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Abductor Pollicis Brevis

Last updated on Monday, April 13 2009 by blondarb

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Muscle Name: abductor pollicis brevis


Abbreviation: APB

Spinal Nerve Roots:

Brachial Plexus Trunks:
    lower trunk

Brachial Plexus Cords:
    medial cord

Named Nerves:
    median nerve

Proximal Attachment: Transverse carpal ligament, the scaphoid and trapezium  

Distal Attachment: Radial base of proximal phalanx of thumb and the thumb extensors

Action: Abduction of the thumb by acting across the carpometacarpal joint and the metacarpophalangeal joint. It also assists in opposition and extension of the thumb.

Needle Insertion:  With the hand supinated, the needle is inserted into the patients lateral thenar eminence, at the middle of the metacarpal bone.

Activation for EMG:  With the hand supinated, have the patient abduct the thumb.


  • If the needle is inserted too laterally the opponens pollicis will be sampled.
  • If the needle is inserted too medially the flexor pollicis brevis (median and ulnar innervation) will be sampled
  • This is considered to be more painful than most intrinsic hand muscles.