Department of Anatomy, Southern Medical University Guangdong Provincial Key laboratory of Medical Biomechanics, Shenzhen Digital Orthopedic Engineering Laboratory, Guangzhou, China.
Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China.
Orthop Surg. 2020 Aug;12(4):1285-1292. doi: 10.1111/os.12742. Epub 2020 Aug 9.
This study aimed to investigate the strength of a novel micro-dynamic pedicle screw by comparing it to the traditional pedicle screw.
Forty-five lumbar vertebrae received a traditional pedicle screw on one side and a micro-dynamic pedicle screw on the other side as follows (traditional group vs micro-dynamic group): 15 vertebrae underwent instant pull-out testing; 15 vertebrae underwent 5000-cyclic fatigue loading testing; and 15 vertebrae underwent 10,000-cyclic fatigue loading testing and micro-computed tomography (micro-CT) scanning. The peek pull-out force and normalized peek pull-out force after instant pull-out testing, 5000-cyclic and 10,000-cyclic fatigue loading testing were recorded to estimate the resistance of two types of screws. Bone mineral density was recorded to investigate the strength of the different screws in osteoporotic patients. And the semidiameter of the screw insertion area on micro-CT images after fatigue were compared to describe the performance between screw and bone surface.
The bone mineral density showed a weak correlation with peek pull-out force (r = 0.252, P = 0.024). The peek pull-out force of traditional pedicle screw after 10,000-cyclic fatigue loading were smaller than that of instant pull-out test in both osteoporotic (P = 0.017) and healthy group (P = 0.029), the peek pull-out force of micro-dynamic pedicle screw after 10,000-cyclic fatigue loading was smaller than that in instant pull-out test in osteoporotic group (P = 0.033), but no significant difference in healthy group (P = 0.853). The peek pull-out force in traditional group and micro-dynamic group underwent instant pull-out testing (P = 0.485), and pull-out testing after 5000-cyclic fatigue loading testing (P = 0.184) did not show significant difference. However, the peek pull-out force in micro-dynamic group underwent pull-test after 10,000-cyclic fatigue loading testing was significantly greater than that measured in traditional group (P = 0.005). The normalized peek pull-out force of traditional groups underwent instant pull-out testing, pull-out test after 5000-cyclic and 10,000-cyclic fatigue loading testing significantly decreased as the number of cycles increased (P < 0.001); meanwhile, the normalized peek pull-out force of micro-dynamic groups remained consistent regardless of the number of cycles (P = 0.133). The semidiameter after the fatigue loading test of the traditional screw insertion area was significantly larger than that of the micro-dynamic screw insertion area (P = 0.013).
The novel micro-dynamic pedicle screw provides stronger fixation stability in high-cyclic fatigue loading and non-osteoporotic patients versus the traditional pedicle screw, but similar resistance in low-cycle fatigue testing and osteoporotic group vs the traditional pedicle screw.
本研究旨在通过比较新型微动力椎弓根螺钉与传统椎弓根螺钉，来研究新型微动力椎弓根螺钉的强度。
45 个腰椎一侧接受传统椎弓根螺钉，另一侧接受微动力椎弓根螺钉，具体如下（传统组与微动力组）：15 个椎体进行即刻拔出试验；15 个椎体进行 5000 次循环疲劳加载试验；15 个椎体进行 10000 次循环疲劳加载试验和微计算机断层扫描（micro-CT）扫描。记录峰值拔出力和即刻拔出试验后的归一化峰值拔出力，以评估两种类型螺钉的阻力。记录骨密度以研究不同螺钉在骨质疏松患者中的强度。并比较疲劳后 micro-CT 图像上螺钉插入区域的半直径，以描述螺钉与骨表面之间的性能。
骨密度与峰值拔出力呈弱相关（r = 0.252，P = 0.024）。在骨质疏松组（P = 0.017）和健康组（P = 0.029）中，10000 次循环疲劳加载后传统椎弓根螺钉的峰值拔出力均小于即刻拔出试验，骨质疏松组微动力椎弓根螺钉 10000 次循环疲劳加载后的峰值拔出力小于即刻拔出试验（P = 0.033），但健康组无明显差异（P = 0.853）。传统组和微动力组即刻拔出试验的峰值拔出力（P = 0.485）和 5000 次循环疲劳加载试验后的拔出试验（P = 0.184）无显著差异。然而，微动力组 10000 次循环疲劳加载后的峰值拔出力明显大于传统组（P = 0.005）。传统组即刻拔出试验、5000 次循环和 10000 次循环疲劳加载试验后的归一化峰值拔出力随着循环次数的增加而显著降低（P < 0.001）；而微动力组的归一化峰值拔出力不受循环次数的影响（P = 0.133）。传统螺钉插入区域在疲劳试验后的半直径明显大于微动力螺钉插入区域（P = 0.013）。
新型微动力椎弓根螺钉在高循环疲劳加载和非骨质疏松患者中提供了更强的固定稳定性，与传统椎弓根螺钉相比，但在低循环疲劳试验和骨质疏松组中与传统椎弓根螺钉的阻力相似。
