An investigation into whether changes in the posterior tibial slope affect the outcome of cruciate-retaining total knee arthroplasty by affecting tibiofemoral articular contact kinematics

AIMS: The outcomes of total knee arthroplasty (TKA) are affected by many factors. This study aims to evaluate whether changes in the posterior tibial slope (PTS) affect patients’ outcomes after cruciate-retaining TKA by affecting tibiofemoral articular contact kinematics. It was hypothesized that changes in PTS affect the outcomes of PCR TKA by affecting tibiofemoral articular contact kinematics. METHODS: A total of 60 knees (30 patients) that underwent posterior cruciate-retaining TKA (with the same size prosthesis) for medial osteoarthritis were assessed preoperatively and one year postoperatively. Before and after TKA, changes in the PTS, as seen on lateral radiographs, were noted. The knees were placed in groups according to these PTS changes (preoperative value − postoperative value): group 1 >3° change and group 2 ≤3° change. Knee kinematics were observed under mid-flexion weight-bearing conditions and were compared between the two groups using the two-dimensional/three-dimensional registration technique. Pain was measured using the visual analog scale, and knee function was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Knee Society Score (KSS). RESULTS: Group 2 experienced paradoxical anterior motion of the medial femoral condyle postoperatively, but group 1 did not. A comparison of the results of the TKA between the two groups showed a significant difference in pain using the visual analog scale, and knee function of the KSS and the WOMAC (P < 0.05). The postoperative results were better in group 1 than in group 2. CONCLUSIONS: These results suggest that achieving a greater change in the PTS improves outcomes in patients undergoing posterior cruciate-retaining TKA because it reduces the paradoxical motion of the medial femoral condyle.