Extensors of the Wrist & Digits

abductor pollicis longus brachioradialis deep extensors extensor carpi radialis brevis extensor carpi radialis longus extensor carpi ulnaris extensor cummunis extensor digiti minimi extensor digitorum extensor indicis extensor pollicis brevis extensor pollicis longus extensor retinaculum supinator wrist extensors

Extensors - Superficial Layer

  • Situated on the posterior aspect of the forearm
  • As with the flexors the extensors are divided into 2 layers
    • Superficial layer arising in whole or in part form the Common Extensor Origin or Tendon (from lateral epicondyle, lateral collateral ligament of elbow and adjacent fascia)
    • Includes - Extensor carpi ulnaris, extensor digiti minimi, extensor digitorum (communis), extensor carpi radialis longus and brevis (supinator)  (brachioradialis)

    Extensor Carpi Ulnaris

    • Forms medial border of forearm
    • O: From 2 heads
      • Humeral - from Common Extensor Origin (CEO)
      • Ulna - Posterior border of ulna (via a common aponeurosis with FCU and FDP)
    • Forms a long tendon which inserts into the dorsal surface of the base of the 5th metacarpal
    • A: Extension and ulnar deviation of the wrist
    • NS: Posterior interosseous nerve C7, 8 (deep branch of the radial nerve)

    Extensor Digitorum (Communis)

    • Forms four tendons to each of the 4 fingers
    • Over the posterior aspect of the MCP joints forms the dorsal digital expansion
    • O: Common Extensor Origin (CEO)
    • A: Finger and wrist extensor 
    • NS: Posterior Interosseous nerve (C7, C8)

    Extensor Digitiorum

    • The distal attachment of the extensor digitorum is extensive with the tendon proper passing to the dorsal aspect of the intermediate phalanx
    • At the level of the heads of the metacarpals form the dorsal digital expansion which is an aponeurotic extension which pass medially and laterally to the provide attachments for the interossei and the lumbricals
    • The expansion forms 2 slips that apps to the distal phalanx

    Extensor Digiti Minimi

    • From the Common Extensor Origin (CEO)
    • To the ulnar side of the extensor mechanism of the Vth digit
    • A: Extension of the 5th MCP and wrist joint
    • NS: Posterior interosseous nerve C7, 8

    Extensor Carpi Radialis Longus

    • From lower 1/3 of the lateral supracondylar ridge and lateral intermuscular septum
    • To the posterior aspect of the base of the 2nd metacarpal
    • A: extension and radial deviation
    • NS: Radial nerve (C6, 7)

    Extensor Carpi Radialis Brevis

    • From Common Extensor Origin (CEO)
    • To the posterior aspect of base of the 3rd metacarpal
    • A: Extension and radial deviation 
    • NS: Posterior interosseous nerve C6, 7

    Brachioradialis and Supinator

    • Often grouped with the posterior antebrachial muscles as they share a common nerve supply and attachment
    • Brachioradialis is a flexor of the elbow (covered with the elbow flexors)
    • Supinator produces supination of the forearm 

    Supinator

    • Arises from 2 heads
      • Humeral Head - from lateral collateral ligament and Common Extensor Origin (CEO)
      • Ulna Head - from supinator crest on the lateral aspect of upper ulna
    • Wraps around the radius before inserting into the lateral and posterior aspects of the proximal 1/3 of the shaft of radius
    • A: supination of radioulna joints
    • NS: Posterior interosseous nerve C5, 6

    Deep Extensors

    • All arise from the posterior aspect of the radius, ulna and interosseous membrane
    • The majority act on the thumb (abductor pollicis longus, extensor pollicis longus and extensor pollicis brevis) and one acts on the index finger (extensor indicis)

    Abductor Pollicis Longus

    • Arises form the posterior aspect of the upper radius, interosseous membrane and ulna
    • Forms a long tendon which passes under the extensor retinaculum with extensor pollicis brevis
    • Inserts into the radial side of the base of the 1st metacarpal 
    • A: abduction of the CMC joint of the thumb and extension of the wrist
    • NS: Posterior interosseous nerve C7, 8

    Extensor Pollicis Longus

    • From posterior surface of middle 1/3 of ulna and adjacent interosseous membrane
    • Tendon passes around the dorsal tubercle and under the extensor retinaculum
    • Inserts into the dorsal aspect of the distal of the distal phalanx of the thumb
    • A: extension of IP, MCP and wrist joint
    • NS: Posterior Interosseous nerve (C7, 8)

    Extensor Pollicis Brevis

    • From posterior surface of lower 1/3 of radiusand adjacent interosseous membrane below APL
    • Tendon passes under the extensor retinaculum with APL
    • Inserts into the dorsal aspect of the distal of the proximal phalanx of the thumb
    • A: extension of MCP and wrist joint
    • NS: Posterior Interosseous nerve (C7, 8)

    Extensor Indicis

    • Arises from the posterior surface of the lower 1/3 of the ulna and adjacent interosseous membrane
    • Inserts into the extensor mechanism of the index finger
    • A: Extension of the MCP joint of the index finger and the wrist
    • NS: Posterior interosseous nerve C7, 8

    The Extensor Retinaculum

    • Strong fibrous band of deep fascia 
    • Attached firmly to lower radius and ulna
    • Compartmentalised by intermuscular septa containing APL and EPB(most lateral compartment), ECRL and B, EPL and EI, ED, EDM, ECU
    • As tandons pass under the retinaculum the are covered in a synovial tendon sheath – tendons sharing a compartment usually share a common sheath

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