The anatomical snuffbox is a colloquial name for the radial fossa, a surface on the hand found at the base of the thumb. Named for the fact that this part of the hand is where smokeless tobacco or snuff users once placed their tobacco before inhaling, it is a small depression between two major thumb tendons. Two muscles that extend the thumb, the extensor pollicis longus and extensor pollicis brevis, send tendons from the back of the forearm into the dorsal or posterior aspect of the thumb. The anatomical snuffbox is the teardrop-shaped hollow visible between these tendons when the thumb is extended.
Several anatomical landmarks can assist in locating the anatomical snuffbox. Situated on the dorsal, lateral aspect of the wrist — meaning that it is found on the back of the wrist on the thumb side — this depression begins where the radius bone in the forearm meets the scaphoid bone in the base of the hand. The distal or lower end of the radius bone can be palpated on the thumb side of the wrist, and a small, rounded protrusion can easily be felt here.
Turning the arm so that the thumb faces upward and locating this protrusion of the radius makes locating the anatomical snuffbox an easier task. To do so, the thumb should be extended toward the ceiling as in forming a hitchhiker’s sign. A small hollow in the shape of a rounded triangle or teardrop will become visible just beyond the end of the radius upon stretching the thumb upward. The anatomical snuffbox is formed by the borders of several anatomical structures of the hand and wrist. On either side of the snuffbox, tapering as they enter the thumb, are the tendons of the extensor pollicis longus and brevis muscles, with the extensor pollicis longus forming the inside border and the extensor pollicis brevis forming the outside border. Both tendons are visible against the skin and can be easily felt as the thumb is extended.
Forming the proximal edge of the anatomical snuffbox, that nearest the wrist, is a surface on the radius known as the styloid process. The styloid process can be felt regardless of thumb position. On the distal or opposite end of the snuffbox is a pointed border formed by the convergence of the two extensor tendons, which enter the thumb side by side.
Beneath the anatomical snuffbox, forming what is referred to as the floor of this depression, are two of the carpal bones: the scaphoid and the trapezium. These small wrist bones can also be felt with the thumb in any position, with the scaphoid filling most of the space beneath the snuffbox. Running through the snuffbox above these bones is not one but three vessels: the radial artery, cephalic vein, and radial nerve. The blood vessels carry blood to and from the thumb, respectively, while the radial nerve sends motor signals from the central nervous system to the extensor tendons in the thumb, producing the movement of thumb extension.