The 6 Types of Joints - Human Anatomy for Artists

Summary

This Proko lesson delves into the six types of synovial joints crucial for artists: hinge, pivot, ball & socket, ellipsoid, saddle, and plane. It emphasizes their unique movements and positions, aiding in realistic pose creation and understanding body limitations. The lesson also introduces the spine's significance and assigns practical exercises for better comprehension, encouraging study and simplified drawing of these joints.

Takeaways

• 💡 The human skeleton's joints define the body's motion and its limitations, with a focus on synovial joints for artists due to their mobility.
• 🎯 Synovial joints are crucial for artists as they allow for movement, unlike fibrous and cartilaginous joints which are mostly immobile.
• 🔍 Importance of understanding synovial joints for accurate representation in art, such as the hinge joint's role in limiting foot movements.
• 🤸‍♂️ Six types of synovial joints are identified: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and Plane, each with unique movement capabilities.
• 📐 Hinge joints permit flexion and extension, exemplified by the elbow joint, which only allows movement in one direction.
• 🔄 Pivot joints enable rotation around a single axis, as seen in the radio-ulnar joint, allowing for pronation and supination of the forearm.
• 🏋️‍♂️ Ball & Socket joints offer the broadest range of motion, including flexion, extension, abduction, adduction, rotation, and circumduction, with examples being the shoulder and hip.
• 🛤️ Ellipsoid joints resemble ball & socket joints but restrict rotation, allowing movement on two axes, such as in the wrist.
• 🤲 Saddle joints, like the carpometacarpal joint of the thumb, feature a unique structure that allows for a combination of movements with slight rotation.
• 🛴 Plane joints, while less mobile, permit gliding or rotation and are often found in groups, like in the hand and foot.
• 📝 Assignments for the lesson include finding and studying the movement of these joints on oneself and drawing them in simplified forms for better understanding and application.

Q & A

What is the primary focus of this Proko lesson?

The primary focus of this Proko lesson is to teach about the types of synovial joints in the human body, which are important for artists to understand when drawing moving figures.

Why are synovial joints particularly important for artists?

Synovial joints are important for artists because they are the joints that allow movement, such as the shoulder and knee, and understanding them helps in accurately depicting motion and poses in art.

What types of joints are not considered important for artists in this context?

Fibrous and cartilaginous joints are not considered important for artists in this context, as they hardly move or do not move at all, unlike synovial joints.

How many types of synovial joints are there, and what are they?

There are six types of synovial joints: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and Plane.

What is the basic movement allowed by a hinge joint?

A hinge joint allows movement only on one axis, permitting flexion and extension, similar to the way a door opens and closes.

How does a pivot joint differ from a hinge joint in terms of movement?

A pivot joint allows rotation around one axis, but along the long axis of the bone, enabling movements like pronation and supination of the forearm.

What kind of movement does a ball & socket joint allow?

A ball & socket joint allows movement in all axes, including flexion, extension, abduction, adduction, rotation, and circumduction, providing the greatest range of motion.

What is unique about the ellipsoid joint compared to the ball & socket joint?

The ellipsoid joint is similar to a ball & socket joint but does not allow rotation due to its oval shape and ligaments, though it can still rotate on two axes.

How does the saddle joint differ in structure from other synovial joints?

The saddle joint has a unique structure where both bones have a concave and convex surface that fit together, allowing for a combination of movements including flexion, extension, abduction, adduction, circumduction, and slight rotation.

What is the main function of a plane joint?

A plane joint allows for gliding or rotation movements, typically found in groups such as the carpals of the hand and the tarsals of the foot.

What special assignment is given to the viewers of the lesson, and where should they post their work?

The viewers are assigned to find and study the movements of the synovial joints on themselves and to draw them as simple versions. They should post their drawings in the Facebook group at facebook.com/groups/anatomy4artists for critique.

What additional resources are available for viewers to enhance their understanding of anatomy?

Additional resources include a PDF ebook that visually defines all the anatomical terms, another PDF ebook classifying every joint in the body by type, and a 3D model of Robo Skelly, all available as premium features at proko.com/anatomy.

