The sciatic nerve originates from nerve roots at the L4 through S3 levels of the lumbar and sacral spine. In a healthy spine, these nerve roots exit through openings called foramina with adequate space. Approximately 90% of sciatica cases result from a herniated disc pressing against one of these nerve roots, creating inflammation and irritation that generates pain signals.
When a disc herniates, its gel-like nucleus pulposus protrudes through the outer annulus fibrosus and contacts the adjacent nerve root. This mechanical compression triggers an inflammatory cascade, releasing cytokines and prostaglandins that sensitize the nerve and amplify pain transmission along its entire pathway down the leg.
Spinal stenosis, the gradual narrowing of the spinal canal, represents another common cause. As degenerative changes accumulate over years, bone spurs and thickened ligaments encroach on the space available for nerve roots, creating chronic compression that worsens with standing and walking.
