The lumbar spines of twenty-one dogs were used as an experimental model. The animals were divided into three groups. In the first group, selective damage to the perimeningeal blood vessels was induced and the resultant hematoma was left untouched in the spinal canal. In the second group, the posterior longitudinal ligament was incised, and in the third group, the posterior longitudinal ligament was incised and damage induced to the perimeningeal blood vessels. The pathology examination revealed: (1) the hematoma itself did not lead to the formation of perineural fibrosis, (2) the incision of the posterior longitudinal ligament led to the formation of a limited amount of fibrosis, and (3) the coexistence of hematoma and incision of the posterior longitudinal ligament led to the formation of extensive perineural fibrosis. When discs are removed using microsurgical techniques, it is possible to avoid the formation of the postoperative hematoma and consequently to eliminate the perineural fibrosis.