Palmar interossei !
The palmar interossei are small muscles between the palm bones on the palm side; they bring the fingers together toward the middle finger.
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What it is
Small muscles between the metacarpals on the palm side.
What it does
Bring the fingers together.
Key facts
- Origin
- Palmar surfaces of the 2nd, 4th and 5th metacarpals
- Insertion
- Extensor expansions and proximal phalanges of the same fingers
- Action
- Adduct the fingers toward the middle finger (PAD)
- Nerve
- Deep branch of the ulnar nerve (C8–T1)
- Blood supply
- Palmar metacarpal arteries
Relations
- In front
- The deep palmar arch and the deep branch of the ulnar nerve, then the long flexor tendons and lumbricals; the adductor pollicis in front of the first
- Behind
- The dorsal interossei
- Course
- Their tendons pass dorsal to the deep transverse metacarpal ligament into the extensor mechanism on the side facing the middle finger
How to find it
Not palpable: they lie on the palmar side between the metacarpals, deep to the deep palmar arch. Their action shows when the straightened fingers are squeezed together.
Examination
- Card test: weak grip on a card between the extended fingers indicates weak palmar interossei (ulnar nerve)
- Wartenberg sign: the little finger rests abducted because the 3rd palmar interosseous cannot oppose extensor digiti minimi
On imaging
On MRI and ultrasound they lie on the palmar side of the metacarpals, deep to the flexor tendons and next to the dorsal interossei. They are not usually seen on their own. With ulnar nerve palsy, MRI shows oedema and then fatty atrophy of all the interossei, with the hypothenar muscles as well when the lesion lies above the deep branch.
Clinical notes
- Weak finger adduction and loss of fine pinch are early functional complaints in ulnar nerve compression
- Together with the dorsal interossei they flex the MCP and extend the IP joints; their loss gives the intrinsic-minus (claw) position
- In rheumatoid arthritis the pull of the intrinsic muscles, these included, adds to ulnar drift and palmar subluxation of the fingers at the MCP joints
Anatomical variants
- Classically unipennate, but only about three in five were in one study
- The count varies with whether the thumb slip is treated as a palmar interosseous
Memory aid
PAD and DAB: Palmar ADduct, Dorsal ABduct, both measured from the middle finger.
Test yourself
Think of the answer, then tap the question to see it.
What do the palmar interossei do, and why does the middle finger have none?
They adduct the fingers toward the middle finger, which is the axis they are drawn toward.
What is the card test for the palmar interossei?
A card held between the extended fingers is easily pulled out in ulnar nerve palsy.
What position results from loss of the palmar and dorsal interossei?
The intrinsic-minus (claw) position, since together they flex the MCP and extend the IP joints.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- musculi interossei palmares TA2 2534
- Official Spanish (DeCS)
- Músculos interóseos palmares
- English (TA2)
- Palmar interossei
Related
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Palmar Interosseous Muscle.
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Representative model, for educational purposes only.
