.

4. The fourth is to maintain good posture and ergonomics as much as possible, which will reduce the repetitive stress and strain on your discs and other spinal structures overall.

5. The fifth is to quit smoking. In general, smoking tends to worsen neck and back pain because it reduces the blood flow to the spine, and also there are a number of toxins in cigarette smoke that can adversely affect the discs and other spinal structures.

6. Lastly, there is also a limited degree of evidence that supplementation with vitamin C and glucosamine can be beneficial for your discs as well. Vitamin C is essential for the synthesis of collagen, and glucosamine is a component of cartilage, so it makes logical sense why they could potentially help. In addition, since Vitamin C is also a powerful antioxidant in addition to its role as a cofactor for collagen production, it also has an anti-inflammatory effect. Interestinly, a review article by Carr and McCall actually covered multiple studies that showed that vitamin C had benefit for spinal pain in general, not just for the discs. Of course, while these supplements can potentially provide modest benefit, they aren’t going to necessarily make or break anything, but if you are someone who is interested in complementary and holistic medicine, these two supplements are definitely two that you can look into and talk to your doctor about.

So that should really cover all of the essentials that you need to know about your intervertebral discs. I hope you found the video valuable, and if there are any topics within this video that you want me to go into further depth on in a future video, please let me know in the comments below. Thanks for watching everyone.

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