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

The purpose of this study was to retrospectively examine the relationship between preoperative and postoperative alignment in robotic unicompartmental knee arthroplasty (UKA) and postoperative patient-reported outcome measures.

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.

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).

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.