Anatomical Snuffbox
Boundaries
| Boundary | Structure |
|---|---|
| Anterolateral (radial) | APL + EPB tendons |
| Posteromedial (ulnar) | EPL tendon |
| Proximal (base) | Styloid process of radius |
| Distal (apex) | Base of 1st metacarpal |
Floor
- Scaphoid (proximal) + Trapezium (distal)
Roof
- Skin + superficial fascia
Contents
- Radial artery — sole named content; lies on floor
Roof Crossings (Superficial)
- Cephalic vein — medial to lateral; IV access site
- Superficial radial nerve — lateral to medial; supplies lateral 2/3 dorsum + dorsal lateral 3½ digits
Radial Artery in Snuffbox
- Enters from above; lies deep to APL, EPB, EPL tendons
- Superficial to lateral wrist ligament, scaphoid, trapezium
- Exits → proximal 1st interosseous space → between heads of 1st dorsal interosseous → forms deep palmar arch
- Branches: lateral thumb + 1st dorsal metacarpal artery (thumb + index adjacent sides)
Applied Anatomy
- Scaphoid fracture — snuffbox tenderness on deep palpation = cardinal sign; mechanism: FOOSH; may not show on initial X-ray → immobilise, repeat at 10–14 days
- AVN of scaphoid — waist fracture devascularises proximal fragment → avascular necrosis → non-union
- Radial pulse — palpable in proximal snuffbox against scaphoid (alternative to wrist)
- Cephalic vein — visible in roof; used for IV cannulation
- Superficial radial nerve — rolled against EPL tendon; tenderness = Wartenberg’s syndrome
The anatomical snuffbox is an elongated triangular depression seen on the lateral side of the dorsum of the hand when the thumb is fully extended (hyperextended). It was traditionally used to place a pinch of snuff (powdered tobacco) for inhalation.
Boundaries
| Boundary | Structure |
|---|---|
| Anterolateral (radial / anterior) | Tendons of abductor pollicis longus (APL) and extensor pollicis brevis (EPB) |
| Posteromedial (ulnar / posterior) | Tendon of extensor pollicis longus (EPL) |
| Proximal (base / superior) | Styloid process of the radius |
| Distal (apex) | Base of the 1st metacarpal |
Memory: “APL + EPB anteriorly; EPL posteriorly”
Floor
Formed by two carpal bones:
- Scaphoid (proximal)
- Trapezium (distal)
The scaphoid forms the major part of the floor and is the clinically important structure here.
Roof
Formed by:
- Skin
- Superficial fascia
Contents
Radial artery — the sole named content, running in the floor of the snuffbox.
Structures Crossing the Roof (Superficial to Deep)
| Structure | Direction of Crossing |
|---|---|
| Cephalic vein | Medial to lateral — originates from dorsal venous arch, runs proximally through the snuffbox, curves round the lateral border of the wrist to reach the anterior aspect of the forearm |
| Terminal branches of superficial radial nerve | Lateral to medial — cross the roof and supply skin over lateral 2/3 of dorsum of hand and dorsal surface of lateral 3½ digits (excluding nail beds) |
Radial Artery in the Snuffbox
| Feature | Detail |
|---|---|
| Entry | Winds round the lateral side of the wrist after leaving the forearm; enters the snuffbox from above |
| Position | Lies on the floor — deep to APL, EPB, and EPL tendons; also crossed by branches of superficial radial nerve |
| Relations to bone | Superficial to the lateral ligament of the wrist joint, scaphoid, and trapezium |
| Exit | Passes distally to reach the proximal end of the 1st interosseous space; passes between the two heads of the 1st dorsal interosseous muscle to enter the palm |
| Continuation | Forms the deep palmar arch in the palm |
Branches Given in the Snuffbox
- Branch to the lateral side of the dorsum of the thumb
- 1st dorsal metacarpal artery — arises just before entering the 1st interosseous space; divides into two branches for adjacent sides of thumb and index finger
Applied Anatomy
1. Palpation of Radial Pulse
The radial artery is superficial and palpable in the proximal part of the snuffbox where it lies against the scaphoid. This is an alternative site to the classic radial pulse at the wrist.
2. Scaphoid Fracture — Tenderness in the Snuffbox
The scaphoid forms the floor of the snuffbox. Tenderness on deep palpation of the snuffbox is the cardinal clinical sign of a fracture of the scaphoid.
Mechanism: fall on an outstretched hand (dorsiflexion force transmitted through the scaphoid).
A scaphoid fracture may not be visible on initial X-ray — if snuffbox tenderness is present, treat as fracture and repeat X-ray at 10–14 days.
3. Avascular Necrosis of the Scaphoid
The scaphoid has a precarious blood supply — nutrient vessels enter mainly through the distal tubercle and dorsal surface of the distal half. A fracture through the waist of the scaphoid may deprive the proximal fragment of its blood supply → avascular necrosis of the proximal pole. This is the most serious complication of scaphoid fracture, and the reason for its tendency to non-union.
4. Cephalic Vein — Intravenous Access
The cephalic vein is visible and accessible in the roof of the snuffbox. It is a commonly used site for IV cannulation and venepuncture, particularly when antecubital veins are inaccessible.
5. Superficial Radial Nerve — Clinical Test
The terminal branches of the superficial radial nerve can be rolled against the tendon of extensor pollicis longus in the snuffbox. This is useful for examining nerve tenderness or entrapment (Wartenberg’s syndrome — compression of the superficial radial nerve).
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My Sticky Notes
Personal revision notes, mnemonics and reminders.
