Muscles abducting / adducting / opposing the thumb

Abductor pollicis longus

Abductor pollicis brevis

Opponens pollicis

Adductor pollicis

Palmaris brevis

Abductor pollicis longus

Abductor pollicis longus lies deep to extensor digitorum in the posterior compartment of the forearm. It arises from the upper part of the posterior surface of the ulna below anconeus, the middle third of the posterior surface of the radius below supinator and the intervening interosseus membrane.

As the muscle passes distally, it emerges from its deep position to lie superficially in the lower part of the forearm. The tendon forms above the wrist and passes, with that of extensor pollicis brevis, with the same synovial sheath below the extensor retinaculum, where it lies in a groove on the lateral surface of the radial styloid process. The tendon inserts primarily into the radial side of the base of the first metacarpal, with a slip which passes to the trapezium, and another which passes to abductor pollicis brevis and the fascia over the thenar eminence. 

Nerve supply

Abductor pollicis longus is supplied by the posterior interosseus branch of the radial nerve, root value C7, 8. The skin over the muscle is supplied by roots C6, 7.

Action

By itself, the muscle puts the thumb into a mid-extended and abducted position. Working with the extensors, abductor pollicis longus helps to extend the thumb at the carpometacarpal joint, while, with abductor pollicis brevis, it abducts the thumb.

Palpation

Palpation of this muscle is described with extensor pollicis brevis.

Abductor pollicis brevis

Abductor pollicis brevis is the most lateral and superficial of the three muscles forming the thenar eminence. It takes its origin mainly from the front of the flexor retinaculum, extending onto the tubercles of the scaphoid and trapezium with an occasional contribution from the tendon of abductor pollicis longus. The muscle forms a short tendon which attaches to the radial side of the base of the proximal phalanx of the thumb, with some fibres reaching the expansion of the extensor pollicis longus tendon.

Nerve supply

Abductor pollicis brevis is supplied by the median nerve, root value T1. The skin over the muscle is supplied by root C6. 

Action

Abductor pollicis brevis abducts the thumb at both the carpometacarpal and metacarpophalangeal joints, causing it to move anteriorly at right angles to the palm. In order to achieve this position there must be some medial rotation at the carpometacarpal joint, the remainder occurring at the metacarpophalangeal joint. This movement is of great significance in terms of the function of the hand as the thumb can be moved towards the fingertips(opposition) where it can carry out precision tasks that require a pincer grip. Because of its partial insertion into the long extensor tendon of the thumb, abductor pollicis brevis can aid in flexion of the metacarpophalangeal joint and extension of the interphalangeal joint.

Opponens pollicis

Opponens pollicis is covered by abductor pollicis brevis. Arising from the flexor retinaculum and tubercle of the trapezium, it inserts into the whole length of the lateral half of the anterior surface of the first metacarpal.

Nerve supply

Opponens pollicis is supplied by the median nerve, root value T1. Occasionally, it may be supplied by the ulnar nerve. The skin over the muscle is supplied by root C6.

Action

Opponens pollicis produces the complex movements of the thumb called opposition where the first metacarpal is drawn forwards and medially in an arc towards the fingers. The movement involves, in order of action, abduction, medial rotation, and finally flexion and adduction at the carpometacarpal joint of the thumb. The importance of this action is that the tip of the thumb can be brought into contact with the tip of any finger, thus allowing for very precise action of the hand.

Palpation

The three muscles forming the thenar eminence of the thumb are closely packed together and covered with tough fascia which makes identification of individual muscles difficult. However, if the thenar eminence is carefully palpated during resisted movements, all but opponens pollicis can be identified. If abduction of the thumb is resisted(that is movement away from the palm in a plane of 90° to the palm) abductor pollicis brevis can be identified in the lateral part of the thenar eminence.

Adductor pollicis

Adductor pollicis is found in the web space of the thumb on its palmar aspect, and has oblique and transverse heads. The oblique head arises from the sheath of the tendon of flexor carpi radialis, the bases of the second, third and fourth metacarpals, and the trapezoid and capitate bones. The transverse head arises from the longitudinal ridge on the anterior surface of the shaft of the third metacarpal. Between these two heads, the radial artery passes to gain access to the palmar aspect of the hand. Both heads are inserted into the medial side of the base of the proximal phalanx of the thumb by a tendon containing a sesamoid bone.

Nerve supply

Adductor pollicis is supplied by the deep branch of the ulnar nerve, root value C8 and T1. The skin over the muscle is supplied by roots C6 and 7.

Action

Adductor pollicis is a strong muscle that brings the thumb back to the palm from a position of abduction. Also, it is active in the later stages of opposition. Functionally, the strength of this muscle can be demonstrated when the tip of the index finger and thumb are held together in a pincer grip and an attempt is made to pull them apart. Consequently, adductor pollicis is an important muscle in maintaining the precision grip of the hand.

Palpation

Adductor pollicis is found in the web between the thumb and index finger, and can be felt on the palmar aspect when the movement of adduction is resisted.

Palmaris brevis

Palmaris brevis is a superficial muscle found covering the hypothenar eminence of the little finger. It arises from the medial border of the palmar aponeurosis and the front of the flexor retinaculum and inserts into the skin of the medial border of the hand.

Nerve supply

Palmaris brevis is supplied by the superficial branch of the ulnar nerve, root value T1. The skin over the muscle is supplied by root C8.

Action

Contraction of the muscle wrinkles the skin on the ulnar side of the hand. This muscle is included in this section as its main function is to assist the thumb in producing a good grip.