Hinge joints allow motion in how many anatomical planes?

• A. One plane
• B. Two planes
• C. Three planes
• D. Infinite planes

Answer: (A)

Hinge joints are uniaxial, meaning they move in one plane. They primarily allow flexion and extension in the sagittal plane around a single axis, like a door hinge that opens and closes. The joint surfaces and ligaments strongly constrain side-to-side movement and rotation, so the main motion remains in that single plane. A tiny amount of rotation can occur when the joint is flexed, but it isn’t considered a primary plane of motion, so the functional movement is effectively in one plane.