The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three

thenar muscles The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The w ...

. It has both a superficial part and a deep part.

Origin and insertion

The muscle's superficial head arises from the distal edge of the flexor retinaculum and the tubercle of the trapezium, the most lateral bone in the distal row of

carpal bones The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός ...

. It passes along the radial side of the tendon of the

flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniq ...

. The deeper (and medial) head "varies in size and may be absent."Gray's 37th British Edition, p. 630" It arises from the

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

and capitate bones on the floor of the

carpal tunnel In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor ( palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the ...

, as well as the

ligaments A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have ligam ...

of the distal

carpal The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In huma ...

row. Both heads become tendinous and insert together into the radial side of the base of the proximal

phalanx The phalanx (: phalanxes or phalanges) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar polearms tightly packed together. The term is particularly used t ...

of the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

; at the junction between the tendinous heads there is a

sesamoid In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Greek word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be presen ...

bone.''

Gray's Anatomy ''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter and first published in London in 1858. It has had multiple revised editions, and the current edition, the 42nd (October 2020 ...

'' 1918, see infobox

Innervation

The superficial head is usually innervated by the lateral terminal branch of the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

. The deep part is often innervated by the deep branch of the

ulnar nerve The ulnar nerve is a nerve that runs near the ulna, one of the two long bones in the forearm. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or ...

( C8, T1).

Blood supply

The flexor pollicis brevis receives its blood supply from the superficial palmar branches of radial artery.

Action

The flexor pollicis brevis flexes the thumb at the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...

, as well as

flexion Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

and

medial rotation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

of the 1st metacarpal bone at the

carpometacarpal joint The carpometacarpal (CMC) joints are five joints in the wrist that articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones. The CMC joint of the thumb or the first CMC joint, also known as the trapeziometaca ...

Pathology

Flexor pollicis brevis can, rarely, be completely absent at birth due to a congenital issue (as can the other muscles of the

thenar eminence The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The w ...

Additional images

Image:Musculusflexorpollicisbrevis.png, The muscles of the left hand. Palmar surface. (Flexor pollicis brevis visible at center right, near thumb.) File:Braus 1921 215.png, Caput profundum of the Flexor pollicis brevis muscle File:Hand dissection 9.jpg, Flexor pollicis brevis muscle Image:Gray219.png, Bones of the left hand. Volar surface. Image:Gray415.png, Front of the left forearm. Deep muscles. Image:Carpal-Tunnel.svg, Transverse section across the wrist and digits. Image:Gray815.png, Superficial palmar nerves. Image:Gray817.png, Deep palmar nerves. File:Slide1yyy.JPG, Flexor pollicis brevis muscle File:Slide2VVV.JPG, Flexor pollicis brevis muscle File:Slide2AAAA.JPG, Flexor pollicis brevis muscle File:Slide7BBBB.JPG, Flexor pollicis brevis muscle File:Slide16BBBB.JPG, Flexor pollicis brevis muscle File:Slide8IIII.JPG, Flexor pollicis brevis muscle File:Slide3OOOO.JPG, Flexor pollicis brevis muscle File:Slide13OOOo.JPG, Flexor pollicis brevis muscle File:Slide250000.JPG, Flexor pollicis brevis muscle File:Slide17PPPP.JPG, Flexor pollicis brevis muscle File:Slide1MAI.JPG, Muscles of hand. Cross section.

References

{{Authority control Muscles of the upper limb