Summary
The contribution of tibial external rotation is often overlooked in ACL tears. It plays a critical role in ACL tear mechanism and should be adequately evaluated during the diagnosis, including anteromedial laxity, posterolateral corner and meniscal ramp lesions. Treatment and prevention strategies should also target abnormal external rotation to protect the ACL graft and allow a safer RTS.
Abstract
The role of tibial external rotation (ER) in the injury mechanism of anterior cruciate ligament (ACL) tear is often misunderstood and neglected. Several video analysis studies and finite elements model (FEM) simulations show that the ACL tears with slight knee flexion, axial and posteroanterior (PA) load and knee valgus that combines femoral internal rotation (IR) and tibial ER. Although the ACL is fit to restrict tibial IR, when loaded with ER, the ACL is not able to resist the rotational torque and starts to tear at the anteromedial (AM) bundle. Due to the important role of the ACL in restricting tibial IR, most of research in focused on IR. However, we must also consider the tibial ER as it plays an important role in the ACL tear mechanism. During physical examination, we should examine if there is anteromedial rotational laxity (anterior drawer with external rotation) and posterolateral laxity (dial test). Injury to medial collateral ligament (especially its deep fibers), posterolateral corner and meniscal ramp lesions should be sought during magnetic resonance imaging evaluation as they can increase ER laxity. Instrumented tools such as the Porto Knee Testing Device (PKTD) can contribute to measure the tibial ER laxity (either isolated and associated with PA). In case of combined lesions to the ACL tear (medial and posterolateral), these should be treated concomitantly during surgery. When repairing the ACL, the use of InternalBrace has shown to reduce the stress and strain at the ACL during ER, and shift them to the InternalBrace structure. The role of lateral extra-articular tenodesis (LEAT) is clearly understood, with benefits in reducing the risk of graft tear and also a potential to reduce ER laxity. However, the possibility of anteromedial argumentation procedures remains mostly unexplored and elusive. The role of ER should also be further explored in primary and secondary prevention strategies, by including sport-specific reactive decision-making exercises that mimic the ACL injury mechanism, including tibial ER. The ultimate goal should be to make our athletes fitter with withstand the external stress during an inciting event that places the ACL at risk, and to better prepare them for a safer and more successful return to sports.