How reliable are surgeons at assessing soft-tissue laxities in robotic arm-assisted total knee arthroplasty?

Aims: Regardless of one's alignment philosophy and belief in ligament releases, the precise estimation of soft-tissue laxities is crucial in total knee arthroplasty (TKA). This study prospectively assessed the reliability of surgeons' and assistants' measurements of ligament tension during robotic arm-assisted TKA. Methods: A prospective, surgeon-blinded study was performed in 123 patients undergoing TKA by six surgeon/assistant pairs. Ligament tensions were captured using manual stress and instrumented distraction techniques for four gaps: medial extension, lateral extension, medial flexion, and lateral flexion. Assessors were blinded during gap measurements. The primary outcome was intrarater and inter-rater reliability using intraclass correlation coefficients (ICCs). Secondary outcomes were the reliability of manual compared with instrumented distraction measures and comparison of planned pre-resection virtual gaps against actual post-implantation laxities. Results: The intrarater mean ICC for surgeons' measurements of gap laxities was 0.95 (0.90 to 0.97) and 0.94 (0.91 to 0.96) for assistants' measurements. These results indicate excellent reliability for all four gaps for both surgeons and assistants. For inter-rater reliability, both extension gaps returned an ICC > 0.90, indicating excellent reliability between surgeons and assistants. Lateral flexion ICC was 0.75 and medial flexion 0.86, indicating good reliability. Comparing manual with instrumented distraction techniques, the mean ICC was 0.72, indicating moderate reliability (0.55 to 0.88). The mean difference between planned and final gap measures was 0.5 mm (-1.5 to 3.0, SD 0.71). Conclusion: Surgeons' ability to assess knee laxities using manual stressing during robotic arm-assisted TKA has excellent intrarater and good-to-excellent inter-rater reliability. Distraction values for the medial side were more reliable than the lateral side, where constitutional laxity and the technical challenge of assessment may increase variability. High reliability of manual stressed gap assessment in robotic arm-assisted TKA should give surgeons confidence in using this information for measuring and achieving soft-tissue balance.