Deep Distal Four Group

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The muscles of the Deep Distal Four Group are located in the Deep Layer of the Posterior Compartment of the forearm. The deep distal four group is composed of:

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

ATTACHMENTS:

• Posterior radius, ulna, and interosseus membrane to the thumb and index finger.
  • The three “pollicis” muscles attach onto the thumb.
  • The “indicis” muscle attaches onto the index finger.

ACTIONS:

• Abducts, extends, and laterally rotates the thumb at the carpometacarpal joint.
• Extends the thumb at the metacarpophalangeal and interphalangeal joints.
• Extends the index finger at the metacarpophalangeal and interphalangeal joints.
• Radially deviates and extends the hand at the wrist joint.
• Supinates the forearm at the radioulnar joints.

NOTES:

1. The bellies of these muscles lie deep in the distal posterior forearm.
2. The three “pollicis” muscles form the borders of the anatomic snuffbox.
3. The distal tendons of the abductor pollicis longus and extensor pollicis brevis travel together in a common synovial sheath and are involved in deQuervain’s syndrome (deQuervain’s stenosing synovitis).