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Craniovertebral ligaments

Ligaments connecting the skull to the vertebrae.

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Transcript

Hey everyone! It's Nicole from Kenhub, and welcome to our tutorial on craniovertebral ligaments. In this video, we'll be looking at the ligaments that help to support the connection of our skull to our vertebrae. In this video, we're going to be looking at bones associated with the craniovertebral ligaments, the ligaments themselves, and we'll finish off with some clinical correlations. So let's start by looking at this image and identifying the bones that we're interested in, and we're looking at a posterior aspect of the axial skeleton.

Beginning with the superior aspect, we can see the skull or the cranium, and next, we come across the vertebral column or spine, which can be divided into five sections – the cervical vertebrae which are highlighted in green here, the thoracic vertebrae, the lumbar vertebrae, the sacrum, and finally, the coccyx. Attached to the thoracic vertebrae are the ribs and attached to the sacrum are the bones that make up the pelvis.

So since we're looking at the craniovertebral ligaments, our focus is going to be on the superior aspect of the vertebral column where the cervical vertebrae meet the cranium. Now, let's have a closer look at the seven cervical vertebrae that we can see highlighted in green on this image here, but note that it's the first two that we are particularly interested in today.

So as well as being called C1 and C2, each of these vertebrae have a more special or specific name because they're quite different from the rest of the vertebrae. So, the first cervical vertebrae is called the atlas, and we can see it here as the most superior cervical vertebrae. The atlas took its name from the Greek name “Atlas” which refers to a Titan in Greek mythology condemned to hold up the earth for eternity. So, we can say that the vertebra atlas has the same fate as the first cervical vertebra supports the globe of the head.

C2’s other name is the axis, and the axis is just inferior to the atlas just here. And these names atlas and axis are what are used when defining joints between these bones and the other ones that they articulate with.

So, let's first have a look at the third to sixth cervical vertebrae, and these vertebrae all have very similar features to each other and a more typical vertebrae. So, we'll look at them first and then we'll see how the atlas and the axis compare.

So here we're looking at a typical cervical vertebra from a superior view and the inferior aspect which is at the top part of the image is where we can find the vertebral body. The bodies of the cervical vertebrae are relatively small leaving room for this large foramen called the vertebral foramen, and when all of the vertebrae is stacked on top of each other as they are in our bodies, these foramen all together form a continuous tube called the vertebral canal. And this canal is what allows for the protected passage of our spinal cord. And the posterior aspect helping to form the vertebral foramen is the vertebral arch, and protruding off the arch is the short spinous process which is bifid in shape.

Laterally, we have the transverse processes, and within each of these, we have a transverse foramen. The transverse foramina are specific to cervical vertebrae and allow for passage of the vertebral artery. The pieces of bone that we see here are the pedicles and the parts that we see posteriorly between the transverse processes and the spinous process are the laminae. And finally, each vertebra has four articular facets that will articulate with another vertebra.

On the superior aspect are two superior articular facets for articulation with the vertebra immediately superior to it, and on the inferior aspect are – you guessed it – two inferior articular facets for articulation with the vertebra immediately inferior to it. When these articular facets articulate, they form what is called a zygapophysial joint or facet joint. Keeping these bony features in mind, let's have a look at the atlas and axis again, C1 and C2, to see how they compare.

The atlas or C1 as we have already said is the most superior cervical vertebra and, in this image, we're looking at it from a superior view and the inferior aspect is up here towards the top of the screen and the posterior aspect is here at the lower part of the screen. Firstly, I'm just going to point out this large hole in the middle, and this is the vertebral foramen. The foramen in the atlas is larger than the other cervical vertebrae, but we'll see that it's not the only spinal cord that takes up space in this foramen.

To make up this foramen, we can divide the circular structure into four parts – the anterior part, the posterior part, and two lateral parts, one on either side. So, you may have noticed that there is no vertebral body in the atlas and the inferior aspect which runs from here to here instead has an anterior arch, and this is what we can see highlighted in green. In the midline of the anterior arch, there's a small anterior projection or tubercle called the anterior tubercle.

