新型Y型椎弓根螺钉在骨质疏松人工骨模块下的生物力学研究

Biomechanical study of a newly-designed Y type pedicle screw in osteoporotic synthetic bone

目的评价新型设计的Y型椎弓根螺钉(Y type pedicle screw,YPS)在骨质疏松人工骨模块(简称"模块")中的生物力学稳定性。方法将模块随机分成3组(n=20),用手钻垂直钻入模块中,制备直径3.0 mm、深30.0 mm的钉道。分别将YPS、膨胀式椎弓根螺钉(expansive pedicle screw,EPS)、中空骨水泥椎弓根螺钉(bone cement-injectable cannulated pedicle screw,CICPS)打入已制备好钉道的各组模块中。12 h后行X线检查,并在E10000万能材料试验机上分别对YPS组、EPS组、CICPS组进行生物力学稳定测试,记录最大轴向拔出力、最大旋出力和周期抗屈最大载荷。结果 X线片观察示,YPS组主钉和中芯钉均被周围的聚氨酯材料包绕,中芯钉从主螺钉的中下1/3穿出后,与主钉形成15°夹角,插入的中芯钉最低点与主螺钉位于同水平线上;EPS组螺钉尖端明显膨胀,形成爪型结构;CICPS组骨水泥主要分布于螺钉前部,在骨小梁中弥散,形成稳固的"螺钉-骨水泥-骨小梁"复合体。生物力学检测示,YPS、EPS、CICPS组的最大轴向拔出力分别为(98.43±8.26)、(77.41±11.41)、(186.43±23.23)N,最大旋出力矩分别为(1.42±0.33)、(0.96±0.37)、(2.27±0.39)N/m,周期抗屈试验的最大载荷分别为(67.49±3.02)、(66.03±2.88)、(143.48±4.73)N。CICPS组各指标均明显高于YPS组和EPS组,差异有统计学意义(P<0.05);YPS组最大轴向拔出力和最大旋出力矩显著高于EPS组,差异有统计学意义(P<0.05),但YPS组和EPS组间比较最大载荷差异无统计学意义(P>0.05)。结论相比于EPS,YPS能有效提升其在模块中的最大轴向拔出力和最大旋出力,为骨质疏松条件下的螺钉设计和不同固定方式选择提供了新思路。

Objective To evaluate the biomechanical stability of a newly-designed Y type pedicle screw （YPS） in osteoporotic synthetic bone. Methods The osteoporotic synthetic bone were randomly divided into 3 groups （n=20）. A pilot hole, 3.0 mm in diameter and 30.0 mm in deep, was prepared in these bones with the same method. The YPS, expansive pedicle screw （EPS）, and bone cement-injectable cannulated pedicle screw （CICPS） were inserted into these synthetic bone through the pilot hole prepared. X-ray film examination was performed after 12 hours; the biomechanical stability of YPS, EPS, and CICPS groups was tested by the universal testing machine （E10000）. The test items included the maximum axial pullout force, the maximum running torque, and the maximum periodical anti-bending. Results X-ray examination showed that in YPS group, the main screw and the core pin were wrapped around the polyurethane material, the core pin was formed from the lower 1/3 of the main screw and formed an angle of 15° with the main screw, and the lowest point of the inserted middle core pin was positioned at the same level with the main screw; in EPS group, the tip of EPS expanded markedly and formed a claw-like structure; in CICPS group, the bone cement was mainly distributed in the front of the screw and was dispersed in the trabecular bone to form a stable screw-bone cement-trabecular complex. The maximum axial pullout force of YPS, EPS, and CICPS groups was （98.43±8.26）, （77.41±11.41）, and （186.43±23.23） N, respectively; the maximum running torque was （1.42±0.33）, （0.96±0.37）, and （2.27±0.39） N/m, respectively; and the maximum periodical anti-bending was （67.49±3.02）, （66.03±2.88）, and （143.48±4.73） N, respectively. The above indexes in CICPS group were significantly higher than those in YPS group and EPS group （P〈0.05）; the maximum axial pullout force and the maximum running torque in YPS group were significantly higher than those in EPS group （P〈0.05）, but there was no significant difference in the maximum periodical anti-bending between YPS group and EPS group （P〉0.05）. Conclusion Compared with EPS, YPS can effectively enhance the maximum axial pullout force and maximum rotation force in the module, which provides a new idea for the design of screws and the choice of different fixation methods under the condition of osteoporosis.