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Flexor Pollicis Brevis Muscle Anatomy

Last updated on: June 27, 2024

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The flexor pollicis brevis (FPB), the short flexor of the thumb, is located medial to the abductor pollicis brevis. It has two bellies, superficial and deep head, they are located on opposite sides of the tendon of the flexor pollicis longus. These two bellies share (with each other and often with the abductor pollicis brevis) a common, sesamoid-containing tendon at their distal attachment.

Flexor Pollicis Brevis Muscle Anatomy

The flexor pollicis brevis muscle heads’ origin is:

The superficial Head originates from the crest of the trapezium and flexor retinaculum.
The deep head originates from trapezoid and capitate bones and also from the palmar ligaments of the distal row of carpals bones.

The two heads unit after passing deeply from Flexor Pollicis Longus tendon on the radial sesamoid bone and the base of the proximal phalanx of the thumb.

See Also: Hand Anatomy, Bones & Muscles

The bellies usually differ in their innervation: The larger superficial head of the flexor pollicis brevis is innervated by the recurrent branch of the median nerve, whereas the smaller deep head is usually innervated by the deep palmar branch of the ulnar nerve.

Its blood supply comes from the superficial palmar branch of the radial artery.

The flexor pollicis brevis flexes the thumb at the carpometacarpal and metacarpophalangeal joints and aids in opposition of the thumb.

Origin	The superficial Head originates from the crest of the trapezium and flexor retinaculum. The deep head originates from trapezoid and capitate bones and also from the palmar ligaments of the distal row of carpals bones.
Insertion	Lateral side of base of proximal phalanx of thumb
Innervation	The flexor pollicis brevis is mostly innervated by the recurrent branch of the median nerve (C8, T1). The deep part is often innervated by the deep branch of the ulnar nerve.
Blood Supply	Superficial palmar branch of the radial artery
Action	Flexes thumb

To test the flexor pollicis brevis, flex the thumb against resistance. If acting normally, the muscle can be seen and palpated; however, keep in mind that the flexor pollicis longus also flexes the thumb.

References & More

Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
Clinically Oriented Anatomy – 8th Edition
Physiopedia – Flexor Pollicis Brevis