The Biomechanics Influence of unilateral laminectomy and discectomy surgery on the adjacent different grades of Disc Degeneration

Objectives: To study the stress distribution of the adjacent different grades of disc degeneration underwenting unilateral laminectomy and discectomy surgery using non-linear finite element analysis. Methods: Based on the lumbar CT scans, the finite element model (FEM) of lumbar spinal segment(L3-L5) was established. According to L3-L4 intervertebral disc degeneration, different grades of disc degeneration (healthy, mild, moderate and severe) models were established and unilateral laminectomy and discectomy surgery were also established. Physiological action such as flextion, extension, lateral bending and lateral rotation was simulated and the von Mises stress in the nucleus pulposus and annulus fibrosus matrix of L3-L4 disc was investagated. Results: After unilateral laminectomy and discectomy surgery, the extremum value of von Mises stress of nucleus pulposus and annulus fibrosus matrix was maximum during extension and minimus left bending in the healthy intervertebral disc. Compared with healthy disc, the increment of extremum value was found during left bending in the mildly degenerated disc. When the value decreased in the moderately degenerated disc, but still higher than that in the healthy disc. When the adjacent disc is severly degenerated, the extremum value of nucleus pulposus decreased, in addition to axial rotation, and even lower than that of healthy disc. The value of annulus matrix decreased and still higher than that of healthy disc, especially during left bending. Conclusions: After unilateral laminectomy and discectomy surgery, avoiding lateral bending will reduce the abnormal stress in the degenerated disc and decreased the risk of accelerating disc degeneration.