Dorsal Interossei (Hand)
| Dorsal Interossei (Hand) | |
|---|---|
| Muscle Type | |
| Origin | 1st, lateral head: Proximal 1/2 of the ulnar border of MC1
1st, medial head: radial border of MC2 2nd, 3rd, 4th: Adjacent sides of MC bones in each interspace |
| Insertion | 1st: Radial side index finger, to base of proximal phalanx
2nd: Radial side middle finger 3rd: Ulnar side middle finger, chiefly extensor expansion 4th: Ulnar side ring finger |
| Action | Abducts the index, middle, and ring fingers from the midline (axial line) through the third digit. Assists in flexion of MCPJs and extension of ICPJs of the same fingers. The first also assists in thumb adduction. |
| Synergists | Abductor Digiti Minimi (Hand), Lumbricals |
| 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).
Dorsal Interossei
Patient: Sitting or supine
Fixation: Stabilisation of the adjacent digits
Test and Pressure: Against midline of the phalanx:
1st: abduction of index finger towards thumb. Apply pressure against radial side of the index finger towards the middle finger.
2nd: Abduction of the middle finger towards the index finger. Hold the middle finger and pull in the direction of the ring finger.
3rd: Abduction of the middle finger towards the ring finger. Hold the middle finger and pull into the index finger.
4th. Abduction of the ring finger towards the little finger. Hold the ring finger and pull towards the middle finger.
