Description

Structures covered in this video:

Fibrous Joints (Syndesmoses):
• Anterior longitudinal ligament (Ligamentum longitudinale anterius)
• Posterior longitudinal ligament (Ligamentum longitudinale posterius)
• Anterior sacrococcygeal ligament (Ligamentum sacrococcygeum anterius)
• Superficial posterior sacrococcygeal ligament (Ligamentum sacrococcygeum posterius superficiale)
• Ligamenta flava (Ligamenta flava)
• Intertransverse ligaments (Ligamenta intertransversaria)
• Interspinous ligaments (Ligamenta interspinalia)
• Supraspinous ligament (Ligamentum supraspinale)
• Nuchal ligament (Ligamentum nuchae)

Cartilaginous Joints (Symphyses):
• Intervertebral disc (Discus intervertebralis)
• Annulus fibrosus (Anulus fibrosus)
• Nucleus pulposus (Nucleus pulposus)
• Lumbosacral symphysis (Symphysis lumbosacralis)
• Sacrococcygeal symphysis (Symphysis sacrococcygea)

Synovial Joints:
• Zygapophysial joints / Facet joints (Articulationes zygapophysiales)
• Lateral atlanto-axial joints (Articulationes atlantoaxiales laterales)
• Median atlanto-axial joint (Articulatio atlantoaxialis mediana)
• Atlanto-occipital joint (Articulatio atlantooccipitalis)
• Posterior atlanto-occipital membrane (Membrana atlantooccipitalis posterior)
• Anterior atlanto-occipital membrane (Membrana atlantooccipitalis anterior)
• Lateral atlanto-occipital ligament (Ligamentum atlantooccipitale laterale)
• Transverse ligament of atlas (Ligamentum transversum atlantis)

Bony Joints (Synostoses):
• Sacral vertebral fusion (Synostoses of vertebrae sacrales)
• Coccygeal vertebral fusion (Synostoses of vertebrae coccygeae)

Clinical anatomy and conditions discussed:
• Disc herniation (Herniated disc)
• Sciatica (Nerve root compression at L5/S1)
• Facet joint arthropathy
• Rheumatoid arthritis affecting the transverse ligament
• Atlantoaxial instability
• Degeneration of intervertebral discs
• Nerve root compression symptoms (pain, numbness, weakness)

Movements enabled by vertebral joints:
• Flexion
• Extension
• Lateral flexion
• Rotation

Function of vertebral joints and ligaments:
• Stability of vertebral column
• Protection of spinal cord and nerve roots
• Shock absorption
• Controlled mobility
• Prevention of hyperextension and hyperflexion

Sources:
• Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.
• Standring S. (2020). Gray’s Anatomy, 42nd edition.
• Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
• White TD, Folkens PA. (2005). The Human Bone Manual

