Comparison of Revision Unicompartmental Knee Arthroplasty to Primary and Revision Total Knee Arthroplasty: A Gradient of Complexity

Unicompartmental knee arthroplasties (UKAs) are often revised to total knee arthroplasty (TKA), but concerns remain surrounding revision rates and perioperative outcomes of UKA revision to TKA. The primary aim of this study was to compare revision rates of UKA revision to TKA to matched cohorts of both primary and revision TKA procedures. Secondary aims were to compare the intraoperative outcomes, implants characteristics, and functional outcomes. This was a single centre cohort study of all consecutive patients who underwent UKA revision to TKA from 2012 to 2023. Patients undergoing elective revision of UKA to TKA with minimum one year follow-up were included and matched 1:1:1 to patients undergoing primary TKA and first-time aseptic revision TKA. Demographic data, indications for surgery, surgical details, and postoperative outcomes, including revision rates, complications, WOMAC scores and range of motion (ROM), were collected and compared between groups. Differences in continuous data were assessed using unpaired Students t-test and categorical data using Pearson's Chi-squared test or Fisher's exact test where applicable. When comparing differences in continuous outcomes between the three procedure groups, one-way analysis of variance (ANOVA) with post hoc Tukey HSD test was utilized. Kaplan-Meier survival analysis with log-rank test was performed for complications requiring reoperation. Statistical significance for all analyses was set at α=0.05. Exactly 100 patients were identified that underwent a revision of a UKA to TKA during the study period, that were matched to primary and revision TKAs (total n=300). No significant difference was found in revision rates between UKA to TKA and revision TKA groups, though reoperation rates were higher for UKA revision compared to primary TKA (p=0.005) (Table 1). UKA revision to TKA cases had longer operative times (103.0min vs. 72.7min, p There was no difference in level of polyethylene bearing constraint between primary and revision UKA to TKA cases, however, revision TKA cases more commonly required constrained condylar knee level constraint. UKA revision to TKA demonstrated ROM similar to primary TKA and superior to revision TKA (p=0.05). The conversion of a UKA to a TKA is more complex than performing a primary TKA but less so than a revision TKA. Patients should be warned that these cases have higher revision and reoperation rates than primary TKAs, however, functional outcomes at 1-year and range of motion are similar to primary TKA. Typically, a standard posterior-stabilized implant can be utilized for this conversion, however, surgeons should be prepared that these cases often require stems and augments on the tibial side. For any figures or tables, please contact the authors directly.