<jats:title>Abstract</jats:title><jats:sec> <jats:title>Background</jats:title> <jats:p>The normal knee kinematics during asymmetrical kneeling such as the sitting sideways remains unknown. This study aimed to clarify <jats:italic>in vivo</jats:italic> kinematics during sitting sideways of normal knees.</jats:p> </jats:sec><jats:sec> <jats:title>Methods</jats:title> <jats:p>Twelve knees from six volunteers were examined. Under fluoroscopy, each volunteer performed a sitting sideways. A two-dimensional/three-dimensional registration technique was used. The rotation angle, varus-valgus angle, anteroposterior translation of the medial and lateral sides of the femur relative to the tibia, and kinematic pathway in each flexion angle was evaluated.</jats:p> </jats:sec><jats:sec> <jats:title>Results</jats:title> <jats:p>Bilateral knees during sitting sideways showed a femoral external rotation relative to the tibia with flexion (ipsilateral: 13.7 ± 3.5°, contralateral: 5.8 ± 6.8°). Whereas the ipsilateral knees showed valgus movement of 4.6 ± 2.5° from 130° to 150° of flexion, and the contralateral knees showed varus movement of -3.1 ± 4.4° from 110° to 150° of flexion. The medial side of the contralateral knees was more posteriorly located than that of the ipsilateral knees beyond 110° of flexion. The lateral side of the contralateral knees was more anteriorly located than that of the ipsilateral knees from 120° to 150° of flexion. In the ipsilateral knees, a medial pivot pattern followed by a bicondylar rollback was observed. In the contralateral knees, no significant movement followed by a bicondylar rollback was observed.</jats:p> </jats:sec><jats:sec> <jats:title>Conclusion</jats:title> <jats:p>Even though the asymmetrical kneeling such as sitting sideways, the knees did not display asymmetrical movement.</jats:p> </jats:sec>