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Bones, ligaments and joints of the thoracic and lumbar spines.
Hello everyone! This is Joao from Kenhub. Welcome to another tutorial. This time, I'm going to be talking about the thoracic vertebrae and comparing them to the lumbar vertebrae.
Now, keep in mind that these are bones that you find on the different portions of the vertebral column known as spines, and these spines are known as the thoracic spine as, of course, where you’re going to be finding the thoracic vertebrae and the lumbar spine where you’re going to be finding the lumbar vertebrae.
Now, let’s briefly talk about the thoracic spine. This is where you’re going to be finding twelve thoracic vertebrae. And these vertebrae, as you can see here on this image clearly, are articulating with twelve pairs of ribs. So this is right on the dorsal portion of your body, and the thorax or the thoracic cage being formed here by the backbone, of course, the thoracic vertebrae, and the ribs. Now, this region of the spine is slightly more rigid and less flexible than the cervical region or the cervical vertebrae right on your neck, right here, if we could show it right on this image.
And knowing that, we’re going to move on to the lumbar spine a little bit further down, as you can see here on this portion. And now zoomed in, you can see that there are five lumbar vertebrae, and these are comparatively larger than the other vertebrae, the cervical and the thoracic vertebrae, because these vertebrae are bearing all the weight. As you can see here, they’re bearing a lot of weight, so they need to be large, of course. Now, they’re fairly mobile but not too much, just enough to produce movement within the spine, the vertebral column, but not as nearly as mobile as the cervical spine, of course.
You have a lot more movement within your neck than the lower portion of your back.
As I quickly describe where you can find lumbar and thoracic vertebrae, now, we’re going to move on and talk about the topics—so I'm going to introduce you to the topics that we’re going to be covering throughout this tutorial, the specific topics. And the first one is the bony structures. So we’re going to look at the different types of bony structures that you find between the thoracic and lumbar vertebrae and, of course, compare them.
The second topic and this is a brief introduction to intervertebral discs that we’re going to be doing here, this, let’s say, the second part of this tutorial, because later on, I want to do a tutorial where I specifically cover this topic in a lot more detail. Now, the last portion of this tutorial will be dedicated to ligaments and joints that you find throughout thoracic vertebrae and also lumbar vertebrae. Now, just a few of them because there are a few more that we need to discuss, but this is going to also be done in a separate tutorial.
Now, let’s move on to the very first topic here on our list: the bony structures of the thoracic lumbar vertebrae. And the first one that we’re going to be discussing is the largest portion of the vertebra. This is known as the body of the vertebra. Now, keep in mind I'm going to be doing this throughout this tutorial, is a comparison between thoracic and lumbar vertebrae. And here on your left, you have a thoracic vertebra, and here, actually two lumbar vertebrae—now, actually, two bodies clearly highlighted here in green of lumbar vertebrae. Now, keep in mind and as I mentioned, this is a body, so this is the largest portion of the vertebra. And this is going to be used as a major supportive portion of this bone. So this is where the all the weight is going to beared upon, and this is, of course, a large portion of the vertebra.
Now, keep in mind, as humans, we adopted, through evolution, an upright position or posture. And for that reason, as you move towards the sacrum, so as you’re removing from the cervical spine all the way down to the lumbar spine, you can notice that the bodies of these vertebrae are going to start increasing towards the sacrum—so towards the lumbar spine. Why? Because if you notice, the lumbar spine is carrying a lot more weight than, for example, the cervical spine. And for that reason, the bodies need to be way larger, and you can clearly see here that the thoracic body here is slightly smaller than, for example, a lumbar body. For that reason, one of the characteristics is saying that the thoracic body is medium-sized. And you can notice here that it has a slight shape of a heart, slightly shaped as a heart. And here, the lumbar body is, of course, larger than the thoracic body and slightly shaped as a kidney. So these are characteristics that distinguish these bodies of these vertebrae.
Moving on to the second bony structure, this is known as the vertebral arch. And the vertebral arch is, of course, as the name indicates, is an arch that you find within the vertebra. And I'm showing you right here with the mouse cursor, as you can see, and this is where you should find the arch. Now, the arch is formed by two structures, the pedicles and laminae, which are two other bony structures that we’re going to talk about right now.
Now, the first one is known as the pedicle, so the pedicles or each vertebrae has two pedicles that arise posterior laterally from the vertebral body, as you can see here on these two examples. These are the pedicles. Now, they form the side of the arch, which consists of a pair of pedicles. And one important thing about the lumbar pedicles is that they are strong and directed posteriorly.
Now, in terms of the laminae, these or the lamina of the vertebral arch, these are supported by the pedicles, and they fuse in the midline to form the roof of the vertebral arch. Now, the lumbar laminae are thick—one important distinction between these laminae and also those that you find within the thoracic vertebrae.
