The herniated nucleus pulposus in lumbar disc herniation stops in front of the posterior longitudinal ligament is called “herniation”, while the one that crosses the posterior longitudinal ligament into the spinal canal is called “prolapse”. The nucleus pulposus is divided into 3 types according to the posterior protrusion site: 1. Posterior lateral protrusion type The weakest posterior part of the fibrous ring is on both sides of the midline of the intervertebral disc, which is weak in itself and lacks the support of the strong central fibers of the posterior longitudinal ligament, so it is the most common site of lumbar disc protrusion. Clinically it is the most common, accounting for about 80%. 2.Central protrusion type The nucleus pulposus protrudes through the central posterior part of the fibrous ring and reaches under the posterior longitudinal ligament. In addition to causing sciatic nerve symptoms, it can also stimulate or compress the cauda equina nerve, manifesting as perineal paralysis and urinary and fecal disorders. The nucleus pulposus protrudes posteriorly through the posterior fibrous ring and posterior longitudinal ligament into the spinal canal and into the intervertebral foramen, which is easily missed and has a low incidence of about 1%.