Effect of Changes in the Posterior Tibial Slope on Femorotibial Articular Contact Kinematics after Cruciate-Retaining Total Knee Arthroplasty: Do the Changes Affect Outcomes?

Background Total knee arthroplasty (TKA) outcomes are affected by many factors.This study aimed to evaluate whether changes in the posterior tibial slope (PTS) affects patients’ outcomes after cruciate-retaining TKA by affecting femorotibial articular contact kinematics. Methods Altogether, 20 knees in 10 patients who underwent posterior cruciate ligament-retaining TKA using the same size prosthesis for medial osteoarthritis were assessed preoperatively and 1 year postoperatively. PTS changes seen on lateral radiographs before and after TKA were calculated. Knees were placed in groups according to the PTS change at 1 year postoperatively (preoperative value − postoperative value). Group 1 had a >3° change and group 2 a ≤3° change. Knee kinematics under the weight-bearing mid-flexion condition were compared between the two groups via two-dimensional/three-dimensional registration. Pain was measured using the visual analog scale, and knee function was based on the Western Ontario and McMaster universities (WOMAC) osteoarthritis index and Knee Society Score (KSS) questionnaire results. Results Group 2 experienced paradoxical anterior motion of the mediofemoral condyle postoperatively, whereas group 1 did not. Comparison of TKA results between the two groups showed a significant between-group difference in pain and knee function of the KSS and in the WOMAC osteoarthritis index score (P ≤ 0.05). Postoperative results were better in group 1 than in group 2. Conclusions Achieving a greater change in the posterior tibial slope apparently improves outcomes in patients undergoing posterior cruciate ligament-retaining TKA because it reduces the paradoxical medial femoral condylar movement.