Two Different Knee Rotational Instabilities Occur With Anterior Cruciate Ligament and Anterolateral Ligament Injuries: A Robotic Study on Anterior Cruciate Ligament and Extra-articular Reconstructions in Restoring Rotational Stability

Purpose: To determine the effect of 2 extra-articular reconstructions on pivot-shift rotational stability and tibial internal rotation as a basis for clinical recommendations. Methods: A robotic simulator tested 15 cadaver knees. Group 1 (anterior cruciate ligament [ACL] cut) underwent ACL bone-patellar tendon-bone reconstruction followed by sectioning the anterolateral structures and an extra-articular, manual-tension iliotibial band (ITB) tenodesis. Group 2 (ACL intact) tested the rotational stabilizing effect of a low-tension ITB tenodesis before and after sectioning the anterolateral ligament/ITB structures. Lateral and medial tibiofemoral compartment translations and internal-external tibial rotations were measured under Lachman, 5N.m tibial rotation, and 2 pivot-shift simulations using 4-degree-of-freedom loading. Statistical equivalence was defined within 2 mm tibiofemoral compartment translation and 2 degrees tibial rotation at P < .05. Results: The bonepatellar tendon-bone ACL reconstruction (group 1) restored pivot-shift lateral compartment translation within 0.7 mm (95% confidence interval [CI], -0.6 to 1.9; P = .70) of normal. The internal rotation limit was not affected by ACL sectioning or reconstruction. After anterolateral ligament/ITB sectioning there was no change in pivot-shift lateral compartment translation, however internal rotation increased 2.9 degrees (95% CI, 0.6-5.2; P = .99) at 90 degrees flexion. The manual-tension ITB tenodesis (fixated 13-22 N tension) decreased pivot-shift lateral compartment translation 4.8 mm (95% CI, 1.4-8.1; P = .99) and internal rotation by 21.9 degrees (95% CI, 13.2-30.6; P = .99) at 90 degrees flexion. The ACL forces decreased 45.8% in the pivot-shift test. In group 2 knees, with the ACL intact, the anterolateral ligament/ITB sectioning had no effect on pivot-shift translations; however, the internal rotation limit increased by 4.3 degrees (95% CI, 1.9-6.8; P = .99) at 60 degrees flexion. The low-tension ITB tenodesis (fixated 8.9 N tension) had no effect on pivot-shift translations and corrected internal tibial rotation with a mild overconstraint of 4.2 degrees (95% CI, 1.9-6.8; P = .99) at 60 degrees flexion. Conclusions: A low-tension ITB tenodesis, fixated at neutral tibial rotation to avoid constraining internal tibial rotation, has no effect in limiting abnormal pivot-shift subluxations.