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.
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。.
Keywords: Osteoporotic synthetic bone; Y type pedicle screw; biomechanical stability.