By Jonathan Chu, MD
Interventional Pain Medicine
PM&R

If you clicked on this video, you’ve probably been experiencing some low back and neck pain, and when you went to see your doctor, they may have thrown around a lot of terms you’re just not familiar with, like herniated disc, pinched nerve, foraminal stenosis, and the like.

Thus, in this video, I’m going to go over the entire anatomy of your spine in a comprehensive, yet easily understandable fashion, so that you can learn exactly how your spine works, what all those terms on your MRI mean, and what is happening in your spine that is causing you so much pain. Think of it as a free masterclass taught by an interventional pain doctor, intended for an audience of ordinary people just like you.

Now the spine is a very complex structure with lots of parts, both superficial and deep, including bones, ligaments, nerves, and surrounding muscles, so let’s start deep, and then work our way outward.

The easiest place to start would be the bones of the spine, which are known as vertebrae, and in many ways they can be thought of as the fundamental structural unit of the spine.

The human spine consists of 33 of these vertebrae, and they serve to give the spine a bony structure, which allows you to stand upright, and they also help to encase and protect the spinal cord.

The vertebrae look like this. Let’s go through the important parts.

The largest part of this bone, is known as the vertebral body, in the front of the spine. These are the parts that stack up on top of each other, and are thus responsible for much of the load bearing of the spine, along with discs, which I will talk about later.

Now, another important part of the vertebra is the lamina, which is the arch of bone in the back. This arch wraps around the back of the spine, and thus helps to protect the spinal cord from the back.

Another important part of the vertebrae is known as the pedicle. These are a pair of bony bridges that connect the vertebral body in the front, to the lamina arch in the back.

Now it’s important that these three bony structures, the vertebral body, the pedicles, and the lamina, form a protective ring that wraps around and protects the spinal cord at every single level.

The best way to visualize the relationship between the vertebral body, the pedicle, and the lamina, is to look at the whole thing from a top-down view.

Here you can see how the large bony vertebral body is in the front, the pedicles form the sides, and the bony arch of the lamina is in the back, and then in between is the large hole for the spinal cord, which is called the vertebral foramen.

Collectively, the vertebral foramen of multiple vertebrae form what is known as the central canal, or more commonly, the spinal canal. This is extremely important, because the spinal cord runs down through the spinal canal along the entire spine.

It’s also important to note that the spinal cord actually transitions into becoming a bundle of nerves at the upper region of the lumbar spine. This bundle of nerves is known as the cauda equina, and this literally translates to “horse's tail,” in Latin, because that’s what this bundle of nerves looks like, and these nerves of the cauda equina supply your legs and pelvic muscles.

Now this is where I’m going to tie in an important clinical correlation. Many of you may have heard of the term lumbar stenosis, and some of you may even be suffering from it, since it is an extremely common condition.

Lumbar refers to the lower back or the lower spine, and stenosis means narrowing. So lumbar stenosis refers to when there is a narrowing of the central canal, aka spinal canal, at one or more levels in the lower spine. Oftentimes when this happens, the radiologist will comment on this and note the severity of the narrowing on his or her report.

This often occurs when there is degeneration of the spine and subsequent thickening of ligaments or bony structures, or there are bulges of the cartilage discs into the spinal canal. This narrowing can potentially cause pinching, irritation, and inflammation of the spinal cord or the nerves of the cauda equina, and thus can cause a lot of problems in terms of both pain and difficulty walking.

Now, it is important to note that if this narrowing suddenly becomes very severe, it can cause a rare, but very serious condition known as cauda equina syndrome. The most important symptoms associated with cauda equina syndrome are loss of bowel and bladder control and numbness in the private areas, and thus, if you do experience those symptoms, it’s something you should call your doctor about right away, or go to the ER if your doctor is not available.

Now, let’s go back to talking about the vertebral bone. The next part of the bone I’m going to mention are the articular processes, which are these small bony protrusions that come off of the pedicle and lamina, both above and below. These bony prominences actually come together and form something known as the facet joints between the vertebrae.

