Muscles of the posterior forearm- superficial layer

Brachioradialis

  • Proximal origin
    • Proximal 2/3rds of the supracondylar ridge of the humerus
  • Distal insertion
    • Lateral surface of the distal end of the radius (proximal to the styloid process)
  • Innervation
  • Action
    • Relatively weak flexion of the elbow, maximal when forearm is in mid-pronated position

Extensor carpi radialis longus

  • Proximal origin
    • Lateral supracondylar ridge of the humerus
  • Distal insertion
    • Dorsal aspect of the base of the 2nd metacarpal
  • Innervation
  • Action
    • Extend and abduct the hand at the wrist joint
    • Also active during fist clenching

Extensor carpi radialis brevis

  • Proximal origin
    • Lateral epicondyle of the humerus (as the common extensor origin)
  • Distal insertion
    • Dorsal aspect of the base of the 3rd metacarpal
  • Innervation
  • Action
    • same as ERCL

Extensor digitorum

  • Proximal origin
    • Lateral epicondyle of humerus (common extensor origin)
  • Distal insertion
    • Extensor expansions of medial 4 digits
  • Innervation
  • Action
    • Extends medial 4 fingers primarily at MCP joints (though also at IP joints)

Extensor digiti minimi

  • Proximal origin
    • Lateral epicondyle of the humerus (common extensor tendon)
  • Distal insertion
    • Extensor expansion of the 5th digit (little finger)
  • Innervation
    • Posterior interosseous nerve- C7 (C8)
  • Action
    • Extends the 5th finger primarily at MCP joint (secondary at IP joints)

Extensor carpi ulnaris

  • Proximal origin
    • lateral epicondyle of the humerus and posterior border of the ulna via a shared aponeurosis
  • Distal insertion
    • Dorsal aspect of the base of the 5th metacarpal
  • Innervation
  • Action
    • Extends and adducts the hand at the wrist joint (also active during fist clenching)

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