Description

 
This video is about joint classification, structure, function, and clinical relevance.

Topics covered in this video: • What are joints?
• Joint classification based on structure and function
• Types of joints in the human body
• Examples of fibrous, cartilaginous, and synovial joints
• Subtypes of each joint category with real anatomical examples
• Clinical relevance of joints (e.g., high ankle sprains, TMJ, arthritis)
• Supporting structures: ligaments, bursae, menisci, labrum, fat pads
• Functional mobility: synarthrosis, amphiarthrosis, diarthrosis
• Synovial joint types:
 – Ball-and-socket joint (shoulder, hip)
 – Ellipsoid joint (wrist)
 – Saddle joint (thumb)
 – Hinge joint (elbow, knee, fingers)
 – Pivot joint (atlantoaxial, radioulnar)
 – Plane joint (acromioclavicular, vertebral facet joints)

Joint classification explained:
• Fibrous joints – sutures (suturae), syndesmoses, gomphoses
• Cartilaginous joints – synchondroses (hyaline cartilage), symphyses (fibrocartilage)
• Synovial joints – contain a joint cavity filled with synovial fluid
 – include articular cartilage, synovial membrane, joint capsule
 – supported by ligaments, tendons, labrum, bursae, menisci

Clinical anatomy references include:
• Atlantoaxial joint (articulatio atlantoaxialis mediana)
• Glenohumeral joint (articulatio humeri)
• Temporomandibular joint (articulatio temporomandibularis)
• Proximal radioulnar joint (articulatio radioulnaris proximalis)
• Pubic symphysis (symphysis pubica)
• Costochondral joints (junctiones costochondrales)
• Intervertebral discs (disci intervertebrales)
• Distal tibiofibular syndesmosis (syndesmosis tibiofibularis distalis)

Whether you’re a medical student or revising anatomy for clinical practice, this video breaks down complex arthrology in a visual, memorable way.

Transcript

 
0:00
Joints. They come in many forms, but at their core, joints exist to link bones
0:05
together and allow movement. Some let you rotate your arm in every direction,
0:10
some move just a little bit, and some, like the joints in your skull, don’t move at all.
0:16
You don’t really think about them, until something goes wrong. When joints wear down,
0:21
become inflamed, or stop working properly, even the simplest movements can become difficult.
0:27
So, why are some joints flexible while others are completely rigid? What makes
0:32
one joint allow movement while another barely moves at all? And how do we actually classify
0:38
all the different joints in the body? In this video, we’ll start by answering
0:43
the fundamental question – what are joints? Then, we’ll go through all the joints in the body and
0:49
classify them based on their structure and function. As we go through them,
0:54
we’ll also highlight their clinical relevance, understanding how joint problems develop and
0:58
what makes them vulnerable to damage. Hey everyone, my name is Taim. I’m a
1:02
medical doctor, and I make animated medical lectures to make different topics in medicine
1:06
visually easier to understand. If you’d like a PDF version or a quiz of this presentation, you can
1:11
find it on my website, along with organized video lectures to help with your studies.
1:15
Alright, let’s get started! So what are joints?
What are Joints?
1:19
Just, in simple terms, The point at which two bones lay adjacent to each
1:24
other (with or without the ability to move) is called a joint. Let’s visualize this.
1:30
Here we see a bone. Here is another bone. The point at which they lay adjacent to
1:35
each other is a joint. Here are two bones, between them, a joint. Here are two bones,
1:41
between them a joint. And even, I’ll surprise you now. Even between your skull bones, is a joint.
1:48
So joints come in different shape, and they are structurally and functionally different.
1:54
For example. The shoulder joint is
1:56
called the glenohumeral joint. Structurally, we call this a Synovial joint, Functionally,
2:02
it’s a Diarthrosis, since it’s a freely movable joint. And we subclassify it as a ball-and-socket
2:09
joint, which provides free rotational movement. Between the articular surfaces of vertebrae,
2:15
we got the facet joint, or zygapophyseal joints. They are synovial joints,
2:20
functionally movable so diarthrosis as well, but subclassified as plane joint,
2:26
allowing only gliding movements. Okay, let’s take another example, in the skull we got
2:32
sutures. Or lambdoid suture is what we’re pointing at specifically now. Structurally,
2:37
it’s a strong fibrous joint. And functionally, a Synarthrosis, meaning a joint that does not move.