Now, I want to distinguish a few bony structures known as vertebral processes because these are quite common and quite distinguishable within vertebrae, and these, of course, are the vertebral processes. Now, there are five that we’re going to distinguish, five types specifically. And within those five types, we’re going to find two types of articular facets—so places within these processes that are going to be used for articulation either with other vertebrae or with other bones.
Now, let’s start with the very first process, and this is known as the spinous process. And it is, or starts from the vertebral arch where the laminae fuse right on this circle. Here, this is where the laminae are fusing and, of course, this is where this process starts. And it serves as an attachment point for vertebral musculature and also ligaments. Now, in terms of the thoracic spinous processes, they are long and they are inclined slightly downward. They’re quite inclined when compared, for example, with the lumbar spinous processes that are short, as you can see here, slightly flat and also quadrangular. And they are projected slightly backward but not as projected downward as you see, for example, the thoracic spinous processes.
Moving on to the second on our list of processes, this is known as the transverse process. And I'm using here a thoracic vertebrae to exemplify this type of process. And as you can see, it is starting on each side of the vertebral arch where the pedicles and laminae fuse, right about here. Now and as you can see here, there are two, two transverse processes on this thoracic vertebra, and they’re also used as attachment points for the vertebral musculature and ligaments. One important point to add here on transverse processes is that T1 and T10 have costal facets, which articulate with the tubercles of the ribs 1 to 10. As you can see here on this image, the transverse process or the transverse processes here are articulating with the tubercles of the ribs.
Moving on to the other type of processes, this is known as the costal process. And this is an alternative name that we use to the transverse processes of the lumbar vertebrae. So just what we saw on the previous slide, but this time applied to lumbar vertebrae. They start on each side of the vertebral body, anterior to the pedicle, as you can see here clearly on this image. And as you can also notice, they’re quite long and slender. Important, important notice, I cannot say how or highlight how important this is that the lumbar vertebrae have no facets for articulation with the ribs. For that reason, these processes are free of any articulation points or facets to be used with the ribs. Different than what we saw on the previous slide, of course, with the transverse processes of thoracic vertebrae.
Moving on to the other type of processes, this is known as the superior articular process, and it is located on the superior surface of the pedicles as you can see here both on the thoracic and also here on the lumbar vertebrae which is, on this cases, we’re looking at this cranially, and here, laterally. And what happens here is that these structures are forming diarthrodial joints with the inferior articular processes of the vertebra immediately above. So we’re also going to talk about other processes which are the inferior articular processes that are forming joints with the superior articular processes of the vertebrae.
Now, important thing to mention is that the thoracic vertebrae have these processes facing posterior medially, while the lumbar vertebrae have them facing medially, as you can see here clearly on these images.
Contained within the superior articular processes, there are other structures that we’re going to talk about known as superior articular facets. Now, these are portions of these processes that are used for articulation with other vertebrae. Now, as you can see here, both on the thoracic vertebrae and the lumbar vertebrae, there are two superior articular facets that are contained within the superior articular processes. Now, one important thing to mention is that on the thoracic vertebrae, these facets are facing backward and laterally, while on the lumbar vertebrae, they’re facing medially just like the processes that we saw on the previous slide.
Moving on and talking about another process, another type of process, this is known as the inferior articular process. As we talked about a superior one, there has to be, of course, an inferior articular process that will, of course, articulate with the superior one. Now, the inferior articular process, as you notice here, is originating here from the inferior surface of the pedicles. And they form diarthrodial articulations or joints with the superior articular processes of the vertebra that you find immediately below.
Now, in terms of the thoracic vertebrae, these processes are facing anterolaterally, but there is an exception, keep that in mind, that the inferior articular processes of the twelfth vertebra face laterally as those that you find on the lumbar vertebrae, they also face laterally. But as well, there has to be an exception, and this exception is on the fifth vertebra. So the fifth vertebra, or the processes, or the inferior articular processes of the fifth lumbar vertebra actually face anteriorly. Also, contained within the inferior articular processes, there are other structures known as the inferior articular facets. Now, on the thoracic vertebrae, they are facing forward and medially, while on the lumbar vertebrae, these structures are facing laterally.
Now, still on the topic of bony structures, we’re going to move on and talk about what I would call a subtopic which is known as vertebral foramina. Now, there are two types that we need to distinguish: vertebral and intervertebral. Well, this is quite a tongue twister for myself as English is my second language. But moving on to the very first one on this list is the vertebral foramen. Now, this is formed by the surface of the body right here and also the arch of the vertebra, both on the thoracic and the lumbar vertebrae. And this structure, this is where the spinal cord and nerve roots will pass through. So this is a very important structure within the vertebral column.
Now, in terms, how do we distinguish these two foramina, these two types of foramina between these two types of vertebrae? Now, if you look here at the thoracic vertebra, it is slightly circular and smaller than the one you find here on the lumbar vertebrae which has a triangular shape. So this is how we distinguish the foramina on these two types of vertebrae.
