The term “elbow” refers to the visible bend connecting the upper arm to the forearm. While commonly understood, human anatomy uses precise names for this region’s complex structures. This article explores the bones, joints, and other anatomical features that collectively form the elbow.
The Bones of the Elbow
The elbow region is formed by three primary bones: the humerus, ulna, and radius. The humerus, the long bone of the upper arm, has a distal end that forms part of the elbow joint. This end features a spool-shaped trochlea, which articulates with the ulna, and a rounded capitulum, which articulates with the radius. Proximal to these surfaces are the medial and lateral epicondyles, bony projections for muscle and ligament attachment. The distal humerus also includes the olecranon fossa posteriorly and the coronoid fossa anteriorly, depressions that accommodate parts of the ulna during movement.
The ulna is located on the medial (little finger) side of the forearm. Its proximal end forms a C-shaped trochlear notch, which fits around the humerus’s trochlea. This notch is bordered by two prominent processes: the olecranon process, forming the bony tip of the elbow, and the coronoid process, located anteriorly. On the lateral side of the coronoid process, the ulna features a radial notch, a small depression where the radius’s head articulates.
The radius is the other forearm bone, positioned on the lateral (thumb) side. Its proximal end includes a cylindrical radial head, which articulates with the humerus’s capitulum and the ulna’s radial notch. Distal to the head is the neck of the radius, followed by the radial tuberosity, an attachment point for the biceps muscle. These three bones work together to create the elbow’s functional movements.
The Elbow Joint Complex
The “elbow” is not a single joint but a complex of three distinct articulations within a common joint capsule. The humeroulnar joint is a hinge joint formed by the articulation between the humerus’s trochlea and the ulna’s trochlear notch. This articulation facilitates the forearm’s flexion (bending) and extension (straightening) movements.
The humeroradial joint involves the articulation between the humerus’s capitulum and the radius’s head. While permitting some rotation, its function also contributes to elbow flexion and extension. These two joints allow the forearm to move through a range of approximately 0 to 145 degrees of flexion.
The proximal radioulnar joint is a pivot joint formed by the articulation between the radius’s head and the ulna’s radial notch. This joint is responsible for the forearm’s pronation (palm-down rotation) and supination (palm-up rotation) movements. Together, these three articulations enable the elbow’s complex and coordinated movements.
Key Anatomical Landmarks
Several other anatomical features contribute to the elbow’s structure and function. The medial epicondyle is a prominent bony projection on the inner side of the distal humerus, easily palpable and serving as an attachment site for wrist and finger flexor muscles. The lateral epicondyle is a less prominent bony projection on the outer side of the distal humerus, providing an attachment point for wrist and finger extensor muscles.
The olecranon forms the distinct bony point at the back of the elbow, particularly noticeable when bent. On the anterior surface, a triangular depression known as the cubital fossa contains important structures like blood vessels and nerves. Strong ligaments, including the ulnar collateral ligament medially and the radial collateral ligament laterally, support the joint complex, providing stability and preventing excessive movement. These landmarks and supporting structures are integral to the elbow’s form and function.