EFFECTS OF STRAIN DISTRIBUTION IN THE INTERVERTEBRAL DISCS ON THE PROGRESSION OF OSSIFICATION OF THE POSTERIOR LONGITUDINAL LIGAMENTS

Study Design. Strain distribution in the intervertebral discs was eval uated biomechanically using an engineering true strain calculation for mula. Objectives. This study was performed to clarify the involvement of dynamic factors in the progression of ossification of the posterior longitudinal ligament. Summary of Background Data. In patients with o ssification of the posterior longitudinal ligament of the cervical spi ne, ossification frequently progresses after laminectomy. This suggest s the involvement of dynamic factors in the progression of ossificatio n. However, these factors have not yet been clarified. Methods. The an alysis was performed on 101 patients with ossification of the posterio r longitudinal ligament by employing dynamic lateral x-ray films of th e cervical spine, The x-ray films were digitized and used as computer data for calculating the strain distribution. x-ray films were obtaine d again 5 years later, and the strain distribution and the presence or absence of progression of ossification were evaluated. Results. The p rogression of ossification of the posterior longitudinal ligament was highly correlated with abnormal strain distribution in the interverteb ral discs. Progression of ossification was frequently observed in area s having disc distortion in tension and extension on the posterior lon gitudinal ligament. Conclusions. In this study, the area of progressio n of ossification corresponded to the area showing uneven strain distr ibution and resultant concentration of dynamic stress. These results s uggest an important role for dynamic factors in the progression of oss ification of the posterior longitudinal ligament.