The FrontalCortex question bank can help you study for the neurology boards.

Abductor Pollicis Brevis

Last updated on Monday, April 13 2009 by blondarb

peer review status unavailable
rating unavailable

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.