Which joints are classified as ball-and-socket joints?

Ball-and-socket joints are characterized by a spherical end of one bone that fits into a cup-like depression of another bone, allowing for a wide range of motion in multiple directions. The hips and shoulders are classic examples of ball-and-socket joints.

In the shoulder joint, the humeral head fits into the shallow glenoid cavity of the scapula, enabling movement such as abduction, adduction, rotation, and flexion. Similarly, in the hip joint, the spherical head of the femur sits in the deep acetabulum of the pelvis, allowing for extensive movements in various planes, including rotation and circumduction.

The other combinations mentioned do not fit this classification due to their structural configurations. The elbow joint is a hinge joint permitting flexion and extension primarily, while the knee serves as a hinge as well with some rotational capabilities, but it does not provide the ball-and-socket structure necessary for the full range of motion. Likewise, the wrists and ankles are examples of complex joints that allow movement but do not have the spherical and cup-like arrangement characteristic of ball-and-socket joints.