Programs used: Complete Anatomy, Biorender, PowerPoint

Transcript

Introduction & Content
0:00
In the last video, we covered the bones of the spine. Today, we’ll learn about the joints,
0:05
ligaments, and discs. How they hold the spine together, and how injury to those structures
0:10
can result in pain, herniation, and instability. So in this video we’ll start with the why do we
0:15
have vertebral joints, how are the vertebral joints structured and how do we classify them?
0:21
The vertebral joints are well organized and it makes so much sense once you know fibrous joints,
0:27
cartilagionous joints, synovial joints and the bony joints. So that’s our goal for today,
0:32
understanding all of these joints, and also look specifically at common
0:36
injuries like disk herniations as well. What’s up everyone, my name is Taim. I’m
0:40
a medical doctor, and I make animated medical lectures to make different topics in medicine
0:44
visually easier to understand. If you’d like a PDF version or a quiz of this presentation, you can
0:49
find it on my website, along with organized video lectures to help with your studies.
0:53
Alright, let’s get started. Why, How, Classification.
Why do we have vertebral joints?
0:57
Why do we have vertebral joints? I think this is one of the things that really makes
1:01
you appreciate the structure of the spine. If the vertebrae were fused together into a single bone,
1:07
we wouldn’t be able to move properly. The vertebral joints allow flexibility and movement,
1:12
making it possible for the spine to bend forward in flexion, bend backward in extension,
1:18
and rotate along its axis. At the same time, they maintain spinal stability and keep the vertebrae
1:24
properly aligned, so the spine doesn’t collapse under its own weight. Another important role of
1:29
the vertebral joints is protecting the spinal cord and the spinal nerves during movement, by keeping
1:34
the vertebral canal stable and minimizing any compression or stretching. They also help absorb
1:41
and distribute mechanical forces, especially when we walk, run, or lift — so that the forces don’t
1:47
damage the bones or nerves. And they also enable coordinated movements of the head and trunk,
1:53
allowing us to perform daily activities. So how are the vertebral joints
How are the vertebral joints structured?
1:58
structured? If we go a little bit down. … And just, take a moment and appreciate all
2:04
the ligaments you see here, they are the ones that stabilize your whole body. We see that the
2:09
vertebral joints are made up of different types depending on what kind of tissue connects
2:14
the bones. First, we have fibrous joints that connect bones by dense fibrous connective tissue,
2:20
and they allow little to no movement. We can also see cartilaginous joints. These are joints
2:26
where the bones are united by cartilage, allowing more flexibility than fibrous
2:31
joints but still providing a lot of stability. And a key example here are the intervertebral
2:33
discs that allow for slight movement between vertebrae and act as important shock absorbers.
2:33
Now, if we look from the lower perspective, we can also see synovial joints. Synovial
2:39
joints are characterized by a joint cavity filled with synovial fluid,
2:43
surrounded by a capsule. They allow much more movement compared to fibrous and cartilaginous
2:48
joints. And we also have bony joints, where two bones fuse together into a single bone over
2:55
time. In the vertebral column, a good example is the fusion of the sacral vertebrae to form
2:56
the sacrum. Once fused, these joints no longer allow movement between the original vertebrae.
2:56
Each of these contribute in their own way to the overall function and stability of the spine. And
Classification of vertebral joints
3:02
this is how they’re generally structured. All the joints fall under these categories.
Fibrous Joints of the Spine
3:08
Awesome, let’s do the fibrous joints first. Fibrous joints in the spine are classified
3:13
as syndesmoses. This means that two bones are connected by a ligament or a sheet of connective
3:19
tissue, without a true joint cavity. They are slightly movable joints to provide stability, what
3:26
we call amphiarthroses. Here you see two bones. They are held together tightly by a flexible rope,
3:33
that’s basically what fibrous joints are. If we look at the spine, you can see that
3:37
they do look different. Some are very short and thin, some are short but a little bit thicker,
3:43
and some are very long, spanning across the whole spine. And because of this,
3:48
we can break the fibrous joints into two groups, the long ligaments and the short ligaments.
3:54
The long ligaments are the ones that run along the full length of the vertebral column. Their
3:59
main job is to limit hyperextension and maintain stability during movement.
4:04
The short ligaments are ligaments that connect adjacent vertebrae directly,
4:09
and they help control motion between individual vertebrae and provide elasticity to the spine.
4:14
Let’s cover the long ligaments first. Starting with the anterior longitudinal
Anterior longitudinal ligament
4:19
ligament. This ligament runs along the front of the vertebral bodies from the base of the
4:24
skull all the way down to the sacrum. Its main job is to prevent hyperextension of
4:29
the vertebral column, which means it stops the spine from bending too far backward.
4:35
At the bottom of the spine, this ligament continues as the anterior sacrococcygeal ligament,
4:41
where it anchors onto the front of the sacrum and coccyx, maintaining
4:45
stability of the lower end of the spine. Alright, next. If we now zoom in a little
4:51
bit and remove the body of one vertebrae, we can see the posterior longitudinal ligament.
Posterior longitudinal ligament
4:56
