Innervation of Hand

Introduction

Introduction to the Innervation of the Hand

The hand receives its motor and sensory innervation from the terminal branches of the brachial plexus: the median, ulnar, and radial nerves. The median nerve supplies the thenar muscles and the radial two lumbricals, while the ulnar nerve innervates the hypothenar muscles, all interossei, the ulnar two lumbricals, adductor pollicis, and the deep head of flexor pollicis brevis. The radial nerve has no motor supply in the hand but provides cutaneous innervation to the dorsum of the radial three and a half digits. The intricate interplay of these nerves underlies the fine motor control and sensory feedback essential for hand function. Understanding their precise territories is critical for localising nerve injuries, diagnosing entrapment syndromes, and planning surgical approaches.

This module details the course, branches, motor and sensory distributions, autonomous zones, and clinical testing of the nerves that supply the hand.

Study

1. The Median Nerve in the Hand

The median nerve enters the hand by passing through the carpal tunnel, deep to the flexor retinaculum. Within or just distal to the tunnel, it divides into its terminal sensory branches and gives off the recurrent motor branch.

Recurrent motor branch: This purely motor nerve curves back to supply the thenar muscles – abductor pollicis brevis, opponens pollicis, and the superficial head of flexor pollicis brevis. Its superficial position in the palm places it at risk during carpal tunnel release or thenar crease lacerations.

Palmar digital branches: The median nerve gives off common palmar digital nerves that divide into proper palmar digital nerves. These provide sensory innervation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger, and also supply the dorsal aspect of the distal phalanges (nail beds) of these same digits.

Motor to lumbricals: The first and second lumbricals receive their innervation from the terminal digital branches of the median nerve, not the recurrent branch.

Palmar cutaneous branch: This branch arises in the forearm, runs superficial to the flexor retinaculum, and supplies the skin over the thenar eminence. It is spared in carpal tunnel syndrome.

2. The Ulnar Nerve in the Hand

The ulnar nerve enters the hand through Guyon's canal, where it lies medial to the ulnar artery. Within the canal or just distal to it, the nerve divides into a superficial sensory branch and a deep motor branch.

Superficial branch: Gives a small motor twig to the palmaris brevis muscle and then divides into palmar digital nerves that supply the palmar aspect of the little finger and the ulnar half of the ring finger. This is the main sensory branch.

Deep motor branch: Passes between the abductor digiti minimi and flexor digiti minimi brevis, then through the opponens digiti minimi. It curves across the palm deep to the flexor tendons, accompanied by the deep palmar arch. It supplies the three hypothenar muscles, all dorsal and palmar interossei, the third and fourth lumbricals, the adductor pollicis, and the deep head of flexor pollicis brevis.

Dorsal cutaneous branch: Arises in the forearm, winds dorsally, and supplies the skin over the dorsum of the hand on the medial side, and the dorsal aspect of the little finger and ulnar half of the ring finger (except the nail beds, which are supplied by the palmar digital nerves from the median or ulnar nerve depending on digit).

Palmar cutaneous branch: Arises in the forearm and supplies the skin over the hypothenar eminence, sparing in lesions within Guyon's canal.

3. The Radial Nerve in the Hand

The radial nerve provides no motor innervation to the intrinsic hand muscles. Its superficial branch, a purely sensory terminal, arises from the radial nerve in the forearm and passes over the anatomical snuffbox. It supplies the skin over the dorsum of the hand on the radial side, the dorsal aspect of the thumb, index, middle, and radial half of the ring finger, up to the level of the proximal interphalangeal joints. The distal dorsal finger segments are supplied by the median and ulnar nerves.

The posterior interosseous nerve, a branch of the radial nerve, carries proprioceptive fibres from the wrist joint but does not provide cutaneous sensation.

4. Cutaneous Innervation and Autonomous Zones

The hand’s sensory innervation is shared by the three nerves with some overlap. The autonomous zones, where each nerve alone supplies sensation, are: median nerve – tip of the index finger; ulnar nerve – tip of the little finger; radial nerve – dorsal first web space (between thumb and index finger). Testing these areas allows precise clinical localisation of nerve lesions.

5. Motor Innervation of Intrinsic Hand Muscles

Thenar muscles (except deep head of FPB) – median nerve (recurrent branch); deep head of FPB and adductor pollicis – ulnar nerve; hypothenar muscles – ulnar nerve; lumbricals 1 and 2 – median nerve; lumbricals 3 and 4 – ulnar nerve; all interossei – ulnar nerve; palmaris brevis – ulnar nerve (superficial branch). This division means that a median nerve lesion at the wrist causes thenar wasting and loss of thumb opposition, while an ulnar nerve lesion produces intrinsic weakness and clawing of the ring and little fingers.

6. Clinical Testing and Nerve Lesions

The clinical examination of hand nerves relies on testing specific muscles and sensory territories. For the median nerve: test thumb opposition (recurrent branch) and pulp sensation of the index finger. For the ulnar nerve: test finger abduction (interossei) and Froment’s sign (adductor pollicis), and pulp sensation of the little finger. For the radial nerve: test the dorsal first web space sensation.

Common entrapment or injury patterns include carpal tunnel syndrome (median nerve at the wrist, sparing the thenar eminence sensation), ulnar tunnel syndrome (Guyon’s canal – pure motor or combined deficits depending on exact site), and superficial radial nerve lesions (sensory loss only, often from wrist injury).

Summary

Summary of Hand Innervation

The median nerve supplies motor to most thenar muscles and the radial two lumbricals, with sensory to the radial three and a half palmar digits. The ulnar nerve supplies all interossei, hypothenar muscles, adductor pollicis, and ulnar two lumbricals, with sensory to the medial one and a half digits and corresponding dorsal skin. The radial nerve provides only sensory innervation to the radial dorsum of the hand. Knowledge of the autonomous sensory zones, motor testing, and typical lesion patterns is fundamental for diagnosing and treating nerve injuries in the hand.