Wang Xiaoyu, Larson A Noelle, Crandall Dennis G, Parent Stefan, Labelle Hubert, Ledonio Charles G T, Aubin Carl-Eric
Department of Mechanical Engineering, Polytechnique Montréal, P.O. Box 6079, Downtown Station, Montreal, Quebec H3C 3A7 Canada.
Sainte-Justine University Hospital Center, 3175, Cote Sainte-Catherine Road, Montreal, Quebec H3T 1C5 Canada.
Scoliosis Spinal Disord. 2017 Apr 17;12:13. doi: 10.1186/s13013-017-0120-4. eCollection 2017.
Efforts to select the appropriate number of implants in adolescent idiopathic scoliosis (AIS) instrumentation are hampered by a lack of biomechanical studies. The objective was to biomechanically evaluate screw density at different regions in the curve for AIS correction to test the hypothesis that alternative screw patterns do not compromise anticipated correction in AIS when using a segmental translation technique.
Instrumentation simulations were computationally performed for 10 AIS cases. We simulated simultaneous concave and convex segmental translation for a reference screw pattern (bilateral polyaxial pedicle screws with dorsal height adjustability at every level fused) and four alternative patterns; screws were dropped respectively on convex or concave side at alternate levels or at the periapical levels (21 to 25% fewer screws). Predicted deformity correction and screw forces were compared.
Final simulated Cobb angle differences with the alternative screw patterns varied between 1° to 5° (39 simulations) and 8° (1 simulation) compared to the reference maximal density screw pattern. Thoracic kyphosis and apical vertebral rotation were within 2° of the reference screw pattern. Screw forces were 76 ± 43 N, 96 ± 58 N, 90 ± 54 N, 82 ± 33 N, and 79 ± 42 N, respectively, for the reference screw pattern and screw dropouts at convex alternate levels, concave alternate levels, convex periapical levels, and concave periapical levels. Bone-screw forces for the alternative patterns were higher than the reference pattern ( < 0.0003). There was no statistical bone-screw force difference between convex and concave alternate dropouts and between convex and concave periapical dropouts ( > 0.28). Alternate dropout screw forces were higher than periapical dropouts ( < 0.05).
Using a simultaneous segmental translation technique, deformity correction can be achieved with 23% fewer screws than maximal density screw pattern, but resulted in 25% higher bone-screw forces. Screw dropouts could be either on the convex side or on the concave side at alternate levels or at periapical levels. Periapical screw dropouts may more likely result in lower bone-screw force increase than alternate level screw dropouts.
由于缺乏生物力学研究，在青少年特发性脊柱侧凸（AIS）器械植入中选择合适数量的植入物受到阻碍。目的是对AIS矫正中曲线不同区域的螺钉密度进行生物力学评估，以检验以下假设：当使用节段平移技术时，替代螺钉模式不会影响AIS预期的矫正效果。
对10例AIS病例进行了器械植入模拟。我们模拟了参考螺钉模式（每融合节段双侧多轴椎弓根螺钉且具有背侧高度可调节性）以及四种替代模式的同时凹侧和凸侧节段平移；螺钉分别在凸侧或凹侧交替水平或根尖水平减少（减少21%至25%）。比较预测的畸形矫正和螺钉受力情况。
与参考最大密度螺钉模式相比，替代螺钉模式的最终模拟Cobb角差异在1°至5°之间（39次模拟），有1次模拟为8°。胸椎后凸和顶椎旋转与参考螺钉模式相差在2°以内。参考螺钉模式以及凸侧交替水平、凹侧交替水平、凸侧根尖水平和凹侧根尖水平的螺钉减少情况下，螺钉受力分别为76±43N、96±58N、90±54N、82±33N和79±42N。替代模式的骨-螺钉受力高于参考模式（<0.0003）。凸侧和凹侧交替减少以及凸侧和凹侧根尖减少之间的骨-螺钉受力无统计学差异（>0.28）。交替减少的螺钉受力高于根尖减少（<0.05）。
使用同时节段平移技术，与最大密度螺钉模式相比，减少23%的螺钉数量仍可实现畸形矫正，但骨-螺钉受力会增加25%。螺钉减少可在凸侧或凹侧的交替水平或根尖水平进行。根尖螺钉减少可能比交替水平螺钉减少更易导致骨-螺钉受力增加幅度较小。
