Median Nerve

TERMINOLOGY

• Arises from medial and lateral cords of brachial plexus (C6-C8, T1)
• In axilla, lies superolateral to artery close to short head of biceps muscle
• Lies medial to brachial artery and vein
• Located deep to bicipital aponeurosis in cubital fossa
• Supplies pronator teres, PQ, and flexors of anterior compartment forearm (except FCU and medial 1/2 of FDP, which are supplied by ulnar nerve)

• Enters forearm by passing between humeral and ulnar heads of pronator teres; located in forearm between FDP and FDS

Courses distally and attached to deep surface of FDS by fascial sheath

Anterior interosseous nerve

– Purely motor nerve

– Arises from median nerve at level of pronator teres

– Located in forearm anterior to interosseous membrane, between FPL and FDP, alongside anterior interosseous artery
• At wrist, median nerve emerges from lateral side of FDS, becomes more superficial, and runs deep to PL tendon toward carpal tunnel

Supplies FPL, PQ, and lateral 1/2 of FDP

• Median nerve lies along axis of ring finger, i.e., to ulnar side of midline
• Lies deep to antebrachial fascia and PL before dipping deeply to enter carpal tunnel
• At distal radioulnar joint: Nerve is rounded, deep to PL, medial and superficial to FCR and FPL, and lateral and superficial to FDS
• Carpal tunnel is fibroosseous tunnel located immediately distal to volar wrist crease

Formed by carpal bones and flexor retinaculum (transverse carpal ligament)

Flexor retinaculum attaches to pisiform, hook of hamate, scaphoid, and trapezium

9 structures pass through carpal tunnel

– 4 FDS tendons, 4 FDP tendons, FPL tendon, and median nerve

– Median nerve is located superficially in carpal tunnel just deep to retinaculum

Tunnel outlet is narrowest part of carpal tunnel
• Branches

Motor to thenar and 1st and 2nd lumbrical muscles

Sensory to radial 1/2 of palm, radial 3.5 digits

– Palmar cutaneous branch typically arises proximal to carpal tunnel

Median nerve divides just distal to carpal tunnel

• Examination of nerve in transverse plane is preferable to longitudinal scanning since it allows nerve to be followed continuously throughout limb
• Use proximal and distal borders of retinaculum as markers of carpal tunnel

• Median nerve may be bifid

If quantifying size of nerve, both components should be measured and summated
• Keep transducer at right angles to nerve as angulation will ↑ nerve caliber

May need to make use of anisotropy to best differentiate nerve from tendons in carpal tunnel

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off