What is a saddle joint classified as?

A saddle joint is classified as a type of synovial joint because of its unique structure and function. Synovial joints are characterized by the presence of a synovial cavity filled with fluid, articular cartilage on the bone surfaces, and a joint capsule. The saddle joint allows for a wide range of movement, including flexion, extension, and circumduction, much like a person sitting on a saddle. A key feature of a saddle joint is that it consists of two bones whose articulating surfaces have both concave and convex regions, allowing them to fit together like a rider and a saddle. This configuration provides significant stability and mobility, which is essential in joints such as the carpometacarpal joint of the thumb, allowing for grasping and opposable thumb movements. Understanding saddle joints as synovial structures helps differentiate them from other joint types, showcasing their anatomical and functional significance in human movement.