Muscles of the posterior forearm- deep layer

Supinator

  • Proximal origin
    • Lateral epicondyle of the humerus; radial collateral and anular ligaments; supinator fossa and crest of the ulna
  • Distal insertion
    • Posterolateral and anterior surfaces of the proximal third of the radius
  • Innervation
  • Action
    • Supinates the forearm

Extensor Indicis

  • Proximal origin
    • Posterior surface of the distal third of the ulna and interosseous membrane
  • Distal insertion
    • Extensor expansion of the 2nd digit
  • Innervation
    • Posterior interosseous nerve- (C7) C8
  • Action
    • Extends the 2nd digit (enables independent extension)
    • helps to extend the hand at the wrist

The next 3 muscles begin in the deeply but ‘outcrop’ superficially.

Abductor Pollicis longus

  • Proximal origin
    • Posterior surface of the proximal halfves of the ulna, radius and interosseous membrane
  • Distal insertion
    • Base of 1st metacarpal
  • Innervation
  • Action
    • Abducts the thumb and extends it at CMC joint

Extensor Pollicis Longus

  • Proximal origin
    • Posterior surface of middle third of the ulna and interosseous membrane
  • Distal insertion
    • Dorsal aspect of base of distal phalanx of the thumb
  • Innervation
    • Posterior interosseous nerve- (C7) C8
  • Action
    • Extends the thumb at IP, MCP and CMC joints

Extensor pollicis brevis

  • Proximal origin
    • Proximal surface of the distal third of the radius and interosseous membrane
  • Distal insertion
    • Dorsal aspect of the base of the proximal phalanx of the thumb
  • Innervation
    • Posterior interosseous nerve- (C7) C8
  • Action
    • Extends the thumb at MCP and CMC joints.
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