Now, let’s move on and talk about the intervertebral foramen, and as the name indicates, this is a foramen that is being formed between two vertebrae. And as you can see, it is formed by this notch here that is formed on the inferior side of this pedicle here of this vertebra, and also, this shallow notch right here on a superior surface of the pedicle of this vertebra that is located right below this top one here. So this is how the intervertebral foramen is formed, and it serves as a passage for the spinal nerves and also the intervertebral arteries which supply the roots and the spinal cord.
Still on the topic of bony structures, we are going to cover now another subtopic known as costal articular surfaces. Now, keep in mind that I mentioned before that ribs only articulate with thoracic vertebrae.
Now, we’re only going to talk about costal articular surfaces on, of course, thoracic vertebrae. And there are three that we need to distinguish. The first two are seen here. On your left, you have here the superior costal fovea or facet. And on your right, you have the inferior costal facet. Now, these articulate with the heads of the ribs, and if I show you here on the lateral view, you can see clearly now the superior costal facet and also, here, the inferior costal facet. And keep in mind that, now, as you see them separately, they are called demifacets meaning their half, because they’re only going to become a full articular surface when these two vertebrae come together, articulate, and the superior and inferior costal facets come together to form a full articulating surface that will articulate with the head of a certain rib.
Now, moving on to another type of costal articular surface that is known as the costal fovea or costal facet of the transverse process that we talked about previously when we mentioned or we highlighted the transverse processes of the vertebrae. And it is found, of course, this articular surface is found in the transverse process and articulates with the tubercle of the ribs. Now, T11 and T12 have no articular facets on their transverse processes. That’s an important thing. And also, I want to use this image here to show you that, here, highlighted in green, this is the costal facet here of the transverse process, right here, that is articulating with the tubercle of this rib right here. Now, a bit over here, you can see that there is another articulation with the head of the rib and the superior costal fovea or facet of the vertebra.
Now, that we just talked about the different bony structures that we find within the thoracic and lumbar vertebrae, it is time for us to do a brief introduction into the intervertebral discs. Now, these are the structures that you see here highlighted in green that lie just between adjacent vertebrae. They are fibrocartilaginous structures—important to mention. And they allow slight movement of the vertebrae and acts kind of like a ligament which holds them together. They are thicker around the thoracic and lumbar regions—very important thing to add.
Now, let’s talk about a few structures that we find within an intervertebral disc. The first one is this here that you find surrounding the disc, which is known as the fibrous ring of the intervertebral disc also known annulus fibrosus. You can also say it in English, the Latin name. And each intervertebral cartilage is comprised at its circumference of a laminae, let’s say, of fibrous tissue and also fibrocartilage. And this is what is known as the annulus fibrosus. And as you can also see here on this image, this forms what is known as multiple layers and reminds us of something that is found in your kitchen: an onion. So every time you see an annulus fibrosus, think about an onion. Maybe you can find a mnemonic that easily associate or relate the two terms. Now, another structure that you will find within an intervertebral disc is this central portion here that is known as the nucleus pulposus. And it’s supported by the annulus fibrosus, so it is surrounded by the annulus fibrosus, and it’s a jelly-like substance and it’s remnant of the notochord. It’s just a little bit of an embryology note here on this topic.
Now let’s move on and talk about the last topic on our list, the ligaments and joints. And keep in mind that I'm just going to briefly go over them because we can go into so much more detail. Now, the first one is a joint. And this joint is known as the zygapophyseal joint, also known as the vertebral arch joint, and these are synovial joints that exist between the articular processes—this superior, as you can see here, and inferior articular processes of, in this case, lumbar vertebrae. And they are defined by their joint capsule which will become tenser as we move on on a cranial caudal direction.
Now, talking about ligaments, this is a group of ligaments known as the intertransverse ligaments. They are short ligaments that exist between the transverse processes.
Now, the next ligament is quite a unique one and is known as the yellow ligament or ligamentum flavum. And it extends segmentally between the vertebral arches, borders the medial and dorsal sides of the intervertebral foramina, and its yellow color is due to the interrupted lattice work arrangement of elastic fibers which form most of the bends, and you can clearly see here on these two images.
The next ligament is the interspinous ligament, also a group of ligaments that you can find throughout the vertebral column. They are also short ligaments which extend between the spinal processes.
Another two ligaments here side-by-side, they are known as the anterior longitudinal ligament here on the left, and on your right, you find the posterior longitudinal ligament. They are ligaments that run on the anterior or posterior to the vertebral bodies. You can also see here different perspectives where you can clearly see them running through or over the vertebral bodies.
The last ligament of this tutorial is known as the supraspinous ligament which begins on the spinal process of the seventh cervical vertebra and extends as far as the sacrum. This ligament is very good because it provides continuous connection between the vertebrae and the sacrum.