Morphotype analysis and intraoperative range of motion in robotic-assisted functional alignment total knee arthroplasty

Background: The adoption of functional alignment strategies in total knee arthroplasty (TKA), often combined with robotic assistance, has increased markedly in recent years. However, perioperative functional outcomes and alignment phenotype distributions remain poorly characterized. Methods: We analyzed intraoperative parameters from 462 robotic-assisted TKA procedures performed by a single surgeon beyond the robotic learning curve. Parameters were captured directly from the robotic platform at key surgical stages: pre- and postbone resection, component placement, ligamentous releases, and soft tissue balancing. Measurements of knee flexion, extension, and hip-knee-ankle (HKA) angle were evaluated to assess dynamic changes throughout surgery. Results: Range of motion was measured intraoperatively using the robotic platform and measurements were obtained against gravity. Mean knee flexion improved significantly from 130.8° to 135.8° after alignment and component positioning ( P <0.001). Mean knee extension improved from 4.2° to −1.3° postoperatively ( P <0.001). Mean HKA returned closer to neutral, shifting from −4.9° preoperatively to −1.74° postoperatively ( P <0.001). Preoperatively, 68.4% of knees demonstrated varus malalignment (HKA ≤ −3°), 19.5% were neutral (HKA −3 to 3°), and 12.1% showed valgus malignment (HKA ≥ 3°). Postoperatively, 41.3% remained varus (HKA ≤ −3°), 56.9% achieved neutral alignment (HKA −3 to 3°), and 1.7% were valgus (HKA ≥ 3°). Shifts in phenotype distributions were significant across all categories ( P <0.001). Conclusions: Functional alignment in robotic-assisted TKA improved intraoperative flexion, extension, and coronal alignment across diverse knee morphotypes. These findings support the use of computer-navigated robotic-assisted devices as an effective platform for achieving functional TKA outcomes.