Robotic-assisted restricted kinematic alignment in total knee arthroplasty: A multicenter retrospective assessment of coronal phenotypes and early postoperative outcomes.

Abstract

The Coronal Plane Alignment of the Knee (CPAK) classification enables phenotype-based total knee arthroplasty (TKA), but its application in robotic-assisted TKA (RATKA) remains underexplored. We aim to describe the distribution of CPAK phenotypes in patients undergoing RATKA using a restricted kinematic alignment (rKA) protocol, evaluate alignment correction within rKA boundaries and report early postoperative functional outcomes. We hypothesized that RATKA would achieve alignment targets within the rKA range while demonstrating expected postoperative functional recovery. This multicenter retrospective study included 200 patients with primary knee osteoarthritis between June and November 2024 at five high-volume centres. All procedures followed a rKA protocol, with target correction within ±3° of constitutional alignment. CPAK distribution, demographic variations, achieved alignment and early postoperative functional outcomes measured by the Knee Injury and Osteoarthritis Outcome Score (KOOS) and Forgotten Joint Score (FJS) were analysed. The cohort (mean age 62.9 years; 60.5% female) showed preoperative arithmetic hip-knee-ankle angle of -5.8° ± 4.6° and joint line obliquity of 173.2° ± 4.1°, predominantly varus (71.5% Type I). Type I alignment was more frequent in males (73.4%), females (70.2%) and those aged >61 years. Of the 71.5% CPAK Type I, 63.5% remained Type I with correction within 0° ± 3°, while 8% were corrected to Type II. All achieved alignment within rKA limits (mean postoperative hip-knee-ankle 173.0° ± 3.2°). Mean postoperative lateral distal femoral angle and medial proximal tibial angle were 85.1° and 87.7°, respectively. Significant improvements were observed in KOOS (80.9 ± 2.3 vs. 40.6 ± 3.5, <i>p</i> < 0.05) and FJS (75.9 ± 1.4 vs. 49.8 ± 1.3, <i>p</i> < 0.05) at 6 months. No early revisions occurred. RATKA performed with a rKA strategy, achieved postoperative alignment within planned rKA limits across CPAK phenotypes. Early functional outcomes at 6 months were satisfactory and consistent with expected postoperative recovery following TKA; however, in the absence of a comparator group, these improvements cannot be attributed solely to the robotic platform or alignment strategy. Level II, retrospective study.