Flexor pollicis brevis muscle
Flexor pollicis brevis is composed of superficial and deep heads. However, the deep head can vary in size and sometimes even be absent.
Like the other thenar muscles, flexor pollicis brevis acts on the thumb and flexes it at the metacarpophalangeal joint.
This article will discuss the anatomy and functions of the flexor pollicis brevis muscle.
Superficial head: Flexor retinaculum, tubercle of trapezium bone
Deep head: Trapezoid and capitate bones
|Insertion||Lateral aspect of base of proximal phalanx 1 (via radial sesamoid bone)|
|Action||Carpometacarpal and metacarpophalangeal joint 1: Thumb flexion|
Superficial head: Recurrent branch of median nerve
Deep head: Deep branch of ulnar nerve (C8, T1)
|Blood supply||Superficial palmar artery, princeps pollicis artery and radialis indicis artery|
Origin and insertion
Flexor pollicis brevis has two heads that originate from the two separate areas;
- Superficial head: arises from the distal border of the flexor retinaculum, as well as the distal part of the tubercle of trapezium bone.
- Deep head: arises from the trapezoid and capitate bones, as well as the palmar ligaments of the distal row of carpal bones.
The deep and superficial heads course obliquely and meet at the radial side of the base of the proximal phalanx of the thumb. Here they insert by a common short tendon which contains an embedded sesamoid bone.
Flexor pollicis brevis is the most medial of the thenar muscles. It lies medial to the abductor pollicis brevis and opponens pollicis muscles, while it is lateral to adductor pollicis muscle.
Along its course, the superficial head of the muscle passes along the radial side of the tendon of flexor pollicis longus, whereas the deep head passes deep to the same tendon. Additionally, the superficial head is commonly blended with the opponens pollicis muscle. The superficial surface of the muscle is crossed by the motor branch of the median nerve.
The two heads of the flexor pollicis brevis usually differ in their innervation. The superficial head of flexor pollicis muscle receives nervous supply from the recurrent branch of the median nerve, whereas the deep head receives innervation from the deep branch of the ulnar nerve, derived from spinal roots C8 and T1.
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Flexor pollicis brevis receives arterial supply from branches of the radial artery; superficial palmar artery, branches of the princeps pollicis artery and radialis indicis artery.
As a part of the thenar muscles, flexor pollicis brevis acts on the thumb and produces flexion at the metacarpophalangeal and carpometacarpal joints. This action aids in opposition of the thumb and, if continued, it produces the medial rotation of thumb.
Flexor pollicis brevis can be tested and palpated on the thenar eminence when the thumb is flexed against resistance.