Which type of joint can bend and straighten but cannot rotate?

Hinge joints are specifically designed to allow movement primarily in one plane, which enables bending and straightening actions similar to a door hinge. This uniaxial movement is characteristic of hinge joints, allowing flexion and extension but preventing any form of rotational movement.

Examples of hinge joints in the human body include the knees and elbows. In these joints, the articulating surfaces are shaped to fit together in a way that limits motion to the bending and straightening movement, ensuring stability and support during physical activities.

In contrast, pivot joints allow for rotational movement around a single axis, such as the joint between the first and second cervical vertebrae. Condyloid joints allow for bending, straightening, and some rotational movement, but primarily enable movement in two planes. Saddle joints provide a greater range of motion than hinge joints, permitting bending and straightening as well as some rotation. Hence, hinge joints stand out for their unique capability to enable flexion and extension while restricting rotational movements.