Transverse Head of Adductor Pollicis (Caput transversum musculi adductoris pollicis)
Educational content only — not medical advice.
Anatomy
The flat, third-metacarpal head of the adductor pollicis, arising from the entire palmar shaft of the third metacarpal and passing transversely across the palm to the ulnar sesamoid. With the oblique head it forms the deep plane of the thumb's web space, and it is the muscle whose weakness defines Froment's sign.
Origin & insertion
From the palmar surface of the shaft of the third metacarpal, to the ulnar base of the proximal phalanx of the thumb with the ulnar sesamoid.
Action
Adducts the thumb in the palm plane — the power component of pinch.
Innervation
Deep branch of the ulnar nerve (C8–T1).
Clinical notes
Froment's sign tests exactly this muscle: when asked to pinch a sheet of paper, the ulnar-palsied thumb compensates with flexor pollicis longus, bending the interphalangeal joint. The muscle also provides the standard access plane for volar approaches to the second and third metacarpals.
Related structures
Educational references
FAQ
What is the role of the Transverse Head of Adductor Pollicis?
The flat, third-metacarpal head of the adductor pollicis, arising from the entire palmar shaft of the third metacarpal and passing transversely across the palm to the ulnar sesamoid. With the oblique head it forms the deep plane of the thumb's web space, and it is the muscle whose weakness defines Froment's sign.
Why is the Transverse Head of Adductor Pollicis clinically important?
Froment's sign tests exactly this muscle: when asked to pinch a sheet of paper, the ulnar-palsied thumb compensates with flexor pollicis longus, bending the interphalangeal joint. The muscle also provides the standard access plane for volar approaches to the second and third metacarpals.
Source & license
BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). license details