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Deep Layer of Posterior Forearm - Details

Deep Layer of Posterior Forearm - Details

Supinator has two heads:

  • The deep head originates on the ulna (specifically, the supinator crest) and wraps around the radius.
  • The superficial head originates on the lateral epicondyle of the humerus (and from the radial collateral and annular ligaments).
  • Both heads insert together on the proximal lateral radius.
  • Supinator supinates the forearm.

Abductor pollicis longus:

  • Originates on the middle third of the posterior radius and ulna (and the interosseous membrane).
  • Inserts on metacarpal one (on the lateral side of its base).
  • Abducts the thumb and hand.

Extensor pollicis brevis:

  • Originates on the radius and interosseous membrane.
  • Inserts via a tendon at the base of the proximal phalanx of the thumb.
  • Extends the thumb and abducts the hand.

Extensor pollicis longus:

  • Originates on the ulna and interosseous membrane.
  • Inserts via a tendon on the base of the distal phalanx of the thumb.
  • Extends the thumb and abducts the hand.

Extensor indicis:

  • Originates on the distal ulna and interosseous membrane.
  • Inserts into the extensor hood of the phalanges of digit 2.
  • Extends digit 2.

Key points:

  • Supinator is the only muscle to insert within the forearm, and the only muscle to act upon it.
  • Each of the "pollicis" muscles (abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus) each act on the thumb and on the hand, because they cross both the wrist and the joints of digit 1 within the hand.
  • Extensor indicis is the only muscle to act on digit 2.

Clinical Correlations:

  • The "anatomical snuffbox" (aka fovea radialis) is bounded anteriorly by the abductor pollicis longus and extensor pollicis brevis tendons anteriorly and the tendon of extensor pollicis longus posteriorly.
  • The radial artery, the scaphoid, and trapezium lie within the boundaries of the anatomical snuffbox; pain in the anatomical snuffbox can be indicative of a fractured scaphoid.

The deep muscles of the posterior forearm are innervated by the radial nerve.

See more: Brachial Plexus