Biomechanical behavior of the posterior elements of the lumbar spine under loading--a study of stress analysis by means of three dimensional photoelastic experiments.

To investigate the biomechanical behavior of the lumbar posterior elements under loading, stress analysis was carried out. The three dimensional photoelastic method was used for stress analysis in this study. The forces applied to the superior and the inferior articular facets were concentrated on the pars interarticularis and transmitted to the pedicle. However, almost no stress was generated in the lamina. Highly stressed areas were found in the pars interarticularis and around the lateral recess. The highest compressive stress was present in the pars interarticularis. The deformation pattern of the lumbar spinal canal was recognized and it became flat as the lateral recess was narrowed and deepened. These results very interestingly correspond to the fact that spondylolysis and lumbar canal stenosis are found in the above-mentioned areas clinically.