BACKGROUND: Unicompartmental knee arthroplasty (UKA) is a bone-preserving alternative to total knee arthroplasty (TKA) for isolated compartment osteoarthritis. Despite evidence that up to 50% of patients may be eligible, its global use remains limited.
METHODS: This registry-based observational study analyzed annual reports from national knee arthroplasty registries in nine countries between 2014 and 2024. Data on UKA usage, fixation method, implant design, and compartment distribution were extracted. Trends were analyzed descriptively and with registry-year-level linear regression estimating the average annual change in each outcome.
RESULTS: In 2024, UKA usage ranged from 3.5% in the United States to 36.6% in Denmark, with all countries except Denmark and the Netherlands below the 20% threshold associated with improved outcomes and all below the approximately 50% considered anatomically eligible. Usage increased significantly overall (B = 0.69; P < 0.001), with significant heterogeneity between countries; the steepest rise occurred in Denmark and the Netherlands. Cemented fixation predominated, but declined significantly, with increasing uncemented use in Sweden and the Netherlands. Mobile-bearing use was heterogeneous, remaining high in Norway and Denmark while declining elsewhere. Medial UKA accounted for most procedures and increased over time, whereas lateral UKA remained rare (less than 2% in all countries).
CONCLUSIONS: A UKA remains underused globally, with substantial international variation in usage, implant selection, and fixation. This variation may reflect surgeon-related factors, differing indication thresholds, and local practice patterns. Wider adoption of evidence-based indications and increased procedural volume may improve outcomes and align clinical practice with anatomical eligibility.
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