Wasting of the Anatomical Snuffbox
Wasting of the anatomical snuffbox indicates atrophy of the muscles that form its boundaries—specifically the abductor pollicis longus, extensor pollicis brevis (radial border), and extensor pollicis longus (ulnar border)—which typically suggests denervation from radial nerve injury, disuse atrophy, or chronic inflammatory conditions affecting the first dorsal compartment.
Clinical Significance
The anatomical snuffbox is a triangular depression on the radial aspect of the wrist formed by:
- Radial border: Tendons of abductor pollicis longus and extensor pollicis brevis
- Ulnar border: Tendon of extensor pollicis longus
- Floor: Scaphoid and trapezium bones
Primary Causes of Wasting
Neurological causes:
- Radial nerve palsy (posterior interosseous nerve branch) - Most common cause of visible wasting
- C7-C8 radiculopathy
- Brachial plexus injury affecting the posterior cord
Musculoskeletal causes:
- Chronic de Quervain's tenosynovitis with muscle disuse 1
- Post-traumatic atrophy following wrist fractures
- Chronic inflammatory arthropathies
Vascular causes:
- Chronic ischemia (rare, as the snuffbox contains the radial artery which can be palpated for pulse assessment) 2
Clinical Pitfalls
Do not confuse snuffbox wasting with:
- Normal anatomical variation in tendon number (the abductor pollicis longus can have 3-14 tendon slips, which may create variable surface anatomy) 1
- Acute swelling that obscures the depression (such as in scaphoid fracture, where tenderness rather than wasting is the key finding) 3
- Generalized hand muscle atrophy from other causes (median or ulnar nerve pathology)
Diagnostic Approach
When wasting is identified:
- Assess motor function: Test thumb extension and abduction against resistance
- Evaluate sensation: Check for sensory loss over the dorsal first web space (superficial radial nerve distribution)
- Palpate the radial pulse in the snuffbox to rule out vascular compromise 4
- Examine for proximal radial nerve injury: Check wrist extension, finger extension at MCPs, and supination
- Consider electrodiagnostic studies if denervation is suspected
The presence of snuffbox wasting is a late finding that indicates chronic pathology (weeks to months), as muscle atrophy requires sustained denervation or disuse.