The Joints

Definition: A joint (articulation) is point of contact between bones or between bone and cartilage.

Part A - Joint Classifications
Part B - Joint Movements

Joint Classifications

Joints are classified by:

• The degree of movement they allow
• The structure of the joint

The three types of joints that we will look at are:

1. Fibrous joints
2. Cartilaginous joints
3. Synovial joints

Fibrous Joints

These joints are also called "fixed" or "immoveable" joints, because they do not move. These joints have no joint cavity and are connected via fibrous connective tissue. The skull bones are connected by fibrous joints.

 

 

Cartilaginous Joints

These joints also have no joint cavity and the bones are connected tightly to each other with cartilage. These joints only allow a small amount of movement, so are also called "partly" or "slightly moveable" joints. The vertebrae are examples of cartilaginous joints.

 

 

Synovial Joints

Most of the joints in the body are synovial joints. These joints are "freely moveable" and are characterised by being surrounded by an articular capsule which contains the synovial fluid. Synovial fluid lubricates the joints, supplies nutrients to the cartilage and it contains cells that remove microbes and debris within the joint cavity. Because of the larger range of movements of these joints, there is an increased risk of injury eg dislocations. Synovial joints are located predominantly in limbs.

Many synovial joints also have ligaments either inside or outside the capsule.

 

 

The range of movement provided by these joints is determined by:

• The closeness of the bones at the point of contact. Closer bones make stronger joints, but movements are more restricted. The looser the fit, the greater the range of movement. However, looser joints are more prone to dislocation.
• The flexibility of the connective tissue and the position of the ligaments, muscles and tendons.

Different Types of Synovial Joints

• Hinge - movement occurs primarily in a single plane eg elbow, knee , ankle, interphalangeal joints.
• Ball and socket - allows movement around 3 axes - flexion / extension, abduction / adduction and rotation, eg shoulder, hip.
• Pivot - a ring of bone and ligament surrounds the surface of the other bone - movement in one plane, primarily rotation eg between the atlas and axis (ie the cervical vertebrae numbers 1 and 2) and the radius and ulna.
• Gliding - Flat bone surfaces allow side to side and backwards and forwards movements eg between carpals, tarsals, between the sternum and the clavicle (sterno-clavicular) and the scapula and the clavicle.
• Condyloid - Not on syllabus
• Saddle joints - eg thumb