RADIUS ANATOMY

GENERAL CHARACTERISTICS

• The radius is located on the thumb side of the forearm (lateral side)
• Classified as a long bone characterized by a prism-like shape
• Features a gentle curve along its length
• Divided into three main sections:
  • Body (shaft)
  • Proximal epiphysis (upper end)
  • Distal epiphysis (lower end)

PROXIMAL EPIPHYSIS (UPPER END)

• The proximal end is relatively small, contributing minimally to the elbow joint structure
• Despite its size, it plays a functional role in elbow joint formation

Head of the Radius

• Structure:
  • Disc-shaped
• Articulations:
  • With the capitulum of the humerus
  • With the radial notch of the ulna
• Function:
  • Encircled by the annular ligament for stability
  • Allows smooth forearm movements during pronation and supination

Articular Facet of the Head

• Location: Proximal surface of the head
• Structure: Shallow, cup-like depression
• Function: Articulates with the capitulum of the humerus, aiding elbow joint movement

Articular Circumference of the Head

• Structure:
  • Smooth, circular boundary of the head
  • Wider on the medial side
• Function:
  • Articulates with the radial notch of the ulna
  • Supported by the annular ligament, ensuring rotational stability of the forearm

Neck of the Radius

• Structure: Narrow, smooth, and slightly constricted portion below the head
• Function:
  • Supports the head of the radius
  • Provides structural integrity and flexibility for forearm movements

BODY OF THE RADIUS

• The body has a prismoid shape, tapering from a narrower upper end to a broader lower end
• Features a slight outward curve creating lateral convexity
• Provides both structural strength and flexibility for forearm movements

Radial Tuberosity

• Location: Just below the neck on the medial side
• Structure:
  • Posterior surface: Rough, for attachment of Biceps brachii tendon
  • Anterior surface: Smooth, accommodates a bursa to reduce friction
• Function: Attachment site for the Biceps brachii tendon

Surfaces of the Body

Anterior Surface (Volar Side)

• Structure:
  • Gently concave along most of its length
  • Flattens and broadens near the distal quarter
• Function:
  • Provides origin for the Flexor pollicis longus muscle
  • Attachment site for the Pronator quadratus muscle, aiding forearm rotation

Posterior Surface (Dorsal Side)

• Structure:
  • Upper third: Convex and smooth
  • Middle third: More defined, aiding in muscle and tendon passage
• Function: Anchor for muscle attachments

Lateral Surface

• Structure: Convex shape
• Function:
  • Upper portion: Insertion point for the Supinator muscle
  • Middle section: Rough ridge for additional muscle attachments

Borders of the Body

Interosseous Border

• Location: Medial edge of the radius
• Function:
  • Divides anterior (volar) and posterior (dorsal) surfaces
  • Strong attachment for the interosseous membrane, stabilizing the forearm

Posterior Border

• Structure: Defined ridge along the middle portion
• Function:
  • Separates the dorsal surface from the lateral surface
  • Serves as a guide for muscle and ligament attachments

Anterior Border

• Structure: Sharp ridge extending from the radial tuberosity to the styloid process
• Function:
  • Separates the anterior and lateral surfaces
  • Attachment site for muscles and tendons

Additional Features

Pronator Tuberosity

• Location: Raised area for the attachment of the Pronator teres muscle
• Function: Facilitates forearm rotation during pronation

Suprastyloid Crest

• Location: Small ridge above the styloid process
• Function: Attachment site for ligaments, stabilizing the wrist joint

DISTAL EPIPHYSIS (LOWER END)

• The distal end is broader and more substantial than the proximal end
• Plays a crucial role in forming the wrist joint
• Connects with the carpal bones—scaphoid and lunate—to enable wrist movements:
  • Flexion
  • Extension
  • Radial deviation
  • Ulnar deviation

Radial Styloid Process

• Location: Prominent conical projection on the lateral surface
• Function:
  • Attachment point for a muscle and ligament
  • Provides wrist stability and supports hand movements

Dorsal Radial Tubercle

• Location: Back surface of the radius
• Features:
  • Characterized by three grooves for tendon guidance
  • Second groove: Deep and narrow, bordered by a sharp ridge, guiding the tendon for thumb extension
• Function: Facilitates tendon movement for hand and thumb extension

Grooves for Extensor Tendons

• Location: Dorsal surface of the radius
• Features:
  • First groove: Broad and shallow
  • Second groove: Deep and narrow
  • Third groove: Channels tendons aiding in finger extension
• Function: Guides tendons for hand and finger extension

Ulnar Notch

• Location: Concave depression on the medial side
• Function:
  • Articulates with the head of the ulna
  • Forms part of the distal radioulnar joint
  • Allows rotational movements like pronation and supination

Carpal Articular Surface

• Location: Triangular, smooth surface at the distal end
• Function:
  • Divided into two areas:
    • One articulates with the scaphoid
    • The other articulates with the lunate
  • Ensures smooth wrist motion during hand movements