CorpusHuman Anatomy
MuscularMuscle group

Thenar muscles

Musculi thenares

Also known as: thenar eminence, abductor pollicis brevis, flexor pollicis brevis, opponens pollicis

Three short muscles that form the thenar eminence at the base of the thumb (abductor pollicis brevis, flexor pollicis brevis and opponens pollicis). They produce opposition, and the recurrent branch of the median nerve supplies them.

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Overview

The thenar eminence contains three muscles arising mainly from the flexor retinaculum and the tubercles of the scaphoid and trapezium.
- Abductor pollicis brevis (superficial, lateral): to the lateral base of the proximal phalanx. Abducts the thumb (moves it anteriorly, perpendicular to the palm).
- Flexor pollicis brevis (superficial, medial): to the lateral base of the proximal phalanx (via the lateral sesamoid). Flexes the MCP joint. Its deep head is often supplied by the ulnar nerve.
- Opponens pollicis (deep): to the whole lateral border of the 1st metacarpal. Rotates the metacarpal medially and flexes it at the saddle-shaped CMC joint, producing opposition.

Opposition, bringing the pulp of the thumb against the pulp of the other fingers, combines abduction, flexion and medial rotation at the CMC joint. It is the basis of precision grip and of human manual dexterity. The thenar muscles are supplied by the recurrent (motor) branch of the median nerve, which curves back into them just distal to the flexor retinaculum. It is very superficial there, which is why it is nicknamed the "million-dollar nerve".

Parts & subdivisions

  1. Abductor pollicis brevis
    Flexor retinaculum, scaphoid and trapezium → lateral base of the proximal phalanx. Abducts the thumb. Usually the first muscle to waste in carpal tunnel syndrome.
  2. Flexor pollicis brevis
    Flexor retinaculum, trapezium (superficial head); capitate and trapezoid (deep head) → base of the proximal phalanx. Flexes the MCP joint.
  3. Opponens pollicis
    Flexor retinaculum and trapezium → lateral border of the 1st metacarpal. Opposes the thumb.

Anatomy

Origin

Flexor retinaculum and the tubercles of the scaphoid and trapezium.

Insertion

Base of the proximal phalanx of the thumb (APB, FPB) and the lateral border of the 1st metacarpal (opponens pollicis).

Action

Abduction, flexion and opposition of the thumb.

Innervation

Recurrent (thenar) branch of the median nerve. The deep head of FPB is frequently supplied by the deep branch of the ulnar nerve.

Nerve roots

C8–T1 (T1 predominant)

Arterial supply

Superficial palmar branch of the radial artery; superficial palmar arch.

Function

  • Opposition of the thumb (precision grip)
  • Abduction and flexion of the thumb

Clinical significance

Carpal tunnel syndrome

Compression of the median nerve under the flexor retinaculum causes nocturnal paraesthesia of the thumb, index, middle and radial half of the ring finger. Signs include positive Phalen and Tinel tests and, later, thenar wasting with weak abduction (APB). Palm sensation is spared because the palmar cutaneous branch passes superficial to the retinaculum.

"Ape hand"

A proximal median nerve lesion causes thenar wasting. The thumb lies flat and adducted beside the index finger and cannot oppose.

Mnemonics

Median-nerve muscles of the hand

LOAF: Lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.