Which joint allows movement around one axis in the transverse plane, such as the radioulnar joint?

• A. Pivot joint
• B. Hinge joint
• C. Ball-and-socket
• D. Saddle joint

Answer: (A)

Movement around a single axis in the transverse plane describes rotation, which is a uniaxial motion. The radioulnar joints rotate the radius around the ulna to allow pronation and supination, a classic example of rotation at a pivot joint. Pivot joints are built to allow this one-axis rotation, while other joints either move mainly in a different plane (like hinge joints, which flex and extend mainly in the sagittal plane), or permit multiple axes of movement (ball-and-socket and saddle joints). So the pivot joint best fits the idea of rotational movement around one axis seen in the radioulnar joints.