What is the anatomical classification of the first carpometacarpal joint?

The first carpometacarpal joint, located at the base of the thumb, is classified anatomically as a sellar or saddle joint. This classification is based on the unique structure of the bones that form this joint. The trapezium bone of the wrist has a saddle-shaped articular surface that articulates with the base of the first metacarpal, which also has a complementary saddle shape. This anatomical configuration allows for a wide range of motion, including opposition, which enables the thumb to touch the other fingers—a critical movement for grasping and manipulating objects.

The saddle joint permits movements in two planes: flexion and extension as well as abduction and adduction, making it distinctly functional compared to other types of joints. This versatility of movement is essential for the intricate hand functions that involve fine motor skills. The saddle joint's unique structure and movement capabilities differentiate it from others, such as hinge joints that restrict movement to one plane or pivot joints that allow rotation about a single axis.