A herniated disc is when an intervertebral disc bulges or herniates back into the spinal canal. When the disc herniates, it can push on a nerve root or a spinal nerve and causes severe pain. Most herniated discs resolve over time, but they can be very painful during the healing process. A disc bulge involves >90 degrees of the total circumference of a disc and does not extend beyond the boundaries of the annulus fibrosus.
A disc herniation is a rupture of disc material beyond the annulus fibrosus. There are two broad categories, protrusion and extrusion. Protrusion refers to a rupture of disc material in which the base is broader than the dome. In general, this does not extend above or below the disc space. An extrusion is a disc rupture in which the dome is wider than the base, with a dumbbell appearance. Extrusions may extend above or below the disc space.
A free fragment is a displacement of disc material that loses its connection with the main disc material. Such fragments can migrate from the disc space.
Herniated discs can be caused by a number of things including trauma, lifting heavy objects, or using poor posture throughout the day.