On the posterior aspect of the anterior arch, there's a small surface or facet called the articular facet for the dens, and we'll see soon how the dens from C2 articulates at this facet. The posterior aspect is quite similar to the anterior aspect and this part now highlighted in green is called the posterior arch, and in its midline here, there is a posterior projection called the posterior tubercle. Comparing two typical cervical vertebrae, we can note that there isn't a proper spinous process, but the posterior tubercle instead.

Now, laterally, we have so much larger masses of bone and these areas are simply called the lateral masses. On the superior aspect of the lateral masses, we can see these large facets highlighted in green and these are the superior articular facets of the atlas. They’re much larger than those in typical cervical vertebrae and we'll see later that these facets are what articulate with the occipital bone.

On each of the medial aspects of the lateral masses, there is a tubercle which we can now see highlighted in green, and these tubercles are attachment points for the transverse ligament of the atlas. Again, we'll look at these later on. And finally to complete the picture, most laterally, we have transverse processes on each side, and just like typical cervical vertebrae, there's a transverse foramen through each of them. And remember, transverse foramina allow for passage of the vertebral arteries which are ascending superiorly to supply the brain.

Alright, now, it's time for the bony features of C2 which is our axis, and we can see it in anatomical position on this image highlighted in green. The axis is the next vertebra in the vertebral column just inferior to the atlas. The axis looks a little bit more like a typical cervical vertebra except for this large prominent projection here and this is what is known as the dens.

In this image, we're looking at the axis from a posterior view, so we can see that the dens is projecting superiorly from the anterior aspect of the axis. The anterior and posterior aspects of the dens each have an articular facet called the anterior articular facet and the posterior articular facet respectively, and we can see the posterior articular facet here on this image. The anterior articular facet on the dens will articulate with C1 which is the atlas and the posterior articular facet on the dens is where we'll see the transverse ligament of the atlas making contact with the axis.

Other aspects of the axis are very similar to typical cervical vertebrae. We can see the bifid spinous process here on the posterior aspect and, laterally, we can see the transverse processes with the transverse foramina.

In order to relate the cervical vertebrae to the cranium, we should move along and have a look at the base of the cranium itself. So in this image, we can see the bone that forms the base of the skull highlighted in green and this bone is the occipital bone. The occipital bone articulates with the atlas and creates the craniovertebral joints which are joints between the cranium and the vertebrae.

Looking at this image now, the occipital bone is still highlighted and we can see that as well as making up part of the posterior aspect of the skull, it continues along the inferior aspect to make up the base of the skull. The large hole that we can see here is called the foramen magnum, and this foramen is what the spinal cord travels through to leave the skull. It is continuous with the vertebral canal formed by the vertebral foramen which we've already described before of all vertebra.

What we can see now highlighted in green are the occipital condyles, and we can think of these as the inferior articular facets of the occipital bone, meaning they are what will articulate with the atlas in the atlanto-occipital joint. Finally, the projection highlighted in green now is the external occipital protuberance, and this will serve as an attachment point for our important ligaments that we’ll see later on.

So, of course, these bones articulate with each other and form joints and joints are formed by the union or the meeting of two or more bones. We'll now take a look at the important joints of the craniovertebral region and as we do so, we’ll identify the ligaments that help to strengthen and stabilize those joints.

The two main craniovertebral joints are the atlanto-occipital joint and the atlantoaxial joint, and both are synovial joints and have a wider range of motion than other joints of the vertebral column and we'll look at each of them in turn. Let's begin with the atlanto-occipital joint.

So as the name suggests, this is the joint between the atlas C1 and the occipital bone and it is the occipital condyles articulating with the superior facets of the atlas which forms the atlanto-occipital joint. The atlanto-occipital joint mainly allows for flexion and extension, so nodding your head, and there's also some lateral flexion and some rotation allowed at this joint.

So this is a zoomed-in image, part of the occipital bone superiorly which is cut here with the atlas in the middle and the axis inferiorly, and we're looking at these bones from the posterior aspect and we can see the bifid spinous process of the axis just here. We can see that the occipital bone has been cut so we're looking right into the foramen magnum just here, and on both the left and the right sides, we can see the occipital condyles articulating with the superior articular facets of the atlas.

