Like most aspects of anatomy and physiology, learning about joints helps us better appreciate the magnificent complexity in our human body.  And it certainly helps us better understand concepts such as movement, stability, range of motion, and importantly prepares us to take proper care of our precious joints. 

The point where one bone meets another (or articulates) is called a joint and as such, they form part of the skeletal system. 

Did You Know?  The study of joints is called anthrology. The study of bones is called osteology. The study of human motion is called kinesiology. 

As with all aspects of human anatomy and physiology, there’s some particular lingo involved, but the good news is that you have likely already heard many of these terms.  Here we will help you file them in your memory bank in the appropriate place!  

Some Joint-related anatomy glossary

Ligaments: A connective tissue connecting bone to bone

Tendons: A connective tissue connecting bone to muscle

Cartilage: A soft gel-like protein padding between bones reducing friction and/or cushioning impact

Meniscus: A type of cartilage found in the knee

When you think of joints, you would be forgiven for assuming all joints relate to movement.  It’s not the complete picture, though certainly where our asana practice is concerned, we tend to focus on the joints that move, particularly those that may be most vulnerable to injury.   Movement is indeed one of the ways of we can classify joints, so let’s begin by looking at the classification of joints.

Classification of Joints

We can broadly classify joints in two ways:

1. The structural classifications – here we look at what kind of materials the joint is made of, such as whether that which binds the bones together is fibrous tissue, cartilage or a fluid-filled joint cavity. 
   
   
2. The functional classification – here we look at how much movement occurs in the joint, is it a lot, some or none at all. 

See Diagram 1 – Classification of Joints

Give me some examples!

• An example of a joint that doesn’t move at all are the suture joints in the skull.  Skull bones need to protect the brain so during childhood the bones knit firmly together with dense connective tissue to form a type of fibrous joint called a suture.   
  
  
• An example of a joint that has a little movement are the cartilaginous discs between vertebrae in the spinal column.  The spinal column plays the crucial role in protecting our spinal cord – the main communication line between our brain and the rest of the body.  The little squishy pads between vertebrae absorb shock and allow us to have a degree of movement in multiple directions.  
  
  
• Examples of a joints with plentiful movements include the elbow, shoulder, knee, and ankle. We’ll break these down a bit further below.

Did You Know?  The shoulder joint, with its vast range of movement, is recognised as the most mobile joint in the body.  The more flexible the joint, the less stable it is, so unsurprisingly, those joints with the most range of motion can be more prone to injury.

Common Movement Glossary

Before we delve a little deeper into the freely movable joints, lets refresh on some of the terminology used to describe movement.

Extension: Increasing the angle of a joint to its resting anatomical position, such as straightening the knees upon standing.

Flexion: Decreasing the angle of a joint such as bending the knee or bending at the elbow, or even bringing the chin closer to the chest.

Hyperextension: The extension of a limb beyond its usual limits. This can happen if we force our legs straight in a standing forward fold, meaning our knees are no longer in line with our ankles (rather our legs resemble a slight C-shape), or if we lock our elbows in a downward dog (again creating a slight bow-shape in the arms).  Some of us are born with hypermobility, while some of us develop it through improper stretching and repetition. Hyperextension puts undue pressure on joints and can result in damage, inflammation, and pain.

Abduction: Moving away from the body’s vertical midline, such as raising your arms out to shoulder height

Adduction: Moving towards the body’s vertical midline, such as lowering the arms next to the body, or squeezing the inner thighs together.

Rotation: An arc or circular movement, such as when we open the hips in tree pose, or roll our shoulders forward or back.

Dorsiflexion: Refers specifically to flexion at the ankle (less used in reference to wrists) where we ease our toes back towards our shin.

Plantarflexion: As above, primarily used in relation to the ankles, it refers to pointing our feet like a dancer.

