• Adducts the thumb.
• Intrinsic hand muscle.
Primary: Adducts carpal-metacarpal joint of thumb.
Secondary: Adducts and assists in flexion of metacarpal-phalangeal joint of thumb; aids in thumb opposition; extends thumb interphalangeal joint.
Palpation: Palpate between thumb and index metacarpals (first web space) as thumb is adducted.
Strength Testing: Position – palmar side up. Stabilize – the wrist. Resist – thumb adduction by applying force to ulnar aspect of thumb (in the direction of thumb palmar abduction).
Possible Substitutions: First dorsal interosseous and flexor pollicis brevis muscles.
• Roots: C8, T1.
• Nerve: Median nerve, thenar branch.
• Innervation Route: C8, T1 → median nerve → thenar branch → adductor pollicis branch.
Origin of Oblique Head: Capitate, index and long metacarpal bases.
Origin of Transverse Head: Long metacarpal palmar surface.
Insertion of Oblique Head: Thumb proximal phalanx base at the ulnar aspect; ulnar sesamoid.
Thumb extensor apparatus.
Insertion of Transverse Head: Thumb proximal phalanx base at the ulnar aspect; ulnar sesamoid.