The authors have experienced 128 cases of herniated lumbar interbertebral disc that underwent laminectomy and discectomy from June, 1989 to May, 1991. We defined that the ruptured disc is extruded transligamentously through the posterior longitudinal ligament(PLL) or sequestered disc. On operation, 42 patients(43 Cases) showed ruptured disc. We analysed the clinical and operative findings of ruptured disc patients and compared these with MRI findings. The results are as follows.

1. The patient with ruptured disc composed 20.7% of the admitted patients with herniated intervertebral disc(HIVD) for treatment and high prevalence of 32.8% among the operated cases. 2. Among the ruptured discs, sequestered discs were 23 cases(53.5%) and extruded 20 cases(46.5%). Among 17 cases of distant migration, downward migration was 2.4 times more common than proximal migration.

3. In sequestered disc, we could get 87% of sensitivity, 90% of specificity, and 90.9% accuracy with magnetic resonance image in distinguishing from the extruded transligamentous ones. So we could get more accurate diagnosis and location of ruptured discs with MRI and could decrease the incidence of the negative disc exploration, failures with chemonucleolysis or percutaneous lumbar discectomy.