Kawaguchi K, Inui H, Taketomi S, et al. - This study was undertaken to investigate the age differences in terms of intraoperative rotational kinematics and postoperative clinical outcomes and to analyze their relationship with classification according to the age group. Researchers evaluated 111 knees of patients who had undergone Oxford unicompartmental knee arthroplasty (UKA) using a navigation system and divided them into two groups: elderly (aged ≥ 75 years; 48 knees) and nonelderly (aged < 75 years; 63 knees). A navigation system was used to measure intraoperative tibial internal rotational angles relative to the femur during passive knee flexion, and clinical outcomes were analyzed using knee range of motion, the Knee Injury and Osteoarthritis Outcome Score, and the Knee Society Functional Score at 2 years postoperatively. They further assessed the associations between intraoperative tibiofemoral rotational angles and clinical outcomes in the two groups. The results of this study illustrate that intraoperative rotational kinematics and its influence on clinical outcomes were different between elderly and nonelderly patients, and the tibial internal rotational angle could be a more important factor for successful UKA in nonelderly patients.