2:45
Does it make a little bit more sense why we classify joints now?
2:48
The study of Joints is called Arthrology. Prefix Arthro- refers to joints,
2:54
such as in arthroscopy or arthritis. Suffix -logy means the study of. So it’s the study
3:00
of how bones are joined to allow or prevent movement. It, perhaps, more than any other
3:07
subjects in anatomy illustrates the close relationship between structure and function,
Classification of Joints
3:12
Here we can see the shoulder joint again, or the glenohumeral joint. Now, when you look at this,
3:18
see all the components, connective tissue, how it’s built. Some joints are built the same,
3:24
some joints are not. And that is why, we have structural classification. Apart from that, joints
3:30
within the same structural category can move differently, and because of that, we also have a
3:36
functional classification. Structural based on the binding tissue, and functional based on movement.
Structural Classification
3:43
Now, structural classification names and divides joints according to the type of
3:48
binding tissue that connects the bones to each other. Sources may differ a little bit on
3:54
the details of the classification system, but what the majority of sources agree upon is that there
3:58
are three structural classification of joints. There are fibrous joints, consisting of dense
4:05
regular connective tissue rich in collagen fibers. Cartilaginous joints, joined by cartilage.
4:11
Primarily hyaline cartilage. And Synovial Joints, which are not
4:15
directly joined as they have a synovial cavity within an articulating capsule.
Functional Classification
4:20
Joints can also be classified functionally based on the type and degree of movement they allow.
4:27
There is Diarthrosis, Amphiarthrosis and Synarthrosis. These words have a Greek origin,
4:34
but diarthroses are freely movable joints, so all synovial joints are classified as
4:39
diarthroses. Example is the Shoulder joint. Amphiarthrosis allows slight mobility.
4:46
Most amphiarthrosis joints are cartilaginous joints. Examples are
4:50
the intervertebral discs between the vertebrae. Synarthrosis allow very little movement to the
4:56
point that they really do not allow mobility at all, they’re immovable joints. Can you guess an
5:02
area in the body where those type of joints can be? Well we got the sutures of the skull. Awesome.
5:08
Just a side note – I’m not gonna talk about them in this video but depending upon the
Other Classification Systems
5:12
source you’re studying from, joints can also be classified according to the
5:16
number of axes of movement they allow, into non axial, monoaxial, biaxial and
5:22
multiaxial. Another classification system is according to the degrees of freedom allowed,
5:27
others according to the number and shape of the articulating surfaces, whether flat,
5:32
concave, convex, and so on. Lots of different classification systems. But in general if
5:37
you know this system I am showing you now, you’re good. You’ll understand everything.
5:42
Alright. Let’s now focus on these three joints. And let’s start with the fibrous joints.
Fibrous Joints
5:47
These joints are connected by dense fibrous connective tissue and lack a joint cavity,
5:53
resulting in minimal to no movement. And there are three main categories under fibrous joints.
5:59
There are Sutures, there are syndesmoses, and gomphoses.
6:04
Sutures are immovable joints between the joints of the skull. Here’s the
6:08
skull. Between the bones of the skull, are sutures, strong joints. In fetal skulls,
6:14
the sutures are wide to allow slight movement during birth. And they later become rigid.
6:20
Next we got syndesmosis. These are slightly movable joints where bones are connected by
6:26
ligaments or an interosseous membrane. Some of the long bones in the body such as the
6:32
radius and ulna in the forearm, and the tibia and fibula in the legs are joined by a syndesmosis,
6:38
along the interosseous membrane. Makes sense? This membrane serve to unite parallel bones and
6:44
prevent their separation. Syndemoses are slightly moveable, right? Amphiarthrodial we call them,
6:51
functionally as we saw earlier. Another example is the distal tibiofibular joint. Here we see the
6:57
posterior tibiofibular ligament which is one of the three ligaments of the inferior tibiofibular
7:02
joint, the others being the anterior tibiofibular and the transverse tibiofibular ligaments. And it
7:09
kinda makes sense. Why do we not want them to be completely fixed, like in our skull?
