Chen Po-Quang, Lin Son-Jyh, Wu Shing-Sheng, So Hon
Department of Orthopedic Surgery, National Taiwan University, Taipei, Taiwan 10660, Republic of China.
Spine (Phila Pa 1976). 2003 May 1;28(9):881-6; discussion 887. doi: 10.1097/01.BRS.0000058718.38533.B8.
A newly designed spinal implant was tested to evaluate multicycle stiffness and fatigue resistance.
To investigate the effect of different materials, connecting plate, and pedicle screw design on the mechanical performance of the spinal implant.
The addition of cross-linkages did not significantly increase implant compression/flexion stiffness, but accelerated fatigue failure at the rod junctions. Both Ti-6Al-4V spinal implants and the 316L stainless-steel counterparts have been used extensively for clinical cases; however, design factors establishing the proposed superiority of the Ti-6Al-4V implant for fatigue resistance have not, as yet, been extensively studied.
Twenty implants with connecting plates (two materials by two screw designs by five implants) and five implants without connecting plates were assembled to UHMWPE blocks and cyclically loaded from 60 N to 600 N at a frequency of 5 Hz.
Failure sites for the tested prototypes were at the cephalic screw hubs or rod-plate junctions. All Ti-6Al-4V implants demonstrated reduced stiffness compared to the structurally identical 316L analogs. The use of connecting plates raised the stiffness of the 316L prototypes without cross-links. However, elimination of the connecting plate avoided stress concentration at the rod/plate junctions and increased fatigue life. The Ti-6Al-4V new system with the minimal notch effect at the screw hubs achieved greater fatigue resistance than its 316L counterpart. By contrast, enlargement of the inner-hub diameter resulted in greater gains for fatigue resistance than for stiffness, especially for Ti-6Al-4V variants.
Although Ti-6Al-4V was superior to 316L for endurance-limit properties, structural design of the Ti-6Al-4V implant dramatically affects fatigue resistance. This may explain the differences between existing studies and the current report, comparing fatigue life for implants made from these two materials. Our results reveal that Ti-6Al-4V must be carefully treated because of sensitivity to notch, with special consideration given to screw-hub design.
对一种新设计的脊柱植入物进行测试，以评估其多周期刚度和抗疲劳性。
研究不同材料、连接板和椎弓根螺钉设计对脊柱植入物力学性能的影响。
增加交联并没有显著提高植入物的压缩/弯曲刚度，但会加速杆连接部位的疲劳失效。Ti-6Al-4V脊柱植入物和316L不锈钢同类产品都已广泛应用于临床病例；然而，确定Ti-6Al-4V植入物在抗疲劳性方面具有优势的设计因素尚未得到广泛研究。
将20个带有连接板的植入物（两种材料、两种螺钉设计，每种设计5个植入物）和5个不带连接板的植入物组装到超高分子量聚乙烯块上，并以5Hz的频率从60N循环加载至600N。
测试原型的失效部位在头端螺钉枢纽或杆-板连接部位。与结构相同的316L类似物相比，所有Ti-6Al-4V植入物的刚度均降低。连接板的使用提高了无交联的316L原型的刚度。然而，去除连接板可避免杆/板连接部位的应力集中并延长疲劳寿命。在螺钉枢纽处具有最小切口效应的Ti-6Al-4V新系统比其316L同类产品具有更高的抗疲劳性。相比之下，扩大内枢纽直径对疲劳寿命的提升比对刚度的提升更大，尤其是对于Ti-6Al-4V变体。
尽管Ti-6Al-4V在耐力极限性能方面优于316L，但Ti-6Al-4V植入物的结构设计对抗疲劳性有显著影响。这可能解释了现有研究与本报告之间在比较这两种材料制成的植入物疲劳寿命方面的差异。我们的结果表明，由于对切口敏感，必须对Ti-6Al-4V进行仔细处理，尤其要特别考虑螺钉枢纽设计。
