Joints

A joint is a place where two bones meet, or a bone meets a cartilage; no bony part of the body can move without one.

Muscles generate the force, and the joint acts as the fulcrum for the movement.

By structure there are three kinds: fibrous, cartilaginous and synovial.

Fibrous joints allow no movement. Example: the sutures, dense fibrous tissue joining the flat skull bones end to end to form the cranium.

In cartilaginous joints the bones are held together by cartilage. Example: the joints between adjacent vertebrae, which permit limited movement.

Synovial joints have a fluid-filled synovial cavity between the two articulating surfaces and allow considerable movement, so they matter most for locomotion.

Synovial joint examples: ball and socket (humerus and pectoral girdle), hinge (knee), pivot (atlas and axis), gliding (between the carpals) and saddle (carpal and metacarpal of the thumb).