DOES ROBOTIC-ASSISTED SURGERY OR FUNCTIONAL ALIGNMENT IMPROVE INTRAOPERATIVE BALANCE IN TOTAL KNEE ARTHROPLASTY? A SECONDARY ANALYSIS OF THE RASKAL TRIAL

Abstract Background This study assessed rates of imbalance in total knee arthroplasty (TKA) and its effect on patient-reported outcome measures (PROMs), comparing robotic-assisted surgery (RAS) versus computer-assisted surgery (CAS), and functional alignment (FA) versus mechanical alignment (MA). Methods A pre-specified secondary analysis of the RASKAL trial was performed in 303 patients randomized to RAS or CAS, and FA or MA. Intraoperative compartment loads were measured using a sensor matching the thickness as the final articular insert after any soft-tissue releases. Surgeons were blinded to sensor readings. The primary outcomes included the proportion of TKAs with minor imbalance (intercompartmental (ICPD) 15–40lb) and major imbalance (ICPD>40lb); the frequency of absolute compartmental loads >60lb at any flexion angle; and the proportion of cases with condylar lift-off. Secondary outcomes assessed the effect of imbalance on PROMs from baseline at 3, 6, 12 months and at 2 years. Results The proportion of TKAs with minor or major imbalance was similar comparing RAS versus CAS, and FA versus MA at 10° and 90°, and across factorial groups. At 45° of flexion, a higher proportion of knees had minor imbalance with CAS compared to RAS (39.3% vs 24.8% respectively; p=0.015). There were no differences between groups in the proportion of TKAs with compartment load >60lb, or in the incidence of condylar lift-off. Furthermore, there were no differences in KOOS-12, Oxford Knee Score, Forgotten Joint Score, EQ-5D-5L, or VAS pain between knees with minor and major imbalance at any timepoint. Conclusions This study provides robust evidence that use of robotic-assisted technology does not significantly improve intraoperative balance in TKA compared to computer-assisted surgery, despite it delivering modest improvements in mid-flexion balance. While achieving balance is considered a key objective in TKA, neither imbalance nor condylar lift-off was associated with differences in patient-reported outcomes.