Median nerve, Ulnar nerve and Radial nerve are the 3 major nerves of the upper limb originating from the brachial plexus.
Some important neuroanatomic relationships in the forearm are:
1. Medial nerve: Crossed by brachial artery from lateral to medial just above the elbow to lie medial to brachial artery in cubital fossa.
2. Anterior interosseous nerve: Splits pronator teres and runs between flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP).
3. Ulnar nerve: Between flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP).
4. Radial nerve: Between brachialis and brachioradialis.
5. Posterior interosseous nerve: Splits supinator
Course and innervation of these nerves have been simplified and tabulated below:
|Part of upper limb||Ulnar nerve||Supply||Median nerve||Supply||Radial nerve||Supply|
|Origin||Medial cord (C8-T1)||Lateral and Medial cord (C5-T1)||Posterior cord (C5-T1)|
|Axilla||Medial to axillary artery||None||Lateral to axillary artery||None||Behind axillary artery – exits axilla via Triangular interval||Long and medial head of triceps|
Posterior cutaneous nerve of arm
|Proximal arm||Medial to brachial artery||None||Lateral to brachial artery||None||Posterior compartment (Spiral groove – from medial to lateral)||Lateral head of triceps and Anconeus|
Lateral cutaneous nerve of arm and Posterior cutaneous nerve of forearm
|Distal arm||Posterior compartment (over medial head of triceps) after piercing medial intermuscular septum||None||Anterior compartment (Crosses brachial artery from lateral to medial at coracobrachialis insertion) – runs under biceps||None||Anterior compartment (Pierces lateral intermuscular septum ~10 cm proximal to lateral epicondyle) – in front of lateral epicondyle between Brachialis and BR/ECRL||Brachialis|
|Elbow||Passes behind medial epicondyle (cubital tunnel)||Elbow joint||Cubital fossa (Medial to brachial artery; Beneath lacertus fibrosus)||Elbow joint||Divides|
|Forearm||Enters between 2 heads of FCU||FCU||Enters between 2 heads of PT||PT||SBRN – sensory (travels under BR and emerges between BR and ECRL ~8 cm proximal to radial styloid)|
|Travels between FCU and FDP||Ulnar 2 FDPs||Branches to anterior compartment muscles of forearm||PL, FCR, FDS||DBRN (passes through FREAS)|
– Radial neck (radial recurrent vessels)
– Arcade of Frohse (supinator arch)
-Supinator (distal border)
|Palmar cutaneous branch||Hypothenar skin||Anterior interosseous nerve – runs between FDP and FPL||PQ, FPL, lateral 2 FDP||DBRN emerges out of Radial tunnel/FREAS as PIN||Supinator and all 6 muscles of extensor compartment|
|Dorsal cutaneous branch||Dorsal aspect of medial 1 & 1/2 fingers and associated hand area||Travels down forearm entering 2 heads of FDS (sublimis bridge) and runs between FDS and FDP|
|Runs between FCR and PL (gives palmar cutaneous branch)||Thenar eminence sensory|
|Wrist and Hand||Passes superficial to flexor retinaculum and travels under piso-hamate ligament (Guyon’s canal)||Passes deep to carpal tunnel (flexor retinaculum)||SBRN runs as dorsal radial sensory nerve crossing anatomical snuff box lateral to radial artery||Wrist, Dorsal lateral 3 and 1/2 fingers upto distal interphalangeal joint and corresponding dorsum of hand|
|a.||Superficial branch (sensory)||Palmar surface of medial 1 & 1/2 fingers|
|Palmar digital branch||Palmar surface and fingertips of lateral 3 and 1/2 digits|
1st and 2nd lumbricals
|b.||Deep branch (motor)||1 & 1/2 thenar muscles – Adductor pollicis, deep head of FPB|
All hypothenar muscles except palmaris brevis
2 Lumbricals (3rd, 4th)
|Recurrent thenar branch||Thenar muscles (AbPB, OP, Superficial head of FPB)|