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First Palmar Interosseous Muscle
Muscular System

First Palmar Interosseous Muscle

Musculus interosseus palmaris primus

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Quick Facts

Origin: Palmar aspect of second metacarpal bone.

Insertion: Medial aspect of base of proximal phalanx and extensor expansion of index finger.

Action: Adducts index finger at its metacarpophalangeal joint; simultaneously flexes metacarpophalangeal joint and extends interphalangeal joints of index finger.

Innervation: Deep branch of ulnar nerve (C8-T1).

Arterial Supply: Deep palmar arch, perforating branches of deep palmar arch, palmar metacarpal and common palmar digital arteries.

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Origin

The first palmar interosseous muscle originates from the palmar aspect of second metacarpal bone.

Insertion

The fibers of the first palmar interosseous muscle travel inferiorly to the index finger and insert, via a short tendon, onto the:

- medial aspect of the base of the proximal phalanx of index finger;

- extensor expansion of index finger.

Key Features & Anatomical Relations

The first palmar interosseous muscle is found in the interosseous compartment of the hand. It is a short, unipennate skeletal muscle. It is located:

- anterior to the second metacarpal bone and the second dorsal interosseous muscle of hand;

- posterior to the adductor pollicis muscle.

Actions & Testing

The first palmar interosseous muscle is involved in multiple actions:

- adducts the proximal phalanx of index finger (i.e., draws it towards the longitudinal axial line of the middle finger) at the second metacarpophalangeal joint;

- simultaneously flexes the second metacarpophalangeal joint and extends the interphalangeal joints of the index finger, which occurs when the first lumbrical and first dorsal interosseous muscles of hand contract simultaneously with it.

The first palmar interosseous muscle can be tested by adducting the proximal phalanx of index finger at the second metacarpophalangeal joint against resistance (Standring, 2016).

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.

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