Two-Year Outcome Comparison of a Matched Set of Total Knee Arthroplasties Performed With Robotic-Arm-Assisted Functional Alignment Balancing or Manual Instrument-Assisted Adjusted Mechanical Alignment.

Abstract

Alternative strategies in total knee arthroplasties (TKAs) have been developed to obtain improved outcomes utilizing implant realignment and positioning to balance the soft tissues while accepting a nonneutral mechanical alignment. The purpose of our study was to compare 2-year outcomes of a matched set of TKAs with soft-tissue gaps either "functional" balanced via robotic-arm-assisted changes to implant position and alignment prior to bone cuts (R-TKA) or manual instrument-adjusted mechanical alignment (M-TKA). We hypothesized that the R-TKA cohort would have superior patient outcomes. A consecutive series of 210 TKAs matched 2:1 by selecting patients in each cohort with no statistically significant preoperative differences in sex, age, American Society of Anesthesiologist physical status classification system score, Knee Society knee scores (KS-KS) and Knee Society function scores (KS-FS), range of flexion (ROF), and knee coronal alignment. There were 140 R-TKA and 70 M-TKA with the same implants that were reviewed. Tibial pressure sensors were used in all cases to verify balance. Postoperative KS-KS, KS-FS, and ROF were compared at 3 months and 2 years, and Forgotten Joint Scores (FJS) were obtained at 2 years. Both groups achieved equivalent quantitative balance with the pressure sensors. The functional alignment-balanced R-TKA cohort had more component realignments (100 versus 35.7%), fewer soft-tissue releases (40 versus 61.4%), and statistically significant higher mean KS-KS, KS-FS, and ROF at 3 months and 2 years than the M-TKA group. The mean FJS was higher in the R-TKA group (66.3 versus 60.4), but this did not represent a statistical significance. A functional alignment balancing technique using robotic-arm assistance resulted in fewer soft-tissue releases and higher Knee Society outcome scores and knee flexion than with M-TKA at 3 months and 2 years, despite equivalent soft-tissue balance per the pressure sensors. The mean FJS at 2 years was greater, but not statistically significant.