Adductor Pollicis

What is Adductor Pollicis

The adductor pollicis is an intrinsic muscle of the hand that helps with thumb movements. It is sometimes considered the fourth thenar muscle because of its similar location and functions.

Anatomy

Location and Attachments

The muscle has a triangular or fan-shaped structure with two heads.

Origin	Oblique head: 2nd and 3rd metacarpal bases and the capitate bone Transverse head: Palmar surface of 3rd metacarpal’s shaft
Insertion	1st proximal phalangeal base, medial side

Origin

1. Oblique Head

The primary part of the oblique head originates from the palmar surface of the bases of the 2nd and 3rd metacarpals. There are multiple smaller tendon slips, one from the intercarpal ligaments in the surrounding area. Another such slip arises from the tendon sheath of the flexor carpi radialis, a forearm muscle that inserts into the 2nd and 3rd metacarpal base.

From here, the muscle fibers course distally in an oblique manner towards the thumb and then narrow down into a single tendon.

2. Transverse Head

The transverse head arises from the palmar surface of the 3rd metacarpal’s shaft or body. It is the deepest part of the muscle and has a unique fan-shaped structure due to the wide point of origin, which converges into a narrow tendon.

Insertion

The tendon of the oblique head blends medially with the flexor pollicis brevis. A part of it travels further down obliquely underneath the flexor pollicis longus tendon to unite with the lateral aspect of the abductor pollicis brevis.

The transverse head joins the oblique head’s tendon, where it joins the flexor pollicis brevis, and together they insert into the medial or ulnar side of the 1st phalangeal base and its extensor hood. A small sesamoid bone can be found in this region, embedded in the tendons of the adductor pollicis and flexor pollicis brevis muscles.

Relations With Surrounding Muscles and Structures

The adductor pollicis is the deepest muscle in the thenar eminence area. The tendons of the first lumbrical and flexor pollicis brevis (index finger flexors) cross the adductor pollicis on its ventral side.

On its dorsal side lies the first dorsal interosseous muscle with which the adductor pollicis is sometimes blended.

There is a small passage formed by the two heads of this muscle for the deep branch of the ulnar nerve, the radial artery, and the deep palmar arch.

Function

Action

Thumb adduction at the carpometacarpal joint

The adductor pollicis muscle fills the webbing between the index finger and thumb. It is the most powerful intrinsic muscle of the hand, with its primary action being adducting the thumb. It means this muscle allows you to bring the thumb back to the side of the index finger from an abducted or extended position.

As it takes care of the thumb’s adduction, this muscle is vital for the power needed for pinching with your thumb and index finger.

In addition to the above, the muscle also helps with thumb opposition in the later stages of the action. It means this muscle plays a vital role in gripping something with your hand and with jobs that need the dexterity of the fingers.

The functions of the adductor pollicis are antagonistic to those of the abductor pollicis brevis.

Innervation

Nerve

Deep branch of the ulnar nerve (C8 and T1)

Blood Supply

Artery

Deep palmar arch

The primary blood supply comes from the deep palmar arch, formed by the terminal part of the radial artery. The deep palmar branch of the ulnar artery also supplies to this muscle.