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Types of Joints in the Human Body

The Shoulder Joint

The Shoulder Joint

What are Joints?

Joints are articulations in the human skeletal system, in other words, these are places where bones meet.

Joints are held intact by tough skeletal tissues, namely, muscles, ligaments, tendons and cartilage. These tissues play an important role in connecting bones together. They make sure our joints don’t go too far in the wrong direction.

Classification of Joints in the Body

The functional classification of a joint looks at the degree of movement the joint allows. The Structural classification is based on the type of tissue that holds the joint together. A joint can also be classified by counting how many axes of rotation it has.

Functional Classification of Joints in the Body

The functional classification will assign a joint to one of three groups based on the degree of movement they allow:

  • Immovable joints
  • Slightly Movable joints
  • Freely Movable joints

Immovable Joint (Synarthroses)

Immovable joints are called Synarthroses. They allow no movement whatsoever.

The bony plates of the skull are connected to each other by Synarthrotic joints called Sutures. Just like most Synarthroses, sutures are held together by tough fibrous tissue.

Example of Synarthroses - Sutures

Example of Synarthroses - Sutures

Slightly Movable Joints (Amphiarthroses)

Slightly movable joints are called Amphiarthroses. They allow only little motion.

Intervertebral joints allow your spine to move enough for you to walking around freely and perform your day to day activities. The main tissue that keeps most Amphiarthroses intact is cartilaginous tissue.

Freely Movable Joints (Diarthroses)

Freely Movable joints are called Diarthroses. They are the most movable. Some diarthrotic joints move freely in a single axis while others move freely in multiple axes. Even though the shoulder and knee joints are both freely movable, the shoulder joint has a wider range of motion than the knee.

Diarthroses are characterized by articular cartilage (covering the ends of both bones) and a cavity filled with synovial fluid. Synovial fluid is a thick lubricant that reduces friction in the joint during motion.

Intervertebral fibrocartilage discs join vertebrae together

Intervertebral fibrocartilage discs join vertebrae together

The 6 Types of Synovial Joints

  • Pivot Joint

A good example of a pivot joint can be found in the neck, at the base of the skull. This joint is called the Atlantoaxial joint. It allows you to move your head in many different ways, similar to the head movements of a bobblehead doll. The only other spot in the skeletal system with a pivot joint is the elbow. The pivot joint in your elbow allows your forearm to rotate when you wave at someone.

  • Ball and Socket Joint

As the name suggests, a ball and socket joint connects a ball-shaped end of one bone fits to a socket-shaped end of another bone. This arrangement allows movement in almost every direction just like the joystick of a video game. The hip and shoulder joints are perfect examples of a ball and socket joint.

  • Hinge Joint

This joint allows body parts to extend and bend, a lot like the way the hinges of a door allows the door to open and close. A few places where you would find a hinge joint are the knee, jaw and fingers.

  • Condyloid Joint

The Condyloid joint is similar to the ball and socket joint. In a Condyloid joint, an oval-shaped end of one bone fits into an elliptical cavity at the end of another bone. This joint is sometimes referred to as an ellipsoidal joint due to the shapes of the articular surfaces. The wrist joint, metacarpophalangeal joint (joints metacarpals and phalanges) and metatarsophalangeal joint (joints metatarsals and phalanges) are good examples.

  • Saddle Joint

In a saddle joint, a convex-shaped end of one bone meets a concave-shaped end of another bone. The convex end is shaped like a saddle while the concave end fits on it like a rider. Your thumb is attached to your wrist by a saddle joint known as the Carpometacarpal joint.

  • Gliding Joint

A Gliding joint also called a plane joint is a joint where almost flat surfaces of adjacent bones glide against each other. Examples are the Intercarpal joints in the wrists and the Intertarsal joints in your ankles.

Types of Synovial Joints

Types of Synovial Joints

Summary of the Functional Classification of Joints

Functional Class

Short Description

Example

Synarthroses

Immovable

Suture (skull)

Amphiarthroses

Slightly movable

Intervertebral

Diarthroses

Freely movable

Shoulder, Knee, Hip

Test yourself

For each question, choose the best answer. The answer key is below.

  1. Synovial fluid can be found in
    • Immovable joints
    • Freely movable joints
    • Sutures

Answer Key

  1. Freely movable joints

Structural Classification of Joints in the Body

There are 3 types of joints based on the material that holds the joint together:

  • Fibrous joints
  • Cartilaginous joints
  • Synovial joints

Fibrous Joint

Types of Fibrous Joints:

  • Sutures: Short fibers hold the joint intact.
  • Syndesmoses: Long fibers hold this joint together.
  • Gomphoses: Peg and socket joints keep your teeth in your jaw

Suture joints fuse the bony plates of the skull together with very short fibers. Sutures are also described as Synarthrotic joints because they allow no movement at all.

