Stroking the lateral sole from heel to ball and noting absence of movement of the big toe suggests a lesion at which spinal level?

Stroking the lateral sole from heel to ball and noting absence of movement of the big toe suggests a lesion at which spinal level?

• A. Thoracic 8, 9, and 10
• B. Thoracic 10, 11, and 12
• C. Lumbar 5 and Sacral 1
• D. Sacral 2, 3, and 4

Answer: (C)

The movement of the big toe in this plantar-stimulation test relies on the L5 myotome, specifically the extensor muscles of the great toe (extensor hallucis longus). If the spinal level involving L5-S1 is disrupted, the motor output to those toe-extensor muscles is lost, so stroking the lateral sole fails to produce the expected movement of the big toe. This pattern points to a lesion at L5-S1, where the toe-extensor muscles receive their innervation. Higher thoracic levels wouldn’t produce this isolated loss of big toe movement, and sacral levels 2–4 would also not account for the specific big-toe motor deficit.

The movement of the big toe in this plantar-stimulation test relies on the L5 myotome, specifically the extensor muscles of the great toe (extensor hallucis longus). If the spinal level involving L5-S1 is disrupted, the motor output to those toe-extensor muscles is lost, so stroking the lateral sole fails to produce the expected movement of the big toe. This pattern points to a lesion at L5-S1, where the toe-extensor muscles receive their innervation. Higher thoracic levels wouldn’t produce this isolated loss of big toe movement, and sacral levels 2–4 would also not account for the specific big-toe motor deficit.