Nerves and Nerve Lesions of the Upper Limb

Nerves and Nerve Lesions of the Upper Limb

Axillary Nerve (C5/C6, posterior cord)

Exits axilla via quadrilateral space with posterior circumflex humeral artery. Supplies deltoid and teres minor; cutaneous supply over regimental badge area. Injury: surgical neck fracture or anterior glenohumeral dislocation → deltoid paralysis, shoulder abduction >15° lost, numbness over lateral shoulder.

Radial Nerve (C5–T1, posterior cord)

Enters spiral groove of humerus with profunda brachii artery. Gives posterior cutaneous nerve of arm and forearm (no motor to arm except triceps from proximal branches). At lateral epicondyle divides into: posterior interosseous nerve (deep, motor to ALL posterior forearm compartment muscles) and superficial radial nerve (sensory, dorsal radial 3.5 digits and dorsal hand). Mid-shaft humeral fracture → wrist drop (inability to extend wrist and fingers) + sensory loss over anatomical snuff box and dorsal hand; triceps spared (supplied proximal to groove).

Musculocutaneous Nerve (C5–C7, lateral cord)

Pierces coracobrachialis → supplies all anterior arm muscles (biceps, brachialis, coracobrachialis) → continues as lateral cutaneous nerve of forearm (sensory). Injury rare; causes weak elbow flexion + sensory loss over lateral forearm.

Ulnar Nerve (C8/T1, medial cord)

Passes behind medial epicondyle (cubital tunnel) → supplies FCU and medial half of FDP in forearm → enters hand via Guyon's canal. In hand: hypothenar muscles, all interossei, medial 2 lumbricals, adductor pollicis, deep head of FPB. Sensory: medial 1.5 fingers and medial palm. Elbow lesion (cubital tunnel syndrome): ring and little finger claw hand less pronounced (FDP to ring/little not working, so DIP flexion absent = less claw = paradox). Wrist lesion: more pronounced claw (DIP flexion intact) + preserved wrist adduction/flexion (FCU intact).

Median Nerve (C5–T1, medial + lateral cords)

Enters forearm between heads of pronator teres → supplies all anterior forearm muscles except FCU and medial FDP → enters hand through carpal tunnel. In hand: thenar muscles (opponens pollicis, abductor pollicis brevis, lateral head FPB) and lateral 2 lumbricals. Sensory: lateral 3.5 fingers including nail beds (important for fine touch). Carpal tunnel syndrome: paraesthesia/pain in lateral 3.5 digits (worse at night), thenar wasting, Tinel's sign (tapping carpal tunnel), Phalen's test (wrist flexion for 60s). Ape hand (inability to oppose thumb) with thenar wasting.