Prolapsed intervertebral disc is a condition where the gelatinous nucleus pulposus squeezes through the annulus fibrosus and bulges in a posterior or posterolateral direction, beneath the posterior longitudinal ligament. 

This causes pressure symptoms on the root below the level of herniation - most commonly S1, then L5, then L4.

Other defects are rarer, and higher defects ought to be investigated for other causes.

Symptoms include radiative pain of the lower limbs; sensory disturbances to the same area; difficulty lifting the leg; and unilateral or bilateral sciatica.

The pain may be severe or worse with lumbar flexion of the low back, and may be aggravated by a prolonged sitting or standing position in the dermatome area of the affected nerve root.

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