These facet joints are small synovial joints, and they are very important because they are one of the most common causes of back and neck pain. I have a detailed video about facet joint pain that I’ve done earlier on my channel, and I plan to do more in the future since the facet joints are just such a common cause of pain for so many people.

Now the last part of the vertebrae I’m going to talk about is the spinous process. This is a sharp bony protrusion that comes directly off the back of the lamina. Now when you touch, or palpate, your back, the row of bony prominences you feel is actually these spinous processes. One of the most famous and useful anatomical landmarks is the C7 spinous process, which is the spinous process that comes off the lowest vertebrae of your neck, and you usually can feel it quite prominently at the base of your neck.

Now it is important to note almost all of your vertebrae, whether in your neck or low back, have the same basic structure and parts that I discussed earlier. However, the vertebrae do have a slightly different shape depending on the region of your body, and obviously they will have different sizes as well.

The vertebrae in your neck are known as the cervical vertebrae, and these are the smallest in size. The vertebrae in your upper back are called the thoracic vertebrae, and these have a special shape that allows them to connect to your ribs. The vertebrae of your lower back are known as the lumbar vertebrae, and are much larger than your cervical vertebrae since they have to bear the load of your entire upper body.

Now, there are a few exceptions to all of your vertebrae looking similar in shape, and those would be the bones of your tailbone, which are the sacrum, and coccyx. These look very different and funny because they are fused vertebrae, the sacrum having 5 fused vertebrae, and the coccyx having 4. These really aren’t that pertinent to this video, so I’m not going to go into more detail for now, but will describe these a lot more in future videos about sacroiliac joint pain and coccydynia, or tailbone pain.

Now, that was a lot of information, but that covers all of the most important foundational knowledge regarding the vertebrae of your spine, which really are the fundamental bony building blocks of your spine.

Now, the next really important structure that I want to talk about is your intervertebral discs. You’ve probably heard the term a lot, since they are implicated in a lot of different painful conditions of the spine.

As with most medical terms, the name itself actually reveals a lot of information in itself.

Intervertebral means, between two vertebrae, and disc refers to its shape. Thus, the intervertebral discs are oval-shaped pads of cartilage that are located between the vertebral bodies. In many ways they are similar to car tires, and act as shock absorbing cushions, and also allow for your spine to bend and twist.

The outside of your discs are made of tough fibrocartilage and is known as the annulus fibrosis. The inner part of the disc is known as the nucleus pulposus, and is filled with a mucoprotein gel that is composed of loose collagen fibers, proteoglycans, and water.

Now it is important to note that because the disc is primarily made out of cartilage, it really doesn’t have a direct blood supply. Thus, the disc has to receive its nutrition via osmosis from the neighboring vertebrae, since bones have very good blood supply. The fact that the discs lack a good blood supply is one of the big reasons why it can be more difficult to heal from disc injuries, especially when compared to injuries of other areas of the body.

Now, let’s take a look at another really important anatomical relationship, which is how the disc and vertebrae together form the small holes that allow the spinal nerves to exit, and then go on to supply your arms and legs. These small holes are known as intervertebral foramen, or alternatively, neural foramen. The best way to view this foramen is from the side view, where you get a really good view of how the front of the hole is formed by the disc and vertebral bone, the top and bottom are formed by the pedicles, and the back is formed by the facet joint.

It is also very important to note that the intervertebral discs, when injured, can bulge out backwards, and then pinch and irritate the spinal nerves as they come out the intervertebral foramen. They can also bulge out directly backwards and irritate the spinal cord or the cauda equina nerves directly in the central canal. I’m sure that a lot of you have heard the term bulging disc or herniated disc from your imaging reports, and that’s what this is referring to.

