The Interaction of Caseload and Usage in Determining Outcomes of Unicompartmental Knee Arthroplasty: A Meta-Analysis

Background: Outcomes after unicompartmental knee arthroplasty (UKA) are variable and influenced by caseload (UKA/y) and usage (percentage of knee arthroplasty that are UKA), which relates to indications. This meta-analysis assesses the relative importance of these factors. Methods: MEDLINE (Ovid), Embase (Ovid), and Web of Science (ISI) were searched for consecutive series of cemented Phase 3 Oxford medial UKA. The primary outcome was revision rate/100 observed component years (% pa) with subgroup analysis based on caseload and usage. Results: Forty-six studies (12,520 knees) with an annual revision-rate ranging from 0% to 4.35% pa, mean 1.21% pa (95% confidence interval [CI], 0.97-1.47), were identified. In series withmean follow-up of 10-years, the revision-rate was 0.63% pa (95% CI, 0.46-0.83), equating to a 94% (95% CI, 92%-95%) 10-year survival. Aseptic loosening, lateral arthritis, bearing dislocation, and unexplained pain were the predominant failure mechanisms with revision for patellofemoral problems and polyethylene wearexceedingly rare. The lowest revision-rates were achieved with caseload > 24 UKA/y (0.88% pa; 95% CI, 0.63-1.61) and usage > 30% (0.69% pa; 95% CI, 0.50-0.90). Usage was more important than caseload; with high usage (>= 20%), the revision-rate was low, whether the caseload was high (> 12 UKA/y) or low (<= 12 UKA/y; (0.94% pa; 95% CI, 0.69-1.23 and 0.85% pa; 95% CI, 0.65-1.08), respectively); with low usage (< 20%), the revision-ratewas high, whether the caseload was high or low (1.58% pa; 95% CI, 0.57-3.05 and 1.76% pa; 95% CI, 1.21-2.41, respectively). Conclusion: To achieve optimum results, surgeons, whether high or low caseload, should adhere to the recommended indications such that >= 20%, or ideally > 30% of their knee arthroplasties are UKA. If they do this, then they can expect to achieve results similar to those of the long-term series, which all had high usage (> 20%) and an average 10-year survival of 94%. (C) 2017 Elsevier Inc. All rights reserved.