The second dorsal interosseous (DAB: Dorsal ABducts) abducts the middle finger toward the index finger axis, which is the first radial deviation from the middle finger's anatomical position. It is the only dorsal interosseous that abducts from both sides — the middle finger has both a second (radial) and third (ulnar) dorsal interosseous providing bilateral abduction.
| Origin | Adjacent sides of the second and third metacarpals (bipennate) |
|---|---|
| Insertion | Radial base of the proximal phalanx of the middle finger and extensor hood |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Second dorsal metacarpal artery |
| Actions | Abducts the middle finger radially (toward the index finger); Flexes the MCP and extends the IP joints of the middle finger |
|---|
The second dorsal interosseous is assessed in ulnar nerve palsy by resisted index-middle finger spreading (radial deviation of the middle finger). Its atrophy produces the characteristic dorsal hand guttering between the second and third metacarpals. The second DI belly is also the site of targeted botulinum toxin injection for dystonic middle finger posturing in writer's cramp.
Palpated on the dorsal hand between the second and third metacarpals during resisted middle finger radial abduction.
Visible wasting of the second dorsal interosseous from ulnar nerve palsy producing a hollow between the second and third metacarpals, one of the most visible signs of intrinsic hand muscle denervation.