When the disc bulges, or herniates backwards severely enough to cause significant nerve pinching and symptoms that shoot down the arms or legs, this is known by the medical term, radiculopathy. The word element radicular means, pertaining to the spinal nerve root. The word element pathy, is of Greek origin, and means abnormal condition or disease. Thus, radiculopathy means an abnormal condition of the spinal nerve root. Another popular term for this type of pain is sciatica, which is very widely known among the general population, though that term is a little less specific and less accurate, since it is actually the small nerve roots that contribute the sciatic nerve being affected, and not the actual large sciatic nerve in your leg.

Now, another really important clinical correlation is one of the main interventional treatments for pain, which is the transforaminal epidural steroid injection. This is one of the most common procedures utilized to treat lumbar radiculopathy, or painful pinched nerves in the lower spine. In this procedure, your pain doctor will actually use X-ray guidance to drive a spinal needle into the small spot right at the very top of the intervertebral foramen, just above the spinal nerve that is being pinched and irritated. Your doctor can then inject a small amount of steroid and local anesthetic medication, which will help to decrease the inflammation in the area, and hopefully provide you with a few months of good pain relief, which will give you an opportunity to rebuild your strength and mobility in physical therapy.

Now, so far we’ve talked about the bones, the discs, and the nerves, so next let’s zoom a little bit outwards and talk about the muscles.

There are actually multiple layers of muscles that surround the spine and allow you to maintain an upright posture. These muscles are extremely important, and one of the main goals of physical therapy and rehabilitation is to strengthen these muscles, especially the smaller muscles in the deeper layers, which will help to provide better support and protection for your spine to prevent future injuries.

One of the very important deep muscles in your low back is known as the multifidus muscle, which you may have heard your physical therapist talk about. However, though the multifidus is an extremely vital muscle, there are many other important muscles throughout the spine, such as the erector spinae, the quadratus lumborum, and the trapezius, just to name a few. These muscles provide vital support for your spine and not only allow you to maintain a good posture, but also act as a kind of scaffolding to protect your spine from injury. In the future, I will be doing some more videos that go a lot more in depth into these muscles, their function, and their clinical significance.

Now, the very last thing I want to talk about are the natural curves of the spine.

These are, the cervical lordosis, the thoracic kyphosis, the lumbar lordosis, and the sacral kyphosis. Now, this may not mean a lot to you, so let me explain.

Lordosis means swayback posture, or a backwards bend.

Kyphosis refers to a forward bend.

So you see, it’s actually quite simple. Cervical lordosis and lumbar lordosis simply refers to the normal backwards curve in both the neck and low back, under healthy and normal conditions.

All 4 of these curves in your spine allow your spine to serve as a kind of shock absorber, and also help you maintain a natural and pain-free posture.

It can be quite common when someone is having a severe pain flare-up that the muscles get locked into spasms, and thus some of this natural curvature is temporarily lost, and the spine is less effective at absorbing shock during that time.

Also, unfortunately in this modern era, with so much excessive use of electronic devices, people often spend many hours each day in terribly unnatural postures in which these natural curves are lost. As a result, a lot of excess repetitive and unnatural stresses are placed on the spine, which can obviously lead to developing pain conditions in the long term.

Obviously, I could go into much more detail, but I also don’t want to overload you with information. This video was designed to give you a strong overview of the spine and provide you with the most important fundamental information that most patients will find useful and applicable to their own conditions. Hopefully, you found the video valuable, and I’ll see in future videos when I go into more detail about the specific parts of the spine and musculoskeletal system, as well as the conditions that can affect them. Thanks for watching and take care until the next video.

References:

Benzon, H. T., et al. (2018). Essentials of pain medicine (4th ed.). Elsevier.

Braddom, R. L. (Ed.). (2010). Physical medicine and rehabilitation (4th ed.). Saunders/Elsevier.

Cuccurullo, S. J. (2004). Physical medicine and rehabilitation board review. Demos Medical Publishing.

Netter, F. H. (2006). Atlas of human anatomy (4th ed.). Saunders/Elsevier.