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Nerve Supply of the Wrist

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1. Median Nerve

• The median nerve crosses the volar (anterior) aspect of the wrist within the carpal tunnel, just radial and deep to the palmaris longus tendon.
• Its terminal branch, the anterior interosseous nerve (AIN), carries articular (sensory) fibers to the radiocarpal, radioulnar, intercarpal, and carpometacarpal joints on the volar side.
• Injury to the terminal branch of the AIN can cause persistent, dull, aching volar wrist pain.
• The AIN has no cutaneous representation - it is a purely articular/deep sensory branch at the wrist level.
• Localization in Clinical Neurology, 8e, p. 98

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2. Ulnar Nerve

• The ulnar nerve at the wrist is contained within Guyon's canal, between the pisiform and the hook of the hamate.
• The dorsal sensory branch of the ulnar nerve crosses the dorsum of the wrist near the ulnar styloid, supplying the dorsal ulnar skin of the hand.
• Provides articular branches to the ulnar side of the wrist joint.
• Rosen's Emergency Medicine, p. 3687

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3. Radial Nerve - Posterior Interosseous Nerve (PIN)

• The superficial branch of the radial nerve crosses the dorsum of the wrist near the radial styloid, supplying dorsal skin on the radial side.
• The posterior interosseous nerve (PIN) - the deep continuation of the radial nerve - gives articular branches to the joint capsule of the wrist and the four radial metacarpophalangeal joints.
• Injury to the PIN at the wrist spares wrist extension (the extensor carpi radialis longus is supplied more proximally) but affects finger extension.
• THIEME Atlas of Anatomy, p. 4831-4833

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Summary Table

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Muscles Acting on the Wrist and Their Nerve Supply

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Clinical Correlations

• Carpal tunnel syndrome: Compression of the median nerve in the carpal tunnel - sensory loss in radial 3.5 digits, thenar wasting.
• Guyon's canal syndrome: Ulnar nerve compression - weakness of intrinsic hand muscles, sensory loss in ulnar 1.5 digits.
• Wrist drop: Proximal radial nerve injury paralyzing all wrist and finger extensors (innervated by PIN); sensory loss is limited to the dorsal radial web space.
• PIN syndrome: Isolated deep branch injury - finger drop without wrist drop (ECRL spared), no sensory loss.
• Wrist denervation (surgical): Involves sectioning of both the posterior interosseous nerve and the anterior interosseous nerve near the wrist joint, used for chronic wrist pain relief. - Campbell's Operative Orthopaedics 15th Ed, 2026

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Muscles of the Forearm

• Anterior (flexor) compartment - 3 layers, mainly median nerve
• Posterior (extensor) compartment - 2 layers, entirely radial nerve (PIN)

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ANTERIOR COMPARTMENT (Flexor)

"All muscles in the anterior compartment of the forearm are innervated by the median nerve, except for the flexor carpi ulnaris and the medial half of the flexor digitorum profundus, which are innervated by the ulnar nerve."

• Gray's Anatomy for Students, p. 897

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Layer 1 - Superficial (4 muscles, all from medial epicondyle)

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Layer 2 - Intermediate (1 muscle)

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Layer 3 - Deep (3 muscles)

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POSTERIOR COMPARTMENT (Extensor)

"All muscles in the posterior compartment of the forearm are innervated by the radial nerve."

• Gray's Anatomy for Students, p. 906

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Superficial Layer (7 muscles, common origin: lateral epicondyle / supraepicondylar ridge)

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Deep Layer (5 muscles, origin: posterior radius/ulna + interosseous membrane)

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LATERAL (RADIAL) GROUP - Summary

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Nerve Supply - Quick Reference

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Key Clinical Points

• Median nerve injury at elbow: Loss of pronation (PT, PQ), weak wrist flexion (FCR), loss of FDS, FPL, lateral FDP - "hand of benediction" when making a fist
• AIN syndrome: Loss of FPL + lateral FDP only - inability to make "OK sign" (pinch posture); no sensory loss
• Ulnar nerve injury: Loss of FCU + medial FDP (weak ring/little finger DIP flexion); "claw hand" with intrinsic muscle loss
• Radial nerve / PIN injury (posterior interosseous): Finger drop (cannot extend at MCP joints); wrist drop only if radial nerve injured proximal to ECRL origin; no sensory loss with pure PIN injury
• Tennis elbow (lateral epicondylitis): Degeneration at origin of ECRB at the lateral epicondyle