Highlighted here. It runs along the posterior surfaces of the vertebral bodies, but this time
5:02
inside the vertebral canal, just in front of the spinal cord. Here’s another view showing
5:08
you that it runs along the whole spine. Its function is to limit hyperflexion of the spine,
5:14
meaning it prevents excessive bending forward, and it also helps support the intervertebral discs.
Superficial posterior sacrococcygeal ligament
5:20
Then we have the superficial posterior sacrococcygeal ligament. If we look at
5:25
the spine from this view, we’ll see this. We can find the superficial posterior
5:30
sacrococcygeal ligament at the very end, attached to the back of the sacrum and coccyx.
5:36
So those are the long ligaments. They are major stabilizers across the whole length of the spine.
5:42
Now let’s move into the short ligaments. The first short ligament we see is the
Ligamentum Flavum
5:47
ligamenta flava. These are elastic ligaments that connect the laminae of adjacent vertebrae,
5:53
and they are special because they contain a lot of elastic fibers, giving them a yellow color.
5:59
Their job is to maintain posture and assist with the recoil of the spine after flexion,
6:04
like a built-in spring system if it makes sense. Turning the spine a little to the side, we see
Intertransverse Ligament
6:09
the intertransverse ligaments here highlighted in orange. They run between the transverse processes,
6:15
and they limit lateral flexion, helping to keep the spine stable when we bend to the sides.
6:21
Alright let’s highlight some other structures. Here we see the interspinous ligaments,
Interspinous Ligament
6:26
connecting one spinous process to the next. They help limit flexion by resisting the separation
6:31
of spinous processes when you bend forward. And then, we got the supraspinous ligament,
Supraspinous Ligament
6:37
running all the way along the tips of the spinous processes, from the sacrum
6:42
up to the cervical spine. This ligament also limits flexion and keeps the midline of the
6:47
spine together during movement. What’s special here, is that if we look at the cervical region,
Nuchal Ligament
6:52
the supraspinous ligament broadens and becomes the nuchal ligament. The nuchal ligament is
6:58
much thicker and supports the weight of the head, while also serving as a site of muscle attachment.
7:04
So those were the fibrous joints I wanted to mention. Let’s do the cartilaginous joints.
Cartilaginous Joints of the Spine
7:09
Now, just something I need to mention here first. Notice I wrote synchondroses and symphyses.
7:15
Cartilaginous joints in general are connections between bones that are made of cartilage,
7:21
but they are divided into two types based on the kind of cartilage and movement they allow.
7:27
Synchondroses are joints connected by hyaline cartilage and are usually temporary, like the ones
7:33
found during growth, while symphyses are joints connected by fibrocartilage and are permanent,
7:39
providing strength with a little bit of movement. In the adult vertebral column,
7:44
all the cartilaginous joints are symphyses. There are no synchondroses between vertebral
7:49
bodies after development is complete. So first ones are the intervertebral discs.
7:55
These are classic examples of symphyses. They sit between adjacent vertebral bodies
8:00
from the cervical region all the way down to the sacrum, acting as important shock absorbers. Then,
8:06
as we move downward to the junction between the last lumbar vertebra and the sacrum,
8:10
we find the lumbosacral symphysis. This junction needs to be especially strong because of the heavy
8:17
weight-bearing demands in this region, so the fibrocartilaginous disc here is very thick and
8:22
durable. At the very bottom of the spine, there is the sacrococcygeal symphysis, which connects
8:29
the sacrum to the coccyx. In some adults, this joint can even ossify completely over time,
8:36
but early in life, it remains a fibrocartilaginous symphysis, providing slight mobility which can
8:41
be important during activities like childbirth. Let’s now zoom a little bit out. We can see the
Intervertebral Discs
8:47
intervertebral discs distributed along the entire length of the vertebral column. I removed one
8:53
vertebra here, so if we just isolate this specific region, we can see that the intervertebral disc is
8:59
made up of two distinct regions. The outer layer is called the anulus fibrosus, which consists of
9:04
concentric layers of fibrocartilage. This tough structure provides strength and contains the inner
9:11
part. At the center is the nucleus pulposus, which is a soft, gelatinous core rich in water content.
9:18
The nucleus pulposus functions as a hydraulic cushion, absorbing compressive forces and
9:24
distributing them evenly across the disc. How does that look like? As you can see here,
9:30
nerve roots extend from the spinal cord through openings located on either side of
9:35
the vertebrae. The intervertebral discs play a really important role here. They prevent
9:40
friction between the vertebral bodies and allow for smooth, controlled movement during bending,
9:45
twisting, and lifting. However, sometimes the integrity of these discs can be compromised,
9:51
and it can start to degenerate. Disc degeneration may occur, often due to age-related wear and tear,
Disc herniation
9:59
repetitive stress, or trauma. When degeneration weakens the anulus fibrosus,
10:04
the nucleus pulposus can herniate outward, creating what we call a herniated disc.
10:10
This herniated material can compress nearby spinal nerve roots against the hard
10:15
vertebrae. And depending on which nerve root is compressed, patients may experience pain,
10:21
numbness, tingling, or muscle weakness along the distribution of the affected nerve. For example,
10:27
compression of a nerve root in the lumbar spine can cause symptoms down the leg,
10:32
