Adductor pollicis muscle

Origin and insertion

Adductor pollicis arises by two heads which originate from different locations. The transverse head originates from the palmar base of the third metacarpal bone, while the oblique head originates from the capitate bone and palmar bases of second and third metacarpals. From their origin points, the two heads converge into one muscle belly as the fibers run laterally towards the thumb.

The muscle ends in a tendon that contains a sesamoid bone and inserts onto the base of the first proximal phalanx as well as its extensor hood.

Relations 

The adductor pollicis muscle is larger than and deeper to the thenar muscles. On its ventral aspect, adductor pollicis is crossed by the flexor tendons of the index finger, first lumbrical and flexor pollicis brevis muscles. On its dorsal aspect, the muscle is related to or even sometimes conjoined with the first dorsal interosseous muscle. In addition, the two heads of adductor pollicis comprise a passageway through which the deep branch of ulnar nerve, deep palmar arch and radial artery pass.

Innervation

Adductor pollicis muscle receives its innervation from the deep branch of ulnar nerve (root value C8, T1).

Blood supply

Adductor pollicis is vascularized by the deep palmar arterial arch, formed by the anastomosis of the radial artery and the deep palmar branch of ulnar artery.

Function

Adductor pollicis is the most powerful of the intrinsic muscles of the hand. Its main function is the adduction of the thumb which is the movement of the thumb towards the index finger from an abducted position. This action is essential for functions that require pinching and gripping. Additionally, the adductor pollicis aids the later stages of opposition of the thumb.

This movement is a combination of actions, namely adduction, medial rotation, flexion and adduction of the thumb so that it can touch each fingertip of the same hand. Thus, the strength of adductor pollicis can be tested by pushing the thumb against the index finger while the examiner attempts to pull them apart. 

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