Leong J C, Lu W W, Zheng Y, Zhu Q, Zhong S
Department of Orthopaedic Surgery, University of Hong Kong.
Spine (Phila Pa 1976). 1998 Nov 1;23(21):2289-94. doi: 10.1097/00007632-199811010-00008.
The strength of sacral screw fixation achieved with techniques using one sacral screw and two triangulated sacral screws with Chopin block was tested on 10 fresh human sacrum specimens.
To compare the stiffness and the failure strength of single sacral screw fixation and those of two divergent triangulated sacral screw fixation under different loading conditions.
Weak sacral screw fixation is the major cause of failure in instrumented lumbosacral fusion. Although previous studies have evaluated the strength of anteromedially and anterolaterally inserted sacral screws, the strength of two divergent triangulated sacral screws has not been evaluated biomechanically. It is assumed that increasing the number of sacral screws and using a triangulated insertion technique may increase the strength of purchase for lumbosacral fixation.
Ten fresh human sacrum specimens were used in this study. Six specimens were from donors less than 30 years of age (younger group), and the other four were from donors more than 60 years of age (aged group). The specimens were assigned randomly to either one side one S1 pedicle screw inserted anteromedially or to the other side with two screws directed anteromedially and anterolaterally. All specimens were tested with an Instron material testing machine (Instron Limited, High Wycombe, England). The average stiffness under compression, tension, and torsion were calculated from the average slopes of the load deformation curves. The failure load was applied for the final testing.
The results showed significant differences in stiffness between fixation with one screw and fixation with two divergent triangulated screws. With one S1 pedicle screw fixation, the average stiffness was 203 N/mm for compression, 147 N/mm for tension, and 2 Nm/degree for torsion. With two-screw fixation the average stiffness increased to 255 N/mm (126%), 185 N/mm (126%) and 2.4 Nm/degree (120%), respectively. The average failure strength under tension loads was found to be 1450 N in the younger specimens and was reduced to 980 N in the aged specimens.
This study showed that fixation with two divergent triangulated screws to the sacrum was significantly stronger than one-screw fixation for lumbosacral fusion. The strength of fixation seems to have a negative correlation with aging.
采用单枚骶骨螺钉和两枚带肖邦垫块的三角化骶骨螺钉技术对10个新鲜人骶骨标本进行骶骨螺钉固定强度测试。
比较单枚骶骨螺钉固定和两枚发散三角化骶骨螺钉固定在不同加载条件下的刚度和破坏强度。
骶骨螺钉固定薄弱是器械辅助下腰骶融合失败的主要原因。尽管先前的研究评估了经前内侧和前外侧置入的骶骨螺钉的强度，但两枚发散三角化骶骨螺钉的强度尚未进行生物力学评估。据推测，增加骶骨螺钉数量并采用三角化置入技术可能会增加腰骶固定的把持力强度。
本研究使用10个新鲜人骶骨标本。6个标本来自年龄小于30岁的供体（年轻组），另外4个来自年龄大于60岁的供体（老年组）。将标本随机分配至一侧经前内侧置入1枚S1椎弓根螺钉，另一侧经前内侧和前外侧置入2枚螺钉。所有标本均使用英斯特朗材料试验机（英斯特朗有限公司，英国海威科姆）进行测试。根据载荷变形曲线的平均斜率计算压缩、拉伸和扭转时的平均刚度。施加破坏载荷进行最终测试。
结果显示单枚螺钉固定和两枚发散三角化螺钉固定在刚度上存在显著差异。采用1枚S1椎弓根螺钉固定时，压缩平均刚度为203N/mm，拉伸平均刚度为147N/mm，扭转平均刚度为2 N·m/°。采用双螺钉固定时，平均刚度分别增加到255N/mm（126%）、185N/mm（126%）和2.4 N·m/°（120%）。在年轻标本中，拉伸载荷下的平均破坏强度为1450N，在老年标本中降至980N。
本研究表明，对于腰骶融合，两枚发散三角化骶骨螺钉固定明显强于单枚螺钉固定。固定强度似乎与年龄呈负相关。
