Which of the following joints is classified as a hinge joint?

The knee is classified as a hinge joint because it allows movement primarily in one plane, similar to the way a door swings open and closed. This type of joint is characterized by its ability to flex and extend. In the case of the knee, it enables flexion (bending) and extension (straightening) movements, which are crucial for activities such as walking, running, and jumping.

Hinge joints are designed to restrict movement to this single axis, preventing rotation or lateral movement, which contributes to the stability and function of the knee during weight-bearing activities. In contrast, the shoulder and hip joints are ball-and-socket joints, allowing for a greater range of motion in multiple directions. The wrist is a complex joint structure that includes gliding joints and allows for a range of movements, but it does not fit the specific characteristics of a hinge joint.