Extensor Muscles

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Extensor Muscles

• Posterior compartment all innervated by the
  radial nerve or branches.
• Can be categorized into three functional groups
• Muscles that extend and abduct or adduct the hand
  at the wrist
• Extensor carpi radialis longus
• Extensor carpi radialis brevis
• Extensor carpi ulnaris
• Muscles that extend the medial four digits
• Extensor digitorum
• Extensor indicis
• Extensor digiti minimi
• Muscles that extend or abduct the thumb
• Abd pollicis longis
• Abd pollicis brevis
• Extensor pollicis longus

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Extensors can be organized into deep and
superficial groups

• Superficial
• Brachioradialis
• Extensor carpi radialis longus
• Both attached to the lateral supraepicondylar
  ridge of the humerus and adjacent intermuscular
  septum.
• Extensor carpi radialis brevis
• Extensor carpi ulnaris
• Extensor digitorum
• Extensor digiti minimi
• All have attachments to the common extensor
  tendon to the lateral epicondyle

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Deep Extensors

• Deep to the superficial extensors, emerge from
  the lateral forearm
• Abductor pollicis longus
• Extensor pollicis longus
• Extensor pollicis brevis
• Extensor indicis
• Supinator

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The exception forearm muscle Brachioradialis

• An exceptional muscle because it violates the
  rules, technically located in the posterior
  compartment of the UE it is innervated by the
  radial but it is a forearm flexor (and quite a
  good one at that)
• O proximal 2/3rds of the lateral supracondylar
  ridge and the intermuscular septum
• I Lateral aspect of the distal radius proximal
  to the styloid process.
• Innervation Radial nerve before it divides into
  deep superficial
• Action Accessory flexor of the forearm,
  functions best when the forearm is at
  midpronation, testing causes the muscle body to
  become prominent.

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Extensor carpi radialis longus

• O lateral supracondylar ridge of the humerus
• I base of the 2nd metacarpal
• Innervation radial nerve
• Action extends abducts hand at the wrist
• Synergistic function with finger flexors just as
  ECU

• Table 6.8 p 808

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Extensor carpi radialis brevis

• O lateral epicondyle of the humerus
• I Base of the 3rd metacarpal
• Innervation Deep branch
• Action extents and abducts hand at the wrist
• Occasionally arise from a common belly with its
  longer partner.

Table 6.8 p 808
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Extensor carpi ulnaris
Table 6.8 p 808

• O 2 heads
• - lateral epicondyle humerus
• - posterior border of the ulna
• I Medial side of the base of the 5th metacarpal
• Innervation Posterior interosseous branch
• Action extends and adducts hand at the wrist
• Synergistic with finger flexors because it keeps
  the wrist extended to allow increased grip
  strength.

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Extensor digitorum

• O lateral epicondyles of the humerus
• I Extensor expansions of the medial 4 digits
• Innervation Posterior interosseous branch
• Action Extension at the MCP, PIP DIP,
  participates in wrist extension when the fingers
  are extended

• Table 6.8 p 808

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Extensor digiti minimi

• O lateral epicondyles of the humerus
• I Extensor expansion of the 5th digit
• Innervation Posterior interosseous branch
• Action separates the philistines from the
  sophisticates

• Table 6.8 p 808

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Forearm Extensors

• The four tendons of the extensor digitorum pass
  deep to the extensor retinaculum to the medial
  four digits. As the tendons pass over the dorsum
  of wrist they are covered with synovial sheaths.
  The tendons of the index and 5th digit extensors
  join these tendons.
• The extensor indicis joins the extensor digitorum
  as it passes through the extensor retinaculum.
  The extensor digiti minimi has its own sheath.

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• Oblique intertendinous connection at the MCP
  restricts independent extension of the digits,
  except index and 5th.
• The extensor tendons of digits 2-5 form extensor
  expansions on the distal metacarpals.
• The distal tendons form complex mechanical
  structures

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Deep Extensors

• Deep to the superficial extensors, emerge from
  the lateral forearm
• Abductor pollicis longus
• Extensor pollicis longus
• Extensor pollicis brevis
• Extensor indicis
• Supinator

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Extensor indicis

• O posterior surface of the ulna interosseous
  membrane
• I extensor expansion of the 2nd digit
• Innervation Posterior interosseous branch
• Action Extends all the joints of the index
  finger and assists in wrist extension.
• Allows independent index finger action.

• Table 6.8 p 808

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Extensor pollicis longus

• O Posterior surface middle 1/3rd of the ulna
  and interosseous membrane
• I base of the distal phalanx of the thumb
• Innervation posterior interosseous branch
• Action Extends distal phalanx at MCP PIP,
  contributes to thumb abduction
• Medial border of the" snuff box

• Table 6.8 p 808

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Abductor pollicis longus

• O posterior aspect ulna, radius posterior
  interosseous membrane
• I base of the 1st metacarpal
• Innervation posterior interosseous branch
• Action abducts and laterally rotates the
  carpalmetacarpal joint.
• Forms lateral boundary of the snuff box.

• Table 6.8 p 808

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Extensor pollicis brevis

• O posterior surface of the radius
  interosseous membrane
• I base of the proximal phalanx of the thumb
• Innervation posterior interosseous branch
• Action extends proximal phalanx at the MCP
  joint can also extend 1st metacarpal at the
  carpometacarpal joint.
• Also forms the lateral boundary of the snuff
  box.

• Table 6.8 p 808

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Supinator

• O arises from the lateral epicondyles of the
  humerus, radial collateral ligament, annular
  ligament of the radioulnar joint, supinator fossa
  and the crest of the ulna.
• I lateral, posterior anterior surfaces of the
  proximal 1/3rd of the radius
• Innervation Deep branch of th radial nerve
• Action Rotates the radius to supinate the
  forearm and hand, supinates regardless of
  flexion/extension position (vs. biceps).

• Table 6.8 p 808

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• Pronator
• Supinator
• FCR
• FPL
• Ext digitorum
• Pro quad
• FDP
• FCU
• FDS

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