7:14
Well, think about it. The tibia and fibula need to stay firmly connected to provide stability for
7:20
carrying weight, but they also need a little bit of movement to accommodate motion at the
7:25
ankle joint. If they were completely fused, like the sutures in the skull, movements like walking
7:31
or running would put too much stress on the bones and make them more prone to fractures. So,
7:36
having a slight amount of movement helps with shock absorption and flexibility.
7:41
The interosseous membrane also serves as an attachment site for muscles and
7:45
helps distribute forces evenly between the two bones. For example, in the forearm,
7:50
the interosseous membrane between the radius and ulna allows for pronation and supination,
7:56
meaning it helps you rotate your palm up and down. And, have you heard about high ankle sprains
8:02
before? You’ve probably heard of regular ankle sprains where people twist their foot and damage
8:08
the ligaments around the ankle. But in a high ankle sprain, the injury happens at the distal
8:14
tibiofibular syndesmosis, stretching or even tearing the anterior and posterior
8:19
tibiofibular ligaments. This kind of injury takes longer to heal because the tibia and fibula are
8:25
constantly under stress when you walk. So, this is syndesmoses providing slight
8:31
movement which is crucial for function and injury prevention.
8:35
The third classification under fibrous joints is called gomphosis. Gomphosis
8:41
refers to the joints between the dental alveolus and the tooth root,
8:45
meaning the connection between the mandible or maxilla and the tooth root. As you can see here,
8:50
the periodontal ligament secures the tooth in its socket, acting as a fibrous connection.
8:56
At first, it may seem confusing why gomphosis is not classified under syndesmosis,
9:01
since both involve fibrous tissue. However, the key difference is in their function and movement:
9:07
Syndesmoses allow for slight mobility, like the interosseous membrane between
9:12
the tibia and fibula, which helps in shock absorption and stability.
9:16
Gomphosis, on the other hand, is a peg-and-socket joint that normally
9:20
does not allow movement, except in conditions like orthodontic treatment or dental trauma.
9:26
Interestingly, in early development, before the full eruption of teeth,
9:30
the periodontal ligament allows micro-movements, which is why some anatomists describe gomphosis
9:36
as a specialized form of syndesmosis. But in adults, it functions as an immobile joint,
9:42
which is why it remains its own category. Alright so that was the fibrous joints in our
Cartilaginous Joints
9:47
body. Next we have something called cartilaginous joints. Those are bones that are connected
9:53
together by cartilage, allowing limited movement. Cartilaginous joints allow more movement than
10:00
fibrous joints but are still much more limited compared to synovial joints. Their main role
10:05
is to provide structural stability while allowing some degree of flexibility. What
10:11
makes them particularly interesting is that they also serve as growth centers in developing bones,
10:17
which is something we don’t see in the other types of joints.
10:20
Now, cartilaginous joints can be divided into two main types: synchondroses and symphyses.
10:27
But before we go into those, let’s take a step back and talk about the bigger picture,
10:32
because in the world of cartilage, we actually have primary and secondary cartilage. And these
10:37
two categories perfectly align with the two types of cartilaginous joints.
10:42
So, primary cartilaginous joints are called synchondroses. These are joints where bones
10:48
are connected by hyaline cartilage. The key thing about synchondroses is that they
10:52
exist early in life and are later replaced by bone through ossification. That’s why they’re
10:58
often referred to as temporary joints, because many of them disappear as we age.
11:04
A perfect example of this is the epiphyseal growth plates in long bones. These synchondroses allow
11:10
bones to grow in length during childhood and adolescence, but once full growth is achieved,
11:16
they ossify and turn into solid bone. Another example is found in the base of the skull,
11:22
where synchondroses exist between different ossification centers before they fuse.
11:27
But not all synchondroses disappear. Some persist throughout life. A great example
11:33
of this is the costochondral joints, which connect the ribs to their costal cartilage. Now,
11:39
you might have heard that these joints provide flexibility for breathing, but that’s not exactly
11:44
correct. The costochondral joints themselves are immobile—they function as structural stabilizers.
