Unrestricted kinematic alignment on the sagittal plane: Posterior tibial slope and combined flexion do not have boundaries to respect in terms of short-term clinical outcomes and safety.

Abstract

Personalized alignment in total knee arthroplasty (TKA) is gaining traction as a surgical philosophy. True personalization, however, must encompass not only the coronal plane but also the sagittal and axial planes. This study evaluates influence of the Tibial Slope (PTS) and combined flexion (CF) on outcomes in TKA performed using unrestricted kinematic alignment (KA). The aim of the study was to examine the relationship between PTS or CF and both functional outcomes and complication rates. A retrospective review was conducted on 137 patients who underwent primary TKA using KA between November 2022 and June 2023. CF was calculated by combining PTS and DFF values. Patients were categorized into groups based on CF angle (≤7.5° vs. >7.5°) and PTS (<5, between 5 and 10, >10). Clinical outcome measures (KSS, OKS, SF12 and FJS), radiographic alignment parameters and complication rates were analyzed. There were no statistically significant differences between groups regarding implant survivorship, revision rates, mechanical failure, or clinical outcome scores. CF or PTS did not correlate with postoperative coronal alignment parameters or with patient-reported outcome measures (PROMs). Additionally, the change in clinical scores from preoperative to postoperative assessments did not differ significantly between groups, indicating comparable clinical improvement regardless of CF or PTS. The findings suggest that restoration of native femoral and tibial flexion within a kinematic alignment does not adversely affect outcomes or increase complication rates, providing similar clinical benefits regardless the prearthritic CF or tibial slope of the patients, supporting the short-term safety of this "unrestricted" approach in the sagittal plane. Level IV.