Which joint type allows rotation around a single axis?

Which joint type allows rotation around a single axis?

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

Answer: (A)

Rotation around a single axis is typical of a pivot joint. In a pivot joint, one bone spins around a single line of rotation in relation to another bone, allowing a rocking or turning motion. Classic examples include the joint between the atlas and axis in the neck, which lets the head turn side to side, and the proximal radioulnar joint, which enables forearm rotation to turn the palm up or down. Because the movement is essentially a rotation about one axis, this type fits the description best. Hinge joints, on the other hand, move mainly in one plane—bending and straightening like a door hinge—without rotation around a single axis. Ball-and-socket joints provide rotation around multiple axes, offering versatility in many directions (think shoulder or hip). Saddle joints permit movement in two planes and allow some opposing motions, but they do not produce pure rotation around a single fixed axis.

Rotation around a single axis is typical of a pivot joint. In a pivot joint, one bone spins around a single line of rotation in relation to another bone, allowing a rocking or turning motion. Classic examples include the joint between the atlas and axis in the neck, which lets the head turn side to side, and the proximal radioulnar joint, which enables forearm rotation to turn the palm up or down. Because the movement is essentially a rotation about one axis, this type fits the description best.

Hinge joints, on the other hand, move mainly in one plane—bending and straightening like a door hinge—without rotation around a single axis. Ball-and-socket joints provide rotation around multiple axes, offering versatility in many directions (think shoulder or hip). Saddle joints permit movement in two planes and allow some opposing motions, but they do not produce pure rotation around a single fixed axis.