Determinants of revision and functional outcome following unicompartmental knee replacement.

OBJECTIVE: Unicompartmental Knee Replacement (UKR) has important advantages over total knee replacement (TKR) but has a higher revision rate. Outcomes vary between centres, suggesting that risk factors for revision may be modifiable with changes to patient selection or operative technique. The objective of this study was to determine factors affecting revision, patient-reported outcome and satisfaction following UKR.

METHOD: 25,982 cases from three national databases were analysed. Multilevel multivariable regression models were used to examine the effect of patient and surgical factors on implant survival, patient-reported outcome and satisfaction at 6 months and 8 years following UKR.

RESULTS: Of the 25,982 cases, 3862 (14.9%) had pre-operative and 6-month Oxford Knee Scores (OKS). Eight-year survival was 89.1% (95% confidence intervals (CI) 88.3-89.9). OKS increased from 21.9 (SD 7.6) to 37.5 (SD 9.5). Age (Hazard ratio (HR) 0.96 (95% CI 0.96-0.97) per year), male gender (HR 0.86 (95% CI 0.76-0.96)), unit size (HR 0.92 (95% CI 0.86-0.97) per case up to 40 cases/year) and operating surgeon grade (HR 0.78 (95% CI 0.67-0.91) if consultant) predicted improved implant survival. Older patients (≥ 75 years), and those with lower deprivation levels had superior OKS and satisfaction (adjusted mean difference 0.14 (95% CI 0.09-0.20) points per year of age and 0.93 (95% CI 0.60-1.27) per quintile of deprivation). Ethnicity, anxiety and co-morbidities also affected patient-reported outcome.

CONCLUSIONS: This study has identified important predictors of revision and patient-reported outcome following UKR. Older patients, who are least likely to be offered UKR, may derive the greatest benefits. Improved understanding of these factors may improve the long-term outcomes of UKR.