11:51
What actually allows the ribcage to expand and contract during respiration is the elasticity of
11:57
the costal cartilages, not the joints themselves. Now let’s move on to the secondary cartilaginous
12:03
joints, which are called symphyses. Unlike synchondroses, these never fully ossify—they
12:10
stay as cartilage for life. What makes them unique is that they are made of fibrocartilage,
12:15
which is more durable and resistant to pressure. This is why symphyses
12:20
are typically found in high-pressure areas of the body that need both strength and slight mobility.
12:26
One of the most well-known symphyses is the pubic symphysis, the joint that connects
12:31
the two halves of the pelvis. Normally, it only allows minimal movement, but during childbirth,
12:37
hormonal changes make the fibrocartilage more flexible, which temporarily increases mobility
12:43
to allow for delivery. Another great example is the intervertebral discs,
12:48
which sit between the vertebrae of the spine. These discs are actually a type of symphysis,
12:54
and their role is to absorb shock and distribute pressure along the vertebral column.
12:59
To summarize, synchondroses are primarily temporary joints made of hyaline cartilage
13:05
that allow for growth and ossify with age, while symphyses are permanent
13:10
joints made of fibrocartilage that provide shock absorption and strength in high-pressure areas.
Synovial Joints
13:17
And with that, we’ve covered the cartilaginous joints! Next, let’s move on to synovial joints.
13:23
Synovial joints are the most common and most mobile joints in the human body.
13:28
What makes them unique is that they have a joint cavity filled with synovial fluid,
13:34
which reduces friction and allows for smooth movement. These joints are found
13:39
in areas where free movement is essential, like the shoulder, elbow, wrist, and knee.
13:44
But here’s something interesting, you don’t move your elbow the same way you move your
13:49
shoulder or wrist, right? That’s because not all synovial joints are built the same. Their
13:55
structure and movement depend on where they are located and what function they serve.
14:00
Now, even though synovial joints differ in function, they all share some basic
14:06
structures. If we take a closer look, here’s what we see. First, we have the joint cavity, which
14:12
is filled with synovial fluid. This acts as a lubricant and provides nutrients to the cartilage.
14:18
The ends of the bones are covered in articular cartilage, a smooth layer of hyaline cartilage
14:23
that absorbs shock and prevents bone-to-bone contact. Surrounding everything is the synovial
14:29
membrane, which is the inner lining of the joint capsule and is responsible for
14:33
producing synovial fluid. And finally, covering the whole joint, we have the articular capsule,
14:39
which is a fibrous outer layer that holds the joint together and provides structural stability.
14:45
That’s the fundamental setup of a synovial joint. But depending on the location and
14:51
function, some synovial joints have additional supporting structures that
14:55
help with stability, mobility, and protection. For example, let’s take the shoulder joint. Around
15:01
this joint, we can see synovial bursae. Those are small, fluid-filled sacs that act as cushions
15:08
between tendons, muscles, and bones, preventing friction during movement. You’ll find these in
15:13
joints that perform a wide range of motion, and need extra cushion, like the shoulder and knee.
15:18
Another supporting structure are ligaments. Ligaments are strong connective tissue bands that
15:24
reinforce synovial joints and prevent excessive movement. Now, if we remove the humerus from the
15:30
shoulder joint, we can see the glenoid labrum, which is a fibrocartilaginous ring that deepens
15:36
the socket of this joint, making the joint more stable. This is another supporting structure.
15:42
The hip joint has something similar called the acetabular labrum, which serves the same function.
15:47
If we move over to the knee joint, we see another really important supporting structure,
15:52
called the meniscus. Unlike bursae or labrum, menisci are fibrocartilaginous pads that sit
15:58
between the femur and tibia, acting as shock absorbers. Because the knee carries the entire
16:04
body’s weight, it needs extra cushioning, which is why menisci are crucial for knee function.
16:10
Some synovial joints also contain fat pads, which are soft tissue structures that fill spaces within
16:16
the joint, reducing friction and adapting to changes in joint shape during movement.
