The Anterior Morphological Structure of the Male Flexor Pollicis Longus Muscle

Description

Running along the anterior compartment of the forearm, the flexor pollicis longus originates from the anterior surface of the radius and adjacent interosseous membrane, its fusiform belly lying deep to the superficial flexor mass. Distally, its long tendon courses inferiorly and slightly laterally toward the radial side of the wrist, then continues into the thumb to reach the base of the distal phalanx. Medially, the muscle relates to flexor digitorum profundus, while proximally it sits inferior to the elbow crease and anterior to the radial shaft in standard anatomical position. Palpating and teaching deep anterior forearm anatomy often fails without a clean view of flexor pollicis longus. Thumb interphalangeal flexion is its signature action, so weakness following anterior interosseous nerve palsy (a pure motor branch of the median nerve) frequently presents as an inability to flex the thumb IP joint, classically grouped with flexor digitorum profundus to the index finger in the pinch or OK sign deficit. The tendon’s distal course also matters at the wrist, where it runs in close proximity to the carpal tunnel contents and can contribute to tenosynovitis or be encountered during volar approaches to the distal radius. A small muscle, but a frequent exam target. Ideal for upper limb gross anatomy courses, hand surgery and orthopaedics teaching files, and medical publishing that needs a single-structure focus without distractions from surrounding flexor layers. Educators can pair it with median nerve and anterior interosseous nerve diagrams to illustrate compartmental innervation and motor testing at the thumb. Anatomical accuracy verified by SciePro's Medical Advisory Board.