The anatomical snuff box, or Fovea radialis, is a small, triangular depression located on the back of the wrist at the base of the thumb. This feature is important for medical professionals because it acts as a window into deeper structures of the hand. The depression allows for the superficial assessment of underlying bones, arteries, and nerves that are otherwise difficult to reach. Understanding the components of this space is the first step toward proper diagnosis and care for injuries in this area.
Identifying the Snuff Box Location
The snuff box is visible on the radial, or thumb, side of the wrist, on the dorsal aspect of the hand. To clearly identify this feature, a person must fully extend their thumb as far away from their fingers as possible. This action pulls the surrounding tendons taut, creating a distinct, sunken area just past the wrist joint.
The unusual name dates back to the 17th and 18th centuries when powdered tobacco, known as snuff, was popular. People would often place a pinch of the powdered tobacco into this convenient depression before inhaling it. The term “snuff box” therefore became the common, non-medical description for this specific area of the wrist.
The Anatomical Walls and Floor
The distinct triangular shape of this space is defined by the tendons of three muscles that travel from the forearm to the thumb.
The inner, or medial, border of the triangle is formed by the tendon of the Extensor Pollicis Longus muscle, which extends the thumb. The outer, or lateral, border is formed by two parallel tendons: the Abductor Pollicis Longus and the Extensor Pollicis Brevis. These three tendons converge to create the clear boundaries of the depression when the thumb is extended.
Beneath these tendons, the floor of the anatomical snuff box is formed by two carpal bones of the wrist. The proximal bone is the scaphoid, while the distal bone is the trapezium. These bones are directly palpable through the skin in the floor of the depression, making the area relevant for injury assessment.
Nerves and Blood Vessels Within the Space
Several neurovascular structures pass directly through the anatomical snuff box. The most notable of these contents is the Radial Artery, a major blood vessel that supplies the hand.
The Radial Artery crosses the floor of the snuff box on its path from the forearm into the hand. This superficial positioning means the pulse can often be felt distinctly here, serving as an alternative location for checking a patient’s heart rate. The artery’s location is also sometimes used as an access point for certain cardiac procedures.
Another important structure is the superficial branch of the Radial Nerve, which provides sensation to the skin over the thumb and the back of the hand. Because this nerve is close to the surface, it is vulnerable to injury or irritation. The Cephalic Vein, a large vein that collects blood from the dorsal venous network of the hand, also begins its upward journey across the snuff box.
Medical Importance and Common Injuries
The anatomical snuff box is a crucial diagnostic site for physicians examining hand and wrist trauma. Tenderness felt within this depression is a strong indicator of a scaphoid fracture, the most frequently broken carpal bone in the wrist. This injury commonly occurs after a person falls onto an outstretched hand.
The scaphoid bone is particularly susceptible to a complication called avascular necrosis because of its unique blood supply. The artery enters the scaphoid at its distal end and must travel backward to supply the proximal portion of the bone. A fracture through the middle of the bone can sever this delicate blood flow, potentially causing the bone segment closer to the forearm to die without nourishment. Even if an initial X-ray does not clearly show a break, medical professionals treat tenderness in the snuff box with caution, often immobilizing the wrist to prevent complications.
De Quervain’s Tenosynovitis
Another common condition in this region is De Quervain’s tenosynovitis, which involves inflammation of the tendons that form the lateral border of the snuff box (the Abductor Pollicis Longus and Extensor Pollicis Brevis). This condition causes pain and swelling, often stemming from repetitive hand or wrist movements.