AbstractPurposeTo carry out an in vivo kinematic analysis to determine whether adding a lateral extraarticular tenodesis (LET) for those patients with subjective instability and objective residual laxity after a transtibial (TT) anterior cruciate ligament reconstruction (ACLR) reduces anteroposterior and rotational laxity and to evaluate the 2‐year follow‐up clinical outcomes to analyze whether biomechanical changes determine clinical improvement or not.MethodsA total of 19 patients with residual knee instability after TT ACLR who underwent a modified Lemaire LET were prospectively evaluated for at least 2‐year follow‐up. Preoperative, intraoperative, and 6 and 24‐month postoperative kinematic analyses were carried out using the KiRA accelerometer and KT1000 arthrometer to look for residual anterolateral rotational instability and residual anteroposterior instability. Functional outcomes were measured with the single‐leg vertical jump test and the single‐leg hop test. Clinical outcomes were evaluated using the IKDC 2000, Lysholm, and Tegner scores.ResultsA significant reduction in anterolateral rotational instability was detected with the patient under anesthesia (from 3 ± 1.2 to 1.1 ± 1.1 m/s2; p < 0.05) as well as with the patient awake (from 2.1 ± 0.8 to 0.7 ± 1.4 m/s2; p < 0.05). A significant reduction in anteroposterior instability was only present under anesthesia (from 3.4 ± 1.9 to 2.1 ± 1.1 mm; p < 0.05), while no difference was present without anesthesia (from 2.3 ± 1.1 to 1.6 ± 1 mm; n.s.). Postoperative analysis of knee laxity did not show any significant variation from the first to the last follow‐up. Both the single‐leg vertical jump test and single‐leg hop test improved significantly at the last follow‐up (both p < 0.05). The mean values of both the IKDC and Tegner scores showed an improvement (p < 0.05 and p < 0.05, respectively), whereas that was not the case with the Lysholm score (n.s.).ConclusionsThe modified Lemaire LET can improve the kinematics of a non‐anatomic ACL reconstructed knee with residual subjective and objective instability. These kinematic changes were able to lead to an improvement in subjective stability as well as the function of the knee in a small cohort of recreationally active patients. At 2‐year follow‐up, the kinematic changes as well as the level of activity of the patients and the IKDC score show their improvement sustained.Level of evidenceLevel IV.