Which stage describes a disc herniation where the nucleus has breached the annulus but remains within the spinal canal?

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Understanding disc herniation stages involves tracking where the nucleus pulposus lies relative to the annulus fibrosus and the spinal canal. Protrusion (prolapse) means the nucleus bulges but the annulus remains intact around it, keeping the material contained with the disc. When the nucleus breaks through the annulus and extends into the spinal canal, the herniation is an extrusion. The crucial distinction is whether the herniated material stays connected to the disc or becomes a free fragment in the canal. If a fragment is free in the canal, that’s sequestration. Degeneration refers to aging-related changes in the disc, not a specific location of herniated material. So, because the nucleus has breached the annulus and remains within the spinal canal (still connected to the disc), this describes an extrusion.