In the lumbar spine, 90% of the disc herniations occur at which of the following level:

Ans. (d) L4-L5Ref: Maheshwari 5th ed. / 253* Most common site of spinal disc herniation: Lumbar region (95% in L4-L5 or L5-S1).* The second most common site is the cervical region (C5-C6, C6-C7).* Thoracic region accounts for only 0.15% to 4.0% of cases.* Herniations usually occur posterolaterally, where the annulus fibrosis is relatively thin and is not reinforced by the posterior or anterior longitudinal ligament.* In the cervical spinal cord, a symptomatic posterolateral herniation between two vertebrae will impinge on the nerve which exits the spinal canal between those two vertebrae on that side. For example, a right posterolateral herniation of the disc between vertebrae C5 and C6 will impinge on the right C6 spinal nerve.