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Bones, ligaments and joints of the thoracic and lumbar spines.
So, I’m guessing we all remember the charming Quasimodo from our childhood spent engrossed in Disney films. He was the Hunchback of Notre Dame, after all. But it’s probably only recently since you started learning human anatomy that you’re wondering exactly what causes the likes of a hunchback. Hyperkyphosis is a condition in which the thoracic spine is more curved than normal causing the back to appear rounded and hunched and as well as causing a hunchback like we see in Quasimodo. It can also cause back pain, stiffness, and fatigue.
In today’s tutorial, we’re going to be talking about the building blocks of the thoracic and lumbar spines – the thoracic and lumbar vertebrae. Before we start talking about the thoracic and lumbar vertebrae, let me first introduce you to the vertebral column.
The vertebral column which we can see here from a posterior perspective then highlighted in green, is commonly known as the spine or the backbone. It’s made up of five regions – the cervical region, the thoracic region, the lumbar region, the sacral region, and the coccygeal region – and as I said, today we’ll be focusing on the thoracic and lumbar regions.
The thoracic spine is made up of twelve thoracic vertebrae and its main function is to provide stability. Unlike other sections of the vertebral column, the thoracic vertebrae articulates with the ribs to form a strong bony enclosure called the thoracic cage which houses and protects vital organs such as the heart and lungs. In terms of mobility, the thoracic spine assists with the rotation of the vertebral column.
Moving further down the vertebral column, we can see the lumbar spine. The lumbar spine consists of five lumbar vertebrae which are the largest vertebrae of the spine due to the fact that they support the weight of the upper body. The lumbar spine is more mobile than the thoracic spine and is responsible for movements including flexion, extension, lateral flexion and some rotation.
Alright now that we’re familiar with the vertebral column and the regions we’re going to be talking about, let me give you a quick overview of what we’re going to be talking about today in our tutorial. So, first, we’re going to be looking at the bony landmarks of the thoracic and lumbar vertebrae comparing them with one another. Next, we’ll talk about the intervertebral discs which are found between the vertebrae and we’ll then move on to talk about some joints and ligaments found in the thoracic and lumbar regions of the spine. And, finally, we’ll discuss some clinical notes relevant to the thoracic and lumbar spines.
So let’s get started with our first topic – the bony structures of the thoracic and lumbar vertebrae.
Before we start with our first bony landmark, I want to mention that when I describe these vertebrae, I’m focusing specifically on their typical structure. However, when there is a transition between regions of the spine, this is reflected in the morphology of the vertebrae. For example, T1 has some features similar to those seen in the cervical spine as well as the lower thoracic vertebrae, and the lower thoracic vertebrae starts to adopt features found in the lumbar spine.
So we’re going to begin with the largest portion of the vertebra which is the body of the vertebra, and here we have a superior view of both a thoracic vertebra and a lumbar vertebra. And both of their bodies are highlighted in green. So, the vertebral body is the weightbearing portion of the vertebra, and as we move down the spine, the weight supported by these bodies increases, therefore, their size also increases, and we can see this nicely in our image here which shows a lateral view of the spine.
If we look at our thoracic vertebra more closely, we can see that the body is roughly heart-shaped, and when compared with the smaller cervical vertebrae above and the larger lumbar vertebrae below, we can definitely say that the bodies of the thoracic vertebrae are medium-sized.
Okay, let’s have a look at our lumbar vertebra now and we can see that our lumbar vertebra is kidney-shaped and quite large, and these characteristics allow us to distinguish between thoracic and lumbar vertebrae.
So while we’re talking about the vertebral bodies, let’s mention some facets that are found on the bodies of the thoracic vertebrae. So, first, we have the superior costal facet or fovea which we can see here from a lateral perspective highlighted in green, and below it we have the inferior costal facet. And note that these are bilateral structures found on both sides of the vertebra and that they’re exclusive to the thoracic vertebrae.
Individually, these structures are called demifacets, meaning that they form half of the articular surface, but when a superior costal facet comes together with an inferior costal facet, they form a full articular surface which articulates with the head of a rib. And we can see this best when we look at several vertebrae. So, over here, we can see a superior costal facet which comes together with the inferior costal facet of the vertebra above to articulate with the head of a rib.
It’s worth noting here that T1 has a full superior costal facet which articulates with the head of the first rib, and that the vertebrae T10 to T12 only possess a full articular facet on either side of their bodies. They don’t have demifacets.
The next bony structure we’re going to be talking about is the vertebral arch, and we can see it highlighted in green on our thoracic vertebra here, and on our lumbar vertebra over here. The vertebral arch is formed by two structures – the pedicles and the laminae – and I’m going to show you these now.
So here we can see the pedicles and each vertebra has two pedicles which form the walls of the vertebral arch. Next, we have the laminae, and again each vertebra has two laminae and they fuse in the midline to form the roof of the vertebral arch. The vertebral body and the vertebral arch enclose a space which is called the vertebral foramen, and the vertebral foramen houses and protects the spinal cord and can be used to distinguish between the thoracic and lumbar vertebrae.
