Summary

Discrepancies Between Intraoperative Robotic-Assisted and Postoperative Radiographic Mechanical Axis Measurements in Total Knee Arthroplasty

Abstract

Introduction

The use of robotic assistance (RA) in total knee replacement (TKR) surgery has seen a progressive increase in recent years. Its utilization has been associated with improved soft tissue balance, reduced hospital stay, and decreased surgical outliers. Additionally, it may enhance the accuracy of component alignment, although the evidence on this point remains controversial.

Objective

The purpose of this study is to compare the correlation between the intraoperative mechanical axis calculated during imageless robotic-assisted knee replacement surgeries using the CORI Surgical System (Smith & Nephew, Memphis, Tennessee) and the mechanical axis assessed in postoperative weight-bearing long-leg radiographs of the same patients.

Methods

A cross-sectional observational imaging study was conducted at a single center involving patients over 18 years old who underwent imageless robotic-assisted TKR surgery between April and July 2023. Demographic data were collected from clinical records. The intraoperative lower limb mechanical axis achieved, as reported by the RA after TKR implantation, was recorded. Two orthopedic surgeons, specialized in knee surgery (evaluators 1 and 2), independently and blindly determined the mechanical axis on postoperative full-length standing radiographs taken between the first and third months post-surgery. A blinded third evaluator analyzed the results, determining the intraclass correlation coefficient (ICC) for absolute agreement using a two-way random effects model for the mean between the RA-reported axis and each evaluator, as well as analysis of variance (ANOVA). A post hoc Tukey test was performed to assess any differences between the three measurements. A p-value < 0.05 was considered statistically significant.

Results

A total of 21 robotic-assisted knee arthroplasties were included, with 12 females (57.1%) and 9 right knees (42.9%). The average lower limb mechanical axis reported by the robotic assistance (RA) was 0.52° of varus (SD 3.12°), while the average mechanical axis on the postoperative full-leg radiographs was 0.45° of valgus (SD 3.03°) for evaluator 1 and 0.88° of valgus (SD 2.98°) for evaluator 2, respectively. The ICC between the RA and evaluator 1 was 0.49 (95% CI 0.12-0.76), indicating poor correlation; between the RA and evaluator 2, it was 0.61 (95% CI 0.27-0.82), considered a moderate correlation; and between evaluators 1 and 2, it was 0.94 (95% CI 0.85-0.97), considered an excellent correlation. No statistically significant differences were found between the average measured mechanical axis of evaluators 1 and 2 (p = 0.89), but statistically significant differences were found between the average measured mechanical axis of the RA and evaluator 1 (p = 0.0025), as well as between the RA and evaluator 2 (p = 0.0005).

Conclusions

The intraoperative mechanical axis reported by imageless RA in TKR within this cohort shows only a poor to moderate correlation with the actual mechanical axis measured in postoperative weight-bearing long-leg radiographs of the same patients, with statistically significant differences observed in the average mechanical axes. Future prospective studies with a larger number of patients are needed to confirm these findings.