Relooking at double-bundle versus single-bundle anterior cruciate ligament reconstruction: A biomechanical model to evaluate which can confer better rotatory stability

Background: To treat anterior cruciate ligament (ACL) injuries, double-bundle ACL reconstruction has been proposed as a more anatomical approach relative to single-bundle reconstruction. However, controversy remains over which technique is superior in addressing knee instability, particularly rotational laxity. We hypothesize that double-bundle reconstruction better restores rotational knee laxity, while both methods are similar in restoring anterior knee laxity, to intact knee levels. Methods: A controlled laboratory study. Eight cadaveric knees were tested accordingly: (1) static anterior laxity testing under 150 N-anterior tibial loading at 20 degrees, 60 degrees and 90 degrees knee flexion using a material testing machine, followed by (2) dynamic simulated pivot-shift with knee-specific loading involving iliotibial band forces, valgus and internal rotation torques, while the knee was brought from extension to 90 degrees flexion on a 6 degrees-of-freedom custom-designed rig. Tibiofemoral kinematics were recorded using an electromagnetic tracking system for the ACL-intact, ACL-deficient, single-bundle and double-bundle ACL-reconstructed knee conditions. Findings: Double-bundle reconstruction reduced internal rotation under pivot-shift to levels not significantly different from ACL-intact conditions (P > .173), unlike single-bundle that remained significantly higher at 10-40 degrees flexion (P < .05). For anterior laxity, there was no significant difference between double-bundle, single-bundle, and ACL-intact conditions under static testing (P > .175) or pivot-shift (P = .219). The maximum extent of knee envelope laxity was significantly reduced for double-bundle relative to single-bundle, particularly for the rotatory component (P = .012). Interpretation: Double-bundle was biomechanically superior to single-bundle in addressing envelope of rotation, while both techniques restored anterior knee laxity to ACL-intact levels.