If we look at our thoracic vertebra a little bit closer, we can see that its vertebral foramen is small and circular whereas the vertebral foramen of our lumbar vertebra is larger and triangular. So while we’re on the topic of the foramina, let’s have a look at the intervertebral foramen.
So here we can see the intervertebral foramen of the two lumbar vertebrae highlighted in green from a lateral perspective and we’ll just look at this structure on the lumbar vertebrae as this is not a feature that is used to distinguish between the thoracic and lumbar vertebrae. So, as the name indicates, the intervertebral foramen is a foramen that is formed between two vertebrae and the cervical and the thoracic vertebrae have them too. It’s formed by the inferior vertebral notch of a superior vertebra and the superior vertebral notch of an inferior vertebra. Hence, notes that the intervertebral foramen is a bilateral structure found on both sides of the vertebral column and the intervertebral foramina transmits the spinal nerves.
Now let’s have a bit of a chat about the vertebral processes of the thoracic and the lumbar vertebrae. So, generally all vertebrae have a spinous process, two transverse processes and four articular processes, and you’ve probably noticed that we can only see two articular processes in this image. This is because there are two superior articular processes and two inferior ones. And in this illustration, we’re viewing an isolated thoracic vertebra from above so we can see the two superior articular processes.
Okay, so let’s have a look at these processes in a little bit more detail. So, the first process we’re going to be talking about is the spinous process. And the spinous process serves as an attachment point for the interspinous and supraspinous ligaments which we’ll talk about later on in our tutorial. And this is another feature that can be used to distinguish between thoracic and lumbar vertebrae.
On our thoracic vertebra, we can see that its spinous process is long and slender and we can also see that it is angled sharply downwards which serves as protection for the spinal cord. Whereas, the lumbar vertebra has a large flat and quadrangular spinous process.
Okay, let’s move on to our next process which is the transverse process. And on this image, I’ve highlighted this structure in green on our thoracic vertebra and you’ll see why when we move on to our next key term. And as you can see, this is a bilateral structure located on both sides of the vertebra and are used as attachment points for the intertransverse ligaments.
One important point to mention here is that the transverse processes of the first 10 thoracic vertebrae T1 to T10 possess costal facets or fovea, one of which is highlighted in green on our image. And as you can see in the following illustration, the costal facets of the transverse processes articulates with the tubercles of the ribs one to ten.
Now, the lumbar vertebrae also possess transverse processes but instead they’re called costal processes, and again, this is a bilateral structure and serves as attachment points for the intertransverse ligaments. However, unlike the thoracic vertebrae, these processes do not have any articular surfaces.
The next process we’re going to be talking about is the superior articular process, which we can now see highlighted in green on both our thoracic and lumbar vertebrae. The superior articular processes articulates with the inferior articular processes of the vertebra directly above and they do this by their superior articular facets which we can now see highlighted in green.
if we look at our thoracic vertebra more closely, we can see that its superior articular facets are flat and they face posteriorly whereas the lumbar vertebra has superior articular facets that are concave and face posteromedially, and it’s important to understand that the orientation of the articular facets is different between the vertebrae types as this is reflected in their range of movement.
While we’re here, let me mention a structure unique to the lumbar vertebrae which is the mammillary process. And the mammillary process is a small round elevation found on the posterior aspect of the superior articular process and is a site of muscle attachment.
Okay, now onto the inferior articular process. So each vertebra possesses two inferior articular processes which articulate with the superior articular processes of the vertebra below via their inferior articular facets. And let’s look at the inferior articular facets in a little bit more detail. So if we zoom into our thoracic vertebra, we can just about see that its inferior articular facets are flat and they face anteriorly, whereas the lumbar vertebra has inferior articular facets that are convex and they face anterolaterally.
Okay, now that we’ve covered the bony structures of the thoracic and lumbar vertebrae, you should be able to tell the difference between them. Let’s move on now to the intervertebral discs.
So, the intervertebral disc is this structure you can see highlighted in green sandwiched between the two adjacent vertebrae, and these discs make up one-third to one-quarter of the length of the vertebral column as they’re found interposed between adjacent vertebrae from the axis or C2 to the sacrum.
Let’s talk a little bit about the function of these discs. The intervertebral discs contribute to fibrocartilaginous joints which allows slight movement of the vertebral column hence they act as ligaments that holds the vertebrae together. The discs also act as fibrocartilaginous cushions serving as the spine’s shock absorbing system. This cushions the effect of shock and stress produced when an individual walks, runs, bends or twists. And, finally, the intervertebral discs reduce friction between moving vertebrae by preventing vertebral bodies from grinding against one another.
So while we’re here, let’s mention the vertebral endplates, and these are thin cartilaginous interfaces found between the intervertebral discs and the vertebrae above and below. If we look at an intervertebral disc from a superior perspective, we can see that it covers the entire intervertebral surface of the vertebral body. And each disc is made up of two parts – the anulus fibrosus and the nucleus pulposus. And let’s go on to talk about these structures in a little bit more detail.