Types of Synovial Joints
16:22
You see now that even though we’ve got all these different synovial joints in the body,
16:26
they’re structurally different, which is why we classify them into different types.
16:31
The way a joint is built determines how it moves. Some allow a full range of motion, while others
16:39
are more restricted to just bending or gliding. Let’s go through them one by one.
16:44
First, we’ve got the ball-and-socket joint. This is the most mobile type of synovial joint,
16:50
allowing movement in all three planes – flexion, extension, abduction, adduction, rotation,
16:56
and circumduction. You can see this in the shoulder joint and the hip joint. The structure
17:01
is exactly how it sounds, a rounded ball-shaped head fits into a concave socket, making it perfect
17:08
for high mobility. But with great mobility comes great instability, the shoulder, for example,
17:15
is prone to dislocations because the glenoid cavity is shallow compared to the large humeral
17:20
head. That’s why it relies on ligaments, muscles, and the labrum for extra stability.
17:26
Then we have the ellipsoid joint. This joint allows movement in two planes,
17:31
flexion/extension and abduction/adduction, but no rotation. A great example is the wrist joint. The
17:39
oval-shaped articular surface of the radius fits against the ellipsoid shape of the carpal bones,
17:45
allowing movement like bending the wrist up and down or side to side, but notice, it can’t
17:50
rotate as freely as in a ball-and-socket joint. Next, the saddle joint. This one is shaped like
17:58
a saddle, where one bone fits into the other like a rider on a horse. This type of joint is found in
18:04
the thumb at the carpometacarpal joint between the trapezium and first metacarpal. What’s cool about
18:10
this joint is that it allows opposition of the thumb, which is essential for gripping and fine
18:16
motor control. Without this joint, you wouldn’t be able to pinch or grasp objects properly.
18:21
Then we’ve got the hinge joint. This one only moves in one plane, like a door hinge,
18:26
it allows flexion and extension but no side-to-side movement. You’ll find hinge
18:31
joints in the elbow, the humeroulnar joint, knee, or tibiofemoral joint, and interphalangeal joints,
18:38
so fingers and toes. The structure is simple, a convex surface fits into a concave groove,
18:45
which is reinforced by strong ligaments that prevent excess movement. That’s why your elbow
18:51
doesn’t hyperextend easily, the ligaments stop it. Next, the pivot joint. This joint allows
18:58
rotational movement around a single axis. A perfect example is the atlantoaxial joint between
19:06
C1 (atlas) and C2 (axis). This joint is what lets you shake your head “no” because the dens
19:12
of the axis rotates within the ring of the atlas. Another example is the proximal radioulnar joint,
19:19
which allows the forearm to pronate and supinate, that’s how you turn your palm up and down.
19:25
And finally, the plane joint. This one has flat articular surfaces that glide past each
19:31
other in small sliding movements. You’ll find these in the acromioclavicular joint,
19:36
intercarpal joints of the wrist, intertarsal joints of the foot, and the facet joints of
19:41
the vertebrae, or zygapophyseal joints. While they don’t allow much movement individually,
19:47
when combined, like in the vertebral column, they contribute to flexibility and movement.
Classification Scheme of Joints in our Body
19:53
So those were all the types of synovial joints. Each one is designed for a specific function,
19:59
balancing mobility and stability to fit its role in the body.
20:03
And that’s how the joints in our body are organized. If you know the classification,
20:08
you’re guaranteed to be an expert in joints. Every joint has a specific function,
Joint Outro
20:13
whether it’s providing stability, mobility, or a balance between both, and recognizing
20:18
these differences is key to understanding how the body moves, how injuries happen, and even
20:23
how to approach treatment in clinical practice. Now, let’s take this knowledge a step further.
20:30
We are going to go through all the joints in the body, starting from the top. The
20:34
skull joints might seem simple, but they have a far bigger role than you’d expect.
20:39
Click here to watch the next video and see why. If you want a handmade PDF version of this
20:43
lecture, take a quiz to test your knowledge, or access an organized list of all my videos,
20:48
you can find everything on my website. Thanks for watching! See you in the next one.