Shah Kalpit N, Walker Gregory, Koruprolu Sarath C, Daniels Alan H
Department of Orthopaedic Surgery, Warren Alpert School of Medicine, Brown University, Providence, RI, USA.
Orthop Rev (Pavia). 2018 Mar 29;10(1):7541. doi: 10.4081/or.2018.7541.
Instrumentation failure is a common complication following complex spinal reconstruction and deformity correction. Rod fracture is the most frequent mode of hardware failure and often occurs at or near a 3-column osteotomy site. Titanium (Ti) rods are commonly utilized for spinal fixations, however, theoretically stiffer materials, such as cobalt-chrome (CoCr) rods are also available. Despite ongoing use in clinical practice, there is little biomechanical evidence that compares the construct ability to withstand fatigue stress for Ti and Co-Cr rods. Six models using 2 polyethylene blocks each were used to simulate a pedicle subtraction osteotomy. Within each block 6.0×45 mm polyaxial screws were placed and connected to another block using either two 6.0×100 mm Ti (3 models) or CoCr rods (3 models). The rods were bent to 40° using a French bender and were secured to the screws to give a vertical height of 1.5 cm between the blocks. The blocks were fatigue tested with 700N at 4 Hz until failure. The average number of cycles to failure for the Ti rod models was 12840 while the CoCr rod models failed at a significantly higher, 58351 cycles (P=0.003). All Ti models experienced rod fracture as the mode of failure. Two out of the three CoCr models had rod fractures while the last sample failed via screw fracture at the screw-tulip junction. The risk of rod failure is substantial in the setting of long segment spinal arthrodesis and corrective osteotomy. Efforts to increase the mechanical strength of posterior constructs may reduce the occurrence of this complication. Utilizing CoCr rods in patients with pedicle subtraction osteotomy may reduce the rate of device failure during maturation of the posterior fusion mass and limit the need for supplemental anterior column support.
器械故障是复杂脊柱重建和畸形矫正术后常见的并发症。棒材断裂是硬件故障最常见的形式，且常发生在三柱截骨部位或其附近。钛（Ti）棒常用于脊柱固定，然而，理论上更硬的材料，如钴铬（CoCr）棒也可使用。尽管在临床实践中仍在持续使用，但几乎没有生物力学证据比较Ti棒和Co-Cr棒承受疲劳应力的结构能力。使用六个模型，每个模型有两个聚乙烯块，用于模拟经椎弓根椎体截骨术。在每个块内放置6.0×45 mm多轴螺钉，并使用两根6.0×100 mm Ti棒（3个模型）或CoCr棒（3个模型）连接到另一个块。使用法式弯棒器将棒弯曲至40°，并固定到螺钉上，使块之间的垂直高度为1.5 cm。对块进行4 Hz、700N的疲劳测试，直至失效。Ti棒模型的平均失效循环次数为12840次，而CoCr棒模型在显著更高的58351次循环时失效（P=0.003）。所有Ti模型均以棒材断裂作为失效模式。三个CoCr模型中有两个发生了棒材断裂，而最后一个样本在螺钉-郁金香接头处因螺钉断裂而失效。在长节段脊柱融合和矫正截骨的情况下，棒材失效的风险很大。提高后路结构机械强度的努力可能会减少这种并发症的发生。在经椎弓根椎体截骨术患者中使用CoCr棒可能会降低后路融合块成熟期间器械失效的发生率，并减少对补充前路支撑的需求。
