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Anatomical snuffbox

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Definition, location, borders and structures of the anatomical snuff box.

The anatomical snuffbox has one of the most unique name origins among anatomical structures. This shallow depression on the posterolateral aspect of the hand and wrist junction is named after the historical practice of having ground tobacco, otherwise known as “snuff”, placed in the depression and then inhaled through the nose. The depression is deepest and most noticeable when the thumb is fully extended and abducted. Much like the femoral triangle in the supero-anterior aspect of the thigh, the anatomical snuffbox is known for, and used mostly as a way of identifying structures that define its borders and those structures that pass through it.

Key facts about the anatomical snuffbox
Borders Base: distal to the end of the radius
Apex: point towards the thumb
Floor: scaphoid, trapezium
Medial border: extensor pollicis longus
Lateral border: abductor pollicis longus, extensor pollicis brevis
Contents Cephalic vein, (radial) Artery, Radial nerve (Superficial branch), Tendons of extensor carpi radialis longus and brevis
Mnemonic: CARTs
Contents
  1. Anatomical snuffbox location, anatomy and borders
  2. Contents of the anatomical snuffbox
    1. Structures superficial to the extensor retinaculum and outcropping muscle tendons
    2. Structures deep to the extensor retinaculum and outcropping muscle tendons
    3. Mnemonic
  3. Summary
  4. Clinical significance
  5. Sources
+ Show all

Anatomical snuffbox location, anatomy and borders

From anatomical position, the snuffbox is located distal to the end of the radius posterolaterally. The base of this triangular shaped depression is located just distal to the end of the radius with the triangle’s apex pointing towards the thumb. The floor of the snuffbox is made up of the scaphoid and trapezium carpal bones, which are located between the radial styloid process proximally and the base of the 1st metacarpal distally.

Borders of the anatomical snuffbox

The medial and lateral borders of the snuffbox are made up of three muscles that act on the thumb:

Figure 2. Surface landmarks of the anatomical snuffbox

These muscles are called the “outcropping” muscles of the thumb because they protrude out from beneath the extensor digitorum muscle, between it and the extensor carpi radialis brevis muscle.

Unlike the long extensors of the posterior forearm, the outcropping muscles arise from the middle portion of the posterior radius and ulna. As these muscles run distally towards the thumb, they produce a palpable bulge, especially when the thumb is circumducted. The tendons of two of the outcropping muscles make up the lateral border of the anatomical snuffbox; they are the abductor pollicis longus and extensor pollicis brevis. The medial border of the snuffbox is made up of the remaining outcropping muscle, the extensor pollicis longus.

Contents of the anatomical snuffbox

When considering the contents of the anatomical snuffbox, it is helpful to divide the structures into two groups: those that lie superficial to the extensor retinaculum and the tendons of the outcropping muscles, and those that lie deep to these structures. The extensor retinaculum is a thin band of fibrous connective tissue that runs across the posterior aspect of the distal forearm. Its function is to keep the tendons of the extensor and outcropping muscles located below it, from bowing out when the muscles are contracted and tension on the tendons occurs.

Structures superficial to the extensor retinaculum and outcropping muscle tendons

  • Dorsal digital branches of the superficial radial nerve: The radial nerve descends from the posterior compartment of the arm and crosses into the cubital region by passing anterior to the lateral epicondyle of the humerus. It then divides into deep and superficial branches. The cutaneous superficial branch then runs down the forearm under the brachioradialis muscle. As it enters the distal part of the forearm, it enters the roof of the anatomical snuffbox and branches into a number of dorsal digital branches. One of these branches then continues through the snuffbox.
Figure 4. Superficial branch of the radial nerve (ventral view)
  • Cephalic vein: Arising medial to the digital nerve is the cephalic vein. The cephalic vein forms from the dorsal venous network which drains blood from dorsal aspect of the hand. It ascends from the lateral aspect of the forearm and arm, running superficially in the subcutaneous tissue.
Figure 5. Dorsal venous network of the hand (ventral view)

Structures deep to the extensor retinaculum and outcropping muscle tendons

  • Radial artery: The radial artery forms as a branch of the brachial artery as it passes through the cubital fossa. It runs down the lateral aspect of the forearm, deep to the brachioradialis muscle, and at the wrist is lateral to the flexor carpi radialis tendon. It then leaves the forearm by passing posterolaterally to run obliquely along the floor of the anatomical snuffbox.
Figure 6. Radial artery and dorsal digital arteries (dorsal view)
  • Tendons of extensor carpi radialis longus and brevis: As the outcropping muscles emerge from under the extensor digitorum, they run superficial to the tendons of extensor carpi radialis longus and brevis. The tendons of the extensor carpi radialis longus and brevis run medial to the radial artery along the floor of the anatomical snuffbox to insert onto the base of the 2nd and 3rd metacarpals. (Figure 3).

Test your knowledge on the regions of the upper limb with this quiz.

Mnemonic

Do you want an easy way to remember the contents of the anatomical snuffbox? Then use the mnemonic provided below!

CARTs

  • Cephalic vein
  • Artery (radial)
  • Radial nerve (Superficial branch)
  • Tendons of extensor carpi radialis longus and brevis

Summary

Below is a summary of the borders of the anatomical snuffbox, and the structures that pass through the snuffbox.

Borders

  • Proximal = radial styloid process
  • Distal = base of 1st metacarpal
  • Floor = scaphoid and trapezium
  • Medial = extensor pollicis longus
  • Lateral = abductor pollicis longus and extensor pollicis brevis

Contents

  • Superficial = dorsal digital branches of the radial nerve, cephalic vein
  • Deep = radial artery, tendons of extensor carpi radialis longus and brevis

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