ACL Graft Position Affects in Situ Graft Force Following ACL Reconstruction

Background: The purpose of our study was to evaluate the relationship between graft placement and in situ graft force after anterior cruciate ligament (ACL) reconstruction. Methods: Magnetic resonance imaging (MRI) was obtained for twelve human cadaveric knees. The knees, in intact and deficient-ACL states, were subjected to external loading conditions as follows: an anterior tibial load of 89 N at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees of flexion and a combined rotatory (simulated pivot-shift) load of 5 Nm of internal tibial torque and 7 Nm of valgus torque at 0 degrees, 15 degrees, and 30 degrees of flexion. Three ACL reconstructions were performed in a randomized order: from the center of the tibial insertion site to the center of the femoral insertion site (Mid), the center of the tibial insertion site to a more vertical femoral position (S1), and the center of the tibial insertion site to an even more vertical femoral position (S2). The reconstructions were tested following the same protocol used for the intact state, and graft in situ force was calculated for the two loadings at each flexion angle. MRI was used to measure the graft inclination angle after each ACL reconstruction. Results: The mean inclination angle (and standard deviation) was 51.7 degrees +/- 5.0 degrees for the native ACL, 51.6 degrees +/- 4.1 degrees for the Mid reconstruction (p = 0.85), 58.7 degrees +/- 5.4 degrees for S1 (p < 0.001), and 64.7 degrees +/- 6.5 degrees for S2 (p < 0.001). At 0 degrees, 15 degrees, and 30 degrees of knee flexion, the Mid reconstruction showed in situ graft force that was closer to that of the native ACL during both anterior tibial loading and simulated pivot-shift loading than was the case for S1 and S2 reconstructions. At greater flexion angles, S1 and S2 had in situ graft force that was closer to that of the native ACL than was the case for the Mid reconstruction. Conclusions: Anatomic ACL reconstruction exposes grafts to higher loads at lower angles of knee flexion.