Impact of Alignment and Alignment Correction on Outcomes Following Robotic Medial Unicompartmental Knee Arthroplasty

Background: The purpose of this study was to retrospectively examine the relationship between pre-operative and postoperative alignment in robotic unicompartmental knee arthroplasty (UKA) and postoperative patient-reported outcome measures.Methods: A retrospective review of 374 patients who underwent robotic-assisted UKA was conducted. Patient demographics, history, and preoperative and postoperative Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) scores were obtained via chart review. Average follow-up period was 2.4 years (range: 0.4 to 4.5 years) to chart review and 9.5 months (range: 6 to 48 months) to latest KOOS-JR. Preoperative and postoperative robotically-measured knee alignment was obtained from operative reports. Incidence of conversion to total knee arthroplasty (TKA) was determined by review of a health information exchange tool.Results: Multivariate regressions showed no statistically significant relationship between preoperative alignment, postoperative alignment, or degrees of alignment correction and change in KOOS-JR score or achievement of KOOS-JR minimal clinically important difference (MCID) (P > .05). Patients who had >8 degrees of postoperative varus alignment had on average a 20% lower achievement of KOOS-JR MCID compared to patients who had <8 degrees of postoperative varus alignment; however, this difference was not statistically significant (P > .05). There were 3 patients who required conversion to TKA in the follow-up period, with no significant relationship to alignment variables (P > .05).Conclusion: There was no significant difference in KOOS-JR change for those patients who had a larger or smaller degree of deformity correction, and correction did not predict MCID achievement.