Oblique Head of the Adductor Pollicis, Anterior View

Description

Deep in the thenar compartment, the oblique head of the adductor pollicis is presented from an anterior (palmar) perspective as a thick muscular belly coursing from the capitate and adjacent bases of the second and third metacarpals toward the ulnar side of the proximal phalanx of the thumb. Distal fibers converge into a tendon inserting on the ulnar sesamoid and the base of the proximal phalanx, lying medial to the flexor pollicis longus tendon as it enters the thumb. Superficial to it sit the thenar muscles, while the transverse head of the adductor pollicis, if included, would run more horizontally from the shaft of the third metacarpal toward the same ulnar insertion. Slips of palmar aponeurosis, metacarpal ligaments, and digital flexor tendons frame the muscle in the anterior plane. Functionally, this muscle is the power adductor of the thumb at the carpometacarpal and metacarpophalangeal joints, drawing the first metacarpal toward the palm and stabilizing pinch against the index finger. That matters in ulnar nerve lesions: denervation of adductor pollicis (deep branch) weakens key pinch and produces a positive Froment sign as flexor pollicis longus substitutes with interphalangeal flexion. Surgical anatomy is tight here. The deep palmar arch and the deep branch of the ulnar nerve pass in close relation to the metacarpal bases and the adductor mass, relevant during deep palmar dissections and repair of thenar trauma. Hand anatomy courses and operative hand texts use this view to teach thenar layer organization and to clarify why adductor pollicis sits deep to the flexor tendons yet dominates pinch strength. It also fits clinical teaching files on ulnar neuropathy at Guyon canal and tendon transfer planning for pinch reconstruction. Anatomical accuracy verified by SciePro's Medical Advisory Board.