The elbow joint plays a central role in the arm’s overall function, connecting the upper arm to the forearm. This complex joint is essential for a wide range of daily activities, from lifting and carrying objects to precise movements like writing or eating. Its intricate structure allows for both stability and flexibility, enabling the diverse motions that humans rely on every day.
External Appearance
A normal elbow, when viewed externally, presents a distinct and harmonious contour. The skin covering the elbow appears smooth and unblemished, without significant swelling, redness, or visible deformities. At the very tip of the elbow, a prominent bony point, the olecranon, is easily felt, forming the posterior (back) aspect of the joint.
To either side of the olecranon, two other important bony landmarks can be identified: the medial epicondyle on the inner side of the arm and the lateral epicondyle on the outer side. These epicondyles are distinct, rounded projections of the humerus, the upper arm bone. When the arm is fully extended, these three points—the olecranon, medial epicondyle, and lateral epicondyle—form a straight line. The overall contour around the elbow should appear symmetrical and well-defined.
Typical Movement
The normal elbow permits a broad range of movements. The primary actions at the elbow joint are flexion, bending the arm, and extension, straightening it. A healthy elbow can typically flex to a range of 140 to 150 degrees, bringing the forearm close to the upper arm. Full extension usually allows the arm to straighten completely to 0 degrees, or even a slight hyperextension of up to 10 degrees in some individuals.
Beyond bending and straightening, the elbow also contributes to the forearm’s rotational movements: pronation and supination. Pronation turns the palm downwards, while supination turns the palm upwards. These rotations occur between the radius and ulna. A normal elbow allows for 75 to 90 degrees of pronation and 80 to 90 degrees of supination, enabling tasks like turning a doorknob.
Internal Framework
The elbow joint is formed by the articulation of three bones: the humerus, which is the long bone of the upper arm, and the two bones of the forearm, the radius and the ulna. The humerus connects to both the ulna and the radius. Specifically, the trochlea, a spool-shaped part of the humerus, articulates with the trochlear notch of the ulna, forming a hinge-like connection that allows for bending and straightening. The capitulum, a rounded part of the humerus, connects with the radial head, allowing for rotation.
The ulna is the larger of the two forearm bones, located on the side of the little finger. The radius, positioned on the thumb side of the forearm, has a disc-shaped head that articulates with the humerus and the ulna, facilitating forearm rotation. These bony connections and the smooth cartilage covering their surfaces allow for fluid and stable movements.