Optimising outcomes in lateral unicompartmental knee arthroplasty: Analysing 25 years of registry data

PURPOSE: Limited data and experience surround lateral unicompartmental knee arthroplasty (UKA), contributing to uncertainty regarding its broader application in clinical practice. To understand how to optimise lateral UKA outcomes, this study aimed to evaluate the implant survival of lateral UKA and compare it to total knee arthroplasty (TKA) using registry data.

METHODS: Data were obtained from the Danish Knee Arthroplasty Registry, the Danish National Patient Registry and the Danish Civil Registration System. Between 1997 and 2022, all primary lateral UKAs (n = 538) and primary TKAs performed on valgus-aligned knees were included. Propensity score matching (1:4) matched patients by age, sex, weight, Charlson comorbidity index, year of surgery and hospital type. Survival analysis used the Fine-Gray subdistribution hazards model to account for competing risks.

RESULTS: The 5-year cumulative revision risk was 10.1% for lateral UKA and 5.0% for TKA (1997-2022). For lateral UKA, this decreased from 25.0% (1997-2006) to 7.3% (2017-2022); TKA decreased from 4.6% to 3.7%. Surgery after 2011 and use of the fixed lateral Oxford (FLO) implant significantly reduced the risk of revision. Compared to TKA, the subdistribution hazard ratio for revision was 0.7 (95% confidence interval [CI] = 0.2-2.2) for the FLO implant and 3.4 (95% CI = 1.9-6.1) for other lateral UKAs in the period 2017-2022. No differences were found in 90-day readmissions or complications between lateral UKA and TKA, but the 2-year reoperation rate was significantly lower for lateral UKA in both periods.

CONCLUSION: Lateral UKA survival has evolved with improved understanding of knee compartment biomechanics, indications, surgical techniques and implant designs. Lateral UKA with the FLO implant showed lower or similar revision rates compared with TKA.

LEVEL OF EVIDENCE: Level III.