The effects of different tensioning strategies on knee laxity and graft tension after double-bundle anterior Cruciate ligament reconstruction

Background: Double-bundle anterior cruciate ligament reconstruction replicates the 2 functional bundles of the native ligament, the posterolateral and the anteromedial, to control anteroposterior and rotational laxity. Hypothesis: Double-bundle anterior cruciate ligament reconstruction laxity should be affected by the way grafts are tensioned. Study Design: Controlled laboratory study. Methods: Fourteen intact cadaveric knees were instrumented in a 6 degree of freedom rig, and kinematics throughout flexion-extension were recorded with an electromagnetic system under a 90-N anterior force or a 5-N.m internal rotation torque. Anteromedial and posterolateral bundle bovine extensor tendon grafts were fixed to load cells on the tibia, and tension was adjusted to match the intact knee anteroposterior laxity with 3 different protocols: (1) anteromedial bundle first and then posterolateral bundle at 90 degrees and 20 degrees of flexion, respectively; (2) posterolateral bundle first and then anteromedial bundle at 20 degrees and 90 degrees of flexion, respectively; and (3) both bundles together at 20 degrees of flexion. Finally, a single-bundle graft positioned at 10 o'clock was tensioned at 20 degrees of flexion. Results: Lower graft tensions were required to match intact knee laxity in double-bundle anterior cruciate ligament reconstruction. Tension patterns with knee flexion were independent from the tensioning protocol. Protocols 1 and 2 overconstrained anteroposterior laxity, whereas protocol 3 matched intact knee anteroposterior laxity throughout the range of motion. The single-bundle reconstructions had excess anteroposterior laxity in flexion. Rotations were better restored with double-bundle protocols 2 and 3. Conclusion: Knee laxity after double-bundle anterior cruciate ligament reconstruction is affected by the sequence in which the grafts are tensioned. Clinical Relevance: Double-bundle anterior cruciate ligament reconstruction ensures better laxity restoration than does single bundle when both bundles are fixed together.