The anulus fibrosus is the outer fibrous ring of the intervertebral disc that we can now see highlighted in green. It’s made up of a series of fifteen to twenty five concentric layers or lamellae with collagen fibers lying parallel within each lamella. Elastin fibers lie between the lamellae possibly helping the disc to return to its original arrangement following flexion or extension, and the annulus fibrosus is relatively stiff providing strength and withstanding compressive forces.
And I don’t know about you, but its layered appearance reminds me somewhat of an onion or maybe the annual growth rings of a tree.
Anyway, let’s get back to the anatomy. So, the inner core of the intervertebral disc is known as the nucleus pulposus. The nucleus pulposus contains collagen fibers which are organized randomly and elastin fibers which are arranged radially, and these fibers are embedded in a highly hydrated gel which is rich with a unique proteoglycan known as aggrecan, and this gives it a jelly-like consistency. Which begs the question, why does human anatomy always remind me of food?
It’s worth noting that the intervertebral discs are thinnest in the upper thoracic region and that generally the thoracic discs are the same width throughout, whereas in the cervical and lumbar regions, the intervertebral discs are thicker anteriorly which contributes to the normal cervical and lumbar lordosis or curvatures. And we can see this particularly well in the lumbar region.
Okay, after that brief introduction to the intervertebral discs, let’s talk about some joints and ligaments which are found in the thoracic and lumbar regions of the spine. And we’re going to begin with talking about some joints, starting with the zygapophyseal joint. And the zygapophyseal joint is also known as the facet joint and it’s a synovial plane joint. These joints are found between the articular processes of adjacent vertebrae. More specifically, they are found between the superior articular processes of one vertebra and the inferior articular processes of the vertebra above it. And these joints are defined by their joint capsule which is conveniently known as the articular capsule of the zygapophyseal joint.
The last joint I’d like to talk to you about are the costovertebral joints, and these are synovial plane joints that connects the ribs to the vertebrae, therefore, they are only found in the thoracic region of the spine and as I’ve already mentioned, the vertebrae articulates with the ribs in two places – at the head of the rib and at the tubercle of the rib. It’s worth noting here that the intervertebral discs are also joints of the thoracic and lumbar spines and they are known as intervertebral symphyseal joints.
Alright, let’s talk now about the ligaments, and we’re going to focus on ligaments that are found throughout the vertebral column starting with the anterior longitudinal ligament.
As you can see, this ligament runs along the anterior surface of the vertebral bodies and it extends the length of the vertebral column and of course if you have an anterior longitudinal ligament then you must also have a posterior longitudinal ligament. And like its buddy, this ligament runs the length of the vertebral column but instead of running along the anterior surface, it runs along the posterior surface of the vertebral bodies.
Next, we have the ligamentum flavum, and this ligament connects the laminae of adjacent vertebrae as we can see here on our image. Located more laterally we find the intertransverse ligaments and these short ligaments exist between the transverse processes of adjacent vertebrae.
And now for some ligaments associated with the spinous processes of the vertebrae. Over here, we can see the interspinous ligament and these ligaments are found throughout the vertebral column and extend between the spinal processes of adjacent vertebrae.
The last ligament we’ll talk about in this tutorial is the supraspinous ligaments, and the supraspinous ligament begins at the top of the spinous process of the seventh cervical vertebra and extends as far as the sacrum.
Alright, now that we’re familiar with the thoracic and lumbar spines, let’s get clinical.
At the beginning of this tutorial, we briefly mentioned hyperkyphosis which is a condition where the thoracic spine is more curved than normal causing the back to appear rounded and hunched. And in our clinical notes, we’re going to focus on another abnormal curvature of the spine called scoliosis.
Scoliosis is a condition that cause deformation of the vertebral column and normally when we look at the spine from an anterior perspective, we can see that it appears straight. Individuals with scoliosis develop lateral curvatures in their spine resulting in a C-shape or an S-shape. And in our x-ray over here, we can see that lateral curvature of the patient’s spine has caused a rough S-shape to occur.
Severe scoliosis can be debilitating leading to decreased mobility, back pain, and respiratory issues.
Okay so before we bring our tutorial to a close, let’s quickly summarize what we’ve learned today.
So, we started by looking at the bony structures of the thoracic and lumbar vertebrae, and here we saw that it is possible to distinguish between these two types of vertebrae using the vertebral body, the vertebral foramen, the spinous process, and the articular facets.
We then moved on to look at the intervertebral discs which are found between the vertebrae followed by some joints and ligaments of the thoracic and lumbar spines including the zygapophyseal joint which are found between the articular processes of adjacent vertebrae and the anterior longitudinal ligament which runs along the anterior surface of the vertebral bodies. Finally we concluded our tutorial with some clinical notes relevant to the thoracic and lumbar spines.
And that brings us to the end of our tutorial on the thoracic and lumbar spines. I hope you enjoyed it. Thanks for watching. Happy studying!