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Radius

The radius is one of the two long bones of the forearm, situated on the lateral (thumb) side, parallel to the ulna. It extends from the elbow to the wrist and plays a critical role in forearm rotation, wrist motion, and load transmission from the hand to the elbow.
Structurally, the radius widens distally and narrows proximally. Its proximal end forms part of the elbow joint, while the distal end articulates with the carpal bones and the ulna, forming the radiocarpal and distal radioulnar joints respectively.

Synonyms

  • Lateral bone of the forearm

  • Radial shaft

  • Radial long bone

Parts and Features

The radius consists of three parts: upper end, shaft, and lower end.

Upper End:

  • Features the head, neck, and radial tuberosity.

  • Head: Disc-shaped; articulates with the capitulum of the humerus and the radial notch of the ulna, forming the humeroradial and proximal radioulnar joints.

  • Neck: Narrow region below the head, providing attachment to the annular ligament.

  • Radial tuberosity: Roughened medial projection below the neck, serving as the insertion site of the biceps brachii.

Shaft:

  • Slightly curved and triangular in cross-section.

  • Surfaces: Anterior (concave), posterior (convex), and lateral (rounded).

  • Borders: Interosseous border (medial) serves as attachment for the interosseous membrane, connecting the radius to the ulna.

Lower End:

  • Broad and quadrilateral, forming part of the wrist joint.

  • Articulates with the scaphoid and lunate bones at the radiocarpal joint and with the ulna via the ulnar notch (distal radioulnar joint).

  • The styloid process projects laterally, providing attachment for the brachioradialis tendon and the radial collateral ligament of the wrist.

Relations

  • Proximally: Capitulum of humerus and radial notch of ulna

  • Distally: Carpal bones (scaphoid, lunate) and head of ulna

  • Medially: Ulna and interosseous membrane

  • Laterally: Supinator and brachioradialis muscles

  • Anteriorly: Flexor pollicis longus, pronator teres, and flexor digitorum superficialis

  • Posteriorly: Extensor tendons including abductor pollicis longus and extensor pollicis brevis

Attachments

  • Biceps brachii: Inserts at the radial tuberosity

  • Pronator teres: Inserts on the lateral surface of the midshaft

  • Supinator: Wraps around the upper third of the shaft

  • Brachioradialis: Inserts on the lateral surface near the styloid process

  • Flexor and extensor muscles: Originate or insert along the anterior and posterior surfaces

Arterial Supply

  • Radial artery and anterior interosseous artery supply the shaft and distal end

  • Radial recurrent artery supplies the proximal region

Function

  • Forearm rotation: Allows pronation and supination through movement around the ulna

  • Load transmission: Transfers forces from wrist to elbow during weight-bearing

  • Joint formation: Contributes to elbow (proximal radioulnar), wrist (radiocarpal), and distal radioulnar joints

  • Muscle attachment: Provides leverage for flexors, extensors, pronators, and supinators

Clinical Significance

  • Fractures:

    • Radial head fractures: Common in falls on an outstretched hand

    • Colles’ fracture: Transverse fracture near distal end with dorsal displacement

    • Smith’s fracture: Distal fracture with volar displacement

  • Dislocations: Associated with elbow injuries or Monteggia fractures

  • Osteomyelitis: Infection may follow open trauma or surgery

  • Degenerative changes: Seen in chronic wrist stress and rheumatoid arthritis

  • Surgical relevance: Key bone in open reduction and internal fixation (ORIF) procedures and bone grafting

MRI Appearance

T1-weighted images:

  • Cortex: Low signal (dark), sharply defined

  • Marrow: Bright signal (fatty marrow in adults)

  • Muscle: Intermediate signal surrounding shaft

  • Fractures: Appear as low-signal lines crossing the cortex or trabeculae

  • Periosteum: Thin low-signal rim if intact

T2-weighted images:

  • Cortex: Low signal

  • Marrow: Bright, slightly less intense than on T1

  • Cartilage surfaces: Intermediate-to-bright; articular surfaces of radial head and distal end are well delineated

  • Pathology: Edema, contusions, or cystic changes show bright hyperintense signal

  • Joint fluid: Hyperintense around elbow and wrist articulations

STIR:

  • Normal marrow: Intermediate-to-dark signal

  • Pathologic marrow: Bright hyperintensity in trauma, infection, or marrow edema

  • Excellent for early detection of stress injuries or osteitis

Proton Density Fat-Saturated (PD FS):

  • Normal bone: Intermediate-to-dark signal

  • Abnormal: Bright focal or diffuse hyperintensity in edema, contusion, or fracture

  • Highlights periosteal reaction, subtle cortical breaks, or soft-tissue inflammation

T1 Fat-Sat Post-Contrast:

  • Normal bone marrow: Homogeneous mild enhancement

  • Osteomyelitis: Patchy or ring-like enhancement with cortical irregularity

  • Tumors: Intense enhancement with marrow expansion

  • Fractures: Peripheral enhancement due to reactive hyperemia

CT Appearance

Non-Contrast CT:

  • Cortex: High-density, well-corticated bone

  • Trabecular pattern: Uniform honeycomb structure

  • Articular surfaces: Smooth, clearly delineated at head and distal end

  • Pathology:

    • Detects fractures, cortical irregularities, sclerosis, or erosions

    • Visualizes callus formation in healing fractures

    • Excellent for 3D reconstruction of radial head and distal radius fractures

Post-Contrast CT (standard):

  • Enhances periosteal and soft-tissue inflammation around fractures or infection

  • Demonstrates tumor vascularity, cortical destruction, or abscess formation

  • Assists in surgical planning for complex fracture fixation and bone grafting

MRI images

Radius bone coronal cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI images

Radius BONE CT IMAGE

MRI images

Radius bone sagl cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

CT image

Radius BONE CT IMAGE