Dynamic Alignment of the Knee (DyAK) Classification: Advancing Knee Evaluation in Robotic Arthroplasty.

Abstract

Total knee arthroplasty (TKA) has moved toward a more personalized approach, but achieving the ideal coronal alignment is still challenging, as most knees naturally change alignment throughout the range of motion. This study introduced the dynamic alignment of the knee (DyAK) classification, based on robotic hip-knee-ankle measurements in extension (rHKA-E) and flexion (rHKA-90F), and evaluated the clinical impact of changes in DyAK type. This study analyzed 350 patients who underwent robotic TKA using functional alignment principles. The DyAK classification matrix included nine knee phenotypes, with neutral defined as -3 (varus) to 3° (valgus) in rHKA-E and rHKA-90F, respectively. Initial (precut) and final (postimplantation) DyAK types were compared to assess variations in dynamic coronal alignment and their clinical impact, Knee Society Score knee and function, Forgotten Joint Score-12, and Kujala Anterior Knee Pain Scale. Regarding the initial DyAK, type D1 was the most prevalent (58.3%), followed by type D2 (15.1%) and type D4 (9.2%). After implant placement, in the final DyAK, the distribution shifted, with type D5 becoming the most common (46.0%), while type D1 decreased to 26.9% and type D4 increased to 13.1%. Overall, 56.9% of patients experienced a change in DyAK type following TKA. Among them, 32.9% showed a modification in either rHKA-E or rHKA-90F, while 24.0% exhibited changes in both parameters. A statistically and clinically significant difference in the change in Knee Society Score knee was found, with better outcomes in patients who maintained their DyAK type compared with those who showed modifications in both rHKA-E and rHKA-90F (P = 0.004). Dynamic alignment of the knee is a clear, practical, and accurate classification. Integrating DyAK into clinical practice could be a step forward in the personalization of TKA, helping to optimize functional outcomes and improve the understanding of the dynamic nature of the joint. Level III.