Final answer:
The L4/L5 or L5/S1 intervertebral discs are the most commonly herniated vertebral discs. Herniation occurs when the gel-like nucleus pulposus protrudes through a weakened posterior anulus fibrosus, resulting in compression of a spinal nerve and causing pain that radiates down the leg.
Step-by-step explanation:
The most commonly herniated vertebral disc is the L4/L5 or L5/S1 intervertebral discs in the lumbar region. These discs are located in the lower back and can cause a condition called sciatica, which is characterized by pain that radiates from the lower back down the thigh and into the leg. The herniation occurs when the gel-like nucleus pulposus protrudes through a weakened posterior anulus fibrosus, resulting in compression of a spinal nerve.