[Biomechanical evaluation of tendon graft fixation at the tibial site in anterior cruciate ligament reconstruction with Intrafix and bioabsorbable interference screw].

Objective: The fixation strength of the hamstring tendon graft on the tibial side is considered the weak point in anterior cruciate ligament (ACL) reconstruction. This work tested the hypotheses that some of these devices will resist graft slippage under loads better than others, and that some will have higher ultimate strength than others.
Methods: Fourteen fresh frozen human cadaver knees underwent fixation of the hamstring tendon harvested from the knee to be used as graft material to reconstruct the ACL and were divided into two equal groups based on the fixation methods: bioabsorbable interference screw group and Intrafix group. A MTS 858 MiniBionix II testing machine was used to carry out tensile testing under an axial load parallel to the tibial tunnel with a velocity of 10 mm/min. Ultimate failure load, displacement of 100N, displacement of 400N, stiffness and mode of failure were recorded respectively.
Results: The maximum load for the Intrafix fixation group was (719.094+/-160.478) kgxmxs(-2), significantly higher than that of the bioabsorbable interference screw fixation group [(476.640+/-64.226) kgxmxs(-2), P<0.05]. The displacement levels of 100 kgxmxs(-2) and 400 kgxmxs(-2) for the Intrafix fixation group was (1.025+/-0.326) mm and (4.728+/-1.992) mm respectively, not significantly different from those of the bioabsorbable interference screw fixation [(1.335+/-0.539) mm and (7.564+/-4.307) mm respectively, t=0.2173, 0.0944, both P>0.05], and the stiffness of the Intrafix fixation group was (96.770+/-36.848) kgxm(-1)xs(-2) not significantly different from that of the bioabsorbable interference screw fixation group [(63.976+/-31.003 kgxm(-1)xs(-2)), t=0.0967, P>0.05]. After randomized t-test of significance, the displacement levels of 100N and 400N of these 2 groups were not significantly different.
Conclusion: Both tibial site fixation with bioabsorbable interference screw and that with Intrafix in ACL reconstruction with 4-stranded hamstring tendon grafts can meet daily physiological demand. Tibial site fixation with Intrafix shows a higher failure load.