Third Palmar Interosseous (Hand)

Origin, Insertion, Action & Nerve

Attachments explained

The Third Palmar Interosseous (Hand) 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 Third Palmar Interosseous (Hand) contracts, it produces the following movements: Adducts the little finger toward the axial line of the hand (PAD); flexes MCP and extends IP joints.

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 Third Palmar Interosseous (Hand) receives its nerve supply from the Deep branch of 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 ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the Third Palmar Interosseous (Hand), impairing the movements it normally produces (adducts the little finger toward the axial line of the hand (PAD)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Third Palmar Interosseous (Hand) (the OIANS method)

Complete the PAD set with the third palmar interosseous, which pulls the little finger inward toward the middle-finger axis. Its origin from the palmar surface of the fifth metacarpal makes it the most medial of the palmar interossei.

Remember that the palmar interossei serve the index, ring, and little fingers (not the middle finger, which only needs abducting), the exact complement of the dorsal set. Their common deep ulnar nerve supply and dual joint action carry over unchanged.

Frequently asked questions

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