颈前路螺钉矢状角对相邻节段影响的生物力学研究

A biomechanical study of effects of anterior cervical screw sagittal angle on adjacent segments

目的采用三维有限元方法分析颈前路螺钉矢状角（sagittal screw angle,SSA）对相邻节段生物力学的影响,判断SSA是否是引起邻近节段病的危险因素。方法基于健康成年男性C3~7节段CT图像建立颈椎有限元模型。模拟颈前路C5椎体次全切除、C4~6钢板内固定术,按照SSA（0°,0°）（5°,5°）（10°,10°）分别建模,计算在不同的SSA下,C4上终板、C6下终板以及钢板的应力变化情况。结果 C4上终板在前屈时前方区域所受应力最大,随着SSA的增加,C4上终板整体所受的最大应力逐渐减小,SSA增大10°后,C4上终板前方区域的最大应力减小12.67%。C6下终板在前屈时前方区域所受应力最大,随着SSA的增加,C6下终板整体所受的最大应力逐渐减小,SSA增大10°后,C6下终板前方区域的最大应力减小7.99%。钢板在前屈和后伸时其最大应力均较集中于中部区域,并且显著高于上部及下部区域,随着SSA的增加,钢板受到的应力会逐渐增加。结论在颈椎前路融合内固定手术中,增大SSA,可增加钢板承受的应力,同时降低邻近节段终板的应力,从而减少邻近节段病的发生。

Objective To analyze effects of different screw sagittal angles（ SSA） on the stress of adjacent levels, and determine whether SSA is a risk factor of adjacent segment disease（ ASD）. Methods A three-dimensional finite element（ FE） model of intact C3-7 segments was developed and validated based on healthy males. C5 anterior corpectomy and allograft interbody fusion with a rigid anterior screw-plate construction was created from C4 to C6. Three additional FE models were developed from the fusion model corresponding to 3 different combinations of SSA：（ 0°, 0°）,（ 5°, 5°）, and（ 10°, 10°）. Von Mises stress on the C4 superior end-plate, C6 inferior end-plate and screw-plate were analyzed. Results The largest stress appeared when the superior end-plate of C4 was in flexion position in the front area. With the increase of SSA, the peak stress was gradually reduced. When the SSA was increased by 10°, the peak stress was reduced by 12.67%. The largest stress appeared when the lower end-plate of C6 was in flexion position in the front area. With the increase of SSA, the peak stress was gradually reduced. When the SSA was increased by 10°, the peak stress was reduced by 7.99%. The peak stress was noticed in the middle area when the plate was in flexion and extension position, which was significantly larger than that in the upper and lower area. With the increase of SSA, the stress would be gradually raised. Conclusions Larger SSA produces greater stress of the screw plate and lower stress of the end-plate in adjacent segments, reducing the incidence of ASD.