Which of the following is an example of a saddle joint?

A saddle joint is characterized by two opposing surfaces that resemble the shape of a saddle, allowing for a greater range of motion than some other types of joints. In the case of the base of the thumb, or the carpometacarpal joint of the thumb, it allows the thumb to move across the palm, enabling a unique range of motion, including opposition. This feature is essential for functions such as grasping and pinching.

In contrast, the wrist is primarily an example of a complex joint that allows for flexion, extension, and some rotation but does not fit the saddle joint classification. The knee, a hinge joint, primarily allows for flexion and extension with limited rotational ability. The shoulder, identified as a ball-and-socket joint, permits a wide range of motion in multiple axes but does not exhibit the saddle joint characteristics. Therefore, the base of the thumb stands out as the only true example of a saddle joint in the options provided.