The Influence of Surgeon Caseload and Usage on the Long-Term Outcomes of Mobile-Bearing Unicompartmental Knee Arthroplasty: An Analysis of Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) revision rates are variable and known to be influenced by a surgeon's caseload (number of UKAs performed annually) and usage (UKA as a proportion of overall knee arthroplasty practice). It is not known which is more important. We explored the influence of caseload and usage on cemented and cementless UKA. METHODS: A total of 34,277 medial Oxford UKAs (23,707 cemented and 10,570 cementless) from the National Joint Registry were analyzed. UKAs were subdivided by the following: (1) surgeon caseload, into low (<10 UKAs/y) and high (≥10 UKAs/y) categories; and (2) usage, into low (<20%) and high (≥20%) categories. The 10-year revision rates were compared. RESULTS: The 10-year survival of the low-caseload/low-usage cemented and cementless UKA was 82.8% (CI 81.6-83.9) and 86.2% (CI 72.1-93.4), respectively. The 10-year survival of the high-caseload/high-usage cemented and cementless UKA was 90.0% (CI 89.2-90.6) and 93.3% (CI 91.3-94.8), respectively. For cemented UKA, the high-caseload/high-usage group had lower revision rates (hazard ratio [HR] 0.57, CI 0.52-0.63, P < .001) compared to the low-caseload/low-usage group. The high-caseload/low-usage (HR 0.74, CI 0.66-0.83, P < .001) and the low-caseload/high-usage (HR 0.86, CI 0.74-0.99, P = .04) groups also had lower revision rates than the low-caseload/low-usage group. CONCLUSION: Mobile-bearing UKA revision rates improve with both increasing surgeon UKA caseload and usage. Surgeons using cemented UKA who have usage ≥20% and caseload ≥10/year had a 10-year survival of 90%. Higher survivorship was associated with higher caseload, higher usage, and cementless fixation. LEVELS OF EVIDENCE: III.