Hinge joints are a type of synovial joint that allow movement in one direction, similar to the way a door opens and closes. They are characterized by a cylindrical end of one bone fitting into a trough-shaped surface of another bone. This structure enables flexion and extension, making hinge joints essential for activities like bending the elbow and knee. Common examples of hinge joints include the fingers, toes, and the ankle. These joints are supported by ligaments and surrounded by a synovial membrane, which produces fluid to reduce friction during movement. Their design provides stability while allowing a range of motion.