Which joint is an example of a saddle joint?

Which joint is an example of a saddle joint?

• A. Elbow
• B. Knee
• C. Thumb
• D. Shoulder

Answer: (C)

A saddle joint features surfaces that are shaped like a saddle: one bone surface is concave in one direction and convex in the other, allowing movement in two planes. This shape enables bending and straightening as well as bringing the thumb toward and away from the hand—opposition—so the thumb can touch the other fingers. The base of the thumb has this arrangement between the trapezium carpal bone and the first metacarpal bone, which is what gives the thumb its unique range of motion. That combination of two-plane movement with a bit of stability is distinctive for saddle joints. In contrast, the elbow mainly allows movement in one plane (flexion and extension) as a hinge joint. The knee is also primarily hinge-like with a bit of rotation when flexed. The shoulder is a ball-and-socket joint, permitting rotation in many directions. So the thumb’s base joint is the classic saddle joint.

A saddle joint features surfaces that are shaped like a saddle: one bone surface is concave in one direction and convex in the other, allowing movement in two planes. This shape enables bending and straightening as well as bringing the thumb toward and away from the hand—opposition—so the thumb can touch the other fingers. The base of the thumb has this arrangement between the trapezium carpal bone and the first metacarpal bone, which is what gives the thumb its unique range of motion.

That combination of two-plane movement with a bit of stability is distinctive for saddle joints. In contrast, the elbow mainly allows movement in one plane (flexion and extension) as a hinge joint. The knee is also primarily hinge-like with a bit of rotation when flexed. The shoulder is a ball-and-socket joint, permitting rotation in many directions. So the thumb’s base joint is the classic saddle joint.