Topic Overview

⚡ Nerves of the Front of Forearm

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Overview

• The forearm receives its nerve supply from three major nerves:

  1. Median nerve – main nerve of anterior compartment.

  2. Ulnar nerve – supplies medial flexors and some hand muscles.

  3. Radial nerve – supplies posterior (extensor) compartment.

• These nerves also contribute to cutaneous, articular, and muscular branches.

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1. Median Nerve

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Root Value

• C5–T1 (formed by lateral and medial roots from brachial plexus).

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Course

1. Enters forearm between the two heads of pronator teres.

2. Passes downward between flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP).

3. In lower forearm → becomes superficial, lying between tendons of FDS and flexor carpi radialis.

4. Enters palm beneath flexor retinaculum through carpal tunnel.

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Branches in Forearm

A. Muscular Branches

• Supply all superficial and intermediate flexors except flexor carpi ulnaris.

• Supply the lateral half of flexor digitorum profundus.

B. Anterior Interosseous Nerve (A.I.N.)

• Arises about 5 cm below the elbow.

• Runs on the interosseous membrane with the anterior interosseous artery.

• Supplies:

  • Flexor pollicis longus

  • Lateral half of flexor digitorum profundus

  • Pronator quadratus

C. Palmar Cutaneous Branch

• Arises above the wrist.

• Crosses superficial to the flexor retinaculum → supplies skin of thenar eminence and central palm.

• Not affected in carpal tunnel syndrome.

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Relations

• Above: Between two heads of pronator teres.

• Middle: Between FDS and FDP.

• Below: Superficial near wrist between tendons of FDS and FCR.

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Clinical Anatomy

• Pronator syndrome: Compression between two heads of pronator teres → pain/tingling in thumb, index, and middle fingers.

• Anterior interosseous nerve palsy: Loss of flexion at thumb IP joint and index DIP joint → “Pinch sign” (OK sign defect).

• Carpal tunnel syndrome: Median nerve compression at wrist → thenar atrophy, paresthesia in lateral 3½ digits, weakness of thumb opposition.

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2. Ulnar Nerve

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Root Value

• C8–T1 (branch of medial cord of brachial plexus).

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Course

1. Enters forearm by passing between the two heads of flexor carpi ulnaris.

2. Descends on the medial side of forearm, lying on flexor digitorum profundus.

3. In the lower one-third of forearm → accompanied by ulnar artery.

4. Passes anterior to flexor retinaculum, lateral to pisiform bone, through the ulnar canal (Guyon’s canal) into the hand.

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Branches in Forearm

A. Muscular Branches

• To flexor carpi ulnaris.

• To medial half of flexor digitorum profundus.

B. Palmar Cutaneous Branch

• Arises in mid-forearm → supplies skin of hypothenar region.

C. Dorsal Cutaneous Branch

• Arises about 5 cm above wrist → passes backward → supplies skin on dorsum of medial hand and 1½ fingers.

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Relations

• Upper third: Deep to FCU, medial to ulnar artery.

• Lower third: Lies with ulnar artery under deep fascia.

• At wrist: Lateral to pisiform and ulnar artery.

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Clinical Anatomy

• Cubital tunnel syndrome: Compression between heads of flexor carpi ulnaris → numbness in medial 1½ fingers.

• Guyon’s canal syndrome: Compression of ulnar nerve at wrist → sensory loss over medial fingers, weakness of intrinsic hand muscles.

• Ulnar nerve injury at elbow: Claw hand deformity, loss of finger adduction, positive Froment’s sign.

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3. Radial Nerve

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Root Value

• C5–T1 (branch of posterior cord of brachial plexus).

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Course in Forearm

1. Enters anterior compartment between brachialis and brachioradialis (in cubital fossa).

2. Divides into:

   • Superficial branch (sensory).

   • Deep branch (posterior interosseous nerve) – motor.

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Branches

A. Superficial Branch

• Descends under brachioradialis.

• Crosses anatomical snuffbox → supplies skin of lateral dorsum of hand and thumb base.

B. Deep Branch (Posterior Interosseous Nerve)

• Pierces supinator → enters posterior compartment.

• Supplies all extensor muscles of forearm, except brachioradialis and extensor carpi radialis longus (supplied by main radial trunk).

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Clinical Anatomy

• Radial nerve injury in cubital fossa: Loss of finger extension; wrist extension preserved (ECRL & ECRB intact).

• Superficial branch entrapment (Wartenberg syndrome): Pain over dorsum of thumb.

• Posterior interosseous nerve palsy: Weak finger extension without sensory loss.

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Dissection of Nerves of Front of Forearm

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Steps

1. Identify median nerve between heads of pronator teres → trace it deep between FDS and FDP.

2. Note branches:

   • Muscular branches to superficial flexors.

   • Anterior interosseous nerve descending on interosseous membrane.

   • Palmar cutaneous branch near wrist (superficial to retinaculum).

3. Identify ulnar nerve between heads of flexor carpi ulnaris → follow along medial forearm with ulnar artery.

4. Expose radial nerve between brachialis and brachioradialis → trace to its bifurcation into:

   • Superficial branch under brachioradialis.

   • Deep branch entering supinator.

5. Preserve companion arteries and veins while reflecting superficial muscles.