Pollical Palmar Interosseous (of the Thumb)

Origin, Insertion, Action & Nerve

Attachments explained

The Pollical Palmar Interosseous (of the Thumb) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Action & function

When the Pollical Palmar Interosseous (of the Thumb) contracts, it produces the following movement: Adducts the thumb toward the palm.

As part of the Hand group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Pollical Palmar Interosseous (of the Thumb) receives its nerve supply from the Deep branch of the ulnar nerve (C8–T1). This nerve carries fibres from spinal segment(s) C8, T1.

Because a muscle can only contract when its nerve is intact, injury to the Deep branch of the ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the Pollical Palmar Interosseous (of the Thumb), impairing the movements it normally produces (adducts the thumb toward the palm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Pollical Palmar Interosseous (of the Thumb) (the OIANS method)

Treat this as a variant thumb muscle that behaves like an extra palmar interosseous: applying the PAD rule (Palmar ADduct), it pulls the thumb toward the palm, reinforcing adductor pollicis. Framing it that way lets you reason its action instead of memorising a rarity in isolation.

Its innervation follows the deep intrinsic pattern of the hand, the deep branch of the ulnar nerve, the same nerve driving adductor pollicis and the true interossei. Filing it beside those muscles keeps this uncommon slip organised within the ulnar-supplied deep hand group.

Frequently asked questions

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