So to support and strengthen this joint, there are a couple of important structures that I want to point out for you in this image. So, over here, we're looking at a median sagittal section of the cranium and the cervical vertebrae and over here, we have the occipital bone; over here, we have the anterior arch of the atlas, and over here, we have the posterior arch.

So what we can see highlighted in green now is the anterior atlanto-occipital membrane and this membrane is continuous with the joint capsules of the atlanto-occipital joints on both sides and stretches between the foramen magnum and the anterior arch of the atlas.

On the posterior aspect of the atlanto-occipital joint is the posterior atlanto-occipital membrane, which we can now see highlighted in green. And this membrane stretches between the foramen magnum and the posterior arch of the atlas. The space or the opening we can see here allows the vertebral artery to pass through the atlanto-occipital joint to enter the cranium through the foramen magnum.

So after discussing the atlanto-occipital joint with the anterior and posterior membrane, next stop is the atlantoaxial joint. Again, the name says it all, and this is a joint formed between the atlas and the axis. So these two bones which if you remember are the first two vertebrae of our vertebral column make contact and articulate at three different points – so two lateral and one medial.

So the two lateral which we can see highlighted in this image are pretty similar to most vertebral joints. They’re between the superior articular facets of the axis and the inferior articular facets of the atlas. The very unique articulation that occurs between these two bones is in the midline – the one median articulation point. So, this is where the dens from the axis which we can see from a superior view here meets the posterior aspect of the anterior arch of the atlas.

So do you remember the facets we looked at on the atlas and the axis? So we can now see this articular facet for the dens articulating with the anterior articular facet of the dens itself. To stabilize the atlantoaxial joint, there are several ligaments in place, and we're going to be looking at each of them in turn.

So, here they are, and these are the transverse ligament of the atlas, the cruciform ligament of the atlas, the alar ligaments, the apical ligament of the dens, the anterior atlantoaxial membrane, and finally, the posterior atlantoaxial ligaments.

The first ligament that we'll look at is one that keeps the median articulation point in place and this is the articulation between the dens and the posterior aspect of the anterior arch of the atlas. So to keep this joint in place, the ligament wraps around the posterior aspect of the dens, and we can see it now highlighted in green. Specifically, this ligament runs along the posterior articular facet of the dens and this ligament is the transverse ligament of the atlas that we talked about earlier. It runs between the two tubercles of the lateral masses and, by doing so, creates a closed space around the dens, and the transverse ligament along with the longitudinal band form what is called the cruciate or cruciform ligament of the atlas, and it's named this way because it looks like a cross.

So now we can see the superior aspect of the longitudinal ligament in this image, and again we're looking at the occipital bone superiorly, the atlas in the middle, and the axis inferior. And the occipital bone again has been cut so we're looking into the foramen magnum just here. The ligamentous fibers that are running transversely are the transverse ligament of the atlas and the fibers that extend from the middle of the ligament and run superiorly to the occipital body are the superior aspect of the longitudinal band.

In this median sagittal view, we can see both the superior and inferior aspects of the longitudinal band, and this structure here is the transverse ligament. So running superiorly to the occipital bone is the superior portion of the longitudinal band and running inferiorly to the body of the axis is the inferior portion. And these bands together with the transverse ligament make up the cruciate ligament of the atlas which helps keep the median atlantoaxial joint in place. And this joint allows for rotational movement, so when we shake our heads in disapproval of something, we're working our median atlantoaxial joint.

However, in order to prevent excessive rotation of the joint, we have these two ligaments highlighted here that serve as check ligaments, and they’re called the alar ligaments. And in this image, we can see them emerging from the anterolateral aspect of the dens. They run from the dens to the lateral margins of the foramen magnum which we can see in this image here, and we're looking at the posterior aspect of the occipital bone, atlas, and axis. The occipital bone having been cut means that we're looking into the foramen magnum here and we can see the alar ligaments attaching here.

