Lumbar vertebra L4

Function

Its nerve root powers ankle dorsiflexion (tibialis anterior) and carries the knee-jerk afferents. The L4–5 disc is the most frequently herniated in the spine.

Landmarks

• Body
• Iliolumbar ligament attachment
• Spinal canal with cauda equina

Articulations (joints)

• L3 above
• L5 below
• Ilium (variable iliolumbar ligament)

Clinical relevance

L4–5 disc herniation presses the L5 root: foot drop with big-toe numbness and a preserved ankle jerk.