变牙厚椎弓根螺钉的生物力学测试
Biomechanical study of the transitional thread pedicle screw
目的 评价不同变牙厚椎弓根螺钉（transitional thread pedicle screw, TTPS）对螺钉拔出力的影响。 方法 取新鲜小牛胸腰椎标本（T11~L4）5具，共30个椎体(60侧椎弓根)，剔除周围肌肉、筋膜，注意保持骨结构完整，解离成单个椎骨。平均骨密度为（1.186±0.182）g/cm2。TTPS规格有6种：A0（牙厚保持不变）、A1（逐牙加厚0.01mm）、A2（逐牙加厚0.02 mm）、A3（逐牙加厚0.03 mm）、A4（逐牙加厚0.04 mm）、A5（逐牙加厚0.05 mm）。每种螺钉随机置入10侧椎弓根，将标本包埋好并用夹具固定在材料试验机上，设置椎弓根螺钉长轴与拔出力轴线方向重合。设置材料试验机加载速率为0.08 mm/s进行拔出实验，结果输出拔出力-位移曲线、最大轴向拔出力（Fmax）。计算拔出刚度。 结果 A0至A5 6种螺钉的最大轴向拔出力分别为（983.99±324.19）、（1119.84±362.47）、（1067.67±398.00）、（900.04±255.89）、（799.07±406.79）、（850.71±408.11）N。6种不同规格TTPS轴向拔出力间无显著差异（组间差异P=0.216）。6种不同规格的TTPS的拔出刚度间无显著差异（组间差异P=0.07）。 结论 小范围增加螺纹牙厚，对椎弓根螺钉抗拔出力没有显著影响。
Objective To clarify the biomechanical stability of the transitional thread pedicle screw (TTPS) in spinal vertebrae. Methods For this study, 30 calf thoracolumbar vertebra（60 pedicles）, with the mean bone mineral density of (1.186±0.182）g/cm2 , were used. All the specimens were cleaned of soft tissues and separated into individual vertebrae. Each vertebra was prepared and instrumented with one of six pedicle screw. Pilot hole preparation was standardized and coaxial orientation was confirmed by direct inspection. Axial pullout was performed at 0.08mm/s displacement. The typical screw pullout load-displacement curve for the TTPS was illustrated. Results The maximum axial pullout strength of the A0, A1, A2, A3, A4 and A5 screws were (983.99±324.19) N, (1119.84±362.47)N, (1067.67±398.00)N, (900.04±255.89)N, (799.07±406.79)N, and (850.71±408.11)N, respectively. No significant difference in pullout force was noted for the six TTPS. Conclusions There are no differences of pullout strength among screw types.
Pedicle screw / Pullout experiment / Thread properties / Biomechanics
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