| Objective:Build L4/5 non-postoperative three-dimensional finite element model having complete functional segments and three-dimensional finite element model of rear lumbar vertebra for five categories of commonly-used LDH posterior surgery.Analyze differences of stress variations for the rear structure of the above postoperative and non-postoperative lumbar vertebra models under the effect of the oblique pulling method lying on the side and fixed rotary reduction manipulation.Illustrate the safety and dangers of postoperative lumbar vertebra under the operation of oblique pulling and rotary reduction manipulation;Analyze the exerting direction and degree of forces under the safety operation of the above two methods as well as differences of operations compared with the non-postoperative lumbar vertebra.Methods: Collect the CT three-dimensional rebuilding data of the lumbar vertebra for the above 6 volunteers.Build the model in the medical image processing software,reverse engineering software and finite element analysis software relying on the CT three-dimensional rebuilding data of non-postoperative lumbar vertebra,which will get a L4/5 simple and protruded vertebral model having complete functional segment of spinal column.Make a theoretic test on this model.Organize possible situations for the five categories of postoperative model by referring to literatures and combining forms of the above five categories of postoperative lumbar vertebra.Based on the built L4/5 vertebral model,set up models for each postoperative lumbar vertebra and then get 7 types of models for postoperative lumbar vertebra.Make an analysis of forces acting on each model according to the force-exerting conditions about the oblique pulling method and rotary reduction manipulation recorded in literatures.In the oblique pulling operations,observe the stress for the contact surface of facet joints for each model as well as the vertebral pedicle section area of the model after the non operations,full laminectomy and semi-laminectomy.In the rotary reduction manipulation operation,observe the stress for the contact surface of facet joints for each model,for the section area of spinal root after the non operations and semi-laminectomy as well as for the vertebral pedicle section area of the model after the non operations and semi-laminectomy,excluding models after the full laminectomy.Results:(1)Stress of the zygapophyseal joint: the stresses of medium and facet joints for each model are concentrating on the opposite side of the force-loading side of the oblique-pulling method and at the rotary side of the rotary reduction manipulation method.With the stress concentration of the contact surface of facet joints preserving complete structures in the postoperative model,compare the maximum value under the effect of the oblique-pulling force with the maximum value for the non-operative model under the effect of the rotary reduction manipulation force,the latter is relatively higher on the whole.In cases of stress concentration for some of the contact surface of facet joints for each postoperative model,the maximum values under these two operations are far higher than those for the non-operative situations.The postoperative model with partial excision of single-side facet joint achieves the largest difference.(2)Stress of the spinal root: There is no significant stress deviation at both sides of the spinal root for the non-post-operative model under the effect of the rotary reduction manipulation.Meanwhile,the stresses of both sides are the same.For two models experiencing left-side semi-laminectomy,the stress concentration is deviated to the right side of the spinal root.The maximum values for each circumstance are similar and all of these values are far higher than those for non-post-operative models.(3)Stress of the vertebral pedicle section area: the stresses of the vertebral pedicle section area for each model are concentrating on the opposite side of the force-loading side for the oblique-pulling method and on the rotary side for the rotary reduction manipulation method.When the oblique-pulling force is loaded,observe the stress concentration of the vertebral pedicle for each model.The maximum values are generally equal to or slightly lower than those for non-post-operative models,with the difference varying within the scope of 4.50-5.22 Mpa.In cases where the rotary reduction manipulation force is loaded,if models experiencing semi-laminectomy and retaining some facet joints consider the non-operation side as where the stress is concentrated,stresses of the vertebral pedicle section area are higher than those for the non-post-operative models as a whole,achieving a maximum value of10.42-12.51 Mpa.If the operation side is considered as where the stress is concentrated,stresses of the vertebral pedicle section area for those two models are slightly smaller than those for the non-post operative models.Conclusions:(1)When the oblique-pulling method is applied on the non-post-operative L4/5 vertebral body,the opposite sides of the force-loading place of the zygapophyseal joint and the vertebral pedicle are where the stresses are concentrated.This circumstance is also the same for the five categories of L4/5 postoperative vertebral bodies in the research.(2)When the L4 spinal root is regarded as the pivot for the pushing and pulling by the rotary reduction manipulation,stresses of the zygapophyseal joint,the spinal root and the vertebral pedicle are concentrated on the rotary sides for the six lumbar vertebra models,excluding the one experiencing L4 full laminectomy.(3)For the zygapophyseal joint of the segment L4/5,(1)When the two methods we studied here are applied on the vertebral body experiencing partial excision of single-side facet joints,the maximum stress at the stress concentration side will far exceed the safety limited value,when these two methods are forbidden to use;(2)Apply these two methods on the postoperative lumbar vertebra where other three kinds of zygapophyseal joints are damaged,please strictly control the operation force of these two methods if the operation side is where the stress is concentrated and the stress is extremely close to the safety stress limited value;(3)For the postoperative lumbar vertebra where the four types of the zygapophyseal joints are damaged in the research,if the stress is concentrated at the non-operative side,please take into account whether the joint interlocking will be caused at the operation side by the movement between vertebral bodies arising from the operations.Therefore,in spite of the fact that the maximum stress value is within the scope of the safety limited value,we still need to take the operations seriously and even prevent applying operations under such circumstances.(4)If forces produced by the operations are leading to stress concentration on the vertebral pedicle of the L4/5 segment or the L4 spinal root,the maximum stress value should be far less than the safety limited value set in the research.Therefore,we can draw a conclusion that the spinal root and the vertebral pedicle of the vertebral body where stresses are concentrating under the effect of these two forces will not affect the safety of these two operations. |
PDF Full Text Request