Running between the alar ligaments is the apical ligament of the dens, runs from the tip or the apex of the dens to the anterior margin of the foramen magnum, and we can see it highlighted in green on this image. The apical ligament has been found to have remnants of the notochord, which is an embryological structure and it's quite small and weak so it does not have as much clinical significance as the alar and cruciate ligaments.

A bit more externally from the articulation of the dens with the atlas, we have two more structures that support the atlantoaxial joint. The first is the anterior atlantoaxial membrane which we can see highlighted in the image over here and it runs between the anterior arch of the atlas to the body of the axis. The second of these two structures is the posterior atlantoaxial ligaments highlighted here, and this ligament runs between the posterior arch of the atlas to the laminae of the axis.

Okay now that we've looked at some smaller internal ligaments that stabilize some very specific joints, let's now have a look at some much larger ligaments that run across many joints to help with stabilization and strength of the craniovertebral articulations as well as other joints in the vertebral column. So we’re going to begin with the anterior longitudinal ligament, and in this image, we’re looking at a median sagittal section of the cranium and of the cervical vertebrae with the anterior longitudinal ligament being the structure highlighted in green. And this ligament is strong and broad and runs along the anterior aspect of the vertebral bodies.

The anterior longitudinal ligament helps prevent hyperextension of the neck and if you can imagine this neck extending – so the cranium moving towards the right of the screen – the anterior longitudinal ligament would be pulled and stretched. Because of its attachment points to the anterior aspect of the vertebral bodies, it helps to prevent the neck from extending too far.

The posterior longitudinal ligament is a little bit thinner and weaker than its anterior counterpart, but it's still an important ligament supporting the vertebral column and we can see it now highlighted in green. And this ligament runs along the posterior aspect of the vertebral bodies within the vertebral canal. And due to this posterior attachment, the posterior longitudinal ligament helps prevent hyperflexion of the neck.

At the superior aspect of the posterior longitudinal ligament, there's a strong continuation called the tectorial membrane. The tectorial membrane crosses the median atlantoaxial joint and passes through the foramen magnum to attach to the central floor of the cranial cavity, and as we can see in this image, it continues from the posterior longitudinal ligament at the body of C2 and runs to the internal surface of the occipital bone. And while doing so, it covers both the alar and transverse ligaments. And we can see the transverse ligament of the atlas here covered by the tectorial membrane posteriorly.

After discussing the posterior and anterior longitudinal ligaments, next up, we have the nuchal ligament. The nuchal ligament is a large thick ligament that crosses the craniovertebral joints. It runs from the external occipital protuberance to the spinous process of C7. Along its path, it attaches to each of the spinous processes of the cervical vertebrae. The nuchal ligament, similar to the posterior longitudinal ligament, limits the ability of the neck to flex. It also serves as an attachment point in the midline for some muscles such as the trapezius and splenius capitis muscles.

Finally, there are some ligaments that run between structures sequentially all the way along the vertebral column and we're going to be reviewing these ligaments right now.

The laminae of the adjacent vertebral arches are joined by broad, pale yellow elastic tissue called the ligamenta flava and these are highlighted in green in this image. The ligamenta flava extend almost vertically from the lamina above to the lamina below and those of the opposite sides meeting and blending in the midline. And these ligaments bind the lamina of the adjoining vertebra together forming alternating sections of the posterior wall of the vertebral canal. So if we think of the posterior wall of the vertebral canal as one continuous solid structure, the structure is made up of laminae and ligamenta flava in alternating portions.

Most superiorly, a sort of continuation of the ligamenta flava is the posterior atlantoaxial ligament, which we looked at earlier, and it runs between the laminae of the axis to the posterior arch of the atlas. The articular capsules of the zygapophyseal joints are more structures that we can see again and again along the length of the vertebral column. So remember, the zygapophyseal joint is the articulation of inferior and superior articular facets of adjacent vertebrae as we can see highlighted in this lateral view of two vertebrae.

In this image, we can see the articular capsules of the zygapophyseal joints highlighted in green and they’re just anterior to the ligamentum flava which are the yellow structures.

