Which joint moves uniaxially such as the knee?

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

Answer: (D)

Movement around a single axis is what uniaxial joints do. The knee primarily allows bending and straightening in one plane—flexion and extension—so its motion is like a door hinge: a single set of movements around one axis, with little accompanying motion in other directions. That focused, hinge-like motion is why the knee is described as a hinge joint.

Ball-and-socket joints permit movement in multiple directions: flexion and extension, abduction and adduction, and rotation, all around multiple axes, so they’re not uniaxial. Pivot joints allow rotation around a single axis, but the knee’s main action is bending and straightening rather than turning around a long axis. Gliding joints involve sliding movements between adjacent bones and are typically nonaxial or only lightly restricted to a single plane, not the hinge-like flexion/extension seen at the knee.