EPB !
The extensor pollicis brevis is a deep forearm muscle whose tendon reaches the thumb; it straightens the thumb knuckle.
Official name: Extensor pollicis brevis
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What it is
A deep forearm muscle whose tendon goes to the thumb's first bone.
What it does
Straightens the thumb knuckle.
Key facts
- Origin
- Posterior radius and interosseous membrane
- Insertion
- Base of the proximal phalanx of the thumb
- Action
- Extends the thumb at the MCP joint
- Nerve
- Posterior interosseous nerve (C7–C8)
- Blood supply
- Posterior interosseous artery
Relations
- In front
- Abductor pollicis longus (APL), its companion in the first compartment, lying on its palmar side
- Behind
- Across the anatomical snuffbox, the extensor pollicis longus (EPL)
- Deep
- Radial styloid; in the snuffbox the radial artery, the scaphoid and the trapezium
- Superficial
- Branches of the superficial radial nerve and the beginning of the cephalic vein over the snuffbox
How to find it
With the thumb extended and abducted, a hollow (the anatomical snuffbox) appears at its base; EPB is the tendon on the palmar edge of the hollow, traceable to the base of the thumb's proximal phalanx.
Examination
- Finkelstein test: pain over the radial styloid with the thumb folded and the wrist tilted toward the little finger supports De Quervain tenosynovitis
- Resisted MCP extension with the thumb tip kept bent isolates EPB; pain over the first compartment suggests EPB involvement or a separate subcompartment
On imaging
Shares the first extensor compartment with APL. Ultrasound shows de Quervain tenosynovitis as thick tendons with sheath fluid and may show a septum giving EPB its own subcompartment, a reason injection or release fails. With APL it forms the radial border of the anatomical snuffbox, the landmark for examining the scaphoid, which radiographs then show.
Clinical notes
- Tenderness in the snuffbox, between EPB and EPL, raises suspicion of a scaphoid fracture
- Persistent pain after De Quervain surgery often means an unreleased EPB subcompartment
Anatomical variants
- Sometimes absent or fused with APL; extra slips can continue to the distal phalanx or join EPL
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Which thumb joint does the EPB (extensor pollicis brevis) extend, and how does that differ from the EPL?
Only the MCP joint; extension of the thumb tip (IP joint) is the EPL's job.
Why can pain persist after de Quervain surgery, in relation to the EPB?
The EPB often has a separate subcompartment; if it is not released, pain persists.
What does tenderness in the anatomical snuffbox, between EPB and EPL, raise suspicion of?
A scaphoid fracture.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- extensor brevis pollicis TA2 2518
- Official Spanish (DeCS)
- Músculo extensor corto del pulgar
- English (TA2)
- Extensor pollicis brevis
Related
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb: Hand Anatomical Snuff Box; Anatomy, Shoulder and Upper Limb, Wrist Extensor Muscles.
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Representative model, for educational purposes only.
