What type of joint allows for rotational movements around a single axis?

A pivot joint is specifically designed for rotational movement around a single axis, making it the correct answer for this question. This type of joint allows one bone to rotate around another, which is pivotal in certain movement functions in the body.

An excellent example of a pivot joint is the atlanto-axial joint located in the neck, where the first two cervical vertebrae allow for the rotation of the head. This unique structure permits the head to turn from side to side, demonstrating the pivot joint's capability for rotation.

In contrast, other types of joints do not permit this specific rotational movement as their structural design supports different kinds of motion. For instance, a ball-and-socket joint allows for movement in multiple directions, including rotation, but is not restricted to a single axis like the pivot joint. A hinge joint primarily permits bending and straightening motions, similar to that of a door, without the ability to rotate. Meanwhile, a saddle joint permits movement along two axes, allowing for a wider range of motion than a pivot joint but again lacks the single-axis rotational capacity. Thus, the pivot joint stands out for its exclusive functionality in rotational movements around one axis.