Which type of joint allows movement mainly in one plane, including bending and straightening?

Hinge joints are specifically designed to allow movement primarily in one plane, enabling the flexion and extension of body parts. A good example of a hinge joint is the elbow, which allows the forearm to bend towards the upper arm and then straighten back out. This type of joint resembles the mechanism of a door hinge, where movement is restricted to one direction—opening and closing—thereby facilitating actions like bending at the knee or the elbow.

In contrast, ball-and-socket joints, such as the shoulder and hip joints, allow for a wider range of movement, including rotation in multiple planes. Pivot joints, like those found in the neck, permit rotational movement around a single axis rather than simple bending and straightening. Ellipsoid joints provide a greater range of motion than hinge joints but still allow movement across two planes, which is more complex than the uniplanar movement associated with hinge joints.

By focusing on the one-plane movement characteristic of bending and straightening, hinge joints embody the definition provided in the question.