Postoperative Coronal Plane Alignment of the Knee (CPAK) Analysis Following Planned Mechanical Alignment: A Comparison of Manual, Computer-Navigated, and Robotic-Assisted Total Knee Arthroplasty.

INTRODUCTION: The coronal plane alignment of the knee (CPAK) classification provides an objective framework for describing coronal alignment in total knee arthroplasty (TKA). Mechanical alignment (MA) traditionally aims to achieve CPAK Type V, defined by neutral arithmetic hip-knee-ankle angle (aHKA) and neutral joint line obliquity (JLO). However, inconsistency in achieving this target has been reported, and the clinical value of postoperative neutral alignment remains uncertain. This study sought to (1) characterize the postoperative distribution of CPAK phenotypes following MA-TKA across three surgical technologies and (2) determine whether achieving MA targets is associated with improved outcomes. METHODS: A retrospective review was performed of 636 primary TKAs conducted at a single high-volume institution. All procedures followed an MA strategy using manual instrumentation, computer navigation, or robotic-assisted (RA) techniques. Full-length standing radiographs were analyzed to determine preoperative and postoperative CPAK phenotypes. Patient-reported outcomes were assessed preoperatively and at two years. Alignment targets were defined as CPAK Type V, neutral JLO, and neutral aHKA. Multivariable logistic regression analyses identified predictors of achieving alignment targets and evaluated whether alignment achievement independently increased the odds of attaining clinically meaningful outcome thresholds. RESULTS: The postoperative CPAK distribution was significantly different between the three techniques, with multivariable regression analysis outlining RA as a significant positive predictor for achieving both neutral JLO (OR [odds ratio] 4.3, P < 0.001) and CPAK Type V alignment (OR 2.3, P < 0.001). Achieving the neutral targets conferred no significant advantage in clinical outcome. Regression analyses confirmed that none of the alignment targets independently increased the odds of meeting clinical thresholds (P > 0.26). CONCLUSION: Despite the same alignment philosophy, postoperative CPAK phenotype distribution varies significantly by surgical technology, underscoring the value of an objective alignment classification. However, achieving postoperative neutral alignment was not associated with improved outcomes in this cohort.