Saddle Joint

A saddle joint is an articulation between two bones that are saddle-shaped, or concave in one direction and convex in another. It is a type of Synovial Joint. This type of joint is biaxial, and one example is the first carpometacarpal joint between the trapezium (carpal) and the first metacarpal bone of the thumb. This arrangement permits the thumb to flex and extend (within the plane of the palm) as well as abduct and adduct (perpendicular to the palm). This dexterity gives humans the characteristic trait of “opposable” thumbs.