Synovial joints. These joints move freely, are classified from the functional point of view as diarthrosis and are characterized by the presence of articular cartilage, this covers the surfaces of the bones of the joint, is a hyaline cartilage.
Saddle joint is a type of synovial joint . At a saddle joint, both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other (see Figure below). This allows the two bones to fit together like a rider sitting on a saddle. Saddle joints are functionally classified as biaxial joints.
Examples of saddle joints
The primary example is the first carpometacarpal joint, between the trapezium (a carpal bone) and the first metacarpal bone at the base of the thumb. This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm. This movement of the first carpometacarpal joint is what gives humans their distinctive “opposable” thumbs. The sternoclavicular joint is also classified as a saddle joint.
