The elbow is a joint connecting the upper arm to the forearm. It plays a central role in daily activities. This connection allows for both bending and rotational movements, enabling control over the hand and arm.
The Bones of the Elbow
Three bones form the elbow joint: the humerus, the ulna, and the radius. The humerus is the upper arm bone, extending from the shoulder down to the elbow. Its lower end broadens, featuring surfaces that articulate with the forearm bones.
The ulna is one of the two bones in the forearm, positioned on the pinky finger side. It is longer than the radius and is the stabilizing bone of the forearm. The radius, the other forearm bone, runs parallel to the ulna on the thumb side. The radius is typically thicker than the ulna.
How the Elbow Joint Works
The elbow functions through articulations between these three bones. The spool-shaped trochlea, located at the lower end of the humerus, fits into the trochlear notch of the ulna. This humeroulnar articulation forms the primary hinge that enables bending and straightening of the arm.
Lateral to the trochlea on the humerus is the rounded capitulum, which articulates with the cup-shaped head of the radius. This humeroradial articulation contributes to both hinge-like movements and allows for rotational motion of the forearm.
The joint surfaces are covered with smooth hyaline cartilage, which reduces friction and absorbs shock. The entire joint is enclosed within a fibrous joint capsule, a fluid-filled sac that helps lubricate and stabilize the elbow.
The Elbow’s Role in Movement
The elbow joint facilitates movements fundamental to arm function. Flexion involves bending the arm, bringing the forearm closer to the upper arm, while extension is the opposite action, straightening the arm. These movements are essential for tasks like lifting objects, eating, or reaching for items.
Beyond bending and straightening, the elbow also allows for pronation and supination of the forearm. Pronation involves turning the palm downward, such as when typing or turning a doorknob. Supination is the movement of turning the palm upward. These rotational capabilities, involving the radius pivoting around the ulna, enable fine motor control and dexterity for daily activities.