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L4 Vertebra

vertebra lumbalis IV

L4 is at the level of the iliac crests, a key surface landmark, and the L4 nerve root is responsible for the tibialis anterior and knee extension, making L4 disc pathology a common cause of foot drop.

Anatomical Data

Structure & Landmarks

Articulations	L3 above L5 below Bilateral facet joints
Landmarks	Large vertebral body Iliac crest level reference
Ossification	As per lumbar vertebra pattern.

Clinical Relevance

Clinical Notes

L4-L5 disc herniation is the second most common lumbar disc herniation site after L5-S1, compressing the L4 nerve root to produce medial leg pain and numbness with tibialis anterior weakness and diminished patella reflex. The iliac crests are at the L4-L5 level on average, making this the standard landmark for lumbar puncture technique. L4-L5 spondylolysis and spondylolisthesis are less common than at L5-S1 but produce identical symptoms.

Pathology

Common Injuries & Conditions

L4-L5 Disc Herniation

One of the two most common lumbar disc herniations, usually compressing the L5 root and causing sciatica with weakness of ankle and big toe dorsiflexion.

Degenerative Spondylolisthesis

Facet arthritis allows L4 to slip forward on L5, most often in older women, producing lumbar spinal stenosis and neurogenic claudication.

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