The C5 dermatome runs down the lateral (outer) side of the upper arm, over the deltoid region to around the elbow. It is the first dermatome that reaches into the limb. The skin over the lower deltoid, the so called regimental badge area, is a reliable C5 region.
| Nerve root | C5 |
|---|---|
| Area | Lateral side of the upper arm from the shoulder to the elbow |
| How to test | Light touch and pinprick are compared side to side at the ISNCSCI key sensory point: on the lateral (radial) side of the antecubital fossa, just above the elbow crease. |
| Nerve Supply | Axillary nerve (superior lateral cutaneous nerve of arm); Radial nerve (inferior lateral cutaneous nerve of arm); Musculocutaneous nerve (lateral cutaneous nerve of forearm, upper part) |
Carries touch, pain and temperature sensation from this strip of skin to the spinal cord through the C5 dorsal root.
C5 radiculopathy, usually from a C4-C5 disc or foraminal narrowing, gives lateral arm numbness with deltoid and biceps weakness and a reduced biceps reflex. Numbness limited to the regimental badge area with deltoid weakness may instead point to an axillary nerve injury after shoulder dislocation. Dermatome maps differ between sources (Foerster, Keegan and Garrett, and modern evidence-based maps disagree), and neighbouring dermatomes overlap, so borders are approximate.
Root compression at C4-C5 causing pain and numbness on the lateral arm, shoulder weakness and a reduced biceps reflex.
Traction injuries such as Erb palsy damage C5-C6 fibres and cause lateral arm numbness with shoulder and elbow flexion weakness.
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