Which joint type is exemplified by the thumb?

• A. Pivot
• B. Saddle
• C. Ball and socket
• D. Gliding

Answer: (B)

Movement at the base of the thumb is provided by a saddle joint, the carpometacarpal joint between the first metacarpal and the trapezium. A saddle joint has two concave/convex surfaces that fit together like two saddles, allowing movement in two perpendicular planes. This setup enables flexion/extension and abduction/adduction, which together make opposition possible—letting the thumb touch the fingertips for a precise grip. Other joint types don’t match this combination: a pivot joint rotates around a single axis, a ball-and-socket joint offers extensive movement in many directions, and gliding joints allow only small sliding movements. That unique two-planar mobility is why the saddle joint best explains the thumb.