Increasing and decreasing the joint angle occur at which joints?

• A. Pivot joints
• B. Hinge joints and ball-and-socket joints
• C. Plane joints
• D. Sutural joints

Answer: (B)

Changing the angle between two bones happens through flexion and extension. This kind of angular movement is possible at joints designed for bending in one plane or in multiple directions. Hinge joints, like the elbow and knee, allow bending and straightening, so the angle between the adjoining bones can increase or decrease. Ball-and-socket joints, such as the shoulder and hip, permit these movements in addition to other directions, so their angles can also vary significantly. Other joints behave differently: pivot joints mainly rotate around a single axis without a large change in the angle between bones; plane joints allow mainly gliding with little angular change; sutural joints are immovable. So the joints that can both increase and decrease the angle are hinge joints and ball-and-socket joints.