Outlines

00:00

🤖 Understanding Synovial Joints in Art

The first paragraph introduces the importance of synovial joints in the human body for artists, as they are the only joints that allow significant movement, such as the shoulder and knee. It emphasizes the need to focus on these joints for realistic depiction in art, rather than on immovable joints like those in the pubic bones. The paragraph outlines six types of synovial joints: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and Plane, explaining their functions and the movements they allow. The hinge joint, for example, is compared to a door hinge, allowing only flexion and extension, as seen in the elbow. The pivot joint, as in the forearm, allows rotation along the long axis, resulting in pronation and supination. The ball and socket joint, found in the hip and shoulder, is highlighted for its versatility in movement across all axes.

05:02

🏆 Advanced Joint Structures and Their Functions

The second paragraph delves into the ellipsoid joint, which, while similar to the ball and socket joint, has limited rotation due to its oval shape and ligaments. It allows for flexion/extension, abduction/adduction, and circumduction. The saddle joint is described as having a unique structure with both bones featuring concave and convex surfaces, allowing for a range of movements including flexion, extension, abduction, adduction, circumduction, and slight rotation, exemplified by the carpometacarpal joint of the thumb. The plane joint, less dynamic than others, consists of flat surfaces that can glide or rotate, often found in groups such as the carpals of the hand and tarsals of the foot. The spine is mentioned as an important exception for artists among cartilaginous joints. Assignments for the lesson include finding and studying these joints on oneself and drawing them in simplified forms, with resources provided for further study and critique in a dedicated Facebook group.

10:06

📚 Utilizing Simplified Forms for Artistic Anatomy

The final paragraph discusses the benefits of using simplified forms for understanding and applying the anatomy of the skeleton in art. It introduces a 3D model of 'Robo Skelly' available as a premium feature on proko.com/anatomy, which allows users to zoom and rotate the model for a better grasp of the skeletal structure. This tool is intended to assist with the current assignment and future lessons on the skeleton. The paragraph also mentions additional premium resources, including a PDF ebook that visually defines anatomical terms and another that classifies every joint in the body by type, enhancing the learning experience for artists.

Keywords

💡Synovial Joints

Synovial joints are the most common type of joint in the human body and are characterized by their ability to move freely. They are the focus of the video script because they are essential for artists to understand when drawing the human form, as they allow for a wide range of motion. Examples of synovial joints include the shoulder and knee, which are mentioned in the script as joints that artists should pay attention to.

💡Fibrous and Cartilaginous Joints

Fibrous and cartilaginous joints are types of joints that have limited or no movement. They are less relevant for artists drawing dynamic poses, as they do not contribute significantly to the range of motion. The script mentions these types of joints in contrast to synovial joints, highlighting that they hardly move and should not be the focus for artists learning to draw the human body.

💡Hinge Joint

A hinge joint is a type of synovial joint that allows movement in one plane, similar to the way a door opens and closes. It is characterized by its ability to flex and extend but does not permit rotation. The script uses the elbow as a prime example of a hinge joint, demonstrating how it allows for flexion and extension but not rotation.

💡Pivot Joint

A pivot joint allows for rotation around a single axis, with one bone rotating within a ring formed by another bone and ligaments. The script explains the pivot joint using the radio-ulnar joint as an example, which allows for the pronation and supination of the forearm, demonstrating the joint's role in rotational movement.

💡Ball & Socket Joint

The ball & socket joint is a type of synovial joint that allows for the greatest range of motion, including flexion, extension, abduction, adduction, and rotation. The script highlights the shoulder and hip as examples of ball & socket joints, noting that the shoulder's shallow socket provides a wider range of motion at the expense of stability.

💡Ellipsoid Joint

An ellipsoid joint is similar to a ball & socket joint but with an oval-shaped head that restricts rotation while still allowing movement in two axes. The script uses the wrist, or radiocarpal joint, as an example, illustrating how the ellipsoid joint allows for various movements but with less rotational freedom than the ball & socket joint.

💡Saddle Joint

A saddle joint is characterized by its unique structure where both bones have complementary concave and convex surfaces, allowing for a combination of gliding and rotation. The script describes the carpometacarpal joint of the thumb as an example of a saddle joint, emphasizing its ability to perform various movements due to its distinctive shape.

💡Plane Joint

A plane joint consists of two relatively flat surfaces that allow for gliding or rotation, often found in groups. The script mentions the acromioclavicular joint and the joints within the carpals of the hand and tarsals of the foot as examples, noting that while they may not be as complex as other types of joints, they still play an important role in movement.

