Effects of surgery on lumbar spine biomechanics

Lumbar stenosis is one of the most common diseases of the spine in the geriatric population. The standard surgical treatment for lumbar stenosis is a wide midline decompressive laminectomy. This approach entails wide dissection and retraction of the paraspinal muscles and extensive resection of the posterior spinal elements. The disadvantages in functional outcomes associated with this procedure have led surgeons to develop new minimally invasive techniques to reduce the iatrogenic sequelae of an open procedure while achieving similar surgical outcomes. These minimally invasive approaches reduce muscle injury by retracting rather than resecting the ipsilateral musculature and its attachments while preserving the contralateral bone and musculature.;The aim of this study was to compare changes in lumbar spine biomechanics following the traditional open posterior approach with a new minimally invasive approach. A finite element model of the intact lumbar spine was modified to study the biomechanical changes as a result of surgical alteration for treatment of stenosis using these surgical techniques to investigate the impact of graded posterior element removal. A muscloskeletal model of the lumbar spine was used to study the change in muscle activation following surgical alteration to evaluate how graded resection of the lumbar paraspinal muscles affects muscle activity for a variety of movement tasks. Finally, a novel kinematics based finite element model was used to study the biomechanical changes in both active and passive structures following treatment for lumbar stenosis to evaluate how graded resection of both bony and paraspinal muscle tissue affects loading on the intervertebral disc.;The results of these studies show that minimization of bone, ligament and paraspinal muscle removal associated with minimally invasive procedures results in greater preservation of the normal motion, muscle activity and loading of the intervertebral disc of the lumbar spine after surgery. This study suggests that preservation of the posterior spinal elements associated with minimally invasive surgery could minimize the risk of developing de novo post-operative changes in spinal alignment and/or acceleration of facet and disc degeneration.