Oblique Head of the Adductor Pollicis Under the Skin, Palmar View

Description

Centered in the deep thenar compartment, the oblique head of the adductor pollicis arises from the capitate and adjacent bases of the second and third metacarpals, then courses distally and laterally toward the ulnar side of the thumb. Fibers converge on the ulnar sesamoid and the base of the proximal phalanx at the first metacarpophalangeal joint, lying deep to the flexor pollicis brevis and opponens pollicis and medial to the first metacarpal. A palmar, left-hand orientation places the thumb on the image’s left, with carpal and metacarpal landmarks visible beneath the skin, articular cartilage highlighted at the interphalangeal and metacarpophalangeal joints. Small structures matter here. Clinically, adductor pollicis anatomy is inseparable from the deep branch of the ulnar nerve, which passes through the hypothenar region into the palm to innervate both the oblique and transverse heads; denervation produces weak key pinch and the classic Froment sign as flexor pollicis longus substitutes at the interphalangeal joint. Surgeons use this relationship when working around the deep palmar arch and when approaching the adductor canal of the thumb during repair of thenar lacerations, ulnar nerve decompression, or evaluation of intrinsic wasting. The oblique head’s origin on the central metacarpal bases also helps explain why deep palmar pain or stiffness after metacarpal base injuries can limit thumb adduction even when the thumb itself appears intact. Use this palmar view for teaching thenar compartment layering in gross anatomy and hand therapy courses, and for figure placement in textbooks or review articles discussing ulnar neuropathy, intrinsic muscle testing, and key pinch biomechanics. It also fits clinical handouts that correlate metacarpal and carpal surface anatomy with deep muscle attachments. Anatomical accuracy verified by SciePro's Medical Advisory Board.