Anatomy / MSK

Wrist and hand – Extensors

by MEHLMANMEDICAL

Rote memorize this info. Then answer the questions at the end. No pain no gain.

Wrist extension:

  • Extensor carpi radialis longus
    • Extends the wrist.
    • Attaches onto the 2nd metacarpal.
    • Innervated by radial nerve.
  • Extensor carpi radialis brevis
    • Extends the wrist.
    • Attaches onto the 3rd metacarpal.
    • Innervated by deep branch of radial nerve.
  • Extensor carpi ulnaris
    • Extends the wrist.
    • Attaches onto the 5th metacarpal.
    • Innervated by the posterior interosseous nerve (the continuation of the deep branch of radial nerve).

Finger extension (excluding thumb):

  • Extensor digitorum communis
    • Extends the 2nd through 5th fingers at the MCPs, PIPs, and DIPs.
    • Attaches onto the 2nd through 5th fingers through to their distal phalanges.
    • Innervated by the posterior interosseous nerve.
  • Lumbricals
    • Extend the interphalangeal joints of the fingers.
    • (Also flex the MCPs of 2nd to 5th fingers).
    • Lateral two parts (2nd and 3rd fingers) innervated by median nerve.
    • Medial two parts (4th and 5th fingers) innervated by ulnar nerve.

Pinky-only extension:

  • Extensor digiti minimi
    • Extends the 5th finger at the MCP.
    • Attaches onto the 5th proximal phalange.
    • Innervated by the posterior interosseous nerve.

Thumb extension:

  • Extensor pollicis longus
    • Extends the thumb at the MCP and PIP.
    • Attaches onto the proximal and distal phalanges of the thumb.
    • Innervated by the posterior interosseous nerve.
  • Extensor pollicis brevis
    • Extends the thumb at the MCP.
    • Attaches onto the proximal phalange of the thumb.
    • Innervated by the posterior interosseous nerve.

(Should be noted that abductor pollicis longus and brevis also have extensor function on the thumb)

Index finger-only extension:

  • Extensor indicis
    • Extends the index finger (2nd digit) at the MCP, PIP, and DIP.
    • Attaches through to the distal phalange.
    • Innervated by the posterior interosseous nerve.

—

1. A 35-year-old man has his left wrist and hand slashed during a bar fight. He loses the ability to extend his ring finger at the distal interphalangeal joint. Which tendon is likely injured?

2. What muscle(s) extend the little finger?

3. Which muscle(s) extend the wrist?

4. Where do the wrist extensors insert?

5. What are the extensors of the thumb?

6. Where do extensor pollicis longus and brevis insert, and what do they do?

7. What does extensor indicis do?

8. Which extensor muscles are innervated by the posterior interosseous branch of the radial nerve?

9. The posterior interosseous branch of the radial nerve is a continuation of which nerve branch?

10. Which extensor is innervated by the deep branch of the radial nerve, but not the posterior interosseous nerve?



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