a condition commonly known as sciatica. Now imagine this clinical case. A 38-year-old man
Lumbar Disk Herniation: Clinical Scenario
10:38
comes to your clinic. He tells you he was lifting a heavy box at work about two weeks ago when he
10:43
felt a sharp pain that starts in his lower back and radiates down the right side of his buttock,
10:48
thigh, and all the way into the lateral part of his right lower leg and foot. He also mentions
10:54
some tingling and numbness in these areas, and since then, he has noticed some weakness
10:59
when trying to lift his foot Based on this description,
11:02
you immediately start thinking about a possible lumbar nerve root compression.
11:06
To confirm the diagnosis, you order an MRI. So here we have an MRI machine. You send him in,
11:13
scan happens, he goes out. And then you get an mri scan of something like this.
11:19
This sagittal view shows a clear bulging of the intervertebral disc at the lower lumbar level,
11:25
most prominently at the L5/S1 junction. On the axial view,
11:30
you can see the herniated disc material pushing toward the right side of the patient, compressing
11:34
the nerve root exiting there. This matches perfectly with his symptoms on the right leg.
11:40
Putting it all together: the patient has a right-sided L5/S1 disc herniation, compressing
11:46
the right S1 nerve root. This explains his pain radiating down the posterior thigh and calf,
11:51
and numbness. It’s a classic presentation of a disk herniation with nerve root compression.
11:57
And with that, we covered the cartilaginous joints. Next let’s do the synovial joints.
Synovial Joints of the Spine
12:03
Synovial joints are characterized by a joint cavity filled with synovial fluid, surrounded
12:08
by a capsule, and lined by synovial membrane. They allow for a wide range of motion depending
12:14
on their type and structure. In the spine, the first example of a synovial joint is in this area.
Zygapophysial Joint / Facet Joint
12:21
One vertebra is connected with its adjacent vertebra though facet joint.
12:25
It’s called this way because it is formed between the superior articular facet of one
12:30
vertebra and the inferior articular facet of the vertebra above. Add a membrane,
12:36
and we get the zygapophysial joints, or facet joints. These are plane-type synovial joints,
12:42
allowing gliding movements between the vertebrae. Degeneration of these joints is common with aging
12:47
and can lead to facet joint arthropathy, causing localized back pain and referred pain patterns
12:52
that can mimic nerve root compression. If we now turn this image towards the
Lateral Atlantoaxial Joint
12:57
posterior view of the head. We can find the lateral atlanto-axial joints between the first
13:02
cervical vertebra, the atlas, and the second cervical vertebra, the axis. There are actually
13:07
three joints here, two lateral atlanto-axial joints and one median atlanto-axial joint.
13:14
The lateral atlanto-axial joints are synovial plane joints between the inferior articular
13:20
facets of the atlas and the superior articular facets of the axis. These allow gliding movements,
13:26
but the majority of rotation occurs thanks to the median atlanto-axial joint. Just for orientation,
13:33
we can see the ligamenta flava here as well. The median atlanto-axial joint is interesting,
Median Atlantoaxial Joint
13:39
let’s just remove the posterior parts of the vertebra here. This joint is a pivot-type
13:45
synovial joint between the dens of the axis and the anterior arch of the atlas. The dens acts
13:51
like a pivot, allowing the head to rotate from side to side, like shaking the head to say “no.”
13:56
This joint is stabilized by strong ligaments, most importantly the transverse ligament of the atlas,
14:03
which holds the dens tightly against the anterior arch. Damage to this ligament,
14:08
such as from trauma or diseases like rheumatoid arthritis, can cause instability
14:13
and even life-threatening spinal cord compression. Another thing we can see is the atlanto-occipital
Atlantooccipital Joint
14:19
joint. This is a joint between the occipital condyles and the superior articular facets of
14:25
the atlas. It allows mainly flexion and extension, like when you nod your head.
14:30
This joint is supported by membranes and ligaments that strengthen the joint capsule.
14:35
First, we see the posterior atlantooccipital membrane, connecting the posterior margin of
14:40
the foramen magnum to the posterior arch of the atlas. It helps stabilize the joint and leaves
14:46
a small opening for the vertebral artery. Then, the lateral atlantooccipital ligament strengthens
14:52
the capsule on each side. And if we turn over to the anterior view, we can see the anterior
14:58
atlantooccipital membrane, which strengthens the front of the joint and helps limit extension.
15:03
So those were the joints. Let’s move to the last category. Bony joints, or synostoses. Bony joints
Bony Joints of the Spine
15:11
represent the complete fusion of bones, with no remaining joint cavity. In the vertebral column,
15:17
the best examples are the synostoses of the sacrum and synostoses of the coccyx. During development,
15:24
the individual sacral and coccygeal vertebrae are separated, but they later fuse into a single
15:31
sacral bone and a coccygeal bone. With that, we have now finished
Outro
15:35
covering all the joints of the vertebral column, fibrous, cartilaginous, synovial,
15:40
and bony joints. In the next video on the skeletal system series, I’ll cover the bones of the thorax,
15:46
including the ribs and sternum. Click on the next video, and I’ll see you there.
15:50
If you want a handmade PDF version of this lecture, take a quiz to test your knowledge,
15:54
or access an organized list of all my videos,
15:56
you can find everything on my website. Thanks for watching! See you in the next one.