Flexor Pollicis Brevis Muscle – Anatomy, Nerve Supply

The Flexor Pollicis Brevis Muscle is a small, narrow muscle consisting of two portions, the outer and inner. The outer portion is superficial and originates from the flexor retinaculum of the wrist. The inner portion is deep and originates from the ulnar side of the metacarpal bone. These two portions join to form a tendon that inserts in the proximal phalanx of the thumb. This muscle is innervated by motor branches of the median nerve and is supplied by branches of the radial artery. The flexor pollicis brevis flexes and rotates the thumb.

The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part.

Origin and Insertion of Flexor Pollicis Brevis Muscle

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. It passes along the radial side of the tendon of the flexor pollicis longus.

The deeper (and medial) head “varies in size and may be absent.”^[rx] It arises from the trapezoid and capitate bones on the floor of the carpal tunnel, as well as the ligaments of the distal carpal row.^[rx]

Both heads become tendinous and insert together into the radial side of the base of the proximal phalanx of the thumb; at the junction between the tendinous heads there is a sesamoid bone.^[rx]

Nerve Supply of Flexor Pollicis Brevis Muscle

• The superficial head is usually innervated by the lateral terminal branch of the median nerve. The deep part is often innervated by the deep branch of the ulnar nerve (C8, T1).^[rx]
• 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.
• The hand is full of complicated muscles. Learn their anatomy efficiently and actively using Kenhub’s muscle anatomy and reference charts!

Blood Supply of Flexor Pollicis Brevis Muscle

• The flexor pollicis brevis receives its blood supply from the superficial palmar branches of radial artery.^[rx]
• 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.

Function of Flexor Pollicis Brevis Muscle

• The flexor pollicis brevis flexes the thumb at the metacarpophalangeal joint, as well as flexion and medial rotation of the 1st metacarpal bone at the carpometacarpal joint.^[rx]
• 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.

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