Dermatomes
Key dermatomal landmarks allow rapid bedside assessment of spinal cord level after trauma or neurological injury. A handful of well-chosen landmarks covers the entire examination.
✦ The Mnemonic
"Collar, Nipple, Navel, Groin, Sole — Clear Neurological Findings Identify Sites"
Key dermatomal landmarks C4 → S1 for rapid clinical assessment
Clinical Breakdown
The dermatomes follow a predictable segmental pattern on the body surface. On the trunk, they are horizontal bands. On the limbs, they spiral to reflect the limb rotation during embryological development. The upper limb dermatomes run C5 (lateral shoulder) → C6 (thumb) → C7 (middle finger) → C8 (little finger) → T1 (medial forearm).
Clinical application: a patient with a cord injury at T10 has preserved sensation at the umbilicus but absent below. A patient with sensation to the groin (L1) but absent below = injury between L1 and L3. The nipple (T4) and the umbilicus (T10) are the two most reliable trunk landmarks.
Saddle anaesthesia (S2–4 loss): sensory loss in the perineum, genitalia, and inner thighs — the area that would contact a saddle. Along with bladder/bowel dysfunction and bilateral leg weakness, this constitutes cauda equina syndrome — a surgical emergency requiring urgent MRI and decompression.
⭐ Clinical Pearl
Cauda equina syndrome: compression of the cauda equina (L2 and below) causes saddle anaesthesia + bladder/bowel dysfunction (urinary retention most common) + bilateral leg weakness. It is a spinal surgical emergency — decompression within 24–48 hours gives the best chance of recovery. MRI is mandatory.