What are the sensory nerves that innervate the arm?

Sensory Nerves of the Arm

The arm receives sensory innervation from terminal branches of the brachial plexus (C5-T1), primarily through the lateral antebrachial cutaneous nerve (from the musculocutaneous nerve), medial antebrachial cutaneous nerve (from C8-T1 roots), and posterior antebrachial cutaneous nerve (from the radial nerve), with the median and ulnar nerves providing sensory coverage to the hand. 1, 2, 3

Brachial Plexus Origin

• The brachial plexus forms from ventral rami of C5-T1 spinal nerve roots, with occasional contributions from C4 and/or T2 1, 3
• This plexus provides both motor and sensory innervation to the entire upper extremity through its terminal branches 1

Major Sensory Nerves of the Forearm

Lateral Antebrachial Cutaneous Nerve

• This nerve is a purely sensory terminal branch of the musculocutaneous nerve, arising from the lateral cord of the brachial plexus 2, 4
• The anterior branch innervates 26% of the medial anterior forearm and 38.21% of the lateral anterior forearm 5
• The posterior branch covers 24.46% of the lateral posterior forearm 5
• Traumatic avulsion of C5-C7 roots is the primary mechanism causing injury to this nerve 2, 4

Medial Antebrachial Cutaneous Nerve

• Arises directly from the C8-T1 roots of the brachial plexus 2
• The anterior branch innervates 27.67% of the medial aspect of the anterior forearm 5
• The posterior branch covers 7.67% of the anterior region and 34.75% of the posterior region 5

Posterior Antebrachial Cutaneous Nerve

• Covers 41.04% of the posterior forearm 5
• Originates from the radial nerve distribution 5

Hand Sensory Distribution

Median Nerve

• Provides cutaneous sensation to the palmar surface of the thumb, index finger, middle finger, and lateral half of the ring finger 3
• Originates from both lateral and medial cords of the brachial plexus 3

Ulnar Nerve

• Originates from the medial cord, derived from the lower trunk (C8-T1 roots) 3
• Supplies sensation to the little finger and medial half of the ring finger 3

Clinical Significance

Anatomical Landmarks

• A distinctive "drug line" (Voigt-Futcher line) on the upper arm marks the precise border between lateral and medial sensory innervation territories 6
• This line becomes clinically apparent during morbilliform drug eruptions and demonstrates the segmental nature of cutaneous sensory innervation 6

Nerve Coaptations

• Anastomoses exist between branches of the lateral, medial, and posterior antebrachial cutaneous nerves 5
• The middle third of the medial and lateral forearm contains the relatively densest total nerve branch distribution 5

Injury Patterns

• Complete brachial plexus lesions result in weakness, sensory loss, and flaccid loss of tendon reflexes throughout the C5-T1 distribution 1, 3
• Lower trunk injuries (C8-T1) primarily affect ulnar nerve function, leading to deficits in intrinsic hand sensation and motor control 3
• Electrodiagnostic studies confirm the clinical diagnosis of plexopathy and help differentiate it from radiculopathy 1, 4

Perioperative Considerations

• Limiting arm abduction to ≤90° in supine patients reduces the risk of brachial plexus and sensory branch injuries 2
• Position the arm in abduction on an arm-rest with the forearm in supination or neutral position to protect the lateral antebrachial cutaneous nerve 2
• Perform periodic checks of upper-extremity positioning during procedures to avoid excessive stretch or compression 2

Diagnostic Imaging

• MRI of the brachial plexus demonstrates 84% sensitivity and 91% specificity for detecting traumatic root avulsions 2, 4
• MR neurography with T2-weighted sequences is the reference technique for evaluating peripheral nerve pathology 2
• High-resolution ultrasound provides 77-79% sensitivity and 94-98% specificity as a bedside alternative 2