Optimizing the Control of Anteromedial Rotatory Knee Instability: A Biomechanical Validation of Different Anteromedial Reconstruction Techniques

Background: Anteromedial rotatory instability (AMRI) can result from combined injury to the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) complex (superficial and deep [sMCL and dMCL]). Hypothesis: Adding an oblique anteromedial (AM) limb to an sMCL reconstruction improves the control of AMRI. Study Design: Controlled laboratory study. Methods: A 6 degrees of freedom robotic setup simulated clinical laxity in 9 unpaired knees under the following tests: 5-N·m external rotation (ER), 8-N·m valgus rotation (VR), and AM drawer (combined 89-N anterior tibial translation and 5-N·m ER). Knees were tested intact after cutting the sMCL and dMCL and after 5 different reconstructions: modified Lind, short sMCL, and sMCL with the addition of an AM graft limb with 3 different obliquities. Results: After short sMCL reconstruction, AM drawer and ER laxity were not significantly different from either the MCL-deficient state or the intact state. VR was reduced from the MCL-deficient state between 0° and 60° of flexion but not at 90°. For combined sMCL + AM reconstructions, VR was reduced as compared with the MCL-deficient state at all flexion angles. AM drawer laxity and ER laxity were also reduced, similar to the intact state, except at 30° where, for the more oblique T1 and T2 AM reconstructions, laxity was less than in the intact state. The modified Lind reconstruction reduced AM drawer and ER laxity from the MCL-deficient state to values similar to the intact state at all flexion angles. VR laxity was also reduced at all flexion angles, similar to the intact knee at 0° to 30°. However, it was not as good at restraining AM drawer and ER when compared with the sMCL reconstructions with more oblique AM limbs. Conclusion: AMRI appears to be better restrained by adding an oblique AM graft limb to an sMCL reconstruction, replicating the function of the sMCL and dMCL in a cadaveric model. The tibial attachment of the AM limb should be anterior to the sMCL, but its precise attachment on the tibia is less important. This offers surgical flexibility, which may be helpful in avoiding anterior cruciate ligament tibial tunnel coalition. The femoral attachment on the posterior medial epicondyle is critical to optimize graft isometry. Clinical Relevance: Adding an AM limb to a medial reconstruction optimizes the control of AMRI at time zero. The tibial attachment site is less critical, offering surgical flexibility.