Similar patient-reported outcomes 6 months after unicompartmental and total knee replacement for osteoarthritis: a prospective cohort study of 60,145 patients from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND AND PURPOSE: Unicompartmental knee arthroplasty (UKA) is advocated to achieve greater satisfaction and improved function when compared with total knee arthroplasty (TKA), but there is little evidence from large-scale cohorts to support this contention. We aimed to determine, from the patients' perspective, if UKA leads to postoperative differences in satisfaction, knee pain, function, and quality of life when compared with TKA. METHODS: Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) compared PROMs scores for patients with either a UKA or TKA. EQ-5D-5L, Oxford Knee Scores (OKS), and a knee pain rating were recorded preoperatively and 6 months after surgery with additional assessments of satisfaction and patient-perceived change. Comparisons were made for change in mean score after surgery, while percentage change and proportions achieving minimal clinically important change (MCIC) were compared using odds ratios (OR). RESULTS: 3,329 UKAs and 56,816 TKAs were included. UKA patients had higher mean scores for all PROMs measures before surgery, and scores increased similarly to or less than for TKA patients after surgery. Mean OKS was 39 (95% confidence interval [CI] 39-39) after UKA and 38 (CI 38-38) after TKA. Compared with TKA there was a smaller change in mean OKS for the UKA group (-1.3, CI -1.6 to -1.0), which was below the threshold for MCIC. Similar proportions of patients achieved an OKS improvement which met the MCIC threshold. Quality of life improvement after surgery was equivalent for both groups (EQ-5D-5L utility change 0.3 units) as was knee pain improvement (OR 1.1, CI 0.9-1.4) with the UKA group having higher odds of being satisfied (OR 1.2, CI 1.0-1.3) and feeling better (OR 1.12, CI 1.0-1.4), compared with the TKA group. CONCLUSION: Based on patient assessments, the difference between UKA and TKA did not achieve the published threshold for a minimal important difference.