Understanding joint structures & their function

LETS DO THIS

Understanding Joint Structures & Their Functions

Okay, first of all, joints are in the top three most important anatomical thingys you're gonna have to know. I had to understand the basics in like the first three weeks... which I'll admit, I failed to do because I'm lazy. But you're not lazy, and you want to learn! Well, you've come to the right place, so let's get started.

Introduction to Joints

Joints have a pretty simple definition: they are the points where two or more bones meet (articulate). Think of it like this—when you hold a person's hand, you are JOINing together, just as two (or more) bones meet at a joint.

Joints allow movement, provide stability, and support weight-bearing functions. Without them, you'd be as stiff as a board... literally.

They are classified in two ways:

• Structure (What they're made of)

• Function (How much they move)

So let's talk about that.

Classification of Joints

A) Structural Classification (Based on Material & Presence of Joint Cavity)

Fibrous Joints – No joint cavity, bones are connected by dense connective tissue.

• Sutures (e.g., skull) – Immovable.

• Syndesmoses (e.g., distal tibiofibular joint) – Slightly movable.

• Gomphoses (e.g., teeth in sockets) – Immovable.

Cartilaginous Joints – No joint cavity, bones connected by cartilage.

• Synchondroses (e.g., growth plates) – Immovable, hyaline cartilage.

• Symphyses (e.g., pubic symphysis, intervertebral discs) – Slightly movable, fibrocartilage.

Synovial Joints – Most common, contain a joint cavity filled with synovial fluid.

• Components:

• Articular cartilage (hyaline)

• Joint capsule (fibrous layer + synovial membrane)

• Synovial fluid (lubrication & nourishment)

• Ligaments (stabilization)

• Bursae (fluid-filled sacs reducing friction)

• Types of Synovial Joints:

• Plane (Gliding) – e.g., intercarpal joints.

• Hinge – e.g., elbow, knee.

• Pivot – e.g., atlantoaxial joint (C1-C2).

• Condyloid (Ellipsoid) – e.g., wrist (radiocarpal joint).

• Saddle – e.g., thumb (1st carpometacarpal joint).

• Ball-and-Socket – e.g., shoulder, hip.

B) Functional Classification (Based on Movement)

• Synarthrosis – Immovable (e.g., sutures in skull).

• Amphiarthrosis – Slightly movable (e.g., pubic symphysis).

• Diarthrosis – Freely movable (e.g., knee, shoulder).

How Do These Joints Move?

Now that may seem like a lot of information... and I'm afraid it really is only a tiny bit of it. However, I recommend making flashcards for all this info! Apps like Quizlet have pre-made flashcard sets, and trust me, they saved my life when learning this.

Alright, brace yourself—here comes more info, but I have faith in you, so let’s dive in!

• Flexion vs. Extension: Flexion is making the joint angle smaller (think of someone FLEXING their bicep), whereas extension is the opposite—making the joint angle greater.

• Abduction vs. Adduction: Best way to remember? ADDuction is when you ADD something to your midline, whereas ABduction is when something is taken away (think of aliens ABDucting your hand away from your body).

• Rotation: Turning around an axis (imagine a ballerina doing a pirouette).

• Circumduction: Circular movement (swinging your arms around like an inflatable tube man).

• Supination vs. Pronation: I remember this by thinking Supination = Showing your palm to the Sky (S for Sky, S for Supination), while pronation is simply the opposite.

• Dorsiflexion vs. Plantarflexion: I think of PLANTarflexion as pointing my toes to the PLANTS on the ground—boom, easy.

• Inversion vs. Eversion: Inversion = sole of the foot INwards, Eversion = sole of the foot outwards. Easy, right?

Conclusion

Now, there's a lot more I could talk about, so if you have any more questions, shoot me an email (or drop a comment below).

The main things you need to learn:
✔️ Types of joints
✔️ How they move
✔️ Eventually, which muscles cause these movements (but that's a topic for another day).

Get this knowledge locked down now, and your future self will thank you!

🔥 Bonus Tip: If you’re struggling to remember joint movements, get up and ACTUALLY MOVE your body while reading—trust me, it helps.

See you in the next post! 😉

EMAIL ME AT: student2physio@gmail.com