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Where is carpal tunnel located and how it is formed?
Carpal Tunnel 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.
Enumerate the structures passing through the carpal tunnel.
- 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..
Enumerate the structures passing above the flexor retinaculum.
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
Applied Aspect
Carpal tunnel syndrome
It 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 thumb cannot 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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