Extensor Pollicis Longus, Extensor Pollicis Brevis, Abductor Pollicis Longus
Mnemonic
“Two in front, one behind”:
- Lateral (anterior) - abductor pollicis longus and extensor pollicis brevis
- Medial (posterior) - extensor pollicis longus
- Proximal - the styloid process of the radius
- Floor - scaphoid and trapezium
Contents: the radial artery, crossing the floor, and the superficial branch of the radial nerve over the roof.
“Tenderness in the snuffbox is a scaphoid fracture until proven otherwise.” That is the whole clinical point, and the fracture is often invisible on the initial radiograph, so the wrist is immobilised and reimaged at 10 to 14 days, or imaged with MRI.
The scaphoid has a retrograde blood supply, entering distally, so a proximal pole fracture risks avascular necrosis and non-union. Missing it leads to scaphoid non-union advanced collapse.
The radial artery here is a site for arterial line insertion in the “snuffbox” approach.
Expansion
- Posterior (medial) border - Extensor Pollicis Longus tendon
- Anterior (lateral) border - Extensor Pollicis Brevis and Abductor Pollicis Longus tendons
- Floor - Scaphoid and trapezium
- Contents - Radial artery crosses the floor
Memory hook: the long thumb extensor (EPL) is on one side, and the short extensor plus the long abductor (EPB and APL) are on the other side.