Implant placement parameters are associated with post operative dynamic varus and valgus knee angle in robotic assisted TKA

In total knee arthroplasty (TKA), correcting or maintaining coronal knee alignment is essential for high patient function and satisfaction. However, coronal knee alignment achieved during surgery frequently changes with standing, possibly reflecting the change in knee loading and varus-valgus that occurs between non-weightbearing and weightbearing. Moreover, joint alignment also varies as the knee joint flexes and with dynamic activities. While studies have reported coronal knee alignment achieved intraoperatively during TKA surgery, they rarely trace back to the surgical choices and parameters that may predict longer-term knee alignment. Robotic-assisted TKA enables the delivery of a precise surgical plan including the surgical parameters that achieve the final position of the implants, the final intraoperative knee alignment, and the associated soft tissue balance. The objectives of this study were to determine the relationship between intraoperative alignment and in vivo static and dynamic alignment and varus-valgus during tasks of daily living 1-year after surgery, and to quantify the surgical parameters that predict in vivo static and dynamic varus-valgus during tasks of daily living. Activities requiring minimal flexion, like gait and step down, maintained knee alignment consistent with that achieved intraoperatively. However, as knee flexion angles increased during the lunge, knee extension, and leg press dynamic activities, there was a poor relationship between delivered alignment and varus-valgus angle of the knee. Medial gap in flexion, femoral implant valgus-varus and internal-external rotation alignment, and tibial valgus-varus rotation and slope were the most influential surgical parameters, significantly impacting patient frontal plane knee kinematics. These results may inform preoperative planning by illustrating how varus-valgus alignment is affected by proposed surgical plans and thus help reduce the variability in delivered dynamic varus-valgus, ultimately improving long-term outcomes.