INTRODUCTION: Spondylolysis is a fracture of the pars interarticularis and has a high risk of developing spondylolisthesis. There was a wide variation of angle in pars defects in clinical CT scan. We studied the variation in orientation of spondylolytic in different loading conditions and stress variation.
METHODS: An experimentally validated three‐dimensional non‐linear finite element model of the intact L3–S1 segment was used. Spondylolysis was simulated by creating bilateral pars defects with 1.0 mm gap at L5. The angle of pars defect was defined as a line parallel to the posterior cortex of the vertebral body at the lysis level defined the coronal plane, and a second line was drawn tangential to the defect. There are six known angles of pars defect often measured in clinical observation (‐15, 0, 15, 30,45 and 60 degree). Purpose of this study was to analyze the disc stresses at cranial and caudal adjacent level of lumbar spondylolysis in differenet angles change. A loading of 400 N of axial compression and 10 N·m in six motions of lumbar respectively were imposed on the superior surface of the L3 body. Von Mises stresses in the annulus fibrosus and nucleus pulposus at L4/5 and L5/S disc levels were analyzed.
RESULTS SECTION: Spondylolysis increases disc stresses at the affected levels under different angles and it may lead to disc degeneration in measured values. However, the increase in stresses is higher at the affected levels under more horizontal angle of pars defect, when compared to the more vertical angles.
DISCUSSION: The variation in the angles of defects in the pars may affect surgical management. However, less consider about the angles of pars defect in biomechanics and the option for treatment. Our results may be beneficial from a biomechanical perspective and provide treatment options under different angles of pars defect.