In Vivo three-dimensional kinematics of normal knees during sitting sideways on the floor

Background The normal knee kinematics during asymmetrical kneeling such as the sitting sideways remains unknown. This study aimed to clarify in vivo kinematics during sitting sideways of normal knees. Methods 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. Results Bilateral knees during sitting sideways showed a femoral external rotation relative to the tibia with flexion (ipsilateral: 13.7 +/- 3.5 degrees, contralateral: 5.8 +/- 6.8 degrees). Whereas the ipsilateral knees showed valgus movement of 4.6 +/- 2.5 degrees from 130 degrees to 150 degrees of flexion, and the contralateral knees showed varus movement of -3.1 +/- 4.4 degrees from 110 degrees to 150 degrees of flexion. The medial side of the contralateral knees was more posteriorly located than that of the ipsilateral knees beyond 110 degrees of flexion. The lateral side of the contralateral knees was more anteriorly located than that of the ipsilateral knees from 120 degrees to 150 degrees 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. Conclusion Even though the asymmetrical kneeling such as sitting sideways, the knees did not display asymmetrical movement.