Upper Limb Neurology · Anatomy · High Yield

Median Nerve

The median nerve (C6–C8, T1) is the nerve of the anterior forearm and the thenar eminence. Uniquely, it arises from two cords and has a distinctive pattern of innervation: most forearm flexors plus the lateral two lumbricals and the all-important LOAF muscles of the hand.

✦ The Mnemonic

"Precisely Flexing, Creating Really Fine Fingertip Prowess"

Forearm muscles in proximal-to-distal order (PT, FCR, PL, FDS, FDP-lat, FPL, PQ)

PT Pronator Teres Forearm pronation; first median-innervated muscle in the forearm

FCR Flexor Carpi Radialis Wrist flexion and radial deviation

PL Palmaris Longus Absent in ~15%; flexes wrist; tenses palmar fascia

FDS Flexor Digitorum Superficialis All 4 digits; tests: isolate middle/ring PIP flexion

FDP FDP (lateral half) Index and middle fingers — via anterior interosseous nerve (AIN)

FPL Flexor Pollicis Longus Thumb IP flexion; AIN branch

PQ Pronator Quadratus Deep forearm pronation; AIN; tested: elbow flexed to 90°

LOAF Hand muscles Lumbricals 1&2, Opponens pollicis, Abd. poll. brevis, FPB

📚 Clinical Breakdown

The median nerve passes the elbow medial to the brachial artery, between the two heads of pronator teres, and then runs deep to FDS. The anterior interosseous nerve (AIN) branches off in the proximal forearm and supplies FPL, FDP (lateral half), and pronator quadratus — it carries no cutaneous fibres.

High median nerve injury (above the elbow): loss of all median-innervated forearm muscles + hand muscles. The hand adopts a 'hand of benediction' posture when asked to make a fist — index and middle fingers remain extended (loss of FDS/FDP to these digits and lumbricals 1&2), while ring and little fingers flex normally (ulnar nerve intact).

AIN syndrome (isolated AIN palsy): the patient cannot form an 'OK' sign — the index finger cannot flex at the DIP joint (FDP index) and the thumb cannot flex at the IP joint (FPL). No sensory loss — AIN is purely motor. The 'pinch' grip is replaced by a 'pulp-to-pulp' contact instead of 'tip-to-tip.'

Origin Medial + lateral cords (C6–T1)

AIN palsy sign Cannot form 'OK' sign; no sensory loss

CTS motor loss LOAF muscles (thenar wasting)

CTS sensory loss Lateral 3½ fingers (palmar); spares thenar skin

⭐ Clinical Pearl

Carpal tunnel syndrome (CTS) classically wakes patients at night — nocturnal acroparaesthesia. This is because the venous system is less effective at rest, increasing carpal tunnel pressure. The patient shakes the hand for relief (Flick sign), which is very specific for CTS. Repetitive movements, pregnancy, hypothyroidism, rheumatoid arthritis, and acromegaly are common precipitating factors.

← Ulnar Nerve