Interossei (Hand)
| Interossei (Hand) | |
|---|---|
| Muscle Type | |
| Origin | Between each metacarpal bone on adjacent sides |
| Insertion | First/second: Radial side of the extensor expansion of the second and third digits
Third/fourth: Ulnar side of the extensor expansion of the third and fourth digits |
| Action | Finger abduction, also assists the lumbricals in MCP flexion and PIP/DIP extension of fingers II 2-5 |
| Synergists | Abductor Digiti Minimi (Hand) |
| Antagonists | |
| Spinal innervation | C8, T1 |
| Peripheral Innervation | Ulnar Nerve |
| Vasculature | |
Palpation Site
- First dorsal interossei-radial side of the second metacarpal
- second dorsal interossei-radial side of the proximal phalanx of the third digit
- third dorsal interossei-ulnar side of the proximal phalanx of the third digit
- fourth dorsal interossei-ulnar side of the proximal phalanx of the fourth digit
Manual Muscle Testing
The interossei muscles of the hand – four dorsal and three palmar – are tested by finger abduction and adduction movements. The dorsal interossei abduct the index, middle, and ring fingers (away from the midline of the hand), while the palmar interossei adduct the index, ring, and little fingers (toward the hand’s midline). Manual muscle tests typically have the patient extend the fingers and spread them apart or squeeze them together, against the examiner’s resistance. To isolate these motions in an exam, the fingers are usually tested in extension (to minimize the flexion force and better target pure abduction/adduction).
A common clinical method for palmar interossei is the paper pull test: the patient holds a sheet of paper between two fingers (preventing adduction) and the examiner attempts to pull it out – failure to maintain grip indicates weakness in the respective palmar interosseus.
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