AN12.1-15 | Forearm & hand — Summary & Reflection

REFLECT

Return to the opening scenario: the carpenter who cannot flex his index and middle fingers at the distal joints, with sensory loss on the lateral palm and three fingers.

Now answer:
1. Which nerve was injured? (Name the exact branch responsible for the motor loss)
2. Which specific muscles are paralysed? (Name the muscles responsible for distal flexion of the index and middle fingers)
3. Where was the wound? (Proximal to carpal tunnel? Within it? Distal to it?)
4. What clinical test would confirm your diagnosis on examination?

Discussion: The main median nerve is injured at the wrist (the sensory loss indicates the main trunk). The paralysed muscles are FDP to index and middle fingers (the AIN/median nerve branch). The wound is likely proximal to or at the carpal tunnel (sensory branches of the median nerve arise just distal to the retinaculum). Diagnosis: Tinel's sign over the carpal tunnel + testing APB strength (recurrent branch of median nerve).

KEY TAKEAWAYS

Ventral Forearm:
• 8 muscles, 3 layers; mostly median nerve; FCU + medial FDP = ulnar nerve
• AIN (branch of median) = FDP-lateral, FPL, pronator quadratus
• Radial and ulnar arteries = terminal branches of brachial artery

Carpal Tunnel:
• Flexor retinaculum bridges carpal bones = carpal tunnel
• Contents: FDS (4) + FDP (4) + FPL (1) + median nerve only
• CTS = median nerve compression → thenar wasting, lateral 3½ finger numbness

Intrinsic Hand:
• Thenar: 3 median + adductor pollicis (ulnar) | Hypothenar: all ulnar
• Lateral 2 lumbricals: median | Medial 2 lumbricals + all interossei: ulnar
• Claw hand = ulnar nerve injury → ring + little worst affected

Dorsal Forearm:
• 12 muscles; all PIN (radial), except brachioradialis + ECRL = radial nerve proper
• Wrist drop = radial nerve at spiral groove → triceps often spared

Anatomical Snuffbox:
• Floor: scaphoid + trapezium + radial artery | Medial: EPL | Lateral: APL + EPB
• Tenderness = suspect scaphoid fracture (even if X-ray is normal)

Extensor Expansion (ELI):
• Extensor digitorum + Lumbricals + Interossei
• Central slip → middle phalanx | Lateral bands → distal phalanx
• Boutonnière = central slip rupture | Swan-neck = volar plate laxity