So in this midsagittal section of the spine and skull, we're looking at a few vertebrae from an anterior and slightly superior view. The vertebral body of the most superior vertebra has been removed and highlighted in green again are the articular capsules of the zygapophyseal joints. These are the inferior articular facets and the most superior vertebra and these are the superior articular facets of the vertebra inferior to it. The adjoining spinous processes are united by weak, almost membranous interspinous ligaments and these are the structures we can see highlighted in green. In the image, the highlighted structures are the intertransverse ligaments and these ligaments connect adjacent transverse processes of the vertebrae.

So now that we've looked at all these ligaments, what might happen if one of something were to go wrong with them? So there are a lot of different issues that can arise following trauma to the neck and we're going to highlight a few of these now.

So the transverse ligament of the atlas which you can see here in this image highlighted in green can rupture either in isolation or within associated injuries such as an atlas fracture. If the ligament ruptures, the atlas can translate or move anteriorly in relation to the lower cervical spine, and since the ligament is no longer strongly wrapped around the dens, it's more likely that this translation can occur.

The alar ligament can tear from accidents leading to the atlanto-occipital dislocation or condylar fractures and the alar ligaments are prone to tearing if a force is applied when the head is flexed and in rotation. If an alar ligament is ruptured, the range of rotation of the head relative to the neck increases beyond the normal limit of twenty degrees.

Well that was a lot of ligaments, but now we've covered the craniovertebral joints, their associated ligaments, and some clinical correlations. So let's do a quick review to recap what we went over today.

So first we looked at the bones associated with the craniovertebral joints and these were the cervical vertebrae paying special attention to C1 which is the atlas and C2 which is the axis with the dens, and the occipital bone which forms the base of the cranium. Next, we had a look at the atlanto-occipital joint as well as the anterior and posterior atlanto-occipital membranes that help support that joint.

We then went over the atlantoaxial joint which has several associated ligaments supporting and strengthening it. Firstly, the cruciform ligament of the atlas which consists of a transverse ligament and a longitudinal band, and this ligament holds the dens in place to articulate with the atlas. Next, the alar or check ligaments limiting rotation of the neck and the apical ligament of the dens containing embryological remnants is what we talked about. And, finally, the anterior atlantoaxial membrane and the posterior atlantoaxial ligaments complete the list of structures supporting the atlantoaxial joint.

Lastly, we looked at ligaments that ran across or between many joints and these included the anterior longitudinal ligament running along the anterior aspect of the vertebral bodies, the posterior longitudinal ligament which runs along the posterior aspect of the vertebral bodies. Superiorly, this thickens as the tectorial membrane which runs from C2 to the anterior margin of the foramen magnum, and the final continuous ligament we looked at was the nuchal ligament, and this courses from the external occipital protuberance to the spinous process of C7.

The ligaments running between adjacent structures are the ligamenta flava which run between the lamina of adjacent vertebrae, articular capsules of the zygapophyseal joints which secure and support the facet joints into spinous ligaments between the spinous processes of adjacent vertebrae, and finally into transverse ligaments which run between the transverse processes of adjacent vertebrae.

The last thing we're going to do and then I promise I'll let you go is to look at all of the ligaments in this median sagittal section from anterior to posterior. Hopefully, this will help you put it all together and then you'll officially be an expert on craniovertebral ligaments.

So most anteriorly, we have the anterior longitudinal ligament followed by the anterior atlanto-occipital membrane superiorly, and then inferiorly, we have the anterior atlantoaxial membrane. Moving on, we can see the apical ligament of the dens highlighted in this image and lateral to this on either side would be the alar ligaments. Next is the cruciform ligament of the atlas formed by the longitudinal band which we can see highlighted in green and the transverse ligament which is between the two bands. Posterior to this is the posterior longitudinal ligament which are the superior aspect thickens as the tectorial membrane.

Surrounding the articular facets and therefore the facet or zygapophyseal joints are the articular capsules of the zygapophyseal joints. Towards the posterior aspect of the vertebral arches are the ligamenta flava and the posterior atlanto-occipital membrane and posterior to those structures are the interspinous ligaments and finally the most posterior ligament in the cervical region is the nuchal ligament.

That brings us to the end of our tutorial on the craniovertebral ligaments. Hope you enjoyed it. Thanks for watching!

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