What are the upper limb dermatomes and their corresponding spinal nerve roots?

Upper Limb Dermatomes and Corresponding Spinal Nerve Roots

The upper limb is innervated by spinal nerve roots C5 through T1, with the brachial plexus (formed from C5-T1 ventral rami) providing the primary sensory and motor innervation to the entire upper extremity. 1

Spinal Nerve Root Organization

The brachial plexus forms from the ventral rami of cervical segments C5-C8 and the first thoracic nerve (T1), with occasional contributions from C4 and/or T2. 1 These nerve roots pass between the anterior and middle scalene muscles alongside the subclavian artery, then organize sequentially into trunks, divisions, and cords before forming the terminal branches that innervate the upper limb. 1

Clinical Reality: Dermatomes Are Not Fixed Maps

A critical pitfall in clinical practice is assuming that dermatomes follow precise, predictable patterns—they do not. 2, 3 Research demonstrates that:

• The cutaneous region served by one spinal nerve is actually much wider and more variable in location than traditionally recognized, making summary diagrams misleading indicators of true spinal innervation complexity. 2
• In cervical nerve roots, pain follows a dermatomal pattern in only 30.3% of cases (non-dermatomal in 69.7%). 3
• Individual variation is substantial, though within any specific individual there is regular and orderly progression allowing prediction when adjacent nerve information is available. 2

Specific Dermatome Distributions

C5-C6 Dermatomes

• C5-C6 nerve roots provide sensory innervation to the lateral (radial) aspects of the upper limb. 4
• The lateral antebrachial cutaneous nerve (C5-C6 afferents) extends along the lateral forearm and can reach as far as the thumb base in some individuals. 5

C6-C7 Dermatomes

• Both the lateral antebrachial cutaneous nerve and superficial branch of the radial nerve innervate C6 and C7 dermatomes. 5
• In 52.9% of specimens, the lateral antebrachial cutaneous nerve extends proximal to the wrist crease; in 35.3% it reaches the thumb base; and in 11.8% it extends distal to the thumb base. 5

C8-T1 Dermatomes

• C8-T1 dermatomes cover the medial (ulnar) aspects of the hand, little finger, and medial forearm. 4
• The ulnar proper digital nerve of the little finger and medial antebrachial cutaneous nerve provide sensation to these areas. 4

Important Clinical Considerations

Overlapping Innervation

• Maximal innervation areas of adjacent spinal nerves generally overlap considerably. 6
• Each digit receives innervation from two to three different spinal nerves. 6
• Myotomes (muscle innervation territories) tend to be larger than dermatomes and do not necessarily coincide with the dermatome of the same spinal nerve. 2

Diagnostic Limitations

• Dermatomal distribution of pain has poor sensitivity and specificity for diagnosing radicular pain at most nerve root levels. 3
• The only exception is the S1 nerve root (lower limb), which shows reasonable diagnostic utility (sensitivity 0.65, specificity 0.80). 3
• For upper limb nerve root diagnosis, relying solely on dermatomal pain patterns will lead to diagnostic errors in approximately two-thirds of cases. 3

Implications for Nerve Blocks

• When performing regional anesthetic blocks for thumb and radial hand surgery, blocking only the radial nerve is insufficient. 5
• The lateral antebrachial cutaneous nerve must also be considered, as it contributes to innervation of the targeted dermatome in many individuals. 5
• All nerves that might contribute to innervation of a targeted dermatome should be blocked for reliable anesthesia. 5