The third dorsal interosseous abducts the middle finger toward the ring finger. The middle finger has two dorsal interossei (second and third) allowing it to deviate both radially and ulnarly.
| Origin | Adjacent sides of the third and fourth metacarpal shafts |
|---|---|
| Insertion | Ulnar side of the middle finger proximal phalanx and extensor expansion |
| Nerve Supply | Deep branch of ulnar nerve (C8, T1) |
| Blood Supply | Third dorsal metacarpal artery |
| Actions | Abducts the middle finger ulnarly — away from the index finger; Assists middle finger MCP flexion |
|---|
The middle finger can be abducted in either direction — this dual DI supply makes it the reference digit for the hand's abduction-adduction axis. Ring finger trigger in Dupuytren's contracture can involve the third DI as the lateral cord displaces toward it.
Tested by resisted middle finger abduction toward the ring finger.
Lateral cord in ring finger Dupuytren's contracture involving the third dorsal interosseous plane requiring careful identification during fasciectomy.
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