Does Robotic Assistance Improve Restoration of Coronal Plane Alignment of the Knee in Kinematically Aligned Total Knee Arthroplasty? A Comparative Alignment Study

Abstract

To compare Coronal Plane Alignment of the Knee (CPAK) phenotype restoration and component alignment accuracy between robotic-assisted and conventional calipered kinematically aligned total knee arthroplasty (KA-TKA). A retrospective comparative study of 319 primary KA-TKAs (127 robotic, 192 conventional) performed between 2020 and 2024 was conducted. Pre- and six-week postoperative weight-bearing long-leg radiographs were used to determine arithmetic hip–knee–ankle angle (aHKA), joint-line obliquity (JLO), and CPAK phenotype. CPAK transitions were classified as restoration, aHKA-driven change, JLO-driven change, or non-favorable shift. Alignment accuracy of the femoral component (lateral distal femoral angle, LDFA) and tibial component (medial proximal tibial angle, MPTA) within ±3° of the target was compared. Baseline characteristics were comparable between groups, apart from slightly higher age in the robotic cohort. CPAK restoration rates were similar (52.6% vs 52.8%, p = 1.000). aHKA-driven changes occurred in 30.2% versus 22.0% ( p = 0.447), while JLO-driven changes were less frequent in the robotic group (15.1% vs 24.4%, p = 0.053). Robotic assistance improved tibial alignment accuracy (80.3% vs 68.2%, p = 0.024), whereas femoral alignment accuracy was similar (85.0% vs 83.9%, p = 0.898). Robotic KA-TKA improved tibial alignment precision and reduced joint-line obliquity deviation but did not increase CPAK phenotype restoration compared with conventional KA-TKA. These findings suggest that coronal phenotype preservation depends on combined femoral–tibial alignment rather than isolated component accuracy.