Extensor Pollicis Brevis

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The Extensor Pollicis Brevis is in the Deep Layer of the Posterior Compartment of the forearm. It is also a member of the Deep Distal Four Group; the deep distal four group is composed of:

• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extensor indicis

ATTACHMENTS:

• Posterior radius to the thumb.
  • The proximal attachment is onto the distal 1/3 of the posterior radius and interosseus membrane.
  • The distal attachment is onto the base of the proximal phalanx of the thumb.

ACTIONS:

• Extends the thumb at the carpometacarpal and metacarpophalangeal joints.
• Abducts the thumb at the carpometacarpal joint.
• Laterally rotates the thumb at the carpometacarpal joint.
• Radially deviates the hand at the wrist joint.

NOTES:

1. The belly of the extensor pollicis brevis lies deep in the posterior forearm, but its distal tendon become superficial farther distally.
2. The distal tendons of the abductor pollicis longus and extensor pollicis brevis travel together in a common synovial sheath and form the lateral border of the anatomic snuffbox.
3. The distal tendons of abductor pollicis longus and extensor pollicis brevis are involved in deQuervain’s syndrome (deQuervain’s stenosing synovitis).