Comparable clinical outcomes but different postoperative Dynamic Alignment of the Knee (DyAK) patterns between cruciate‐retaining and posterior‐stabilized inserts in functionally aligned robotic‐assisted total knee arthroplasty
Christos Koutserimpas, Enejd Veizi, Sébastien Lustig, Konstantinos DretakisAbstract
Purpose
The influence of polyethylene insert design during robotic‐assisted total knee arthroplasty (TKA) performed according to functional alignment (FA) principles remains poorly understood. This study compared cruciate‐retaining (CR) and posterior‐stabilized (PS) inserts with respect to implant positioning, clinical outcomes, implant survivorship and postoperative dynamic knee behaviour using the Dynamic Alignment of the Knee (DyAK) classification.
Methods
A retrospective comparative study was performed on 284 primary functionally aligned robotic‐assisted TKAs. The cohort comprised 148 CR and 136 PS fixed‐bearing cemented implants with a minimum follow‐up of 3 years (median 44.5 months). Clinical outcomes included Knee Society Score (KSS) and Forgotten Joint Score (FJS). Intraoperative robotic implant positioning, bone resections, polyethylene thickness, DyAK classification, complications and Kaplan–Meier implant survivorship were compared between groups.
Results
The CR group demonstrated greater preoperative varus alignment (median robotic hip–knee–ankle angle [rHKA] 5° vs. 3°, p = 0.01). Compared with PS implants, CR inserts were implanted with greater tibial varus (2° vs. 1°, p < 0.0001), greater posterior tibial slope (3° vs. 1°, p < 0.0001) and slightly greater femoral external rotation ( p = 0.009). Polyethylene inserts >9 mm were required more frequently in the PS group (39.0% vs. 15.5%, p < 0.0001). At final follow‐up, KSS knee ( p = 0.56), KSS function ( p = 0.62) and FJS ( p = 0.06) were comparable between groups. No statistically significant difference in survivorship was detected for aseptic loosening (0.68% vs. 0.74%, p = 0.95) and all‐cause revision (2.03% vs. 1.47%, p = 0.72). The DyAK classification changed significantly more frequently in the PS group than in the CR group (69.9% vs. 52.7%, p = 0.003), despite similar postoperative clinical outcomes.
Conclusion
CR and PS polyethylene inserts showed no significant differences in final clinical scores or implant survivorship at a minimum follow‐up of 3 years but demonstrated different patterns of postoperative dynamic alignment, suggesting that the DyAK classification may provide complementary information beyond conventional outcome measures.
Level of Evidence
Level III.