Carpal Tunnel and Carpal Tunnel Syndrome

Learning Objectives

After reading this post you will know:

  • What is carpal tunnel and how is it formed?
  • Structures passing through the carpal tunnel.
  • Anatomical basis of carpal tunnel syndrome.

 

Q. Describe briefly carpal tunnel.

A. Carpal Tunnel

  •  It is an osseofibrous tunnel formed posteriorly by the concave palmar surface of the carpals and bounded anteriorly by the flexor retinaculum.
  • The  flexor retinacuum is a thick fibrous band ( modification of deep fascia)  that is attached
    • laterally to scaphoid & crest of trapezium.
    • medially to pisiform and hook of  hamate.

    The structures passing through the carpal tunnel are :

  • Median nerve.
  •  Four tendons of flexor digitorum superficialis  muscle
  •   Four tendons of flexor digitorum profundus muscle
    ( All these flexor tendons  are enclosed in a common synovial sheath, referred to as the ulnar bursa.
  •  Tendon of Flexor pollicis longus  which has its own synovial sheath, named as radial bursa.

* The tendon of flexor carpi radialis passes through a separate canal in the lateral part of flexor retinaculum in the groove on trapezium..

Carpal Tunnel

Q. Enumerate the structures passing above the flexor retinaculum from lateral to medial.

A. The structures passing above the flexor retinaculum from lateral to medial are:

  • Palmar cutaneous branch of median nerve
  • Tendon of Palmaris longus
  • Palmar cutaneous branch of ulnar nerve
  • Ulnar artery
  • Ulnar nerve

Q. Describe briefly anatomical basis of Carpal tunnel syndrome.

A. Carpal tunnel syndrome is caused by compression of the median nerve in the carpal tunnel.

  • Causes for compression of median nerve in the carpal tunnel can be :
    • Osteoarthritis involving carpal bones
    • Dislocation of  lunate bone.
    • Tenosynovitis –inflammation of synovial sheaths of long flexor tendons.
    • Myxedema.
    • fluid retention in pregnancy.
  • The characteristic clinical features include:
    • Motor loss:
      • weakness and wasting of thenar muscles which are supplied by median nerve as a result  the thumbcannot be opposed and  remains adducted ( adductor pollicis is supplied by ulnar nerve) this is called ‘Ape thumb deformity‘.
      • Index and middle fingers lag behind while making the fist due to paralysis of 1st and 2nd lumbricals ( supplied by median nerve).
    • Sensory loss:
      • Tingling or numbness in the skin/loss of sensations over  palmar surface of lateral 31/2  digits  including nail be and distal phalanges on dorsum of hand  that are supplied by median nerve.
      • There is no sensory loss in the skin over thenar eminence, as it is supplied by palmar cutaneous branch of median nerve which passes above the flexor retinaculum.
    • Vasomotor changes: 
      • Skin over the palmar surface of lateral 31/2  digits  of hand  feels warmar due to arteriolar dilation,  and drier due to absense of sweating. this occurs due to loss of sympathetic innervation ( postganglionic  sympathetic fibers which accompany median nerve)

 

 

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