The humeroulnar and humeroradial joints are classified as hinge joints.
This means that they primarily allow movement in one plane, similar to the way a door opens and closes. In the case of these joints, the main movement allowed is flexion and extension of the forearm relative to the humerus. The anatomy of these joints facilitates this type of movement, as the articulating surfaces of the bones are shaped to fit together in a way that permits this motion while restricting others.