Syndesmoses can be found in the upper limb connecting radius and the ulna with long fibrous tissue. They allow for slight movement hence they are described as Amphiarthrotic.

Gomphoses means peg in socket. This joint connects the teeth to their tiny bony sockets in the jaw using fibrous tissue. Gomphoses don’t permit movement hence they are Synarthrotic.

Fibrous Joints: (a) Sutures, (b) Syndesmoses, (c) Gomphoses

Fibrous Joints: (a) Sutures, (b) Syndesmoses, (c) Gomphoses

Cartilaginous Joint

A cartilaginous joint uses plates of cartilage to connect two bones together. Just like Fibrous joints, cartilaginous joints have no joint cavity.

Types of Cartilaginous Joints:

  • Symphysis: uses frisbee-like discs of cartilage
  • Synchondroses: uses flexible hyaline cartilage

Symphysis are flat frisbee-like discs of cartilage that joints two bones together. This type of joints can be found between vertebrae where they are referred to as intervertebral discs. They are only slightly movable hence they are described as Amphiarthrotic.

Synchondroses use flexible hyaline cartilage to link two bones together. A good example is the first Sternocostal joint which connects the first rib to the sternum.

Synovial Joint

A synovial joint has a cavities filled with synovial fluid. Synovial fluid lubricates the joint to reduce friction during movement. There are 6 types of Synovial joints, namely Gliding, Hinge, Pivot, Ball and socket, Saddle and Condyloid – these have already been discussed under functional classification of joints above.

Summary of the Structural Classification of Joints

Structural Class

Tissue involved

Example

Fibrous

Fibrous tissue

Suture (skull)

Cartilaginous

Cartilage

Intervertebral

Synovial

Dense connective tissue

Shoulder, Knee, Hip

Classification of Joints by Axes of Rotation

Another way to classify joints is by using their axes of rotation. This method of classifications is based on the number of axes a joint is able to rotate around. This classification is not applicable to Synarthroses and Amphiarthroses because they are not freely movable joints.

This classification separate Diarthroses into 4 classes:

  • Nonaxial: This class contains joints don’t rotate around any particular axis. Gliding joints are freely movable but have no particular axis of rotation.
  • Uniaxial: This class is for joints that rotate around a single axis. The hinge and pivot joint fall in this class.
  • Biaxial: This refers to rotation in two different axes. Condyloid joints and Saddle joints are members of this class. Biaxial joints can flex and extend, abduct and adduct and even perform circumduction.
  • Multiaxial: Joints in this class rotate around more axes than biaxial joints. An example of a multiaxial joint is a Ball and socket joint.
Description of some joint movements

Description of some joint movements

How to classify a joint

To properly classify a joint, you have to consider all three methods discussed above: Functional Classification, Structural Classification and Axes of Rotation. The following table is helpful in classifying joints.

Summary table to classify joints

Structural Class

Types

Functional Class

Axis of Rotation

Example

Fibrous

Sutures

Synarthrotic

N/A

Skull

 

Syndesmoses

Amphiarthrotic

N/A

Tibia and Fibula

 

Gomphoses

Synarthrotic

N/A

Teeth

Cartilaginous

Symphysis

Amphiarthrotic

N/A

Intervertebral

 

Synchondroses

Synarthrotic

N/A

Sternocostal

Synovial

Pivot

Diathrotic

Uniaxial

Neck

 

Ball and Socket

Diathrotic

Multiaxial

Shoulder, hips

 

Hinge

Diathrotic

Uniaxial

Jaw, Knee

 

Condyloid

Diathrotic

Biaxial

Metacarpophalangeal

 

Saddle

Diathrotic

Biaxial

Thumb

 

Gliding

Diathrotic

Nonaxial

Wrist, Ankle, Spine

To properly classify a joint, you should mention the structural class, the type and the functional class. If the joint is diarthrotic, then you should also mention the axes of rotation. Let’s round off with a couple of examples:

  • The elbow joint would be classified as a Synovial, Hinge, Diathrotic, Uniaxial Joint
  • A skull suture would be classified as a Fibrous, Suture, Synarthrotic Joint


Test yourself

For each question, choose the best answer. The answer key is below.

  1. How would you classify a Shoulder joint?
    • Synovial, Ball and Socket, Diathrotic, Multiaxial
    • Synovial, Hinge, Diathrotic, Multiaxial
    • Synovial, Ball and Socket, Diathrotic, Uniaxial

Answer Key

  1. Synovial, Ball and Socket, Diathrotic, Multiaxial