Flexion-dependent differences in tibial rotation measured by navigation and robotic systems during bicruciate-stabilised total knee arthroplasty.

Abstract

This study compared the intraoperative tibial rotational kinematics between navigation-assisted and robotic-assisted bicruciate-stabilised total knee arthroplasty (BCS-TKA). Although both systems can evaluate knee motion intraoperatively, it is unclear whether they provide comparable rotational measurements. We hypothesised that these systems would show different tibial rotation profiles, particularly in deep knee flexion. This retrospective cohort study included 238 knees that underwent BCS-TKA using an image-free navigation system (Precision N) or an image-free handheld robotic-assisted system (NAVIO or CORI). Tibial rotation relative to the femur was measured intraoperatively through 0° to 120° of knee flexion. Patient-reported outcomes were assessed using the 2011 Knee Society Score (KSS). Discrepancies in rotational display between the systems were evaluated by a preliminary bench test using a synthetic bone model. Groups were compared using the Kruskal-Wallis test followed by Dunn's post hoc test with Bonferroni correction. Across all groups, BCS-TKA demonstrated a characteristic pattern of internal rotation in early flexion, slight external rotation in mid-flexion and progressive internal rotation towards deep flexion. At 120° of flexion, tibial internal rotation differed significantly among the three groups (<i>p</i> < 0.05), with the navigation system displaying greater internal rotation than the robotic system, particularly NAVIO (<i>p</i> < 0.01). The robotic system displayed a progressively more externally rotated tibial position beyond 40° of flexion in the bench test. The subjective domains of the KSS improved significantly in all groups at 1 year. Although statistically significant between-group differences were observed in some domains, these differences were inconsistent, and their clinical relevance remains unclear. The robotic platform consistently indicated a more externally rotated tibial position compared to the navigation system, suggesting that the two systems apply different reference orientations for tibial rotation in deep knee flexion during BCS-TKA. Therefore, caution is warranted when comparing intraoperative kinematic data across measurement platforms. Level III, retrospective cohort study.