💡Flexion and Extension

Flexion and extension are movements that occur around a single axis, where flexion refers to the bending of a joint and extension refers to the straightening of a joint. The script explains these movements in the context of hinge joints, such as the elbow, where flexion and extension are the primary movements allowed.

💡Pronation and Supination

Pronation and supination are specific types of rotation that occur at the forearm, allowing the palm to face down (pronation) or up (supination). The script describes these movements as a result of the pivot joint action at the radio-ulnar joint, highlighting the importance of understanding joint function for accurate depiction in art.

💡Circumduction

Circumduction is a complex movement that involves a combination of flexion, extension, abduction, and adduction, resulting in a circular motion of a limb. The script mentions circumduction in the context of ellipsoid joints, such as the wrist, to illustrate the range of motion these joints allow.

Highlights

Joints in the skeleton define the body's motion and its limitations.

Artists should focus on synovial joints, such as the shoulder and knee, as they are movable.

Fibrous and cartilaginous joints hardly move, with some being completely immobile.

Synovial joints are crucial for drawing realistic motion and understanding pose limitations.

There are six types of synovial joints: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and Plane.

Hinge joints allow movement on one axis, preventing rotation in other directions.

The elbow is a prime example of a hinge joint, facilitating flexion and extension.

Pivot joints allow rotation along the long axis, as seen in the radio-ulnar joint below the elbow.

Pronation and supination of the forearm are facilitated by the pivot joint.

Ball & Socket joints permit movement in all axes, providing a wide range of motion.

The hip and shoulder joints are examples of Ball & Socket joints, with differences in socket depth affecting stability and range of motion.

Ellipsoid joints are similar to Ball & Socket but restrict rotation due to ligaments and oval shape.

The wrist, or radiocarpal joint, is an example of an Ellipsoid joint.

Saddle joints have a unique structure allowing for flexion, extension, abduction, adduction, and slight rotation.

The carpometacarpal joint of the thumb is an example of a Saddle joint.

Plane joints consist of flat surfaces that allow gliding or rotation, often found in groups.

The acromioclavicular joint is an example of a Plane joint, adjusting during shoulder elevation.

The spine is an important exception for artists when considering cartilaginous joints.

Assignments for the lesson include finding and studying the movement of the six synovial joints on oneself.

A second assignment is to draw the synovial joints as simple versions for better understanding in perspective.

Proko offers a premium feature with a PDF ebook defining anatomical terms visually.

A 3D model of Robo Skelly is available for premium users to aid in understanding simplified forms for drawing.

Transcripts

The joints of the skeleton define the motion of the body and its limitations.

Hey welcome to another lesson on Proko.

This lesson is about the types of joints in the human body.

As artists we really only need to learn the synovial joints, like the shoulder and knee,

because they move.

Joints that are fibrous and cartilaginous hardly move, and some, like the connection

of the two pubic bones, don't move at all.

When you're learning how to draw, pay attention to synovial joints, and keep your thoughts

away from pubic bones.

If you know where the hinge joint is on this foot, you know that it won't do this or this

when you stand on your toes.

It will do this.

We need to know the position of that hinge joint to make squash and stretch look like

the real thing.

Synovial Joints

There are 6 types of synovial joints.

They have varying shapes, but the important thing about them is the movement they allow.

Joints determine what positions our bodies can take.

We learn them to invent poses.

And we learn the limits to stretch the limits.

The 6 types of synovial joints are: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and

Plane.

Let's go through them one by one.

Hinge

The hinge is a very simple joint.

It allows movement only on one axis.

It's structure prevents rotation this way, or this way.

The head of one bone wraps around the cylindrical head of the other, allowing a very stable

rotation this way.

Going back to the terminology from last week, the hinge joint allows flexion and extension.

That's it!

Thats all it does, but it does it well.

Like the hinges on a door, allow it only to open or close.

The best example of it is the elbow.

Here's the rotation on a simplified skeleton.

Flexion and extension.

So if the elbow only allows flexion and extension, how is it that we are able to twist the forearm?

Well, let's take a look at the next joint..

Pivot

The pivot joint also allows rotation at only one axis.

However, it rotates along the long axis.

A cylindrical bone fits into a ring of bone and ligament, like with the radio-ulnar joint

just below the elbow.

The cap on the radius bone fits nicely into this notch on the ulna bone.

Ligaments complete the ring, holding the bone in place and allow the radius only to rotate

inside of it.

