Tibial Fixation of Anterior Cruciate Ligament Allograft Tendons. Comparison of 1-, 2-, and 4-Stranded Constructs
Abstract:
Background In sum, 1-, 2-, and 4-stranded allografts are used for soft tissue anterior cruciate ligament reconstruction however, the fixation properties of fixation devices are not well assessed. Hypothesis There are no differences in the biomechanical characteristics of 1 Achilles-, 2 posterior tibialis-, and 4 semitendinosus-stranded allograft tibial fixation. Study Design Controlled laboratory study. Methods Sixty-three fresh-frozen porcine tibiae were used to evaluate the fixation of 1-, 2-, and 4-stranded human tendon allografts Achilles, posterior tibialis, and semitendinosus with 3 fixation devices Delta, Intrafix, and Calaxo screws. With use of a materials testing system, each graft was subjected to 500 cycles of loading 50-250 N, 0.75 mmsec to determine displacement and cyclic stiffness, followed by a monotonic failure test 20 mmmin to determine maximum load and pullout stiffness. Results For each graft type, there were no significant biomechanical differences between fixation devices. However, the 1-stranded graft Achilles construct demonstrated significantly higher mean displacement 3.17 1.62 mm, lower cyclical stiffness 156 25 Nmm, lower load to failure 479 87 N, and lower pullout stiffness 140 28 Nmm. In comparison with the 2-stranded graft posterior tibialis, the 4-stranded graft semitendinosus exhibited lower displacement 0.86 0.44 to 1.12 0.51 mm and higher ultimate failure load 832 255 to 656 168 N. Numerous differences in fixation properties were noted when comparing a device to each of the 3 grafts. Conclusion The 1-stranded allograft demonstrated inferior biomechanical tibial fixation properties when compared with 2 posterior tibialis- and 4 semitendinosus-stranded allograft constructs for all fixation devices tested. Clinical Relevance This study demonstrated that not all tibial fixation devices are designed to adequately accommodate different types of anterior cruciate ligament allografts. Biomech