Effects of Anteromedial Portal versus Transtibial ACL Tunnel Preparation on Contact Characteristics of the Graft and the Tibial Tunnel Aperture.

Background: The purpose of this study was to compare the tibial tunnel aperture contact characteristics simulating an anteromedial and transtibial anterior cruciate ligament (ACL) tunnel preparation.

Methods: Seven matched pairs of cadaveric knees were tested. From each knee, a 10-mm quadriceps ACL graft was prepared. The native ACL was arthroscopically removed and tibial tunnels were drilled. In one knee, a transtibial technique was performed with femoral tunnel drilling approached through the tibial tunnel. For the anteromedial technique on the contralateral knee, the posterior tibial tunnel was chamfered with a rasp. The knees were then disarticulated and tibial tunnel aperture geometry was measured. A pressure sensor was placed between the graft and the posterior aspect of the tibial tunnel and the graft was secured with an interference screw. Contact force, contact area, contact pressure, peak contact pressure, hysteresis and stiffness were measured at cyclic loads of 50 N, 100 N, 150 N, and 200 N.

Results: Tibial tunnel aperture area, diameter and deviation from a circle were significantly larger with the transtibial technique ( p < 0.05). There was no significant difference in hysteresis, stiffness, contact area, contact force and mean contact pressure. The peak contact pressure between the ACL graft and the tibial tunnel was significantly higher with the anteromedial technique for 100 N ( p = 0.04), 150 N ( p = 0.01), and 200 N ( p = 0.002) cyclic loading.

Conclusions: Increased peak contact pressure on the graft at the tibial aperture with the anteromedial technique may increase the stress on the graft and possibly lead to failure following ACL reconstruction.