Agreement of Coronal Limb Alignment Measures in Total Knee Arthroplasty: Comparative Analysis of Radiographic and Robotic Measurement in a Retrospective Cohort

Abstract

Introduction One modality within the surgeon’s armamentarium to ameliorate poor surgical outcomes through improved technical performance is robotic-assisted TKA (rTKA) and no study has explored the agreement of the intraoperative alignment obtained by the robot and preoperative radiographic measurement. The purpose of this study is a comparative analysis of knee coronal limb alignment between preoperative standing-alignment measurements and intraoperative imageless robot calculations. Methods Between December 2021 and December 2022, surgeon data were prospectively collected and retrospectively reviewed for all surgical cases that underwent surgery by a single adult reconstruction fellowship-trained surgeon (XXX). Inclusion criteria included (1) primary TKA and (2) a robotically- assisted TKA. Cases were excluded (1) if prospectively assessed radiographic measurements were not recorded and (2) if robotic data corruption occurred. All radiographic measurements were assessed by the senior surgeon during standard preoperative planning. All patients underwent a standardized intra-operative alignment assessment by the senior surgeon as part of the intraoperative robotic workflow. Bland–Altman (BA) plots and Limits of Agreement (LoA) analyses were utilized for comparative analysis. Clinical significance was defined as a maximum allowed difference (MAD) set to 3 degrees, which implied that a LoA > MAD would indicate a clinically significant difference exists and measurements are not in agreement. Alpha values of P<0.05 were considered statistically significant, and 95% confidence intervals (95CI) were reported for precision estimate. Results There were 258 consecutive surgical cases that met the criteria for this descriptive comparative analysis, and 212 (85%) patients had complete data available for analysis. There was a -2.3-degree median difference (95CI -3.6 to -0.9) in alignment as calculated by the robot relative to radiographic measurement. The robot calculation systematically underestimated alignment with a -33.56% (95CI 26.32-40.80) difference, which increased in magnitude with increased variability as demonstrated by -0.23 (95CI -1.96-1.50) slope. BA plot demonstrated a 26.14% (95CI 17.92 34.37) difference for the valgus cohort and 0.07 (95CI -2.07-2.20) slope, whereas the varus cohort demonstrated a 49.6% (95CI 35.5-63.7) difference and 1.44 (95CI -1.5-4.4) slope. Conclusion We found a clinically significant difference necessitates surgeons to be cognizant of the increased uncertainty imposed by the measurement bias for optimal surgical decision-making. Given, standing full length weightbearing radiographs represent 2D alignment of a 3D deformity proven to have known measurement bias and intra-operative robotic data also presents with some degree of measurement bias as shown by our results, coronal limb alignment measurements obtained intraoperative should be interpreted with caution, and measurement bias is a multifactorial problem that will negatively impact decision quality.