Anatomical Snuffbox
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Direct answer
Extend the thumb and a hollow appears at the wrist's radial side — the anatomical snuffbox, named for the tobacco its seventeenth-century users deposited there. Its anterior wall is formed by abductor pollicis longus and extensor pollicis brevis, its posterior wall by extensor pollicis longus hooking round Lister's tubercle, its floor by the scaphoid and trapezium, and its roof — skin and fascia carrying branches of the radial nerve and the cephalic vein's origin. The radial artery crosses the floor, palpable against the scaphoid. The box's clinical fame rests there: tenderness after a fall means a scaphoid fracture, whose proximal fragment dies of ischaemia because the bone's blood supply enters distally and runs retrograde.
What you must remember
- Boundaries: anteriorly the abductor pollicis longus and extensor pollicis brevis tendons (first dorsal compartment), posteriorly the extensor pollicis longus tendon — all radial-nerve tendons crossing the wrist obliquely.
- Floor and roof: the scaphoid and trapezium below, crossed by the radial artery; the roof carries the cephalic vein's origin and the terminal cutaneous branches of the radial nerve supplying the dorsum of the hand's radial half.
- Contents: the radial artery leaving the forearm for the first web space, a branch of the superficial radial nerve, and the crossing tributaries forming the cephalic vein — why the snuffbox is both a pulse site and a cut-down landmark.
- Scaphoid blood supply: the dorsal branch of the radial artery enters the distal half, and the vessel's retrograde course supplies the proximal pole last — so a waist fracture cuts the proximal pole's supply, making avascular necrosis and nonunion the proximal fragment's fate if missed.
- Clinical pathway for snuffbox tenderness: fall on the outstretched hand, tender snuffbox, normal radiograph — treat in a thumb spica and reimage at 10-14 days; the occult fracture is every casualty department's trap.
- De Quervain tenosynovitis: stenosing inflammation of the first dorsal compartment's sheath (abductor pollicis longus and extensor pollicis brevis) — pain over the snuffbox's anterior wall, worse with a Finkelstein test (flexing the thumb into the palm and ulnar-deviating the wrist).
- Allen test: occluding both arteries at the wrist, exhausting the hand's blood by clenching, then releasing each in turn demonstrates the ulnar artery's palmar arch dominance before radial cannulation or harvest.
A tender snuffbox with a normal film
A young man falls off a bicycle onto his palm with a swollen wrist. The scaphoid series is reported normal, yet the snuffbox is exquisitely tender and axial thumb compression hurts. The correct decision is anatomical, not radiological: immobilise in a thumb spica and repeat the films in ten to fourteen days, when bone resorption declares the occult waist fracture. The alternative is the history every exam exists to prevent: the "sprain" discharged untreated, returning a year later with a nonunion and a sclerosed, collapsed proximal pole — avascular necrosis, the retrograde supply severed by the fracture. A few rooms away, a new mother's thumb-base pain worsens with every lift: De Quervain's tenosynovitis of the anterior wall's tendons, positive on Finkelstein testing — inflammation of the boundary, ischaemia of the floor.
How the viva frames the box
Handed a wrist model, the examiner asks for the walls, and the standard error is naming three tendons without their nerve — all are radial, which converts a boundary list into a wiring lesson. The second question is always the floor: scaphoid and trapezium, and the follow-up is the scaphoid's blood supply — retrograde, distal entry, proximal pole at risk — with the expected conclusion that a missed waist fracture ends in avascular necrosis. The third favourite is the radial artery's continuation: it leaves distally between the two heads of the first dorsal interosseous to complete the deep palmar arch — the reason this territory matters to the plastic surgeon raising a flap.
Frequently asked questions
What forms the boundaries of the anatomical snuffbox?
Anteriorly the tendons of abductor pollicis longus and extensor pollicis brevis, posteriorly the tendon of extensor pollicis longus. The roof is skin crossed by the cephalic vein's origin and radial nerve branches; the floor is the scaphoid and trapezium.
Why is a scaphoid fracture prone to avascular necrosis?
Its blood supply enters mainly through the distal half via the dorsal branch of the radial artery and runs retrograde, so a waist fracture cuts off the proximal pole.
What should be done for snuffbox tenderness with a normal radiograph?
Immobilise in a thumb spica and repeat imaging in 10-14 days, or obtain an early magnetic resonance image, because occult scaphoid fractures are invisible on initial films.
What is De Quervain tenosynovitis and how is it tested?
Stenosing inflammation of the common sheath of abductor pollicis longus and extensor pollicis brevis — the snuffbox's anterior wall. Finkelstein's test, flexing the thumb into the palm and ulnar-deviating the wrist, reproduces the pain.
What is the Allen test and why is it performed?
Both radial and ulnar arteries are compressed, the hand clenched to exsanguinate, and the ulnar released to confirm palmar arch filling; it verifies ulnar collateral flow before radial artery cannulation, harvest or flap planning.