The first carpometacarpal joint is the joint located at the base of the thumb, connecting the first metacarpal bone to the trapezium bone of the wrist. This joint is crucial for thumb movement, allowing for a wide range of motion, including opposition, which is the ability to touch the thumb to the other fingers. This joint is classified as a saddle joint, which means it allows movement in two planes. The unique structure of the first carpometacarpal joint enables the thumb to perform essential functions, such as grasping and pinching, making it vital for hand dexterity and function.