Flexor Pollicis Brevis

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Flexor Pollicis Brevis

Flexor Pollicis Brevis(FPB) is present on the radial border of the palm. FPB is one of the muscle of the thenar eminence of the hand.

It also falls under the intrinsic muscle of the hand.[1] Flexor Pollicis Brevis is the small, narrow muscle consisting of the outer and inner portions. The outer portion is termed as the superficial head and the inner portion is termed as the deep head of the muscle.[2]


The superficial Head is originated from the crest of the trapezium and flexor retinaculum.

The deep head is originated from trapezoid and capitate bones and also from the palmar ligaments of the distal row of carpals bones. [3]


The deep head unit with the superficial head after passing deeply from Flexor Pollicis Longus tendon on the radial sesamoid bone and the base of the proximal phalanx of the thumb.[3]


The superficial head has a single innervation by the median nerve and the deep head has a double innervation by the ulnar nerve(deep branch) and the median nerve ( recurrent branch).[3]


It is supplied by the branches of the radial artery.[2]


Flexor Pollicis Brevis flex the metacarpophalangeal and carpometacarpal joints leading to the opposition of the thumb and, if continued, produces the medial rotation of the thumb. Due to this function, we are able to manipulate objects and create tools. It plays role in fine movements like precision, pinching, and power griping.[4]

Flexor Pollicis Brevis and First Dorsal interosseous muscles help in Tip-pinch movements. The movement generally, happen in daily activities like turning a key and opening a package[5]

Clinical relevance

The sensory impairments like numbness, paresthesias, and motor deficits of the superficial belly of FPB is caused by median nerve compression which is occurred in the carpal tunnel syndrome. Circumduction and opposition require well-coordinated, simultaneous movements across each of the three thumb joints ( CMC, MCP, IP), Carpal tunnel syndrome disrupt these motion pattern.[6]


Manual Muscle Testing of FPB

Patient Position: Neutral position of the wrist, forearm supinated, Carpometacarpal(CMC), and IP joint at 0°, thumb in adduction adjacent to the 2nd Metacarpal.

Therapist Position: Comfortable position stabilizing 1st metacarpal to avoid any wrist and CMC movement by one hand fingers and the other hand one finger is placed at proximal phalanx in the direction of extension.

Test: Patient is instructed in native or non-technical language to flex the MP joint of the thumb keeping the IP joint straight.


Grade 5 (Normal): Complete Range of motion(ROM) against maximum resistance.

Grade 4 (Good): Tolerate strong or moderate resistance.

Grade 3 (Fair): Complete full ROM with slight resistance.

Grade 2(Poor): Complete ROM without resistance

Grade 1 (Trace : Palpate the muscle on the ulnar side of the flexor pollicis longus tendon in the thenar eminence.

Grade 0 (Zero): There is no visible and palpable contraction in the muscle.



  1. Okwumabua E, Sinkler MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Hand Muscles. StatPearls [Internet]. 2020 Jan.
  2. 2.0 2.1 Koca K, Ekinci S, Ege T, Ozyurek S, Kurklu M, Battal B, Basbozkurt M. Bilateral congenital absence of flexor pollicis brevis and abductor pollicis brevis muscles with bilateral thenar atrophy: a case report. Clinical Medicine Insights: Arthritis and Musculoskeletal Disorders. 2012 Jan;5:CMAMD-S8443.
  3. 3.0 3.1 3.2 Caetano EB, da Cunha Nakamichi Y, de Andrade RA, Sawada MM, Nakasone MT, Vieira LA, Sabongi RG. Flexor Pollicis Brevis Muscle. Anatomical Study and Clinical Implications. The open orthopaedics journal. 2017;11:1321.
  4. Gupta S, Michelsen-Jost H. Anatomy and function of the thenar muscles. Hand clinics. 2012 Feb 1;28(1):1-7.
  5. Chen CY, McGee CW, Rich TL, Prudente CN, Gillick BT. Reference values of intrinsic muscle strength of the hand of adolescents and young adults. Journal of Hand Therapy. 2018 Jul 1;31(3):348-56.
  6. Marquardt TL, Nataraj R, Evans PJ, Seitz WH, Li ZM. Carpal tunnel syndrome impairs thumb opposition and circumduction motion. Clinical Orthopaedics and Related Research®. 2014 Aug 1;472(8):2526-33.