Answer: saddle joint
Explanation:
A joint is where two bones meet. Synovial joints are one of three types of joints in the body. Synovial joints are unique because they contain a fibrous joint capsule with synovial fluid. Hinge and ball-and-socket joints are both types of synovial joints. Saddle joints are another type of synovial joint.
The saddle joint gets its name because the bone forming one part of the joint is concave (turned inward) at one end and looks like a saddle. The other bone’s end is convex (turned outward), and looks like a rider in a saddle.
Saddle joints are also known as sellar joints. These highly flexible joints are found in various places in the body, including the thumb, shoulder, and inner ear.
How do they move?
Unlike hinge joints, such as those between the bones in your fingers, saddle joints have a much greater range of motion than a simple backward-and-forward movement. Saddle joints have two basic types of movement, known as flexion-extension and abduction-adduction.
Flexion and extension are opposite movements, but they’re easy to visualize. When you bend your elbow, you decrease the angle between your upper arm and your forearm. This is an example of flexion. When you straighten your arm, you’re extending it, increasing the angle between your upper and lower arms. This is an example of extension.
Abduction and adduction are movements related to the midline of a structure. For example, spreading your fingers wide moves them away from the midline down the center of your hand. Adduction is a return toward the midline.
Some saddle joints are also capable of combining flexion-extension and abduction-adduction movements
