High usage of medial unicompartmental knee arthroplasty negatively influences total knee arthroplasty revision rate

Purpose Surgeons with higher medial unicompartmental knee arthroplasty (UKA) usage have lower UKA revision rates. However, an increase in UKA usage may cause a decrease of total knee arthroplasty (TKA) usage. The purpose of this study was to investigate the influence of UKA usage on revision rates and patient-reported outcomes (PROMs) of UKA, TKA, and combined UKA + TKA results. Methods Using the New Zealand Registry Database, surgeons were divided into six groups based on their medial UKA usage: < 1%, 1–5%, 5–10%, 10–20%, 20–30% and > 30%. A comparison of UKA, TKA and UKA + TKA revision rates and PROMs using the Oxford Knee Score (OKS) was performed. Results A total of 91,895 knee arthroplasties were identified, of which 8,271 were UKA (9.0%). Surgeons with higher UKA usage had lower UKA revision rates, but higher TKA revision rates. The lowest TKA and combined UKA + TKA revision rates were observed for surgeons performing 1–5% UKA, compared to the highest TKA and UKA + TKA revision rates which were seen for surgeons using > 30% UKA (p < 0.001 TKA; p < 0.001 UKA + TKA). No clinically important differences in UKA + TKA OKS scores were seen between UKA usage groups at 6 months, 5 years, or 10 years. Conclusion Surgeons with higher medial UKA usage have lower UKA revision rates; however, this comes at the cost of a higher combined UKA + TKA revision rate that is proportionate to the UKA usage. There was no difference in TKA + UKA OKS scores between UKA usage groups. A small increase in TKA revision rate was observed for high-volume UKA users (> 30%), when compared to other UKA usage clusters. A significant decrease in UKA revision rate observed in high-volume UKA surgeons offsets the slight increase in TKA revision rate, suggesting that UKA should be performed by specialist UKA surgeons. Level of evidence III, Retrospective therapeutic study.