ULNA ANATOMY

GENERAL CHARACTERISTICS

The ulna is the medial bone of your forearm, located opposite your thumb side. It plays a crucial role in forming your elbow joint at its upper end. The ulna stabilizes your forearm and wrist, and works with the radius to enable rotational movements.

The ulna is divided into three main sections: the body (shaft), the proximal epiphysis (upper end), and the distal epiphysis (lower end).

BODY OF THE ULNA

The body of the ulna features several key surfaces and borders. The supinator crest runs obliquely along the posterior surface. The anterior surface provides origin for flexor muscles, while the interosseous border connects the ulna to the radius via membrane. The posterior surface and posterior border serve as landmarks and muscle attachment sites. The medial surface gives origin to additional flexor muscles, and the anterior border separates the volar surface from the medial surface.

Overview

The body of the ulna has a prismoid shape, tapering from a thicker upper end to a thinner lower end. It features three borders and three surfaces. The shaft curves dorsalwards and lateralwards, transitioning from prismoid at the proximal end to more rounded distally. This shape provides strength and support while maintaining flexibility for your forearm movements.

Supinator Crest

The supinator crest sits on the posterior surface of the ulna. It runs as an oblique ridge from the dorsal end of the radial notch to the dorsal border. The upper portion provides attachment for the Supinator muscle, while the triangular area above it gives insertion for the Anconeus muscle.

Anterior Surface (Volar Surface)

The anterior surface is primarily concave in its upper three-quarters and becomes broader and flatter in the lower one-fourth. The upper portion gives origin to the Flexor digitorum profundus muscle. The lower portion provides attachment for the Pronator quadratus muscle, which contributes to your forearm rotation.

Interosseous Border (Lateral Border)

The interosseous border separates the volar and dorsal surfaces of the ulna. It originates at the apex of the radial notch. This border provides attachment for the antibrachial interosseous membrane, connecting the ulna to the radius. A triangular area along it contributes to the origin of the Supinator muscle.

Posterior Surface (Dorsal Surface)

The posterior surface is broad and convex in the upper region and tapers to become narrower toward the lower part. An oblique ridge on this surface provides attachment for the Supinator muscle. The triangular surface above the ridge gives insertion for the Anconeus muscle.

Posterior Border (Dorsal Border)

The posterior border is well-marked in the middle one-third of the bone. It forms the boundary between the posterior and medial surfaces and serves as a key anatomical landmark.

Medial Surface

The medial surface is broad and concave in the upper three-quarters and becomes narrower and more convex in the lower one-fourth, where it is subcutaneous. The upper portion provides origin for the Flexor digitorum profundus muscle.

Anterior Border

The anterior border separates the volar surface from the medial surface. It starts at the medial angle of the coronoid process and ends in front of the styloid process.

PROXIMAL EPIPHYSIS (UPPER END)

The proximal end of the ulna is broader than the distal end and contains the key structures that form the hinge mechanism of your elbow joint. These include the olecranon, coronoid process, ulnar tuberosity, radial notch, and trochlear notch.

Olecranon

The olecranon is a robust, curved, beak-like formation located at the upper and dorsal region of the ulna. It fits into the olecranon fossa of the humerus and allows extension of your forearm during movement.

Coronoid Process

The coronoid process is a pyramidal projection at the upper end of the ulna. It fits into the coronoid fossa of the humerus during your forearm flexion. This structure is essential for elbow flexion and joint stability during motion.

Ulnar Tuberosity

The ulnar tuberosity is a rough prominence on the anterior surface near your elbow. It serves as the attachment point for the Brachialis muscle and plays a critical role in your elbow flexion.

Radial Notch

The radial notch is a narrow, elongated depression along the lateral aspect of the ulna. It articulates with the head of the radius and enables the rotational movements of pronation and supination in your forearm.

Trochlear Notch

The trochlear notch is a deep concavity formed by the olecranon and coronoid process. It articulates with the trochlea of the humerus and allows your elbow to function as a hinge joint for flexion and extension.

DISTAL EPIPHYSIS (LOWER END)

The distal end of the ulna is smaller than the proximal end and includes structures for your wrist stability and forearm rotation. Its key features are the head of the ulna, the articular circumference, and the ulnar styloid process.

Head of the Ulna

The head of the ulna is a prominent lateral protrusion at the lower extremity of the bone. It articulates with the radius at the distal radioulnar joint and provides stability for smooth forearm movement.

Articular Circumference of the Head

The articular circumference is a smooth surface that fits into the ulnar notch of the radius. It facilitates articulation between the ulna and radius and enables the rotational movements of pronation and supination.

Ulnar Styloid Process

The ulnar styloid process is a slender, protruding structure at the distal end of the ulna. It serves as an attachment site for ligaments and plays a key role in maintaining your wrist joint stability.

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