The Anatomical Snuffbox
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 abducted.
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 abductor pollicis longus and extensor pollicis brevis.
- 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.
The radial artery crosses the floor of the anatomical snuffbox in an oblique manner. It runs deep to the extensor tendons. The radial pulse can be palpated in some individuals by placing two fingers on the proximal portion of the anatomical snuffbox.
Subcutaneously, terminal branches of the superficial branch of the radial nerve run across the roof of the anatomical snuffbox, providing innervation to the skin of the lateral 3 1/2 digits on the dorsum of the hand, and the associated palm area.
Also subcutaneously, the cephalic vein crosses the anatomical snuffbox, having just arisen from the dorsal venous network of the hand.
Clinical Relevance: Fractures of the Scaphoid
In the anatomical snuffbox, the scaphoid and the radius articulate to form part of the wrist joint. In the event of a blow to the wrist (e.g falling on an outstretched hand), the scaphoid takes most of the force. If localised pain is reported in the anatomical snuffbox, a fracture of the scaphoid is the most likely cause.
The scaphoid has a unique blood supply, which runs distal to proximal. A fracture of the scaphoid can disrupt the blood supply to the proximal portion – this is an emergency. Failure to revascularise the scaphoid can lead to avascular necrosis, and future arthritis for the patient.