The anatomical snuffbox (also known as the radial fossa), is a triangular depression found on the lateral aspect of the dorsum of the hand. It is located at the level of the carpal bones, and best seen when the thumb is extended.
In the past, this depression was used to hold snuff (ground tobacco) before inhaling via the nose – hence it was given the name ‘snuffbox’.
In this article, we shall look at the anatomy of the anatomical snuffbox – its borders, contents, and any clinical correlations.
As the snuffbox is triangularly shaped, it has three borders, a floor, and a roof:
- Ulnar (medial) border: Tendon of the extensor pollicis longus.
- Radial (lateral) border: Tendons of the extensor pollicis brevis and abductor pollicis longus.
- Proximal border: Styloid process of the radius.
- Floor: Carpal bones; scaphoid and trapezium.
- Roof: Skin.
(Note: The terms medial and lateral are used in the context of the anatomical position, where the forearm is supinated. Take care when describing these borders, as when observing a patient’s anatomical snuffbox, the forearm is usually pronated).
It is important to note that the tendons of the muscles form the borders, not the muscles themselves.
The main contents of the anatomical snuffbox are the radial artery, a branch of the radial nerve, and the cephalic vein:
- Radial artery – crosses the floor of the anatomical snuffbox, then turns medially and travels between the heads of the adductor pollicis muscle.
- The radial pulse can be palpated in some individuals by placing two fingers on the proximal portion of the anatomical snuffbox.
- Superficial branch of the radial nerve – found in the skin and subcutaneous tissue of the anatomical snuffbox. It innervates the dorsal surface of the lateral three and half digits, and the associated area on the back of the hand.
- Cephalic vein – arises from the dorsal venous network of the hand and crosses the anatomical snuffbox to travel up the anterolateral aspect of the forearm.
Clinical Relevance: Scaphoid Fracture
The scaphoid bone of the hand is the most commonly fractured carpal bone – typically by falling on an oustretched hand (FOOSH).
In a fracture of the scaphoid, the characteristic clinical feature is pain and tenderness in the anatomical snuffbox.
The scaphoid is at particular risk of avascular necrosis after fracture because of its so-called ‘retrograde blood supply’ which enters at its distal end. This means that a fracture to the middle (or ‘waist’) of the scaphoid may interrupt the blood supply to the proximal part of the scaphoid bone rendering it avascular.
Patients with a missed scaphoid fracture are likely to develop osteoarthritis of the wrist in later life.