ULNA ANATOMY

GENERAL CHARACTERISTICS

• The ulna is the medial bone of the forearm, located opposite the thumb side
• Plays a crucial role in forming the elbow joint at its upper end
• Stabilizes the forearm and wrist, and works with the radius to enable rotational movements
• Divided into three main sections:
  • Body (shaft)
  • Proximal epiphysis (upper end)
  • Distal epiphysis (lower end)

BODY OF THE ULNA

• Has a prismoid shape, tapering from a thicker upper end to a thinner lower end
• Features three borders and three surfaces
• Curves dorsalwards and lateralwards, transitioning from prismoid at proximal end to more rounded distally
• Provides strength and support while maintaining flexibility for forearm movements

Supinator Crest

• Location:
  • On the posterior surface
  • Oblique ridge running from dorsal end of radial notch to dorsal border
• Function:
  • Upper portion: Attachment for the Supinator muscle
  • Triangular area above: Insertion for the Anconeus muscle

Anterior Surface (Volar Surface)

• Structure:
  • Primarily concave in upper three-quarters
  • Broader and flatter in lower one-fourth
• Function:
  • Upper portion: Origin for the Flexor pollicis longus muscle
  • Lower portion: Attachment for the Pronator quadratus muscle (forearm rotation)

Interosseous Border (Lateral Border)

• Location:
  • Separates the volar and dorsal surfaces
  • Originates at the apex of the radial notch
• Function:
  • Attachment for the antibrachial interosseous membrane, connecting ulna to radius
  • Triangular area contributes to origin of the Supinator muscle

Posterior Surface (Dorsal Surface)

• Structure:
  • Broad and convex in upper region
  • Tapers and becomes narrower toward lower part
• Function:
  • Oblique ridge: Attachment for the Supinator muscle
  • Triangular surface above ridge: Insertion for the Anconeus muscle

Posterior Border (Dorsal Border)

• Structure: Well-marked in middle one-third of bone
• Function:
  • Boundary between dorsal and lateral surfaces
  • Key anatomical landmark

Medial Surface

• Structure:
  • Broad and concave in upper three-quarters
  • Narrower and more convex in lower one-fourth, which is subcutaneous
• Function: Upper portion provides origin for the Flexor digitorum profundus muscle

Anterior Border

• Location:
  • Separates the volar surface from the medial surface
  • Starts at medial angle of coronoid process
  • Ends in front of the styloid process

PROXIMAL EPIPHYSIS (UPPER END)

• The proximal end is broader and includes key structures critical to function
• The olecranon and coronoid process form the hinge mechanism of the elbow joint

Overview

• Key Structures:
  • Olecranon
  • Coronoid Process
  • Ulnar Tuberosity
  • Radial Notch
  • Trochlear Notch
• Function: Forms the hinge mechanism of the elbow joint

Olecranon

• Location: Upper and dorsal region of the ulna
• Structure: Robust, curved, beak-like formation
• Function:
  • Fits into the olecranon fossa of the humerus
  • Allows extension of the forearm during movement

Coronoid Process

• Location: Pyramidal projection at the upper end of the ulna
• Function:
  • Fits into the coronoid fossa of the humerus during forearm flexion
  • Essential for elbow flexion and joint stability during motion

Ulnar Tuberosity

• Location: Rough prominence on anterior surface near elbow
• Function:
  • Attachment point for the Brachialis muscle
  • Plays critical role in elbow flexion

Radial Notch

• Location: Narrow, elongated depression along lateral aspect of ulna
• Function:
  • Articulates with the head of the radius
  • Enables rotational movements: pronation and supination

Trochlear Notch

• Structure: Deep concavity formed by olecranon and coronoid process
• Function:
  • Articulates with the trochlea of the humerus
  • Allows elbow to function as hinge joint for flexion and extension

DISTAL EPIPHYSIS (LOWER END)

• The distal end is smaller than the proximal end
• Includes structures for wrist stability and forearm rotation

Overview

• Location: Lower end of the ulna, smaller than proximal end
• Features:
  • Head of the Ulna
  • Ulnar Styloid Process
• Function:
  • Contributes to wrist and forearm stability
  • Facilitates rotational movements of the forearm

Head of the Ulna

• Location: Lower extremity of the ulna
• Structure: Prominent lateral protrusion
• Function:
  • Articulates with radius at the distal radioulnar joint
  • Provides stability for smooth forearm movement

Articular Circumference of the Head

• Structure: Smooth surface fitting into ulnar notch of radius
• Function:
  • Facilitates articulation between ulna and radius
  • Enables rotational movements: pronation and supination

Ulnar Styloid Process

• Location: Slender, protruding structure at distal end
• Function:
  • Attachment site for ligaments
  • Key role in maintaining wrist joint stability