Improved Posterior Slope of the Tibial Component in Unicompartmental Knee Arthroplasty Using an Offset Adjustment Method

Abstract Achieving a consistent patient-specific posterior tibial slope (PTS) in unicompartmental knee arthroplasty (UKA) is critical. Current methods lack standardization, and the influence of offset adjustments on PTS reproducibility in UKA has not been studied. This study aimed to investigate the reproducibility of patient-specific PTS using a jig that adjusts the offset of the proximal and distal tibial rods in UKA. Sixty-four knees underwent UKA with the offset adjustment jig, and 64 served as controls. Preoperative and postoperative PTS were measured on lateral knee radiographs. Statistical analyses compared changes in PTS and outliers between groups. The offset adjustment group showed a moderate correlation (R = 0.53, p < 0.001) between preoperative and postoperative PTS, compared to a weak correlation (R = 0.32, p = 0.009) in the control group. The absolute PTS change was statistically significantly smaller in the offset adjustment group (1.2 degrees vs. 1.9 degrees, p = 0.009). Fewer outliers with PTS changes of 2 degrees or more were observed in the offset adjustment group. Using an offset adjustment jig in UKA significantly improves the reproducibility of patient-specific PTS, reducing deviations and potential biomechanical issues. This method is practical, cost-effective, and compatible with various implant models, offering a reliable solution for achieving precise PTS alignment without extending surgical time.