Britannica Sources used in this answer

How does the elbow joint allow the forearm to bend and straighten?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Front and back views of the human skeleton are shown side by side, with labeled bones including the skull, spine, ribs, pelvis, arms, legs, hands, and feet. Insets detail the bones of the foot and hand, highlighting major bone groups and anatomical terms. — human skeleton Front and back views of the human skeleton.

The elbow is a hinge joint that facilitates the movement of the forearm through the interaction of the humerus (upper arm bone) and the ulna and radius (forearm bones). Specifically, the spool-shaped trochlea at the lower end of the humerus fits into a notch in the ulna, creating the primary hinge mechanism for bending and straightening.1

These movements are driven by the contraction of specific muscle groups:1

Bending (Flexion): This action, which brings the hand closer to the shoulder, is primarily achieved by the contraction of the biceps brachii, brachialis, and brachioradialis muscles.12
Straightening (Extension): This action, which increases the angle at the elbow and moves the hand away from the shoulder, is primarily accomplished by the triceps brachii.12

While these muscles drive the motion, the joint is stabilized by ligaments and a protective capsule that prevent displacement during movement.1