Graft tendon slippage with metallic and bioabsorbable interference screws under cyclic load: a biomechanical study in a porcine model

Introduction The rupture of the anterior cruciate ligament (ACL) is the most common type of knee injury. Reconstructive surgery is the ‘gold standard’ treatment. During the immediate post-operative period, the fixation of the graft is entirely dependent on the ability of the grafted implant to be secured inside the bone tunnel under the cyclical loads associated with daily tasks. Poor fixation can lead to graft slippage, thus impairing the healing and integration of the graft. The aim of this study was to evaluate the biomechanical performance of tendon graft fixation devices with metallic and bioabsorbable interference screws. Methods Twenty ACL reconstructions were carried out in porcine tibias using deep flexor tendons to fix 9 × 20 mm metallic (n=10) and PLLA 70/30 bioabsorbable screws (n=10). To verify the ability of a construct to resist immediate postoperative (PO) rehabilitation protocols for immediate load bearing, a cyclic loading test was applied with 50-250 N of tensile force at 1 Hz for 1000 cycles, and the displacement was measured at 10, 50, 100, 500 and 1000 load cycles to quantify the slippage of the graft during the test. After the cyclic loading test, a single-cycle load-to-failure test was applied. Results The slippage of the graft using metallic screws did not differ (P = 0.616) from that observed when using bioabsorbable screws. Conclusion The results obtained in this experiment indicate that metallic screws may promote a similar amount of graft slippage during low cyclic loading as bioabsorbable screws. Additionally, there was no difference in the biomechanical performance of these two types of screws during high failure loads.引言 前交叉韧带（anterior cruciate ligament, ACL）断裂是最为常见的膝关节损伤类型，重建手术是其公认的“金标准”治疗方案。在术后即刻阶段，移植物的固定效果完全取决于植入移植物在日常活动相关周期性载荷下，于骨隧道内获得可靠固定的能力。固定不佳可引发移植物滑移，进而损害移植物的愈合与整合效果。本研究旨在评估配备金属及生物可吸收界面螺钉的肌腱移植物固定装置的生物力学性能。 方法 本研究采用猪胫骨开展20例前交叉韧带重建实验，以深屈肌腱作为移植物，分别使用9×20 mm金属界面螺钉（n=10）与70/30聚左旋乳酸（PLLA）生物可吸收界面螺钉（n=10）进行固定。为验证重建结构能够抵抗术后即刻康复方案中的即刻负重要求，本实验施加50~250 N拉力、频率为1 Hz的循环载荷，共计1000个循环；并在第10、50、100、500及1000次载荷循环时测量位移量，以量化实验过程中移植物的滑移量。循环加载试验结束后，开展单循环极限载荷试验。 结果 采用金属界面螺钉时的移植物滑移量与生物可吸收螺钉组无统计学差异（P=0.616）。 结论 本实验所得结果表明，在低周期性载荷条件下，金属界面螺钉与生物可吸收界面螺钉可引发程度相近的移植物滑移。此外，两种螺钉在高极限载荷下的生物力学性能无统计学差异。