颈椎前凸角度减小对融合术后邻近节段影响的生物力学研究

The biomechanical effects on adjacent segments after two-level ACDF with reduced lordosis

目的 探讨颈椎前路减压融合术（anterior cervical discectomy and fusion，ACDF）后前凸角度减小对邻近节段的生物力学影响。方法 取6具成人尸体颈椎标本（C2~C7），制备为完整组、C4-6双节段原位固定组、C4-6双节段加压固定（前凸减小）组，于脊柱三维运动实验系统上进行前屈、后伸、侧屈和旋转4种运动状态的测定。记录各组固定节段Cobb角、标本整体及邻近节段的活动度和小关节内压力，比较固定后前凸角度减小对邻近节段运动和压力负荷的影响。结果 完整组前凸Cobb角为13.5°±4.1°，原位固定组15.7°±4.6°，差异具有统计学意义；前凸减小组前凸Cobb角为9°±4°，与完整组差异具有统计学意义。原位固定组及前凸减小组的标本整体活动度在前屈、后伸、侧屈和旋转4种运动状态下均较完整组减小，而上位及下位邻近节段（C3-4、C6-7）活动度则增加，原位固定组和前凸减小组的上位活动度在前屈和后伸运动状态与完整组比较，差异均有统计学差异；原位固定组和前凸减小组的下位活动度在前屈、后伸、旋转运动状态与完整组比较，差异均有统计学差异；上位邻近节段C3-4活动度在后伸运动中，前凸减小组大于原位固定组，差异有统计学意义；下位C6-7活动度在前屈和后伸运动中，前凸减小组大于原位固定组，差异有统计学意义；原位固定组及前凸减小组的上位C3-4小关节内峰值压力和平均压力在前屈、后伸、侧屈、旋转运动中均较完整组高，在后伸与侧屈运动中差异具有统计学意义；前凸减小组与原位固定组比较，C3-4小关节内压力呈下降趋势，差异无统计学意义。结论 颈椎标本双节段ACDF术后，上、下邻近节段活动度和上位小关节内压力升高，而术后颈椎前凸角度的减小会进一步增加邻近节段活动度，可能因此而加速邻近节段退变。

Objective To study the biomechanical effect on adjacent segments of anterior cervical discectomy and fusion （ACDF）. Methods 6 adult human cervical spine specimens （C2-C7） were tested under the following 3 conditions： intact cervical spine group, C4-6 ACDF with normal lordosis group, C4-6 ACDF with reduced lordosis group. The specimens were tested in flexion, extension, bending and rotation on the spine 3D motion experiment system. The Cobb angle, overall range of motion （ROM）, ROM and loads of facet joints at adjacent segments were measured. Results The lordosis Cobb angle was 13.5氨4.1- in intact cervical spine group, 15.7氨4.6- in C4-6 ACDF with normal lordosis group, 9.0氨4.0- in C4-6 ACDF with reduced lordosis group, respectively. After operation the overall ROM of specimens reduced in flexion, extension, bending and rotation, but the ROM of upper and lower adjacent segments increased. The ROM of upper segments （C3-4） in flexion and extension, as well as that of lower segments （C6-7） in flexion, extension and rotation, had significant difference. The extension ROM of upper segment （C3-4） of C4-6 ACDF with reduced lordosis group was found greater than that of C4-6 ACDF with normal lordosis group and the flexion and extension ROM at lower segment （C6-7） of C4-6 ACDF with reduced lordosis group were also greater. Increased max and average stress on C3-4 facet joints was observed in all the 4 types of motion after ACDF and the differences in extension and bending were statistically significant. Comparing C4-6 ACDF with reduced lordosis group and C4-6 ACDF with normal lordosis group, a stress decreasing trend was observed along with the reduced lordosis angle but had no significant difference. Conclusion After 2 level ACDF on cervical spine specimens, ROM of adjacent segments and stress on facet joints increased. The ROM of specimens with reduced lordosis is higher than those with normal lordosis, which may accelerate ASD.