The effect of anterior or posterior tibial tunnel placement of a soft tissue graft with a soft tissue interference screw on fixation biomechanics

We investigated the biomechanical characteristics of anterior or posterior tibial tunnel placement of the soft tissue graft with a soft tissue interference screw in anterior cruciate ligament (ACL) reconstruction. Twelve bovine tibiae and digital extensor tendons were divided into two homogeneously equal groups after they were stripped of all soft tissues. Tibial tunnels were prepared and digital extensor tendons were fixed at nonanatomic (apart from the joint) anterior (n=6, group I) or posterior (n=6, group II) tibial tunnel positions with a soft tissue metal interference screw, 9x30 mm in size. All the specimens were cycled 500 times from 50 to 250 N at 1 Hz frequency in a servo hydraulic test device, after which ultimate load-at-failure testing was performed at a rate of 20 mm/min. The mean screw insertion torque values were 8.2+/-2.4 Nm and 8.4+/-2.8 Nm in groups I and II, respectively (p=0.88). No significant differences were found between the two groups with respect to graft displacement (1.9+/-0.8 mm vs 2.3+/-0.4 mm; p=0.38) and stiffness (132.7+/-10.9 N/mm vs 126.4+/-8.5 N/mm, p=0.98) at the end of cyclic loading. Our results show that the site of nonanatomic soft tissue graft fixation in the tibial tunnel (anterior or posterior) with a soft tissue interference screw do not affect the biomechanical parameters in ACL reconstruction.