A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty

Background: To compare posterior tibial slope (PTS) and incidence of excessive PTS between cruciate-retaining (CR) total knee arthroplasties (TKAs) with the current prosthesis, providing a 1-mm increment of polyethylene insert thickness, and its predecessor, providing a 2-mm increment. Methods: Each of 154 CR TKAs with Persona (current group) and NexGen (predecessor group) prostheses with a minimum follow-up period of 2 years were retrospectively reviewed. Preoperative demographics, including age, sex, and body mass index, were similar. Factors affecting the flexion gap were matched in terms of preoperative range of motion, mechanical axis, PTS, preoperative and postoperative posterior femoral offset (PFO), and PFO ratio. The PTS was evaluated radiographically. The incidence of excessive PTS (PTS > 10°) and the frequency of intraoperative PTS-increasing procedures were investigated. Results: There were no significant differences in preoperative and postoperative range of motion, mechanical axis, PFO, and PFO ratios between the 2 groups. The preoperative PTS was not significantly different, but the postoperative PTS was significantly lower in the current group (4.6° vs 6.2°, P < .001). There was no case of excessive PTS in the current group, but there were 9 cases (5.8%) in the predecessor group (P = .030). The intraoperative PTS-increasing procedure was performed more frequently in the predecessor group (12.3% vs 21.4%, P = .047). Conclusion: The current prosthesis providing a 1-mm increment of polyethylene insert thickness could decrease the PTS and the occurrence of excessive PTS in CR TKA. The target angle for PTS can be decreased in TKA using the current prosthesis in comparison with its predecessor. Level of Evidence: III.