Association of knee flexion angle after posterior-stabilized total knee arthroplasty with postoperative tibial external position relative to the femur and the extent of tibial internal rotation from knee extension to flexion

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BackgroundThis study evaluated the relationship between preoperative and postoperative knee kinematics, moreover, investigated tibial rotational position and the extent of tibial internal rotation from knee extension to flexion as factors to obtain significant knee flexion after total knee arthroplasty (TKA). MethodsFifty-four patients (60 knees total; 15 males, 16 knees; 39 females, 44 knees) who underwent posterior-stabilized TKA using a navigation system were included. Intraoperative knee kinematics involving tibial rotational position relative to the femur and the extent of tibial internal rotation were examined at two time points: 1) after landmarks registration (pre-TKA) and 2) after skin closure (post-TKA). The relationship between the knee flexion angle at one year postoperatively and intraoperative tibial rotational position, or the extent of tibial rotation among several knee flexion angles calculated with a navigation system were investigated. ResultsThe postoperative knee flexion angle was positively associated with the preoperative flexion angle and intraoperative knee kinematics at post-TKA involving tibial external position relative to the femur at knee extension and the extent of tibial internal rotation from extension to 90° of flexion or to maximum flexion. There was a positive relationship between the extent of tibial internal rotation at pre-TKA and that at post-TKA. ConclusionsThe intraoperative kinematics of the extent of tibial internal rotation at post-TKA was influenced by that at pre-TKA. The greater external position of the tibia relative to the femur at knee extension and the greater extent of tibial internal rotation at post-TKA might lead to good knee flexion angle.