The result on the forearm is what we call pronation and supination.

During pronation, the base of the radius rotates over and around the head of the ulna.

The ulna stays relatively still.

Remember, the hinge joint at the elbow, prevents the ulna from twisting.

So all of that twisting happens at the radius.

And by the way, the distal joint of the ulna and radius is also a pivot joint.

The combination of the pivot at the top and at the bottom creates that twisting motion

for pronation and supination.

Ball & Socket

The ball & socket is the champion of all joints.

Hooray for the ball and socket!

It's structure is just like how it sounds.

A ball inside of a socket.

This simple and effective structure allows it to move in all axes - flexion, extension,

abduction, adduction, rotation, and circumduction.

The two ball and socket joints of the body are at the hip and the shoulder.

The hip has a deep socket, which gives it stability, but limits some range of motion.

The shoulder joint has a shallower socket, which gives it greater range of motion, but

takes away some stability.

Maybe that's why a dislocated shoulder is so common.

Ellipsoid

The ellipsoid joint is very similar to a ball & socket.

However, the ligaments and its oval shape prevent rotation.

But it still has the ability to rotate on two axes, which allows flexion/extension,

abduction/adduction, circumduction.

Circumduction is just a combination of all the others in a circular motion.

The ball, or oval head also slides inside the socket.

When it rotates along the wider plane, you can see how it pops out too much from the

socket.

So, it slides in back to center.

A great example of an ellipsoid joint is the wrist, aka radiocarpal joint.

The group of carpal bones rotate inside the socket of the radius.

Saddle

The saddle joint is similar to the ellipsoid, but the rotation is limited mostly because

of the bone structure.

The structure of the saddle is very interesting.

Both bones have a concave and convex surface.

Convex means the surface sticks out, like a hill.

Concave means the surface curves in, like a hole or a cave.

The concave plane of one fits on the convex plane of the other.

It's like a 3D yin yang!

Or a cowboy on a horse!

The saddle makes the bottom piece and the cowboy's legs make the top piece.

The legs of the top piece, which wrap around the body of the bottom piece allow a rotation

this way.

The body of the top piece can glide inside of the legs of the bottom piece.

So, this unique structure allows the joint to flex, extend, abduct, adduct, circumduct,

and very slightly rotate.

An example of a saddle joint on the body is the carpometacarpal joint of the thumb.

Let's see that baby in action!

Plane

Finally, the plane joint.

Not really as interesting as the others, but deserves our love anyway.

It's basically two flat-ish surfaces, one on top of the other.

These surfaces can glide or rotate.

They usually come in groups, like the carpals of the hand and the tarsals of the foot.

Ligaments hold these bones together, but might allow some rotation and gliding.

Another plane joint is the acromioclavicular joint.

That's the one between the clavicle and acromion process of the scapula.

When we elevate the shoulder, the angle in here will adjust to keep the scapula vertical.

The Spine

I mentioned in the beginning that cartilaginous joints are not important for artists, except

in one, big, important case: your spine.

We'll talk about that, in the next lesson.

Assignments

For this lesson, there's two assignments.

The first assignment is to find these joints on yourself and study the movement.

I've posted 6 close-up images of Skelly's joints in the description under this video.

Your second assignment is to draw them as simple versions.

When you try to put them into perspective, you may find it difficult, but I will have

Marshall help you understand how to do it.

Post your drawings in the facebook group, at facebook.com/groups/anatomy4artists.

Marshall, the perspective master will help to critique your assignments in the facebook

group.

Later, Marshall will do a demo to show you how to simplify your forms and move them around.

Last week we studied the language of anatomy.

Just looking at a long list of terms can be daunting and difficult to remember.

That's why I put together a PDF ebook that visually defines all these terms.

This ebook is available as a premium feature at proko.com/anatomy.

This week I've included another PDF ebook showing which of the 6 types every joint in

the body is classified as.

And again it's shown visually, rather than just a list, so you can print these out as

reference.

Another premium feature you'll see this week when you login to your account, is a 3D model

of Robo Skelly.

This is a skeleton with simplified forms.

Simplified forms are a lot easier to understand, to remember and are more practical to apply

to your drawings.

So, you can zoom in and rotate around Robo Skelly directly in your browser.

This will help you with the assignment this week and upcoming lessons when we study the

skeleton in detail.

To get all the premium features, go to proko.com/anatomy