Augmented reality navigation improves intraoperative resection accuracy but may not prevent alignment deviations in total knee arthroplasty.

Purpose: The purpose was to compare intraoperative versus postoperative coronal, sagittal and axial alignment in total knee arthroplasty (TKA) performed using augmented reality (AR) navigation, and determine whether imperfect implant positioning affects postoperative alignment. Methods: A retrospective assessment was conducted on a study cohort of 70 patients (70 knees), who received unrestricted kinematic aligned TKA using AR navigation between February 2022 and April 2023. Implant positioning was assessed on postoperative frontal (divergence between the proximal tibial resection and baseplate) and sagittal radiographs (gaps between the distal femoral resection and implant) to distinguish between knees with adequate and imperfect implant positioning. The deviation between intraoperative and postoperative alignment measurements (lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), hip knee ankle angle (HKA), posterior tibial slope (PTS) and femoral rotation) was assessed, and the number of outliers calculated using thresholds of 1° and 3°. Results: There were considerable proportions of knees with deviations between intraoperative and postoperative LDFA (>1°, 43 [61%]; >3°,14 [20%]), MPTA (>1°, 42 [60%]; >3°, 5 [7%]), HKA angle (>1°, 42 [60%]; >3°, 17 [24%]), and PTS (>1°, 47 [67%]; >3°, 15 [21%]). It is worth noting, however, that most of the relevant deviations were observed in knees that had imperfectly positioned implants (19 of 70, 27%), where the femoral component was inadequately impacted during surgery (15 of 19, 79%) and/or the tibial baseplate had an uneven cement distribution (8 of 19, 42%). Conclusion: The use of AR facilitates precise bone resections during TKA, yet it may not reduce deviations between intraoperative and postoperative LDFA, MPTA, HKA angle or PTS. As with any assistive technology, accurate bone resections alone are not sufficient to grant adequate implant positioning during TKA, which requires meticulous attention from surgeons to ensure sufficient component impaction and uniform cement distributions. Level of Evidence: IV.