Video: Flexor pollicis brevis muscle

Hello there! It’s Matt from Kenhub, and in this tutorial, we will be discussing the flexor pollicis brevis. The thenar musculature consists of four muscles located on the radial side of the palm. Together, they form the ball of the thumb known as the thenar eminence. They originate at different carpal bones and distally attach to the thumb. This tutorial will explore the origin, insertion, innervation and function of the flexor pollicis brevis, one of the thenar muscles.

The flexor pollicis brevis muscle has two heads separated by the tendon of the flexor pollicis longus. The superficial head originates from the flexor retinaculum and the deep head from both the capitate and trapezium bones. The tendon runs to and inserts at the base of the proximal phalanx of the thumb via the radial sesamoid bone.

The flexor pollicis brevis is the only thenar muscle receiving double innervation due to its transformation during the course of embryogenesis. Most frequently, the median nerve supplies the superficial head and, the ulnar nerve, the deep head. However, the innervation pattern is quite variable due to the fact that most people have an interconnection between the recurrent branch of the median nerve and the deep branch of the ulnar nerve at the ball of the thumb.

The main function of each thenar muscle is associated to their names. The flexor pollicis brevis is mainly responsible for bending the thumb, or flexion, at the carpometacarpal joint as well as adduction of the thumb.

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