Four-strand hamstring graft is stiffer than a tripled semitendinosus graft in anterior cruciate ligament reconstruction: a cadaveric study

PURPOSE: The aim of this study was to compare the biomechanics of a four-strand hamstring graft with a tripled semitendinosus graft, with and without adjustable extra-cortical button fixation, in a cadaveric model. METHODS: Four groups of 10 cadaveric hamstrings were tested: In group A, a tripled semitendinosus graft fixated with two adjustable extra-cortical buttons; in Group B, a four-strand semitendinosus and gracilis graft fixated with an adjustable extra-cortical button and a clamp; in group C, a tripled semitendinosus graft fixated to a steel hook and a clamp; in group D, a four-strand semitendinosus and gracilis graft fixated to a steel hook and a clamp. Each group was submitted to a cyclic loading test (1000 cycles between 50 and 250 Newton at a frequency of 0.5 hertz) and a load-to-failure test. Primary outcomes were ultimate failure load and stiffness. Secondary outcomes were graft elongation and graft diameter. RESULTS: There was no difference in ultimate failure load among groups. Group B achieved a median stiffness of 171 N/mm (interquartile range [IQR] 139–204) which was significantly higher than Group A (median 103 N/mm (74–119), p < 0.01). Group B showed more cyclic elongation (4.1 mm (3.4–5.7)) compared to group D (2.3 mm (1.9–3.0)), and also lower stiffness was noted (171 N/mm (139–204) vs 265 N/mm (227–305)). There was no difference in graft diameter among groups. CONCLUSIONS: The results of this study indicate that higher stiffness can be achieved using four-strand hamstring tendon grafts compared to tripled semitendinosus grafts when using femoral extra-cortical buttons, despite comparable graft diameters. Thereby, the use of adjustable extra-cortical fixation devices may result in more cyclic elongation and lower stiffness of the graft.