Radial Nerve, Dorsal Digital Expansion and Anatomical Snuffbox Anatomy Explained
ANATOMY

Radial Nerve, Dorsal Digital Expansion and Anatomical Snuffbox Anatomy Explained

Jan 4, 2026 3 min read

Radial Nerve, Dorsal Digital Expansion, and Anatomical Snuffbox – Complete Anatomy Guide

1. Radial Nerve

Definition

The radial nerve is the largest branch of the posterior cord of the brachial plexus, providing motor supply to extensor muscles of the upper limb and sensory supply to the posterior arm, forearm, and dorsum of the hand.

Root Value

  • C5–T1

Origin

  • Arises from the posterior cord of the brachial plexus

Course

Axilla

  • Lies posterior to the axillary artery
  • Exits the axilla through the lower triangular space
  • Accompanied by the profunda brachii artery

Arm

  • Enters the radial (spiral) groove of the humerus
  • Runs between medial and lateral heads of triceps
  • Supplies triceps brachii
  • Pierces the lateral intermuscular septum
  • Enters the anterior compartment near the lateral epicondyle

Cubital Fossa

  • Lies anterior to the lateral epicondyle
  • Divides into:

* Superficial branch (sensory)

* Deep branch (motor → posterior interosseous nerve)

Forearm

  • Deep branch:

* Pierces supinator

* Continues as posterior interosseous nerve

* Supplies extensor muscles

  • Superficial branch:

* Runs under brachioradialis

* Becomes superficial near wrist

* Supplies dorsum of hand

Branches

Motor

  • Triceps brachii
  • Anconeus
  • Brachioradialis
  • Extensor carpi radialis longus
  • All extensors of wrist and fingers (via posterior interosseous nerve)

Sensory

  • Posterior cutaneous nerve of arm
  • Posterior cutaneous nerve of forearm
  • Dorsal digital nerves to:

* Lateral 3½ digits (proximal parts)

Applied Anatomy

  • Radial nerve palsy:

* Wrist drop

* Loss of finger extension

  • Mid-shaft humerus fracture → injury in radial groove
  • Saturday night palsy → compression in spiral groove

2. Dorsal Digital Expansion (Extensor Expansion / Hood)

Definition

The dorsal digital expansion is a triangular aponeurotic expansion on the dorsum of fingers, formed mainly by extensor digitorum tendon, allowing coordinated finger movements.

Formation

Formed by:

  • Extensor digitorum tendon
  • Contributions from:

* Lumbricals

* Interossei

Structure

  • Central slip:

* Inserts into base of middle phalanx

  • Two lateral bands:

* Reunite to insert into distal phalanx

  • Covers the dorsum of MCP, PIP, and DIP joints

Functions

  • Extension at:

* Metacarpophalangeal (MCP) joints

* Interphalangeal (IP) joints

  • Allows interossei and lumbricals to:

* Flex MCP

* Extend IP joints

Clinical Importance

  • Mallet finger: rupture of terminal tendon
  • Boutonnière deformity: rupture of central slip
  • Claw hand deformity: imbalance of intrinsic muscles

3. Anatomical Snuffbox

Definition

The anatomical snuffbox is a triangular depression seen on the lateral aspect of the dorsum of the hand when the thumb is extended.

Boundaries

Lateral (Anterior) Boundary

  • Abductor pollicis longus
  • Extensor pollicis brevis

Medial (Posterior) Boundary

  • Extensor pollicis longus

Proximal Boundary

  • Styloid process of radius

Floor

  • Scaphoid
  • Trapezium

Roof

  • Skin
  • Superficial fascia
  • Superficial branch of radial nerve
  • Cephalic vein

Contents

  • Radial artery (main content)

Clinical Importance

  • Scaphoid fracture:

* Tenderness in snuffbox

* Risk of avascular necrosis

  • Radial artery palpation site
  • IV cannulation landmark

Quick Exam Correlation Table

| Structure | Key Clinical Point |

| ------------------------ | ----------------------------- |

| Radial nerve | Wrist drop |

| Dorsal digital expansion | Finger extension coordination |

| Anatomical snuffbox | Scaphoid fracture tenderness |

⚡ Interactive MCQ Quiz

Frequently Asked Questions

The radial nerve is a terminal branch of the posterior cord of the brachial plexus with root value C5–T1. It supplies the extensor muscles of the arm and forearm and provides sensory innervation to the posterior upper limb and dorsum of the hand.
The radial nerve is responsible for extension of the elbow, wrist, and fingers, and for sensation over the posterior arm, posterior forearm, and dorsum of the lateral hand.
Wrist drop is the inability to extend the wrist and fingers due to paralysis of extensor muscles following radial nerve injury.
Dorsal digital expansion, also called extensor expansion or extensor hood, is an aponeurotic structure on the dorsum of the fingers formed mainly by the extensor digitorum tendon.
Dorsal digital expansion allows coordinated extension of the interphalangeal joints and enables lumbricals and interossei to flex the metacarpophalangeal joints while extending the interphalangeal joints.
The central slip is a part of the dorsal digital expansion that inserts into the base of the middle phalanx and is essential for extension of the proximal interphalangeal joint.
Boutonnière deformity results from rupture of the central slip of the dorsal digital expansion, leading to flexion of the PIP joint and hyperextension of the DIP joint.
The anatomical snuffbox is a triangular depression on the lateral aspect of the dorsum of the hand that becomes prominent when the thumb is extended.
The lateral boundary is formed by abductor pollicis longus and extensor pollicis brevis, the medial boundary by extensor pollicis longus, and the proximal boundary by the styloid process of the radius.
The floor of the anatomical snuffbox is formed by the scaphoid and trapezium bones.
The main content of the anatomical snuffbox is the radial artery, while the roof contains the superficial branch of the radial nerve and the cephalic vein.
Tenderness in the anatomical snuffbox is a classic sign of scaphoid fracture, which carries a risk of avascular necrosis due to compromised blood supply.
Related Topics
radial nerve anatomy and clinical importance radial nerve course branches and injury radial nerve wrist drop explanation dorsal digital expansion anatomy extensor expansion of fingers anatomy dorsal digital expansion clinical significance intrinsic muscle action on fingers anatomy anatomical snuffbox anatomy and contents boundaries of anatomical snuffbox radial artery in anatomical snuffbox scaphoid fracture snuffbox tenderness hand anatomy for medical students upper limb nerve anatomy exam notes brachial plexus radial nerve detailed anatomy posterior interosseous nerve anatomy hand extensor mechanism anatomy orthopedic clinical anatomy of hand osce anatomy notes upper limb exam oriented hand anatomy guide
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