Effect of fixation angle and graft tension in double-bundle anterior cruciate ligament reconstruction on knee biomechanics

Purpose: To compare the effect of graft fixation angle and tension in double-bundle anterior cruciate ligament (ACL) reconstruction on knee biomechanics. Methods: Fourteen cadaver knees were tested using a robotic system under two loadings: (1) an 89-N anterior tibial load (ATL) at full extension (FE), 15°, 30°, 45°, 60°, and 90°, and (2) combined 7 N m valgus and 5 N m internal tibial torques (simulated pivot-shift test) at FE, 15° and 30°. Four graft fixation angles and tensions were used for the anteromedial (AM) and posterolateral (PL) bundles, respectively: (Recon 1) 30°/20N and FE/20N, (Recon 2) 30°/30N and FE/10N, (Recon 3) 45°/20N and 15°/20N, and (Recon 4) 45°/30N and 15°/10N. Results: All fixation protocols closely restored the intact knee kinematics under ATL and simulated pivot-shift loading. For the AM bundle under ATL, the in situ force (ISF) with Recon 3 at the FE was significantly lower than that of the intact knee. For the PL bundle under ATL, the ISF with Recon 3 at the FE, 15° and 30° was significantly higher than that of the intact knee. In PL bundle under simulated pivot-shift loading, the ISF with Recon 1 and Recon 2 at FE was lower and the ISF of the PL bundle with Recon 3 at the 15° was higher than that of the intact knee. Conclusion: The AM-45°/30N and PL-15°/10N fixation most closely matched intact knee kinematics; however, stabilizing the knee during anterior tibial translation may risk an imbalance of the AM and the PL bundle loading. The results indicate that ACL bundle forces may not be restored even if the clinical assessment shows good results with the Lachman test and pivot-shift test. This may alter the loading on other structures of the knee.