Flexors of the Wrist & Digits

flexor carpi radialis flexor carpi ulnaris flexor digitorum profundus flexor digitorum superficialis flexor pollicis longus flexor retinaculum palmaris longus wrist wrist flexors

Flexors - Superficial Layer

  • Situated primarily on the anterior aspect of the forearm (the only exception being flexor pollicis brevis, flexor digiti minimi and the lumbricals
  • Divided into 2 layers
    • Superficial layer arising in whole or in part form the Common Flexor Origin or Tendon (from medial epicondyle and adjacent fascia)
      • Includes - Flexor carpi ulnaris, Palmaris longus, Flexor carpi radialis (pronator teres) 
      • Under these but still forming part of the superficial layer is Flexor Digitiorum Superficialis

Flexor Carpi Ulnaris

  • Forms medial border of forearm
  • O: From 2 heads
    • Humeral - from CFO
    • Ulna - Medial border of olecranon and posterior border of ulna (via an aponeurosis)
  • Forms a long tendon which inserts into pisiform (investing it) and onto the hook of hamate and base of the 5th metacarpal
  • A: flexion and ulnar deviation of the wrist
  • NS: Ulnar nerve C8, T1

Palmaris Longus

  • Not always present
  • Lies between FCU and FCR
  • O: CFO
  • Forms a ling tendon which passes over the flexor retinaculum to insert into the palmar aponeurosis
  • A: Weak wrist flexor and tightens the palmar fascia
  • NS: Median nerve (C8,T1)

Flexor Carpi Radialis

  • Most lateral of the superficial flexors (lies between palmaris longus and pronator teres)
  • O: CFO
  • Forms a long tendon which passes under the flexor retinaculum (in a separate compartment over trapezium) and inserts into the palmar aspect of the bases of the 2nd and 3rd metacarpals
  • A: Flexion and radial deviation
  • NS: Median nerve (C6,C7)

Flexor Digitorum Superficialis

  • Often described a being the intermediate layer
  • O: from 2 head
    • Medial – CFO, ulnar collateral ligament and medial border of coronoid
    • Lateral – from upper 2/3s of anterior oblique line on radius
  • Forms 4 tendons which pass under the flexor retinaculum (sharing a common synovial sheath with profundus)and insert into the intermediate phalanges of the 4 fingers
  • At the level of the MCP joint the tendons of FDS split to allow the tendons of profundus through
  • The 2 halves of the tendon then twist before re-uniting to form a groove for FDP
  • Before inserting into the intermediate phalanx the tendon splits again
  • A: Flexion of the PIP, MCP and wrist joints
  • NS: Median nerve C7,8, T1

Flexors - Deep Layer

  • These muscles arise from the anterior aspect of the radius, ulna and interosseous membrane
    • Flexor digitorum profundus
    • Flexor pollicis longus
    • Pronator quadratus

Flexor Digitorum Profundus

  • Deep to FDS on medial side of forearm
  • O: Fro medial side of coronoid process, upper ¾ of anterior and medial aspect of the ulna shaft and medial ½ of middle part of IOM
  • Form 4 tendons proximal to the wrist joint which pass to the distal phalanx of the 4 fingers
  • As the tendons pass under the flexor retinaculum they share a common synovial sheath with FDS
  • At the level of the MCP joints they pass through the split in FDS to reach their distal attachment on the palmar aspect of the distal phalanx
  • A: flexion of DIP, PIP, MCP and wrist joints
  • NS: Laterally via the anterior interosseous nerve (C7, 8, T1) and medially via the ulna nerve (C8,T1)

Flexor Pollicis Longus

  • Lateral to FDP
  • O: From anterior surface of radius just below the anterior oblique line but above pronator quadratus and adjacent IOM
  • Forms a tendon proximal to the wrist joint which passes under the flexor retinaculum in its own synovial sheath
  • I: Palmar aspect of base of distal phalanx of thumb
  • A: Flexion of IP, MCP and wrist joint
  • NS: Anterior Interosseous nerve (C8, T1)

The Flexor Retinaculum

  • Strong fibrous band of deep fascia
  • Attached firmly to pisiform scaphoid, trapezium and hook of hamate
  • Converts the anterior aspect of the carpus into a tunnel 
  • Maintains the concavity of the carpal bones
  • Laterally it divides into 2 lamellae 
  • These form a separate tunnel for the tendon of FCR
  • Medially the tendons of FDS, FDP, FPL and the median nerve pass under it

Synovial Sheaths

  • As the tendons pass under the flexor retinaculum they are all encased in a double layer of synovial membrane
  • The sheaths begin at the proximal wrist crease
  • The sheath for FDS and FDP end midway into the palm of the hand (except for the sheath passing to the little finger) - the tendons to the 2nd, 3rd and 4th fingers then have separate sheath from the MC heads 
  • FCR and FPL are encased in their own sheaths

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