Functional Anatomy The Joints

3.2. Overview of Joint Types There are three broad categories of joint type in the body. They are classed according to the degree of movement possible. The three categories are: 1. Immovable Also known as fibrous joints 2. Slightly movable Also known as cartilaginous joints 3. Freely movable Also known as synovial joints We shall look at all these categories in turn.

3.3 Fibrous Joints These are non-movable joints. They are the result of tough fibrous tissue forming where the two bone ends meet. What is the function of a fibrous joint? To provide protection. Examples include: 1. Skull 2. Pelvis Fibrous joint

3.4 Cartilaginous Joint These are slightly-movable joints. They are the result of cartilage forming where the two bone meet. This gives a fair degree of resilience. What is the function of a cartilaginous joint? To act as shock absorbers. Examples include: 1. Invertebral discs 2. Ribs to sternum 3.Where pubic bones meet Cartilaginous Joints

3.5 Synovial Joint These are freely movable joints. The only limitation in range of movement is as a result of bone shape at the joint, and ligaments. What is the primary function of a synovial joint? To provide movement. All synovial joints follow the same basic structure as shown

The key components of your illustration have important roles to play in maintaining the structure of the joint. Ligaments Join bone to bone for stability 2. Capsule Provides stability and protection from infection 3. Cartilage Reduce wear and tear on bones 4. Synovial Fluid Lubricates the joint and provides shock absorption 5. Synovial Membrane Produces synovial fluid In some joints, for example the knee, there are pads of fat and/or discs of cartilage to further help absorb shock and reduce general ‘wear and tear’.

3.6 Types of Synovial Joints Synovial joints can be divided into six basic types. The types are governed by the type of movement or movements they allow. The six basic types are: Gliding Hinge Pivot Condyloid Saddle Ball and Socket

1. Gliding Definition: The bone surfaces are small and flat, or slightly concave and one bones slides over the other. Examples: 1. Carpals and tarsals 2. Ribs and vertebrae 3. Scapula and ribs Movements: Only slight movement is possible due to the restrictions of attached ligaments. Movements possible are: 1. side to side (abduction / adduction) 2. Back and forth (extension/flexion)

2. Hinge Definition: Two bones join in such a way that movement is possible only in one direction, usually at right angles to the bones. Examples: 1. Elbow 2. Knee 3. Ankle Movements: A uniaxial joint allowing movement in only one direction The only movement possible is: Back and forth (extension/flexion)

3. Pivot Definition: A joint constructed in such a way that rotation only is possible (usually about the long axis of the bone) Examples: 1. Atlas and axis of neck 2. Radius and humerous Movements: A uniaxial joint allowing movement in only one direction The only movement possible is: Rotation

4. Condyloid Definition: Also known as an ellipsoid joint. The bone ends make the shape of an ellipse. Examples: 1. Carpals and radius 2. Metacarpals and phalange Movements: A biaxial joint allowing movement in two main directions. The movements possible are: 1. Back and forth (extension/flexion) 2. Side to side (abduction/adduction) 3. Some Circumduction

5. Saddle Definition: The bone ends are shaped like a rider on a saddle Example: 1. Carpal/metacarpal of thumb Movements: A biaxial joint allowing movement in two main directions. Movements possible are: 1. side to side (abduction / adduction) 2. Back and forth (extension/flexion)

6. Ball and Socket Definition: A ball-shaped bone end fits into a socket or cup-shaped bone. Examples: 1. Hip 2. Shoulder Movements: A multiaxial joint allowing movement in many directions around the joint. The movements possible are: 1. Back and forth (extension/flexion) 2. Side to side (abduction/adduction) 3. Rotation 4. Circumduction

The shoulder joint is the most freely moving ball and socket joint we have. The illustration may help you with your answer. Why is the shoulder joint so freely moving? Because the socket is shallow. What do you suppose is the risk of such a freely moving joint? It is easy to dislocate.