A Special Look at Synovial Joints

Synovial joints are distinguished from other joints by the presence of a joint cavity between the articulating bones, called a synovial cavity, named for the synovial fluid that lubricates these joints.  All synovial joints are freely movable and fall into the diarthroses category, making them of special interest to us as yogis as we learn to respect and protect our body.

The bones at synovial joints are covered with a type of cartilage called hyaline cartilage, providing a nice slippery surface for bones to move against.  

Many of the components of synovial joints are avascular, meaning they do not receive a direct blood supply, but can receive nutrients to an extent through passive diffusion of molecules in the area.   We should be mindful that this means in general muscle can heal better and/or faster than joint structures.  Our yoga practice (and any physical movement) wants to always adhere to the guiding principle that prevention is always better.   Some connective tissue, once damaged, will never be as new.

Types of synovial joints

Not all synovial joints move the same way or to the same extent.

1. Hinge Joint – allows movement back and forth (extension and flexion). Eg: Elbow bending and straightening
   
   
2. Pivot Joint – allows a circular rotation/pivoting movement. Eg: the 2 bones in the forearm (radius and ulna) twist around allowing us to turn the palm of our hand upwards or downwards.
   
   
3. Ellipsoid/Condyloid Joint – a joint with an ovoid shape, allows movement in multiple planes. Eg: the wrist joint between the radius in the arm and the carpals in the hand.
   
   
4. Plane/Gliding Joint – bones meet in a flat plane. Eg: the intercarpals in the fingers.
   
   
5. Ball & Socket Joint – where the end of one bone is conical, and the end of the other resembles a cup, allowing for multiaxial movement. Eg: in our hip where the femur bone in the leg meets the pelvis, and in our shoulder where the humerus bone in the arm meets the scapula bone of our shoulder.
   
   
6. Saddle Joint – joints that interlock like opposing saddles,  allowing for multiaxial movement.  Eg: the joint at the base of your thumb.

To see pictures of the various joints, click here

Did You Know? The popping sound that joints sometimes make is the gases present in the synovial fluid (such as oxygen, nitrogen and carbon dioxide) being released when a joint capsule is stretched.   Medical consensus states that it’s not necessarily something that puts us ant any risk.   However, if it is coupled with any pain or swelling, we should consult a healthcare professional. 

What is osteoarthritis?

The word arthritis comes from the Greek: joint =  arthron, and itis = inflammation, and refers to where the protective tissues at the points where bones meet, deteriorates, resulting in pain and stiffness.   The most common form of arthritis, osteoarthritis can affect any joint, but very commonly affects hands, knees, hips, toes and lower back. 

It can be triggered by a sudden injury and can worsen over time without proper management to prevent further deterioration of the cartilage. 

Range of motion exercises can help ease the stiffness out of joints, while strengthening and balancing exercises can help build muscles in the surrounding areas to provide greater stability and take some of the strain off joints.   It’s best to seek professional guidance for exercise suggestions so we don’t inadvertently cause further wear and tear on cartilage.

The bottom line

Generally, joints follow the use-it-or-lose-it principle, and love movement.   Key is paying attention to the sensations in our body and not ignoring the wisdom of our body when it says, “that’s far enough”, and working with an experienced yoga teacher or therapist that can help us move into postures where the load is evenly distributed and avoids hypermobility.   

If conditions such as injury or arthritis are present, a qualified yoga therapist can guide us to movements and postures that provide support to joints, while respecting and protecting the cartilage, ligaments and tendons.

Written by Nicole Small, The Yoga Institute

Learn More:

Already a yoga teacher? Our comprehensive 100-hour Yoga Anatomy & Musculoskeletal module is part of our 650-hour Yoga Therapy Course (or as a standalone  module for eligible yoga teachers)

Not a yoga teacher? Our 500-hour Yoga Teacher Training Diploma includes important foundational knowledge of anatomy and physiology.

Not ready to think about teacher training? Our 100-hour Yoga Studies course comes with an optional Anatomy component, allowing you to deepen your knowledge of how your body can move safely in yoga.