Surgically adjust tibial tunnel in anatomical anterior cruciate ligament single-bundle reconstruction: A time-zero biomechanical study in vitro.

BACKGROUND: The anatomical positioning of the graft during anterior cruciate ligament reconstruction (ACLR) is of great significance for restoring normal knee kinematics and preventing early joint degeneration. Therefore, the adjustment of the mispositioned guide pin becomes extremely important. Our research aims to test the time-zero biomechanical properties in adjusting inaccurate guide pins to the center of the tibial footprint in anatomical anterior cruciate ligament single-bundle reconstruction. METHODS: Porcine tibias and bovine extensor tendons were used to simulate a transtibial ACL reconstruction in vitro. Load-to failure testing was carried out in 4 groups: control group (n = 45): the guide pin was drilled at the center of the ACL footprint; group I, group II and group III (n = 45, respectively): the guide pin was respectively drilled 1 mm, 2 mm and 3 mm away from the center of the ACL footprint. In the experimental groups, a small tunnel with a 4.5 mm reamer is made and the guide pin is shifted to the center of the footprint. All the reamed tibias were scanned by CT to measure the area of the tunnel in the footprint, and time-zero biomechanical properties were recorded. RESULTS: All graft-tibia complexes failed because the grafts slipped past the interference screws. Compare to control group, the ultimate load, yield load, and tunnel exit area in group III decreased significantly (p < 0.05). Regarding to the ultimate load, yield load, tensile stiffness, twisting force and tunnel exit area, t-test showed no significant differences between control group and group I, group II respectively (p > 0.05). Pearson test showed that tunnel exit area was negatively correlated with other characteristics (p < 0.05). CONCLUSIONS: Surgical adjustment of the guide pin to the center of the tibial footprint may have significant influence in time-zero biomechanical properties in anatomical anterior cruciate ligament single-bundle reconstruction when the adjusted tibial tunnel was significantly enlarged compare to the standard tibial tunnel.