Monitoring Surgical Performance and Predicting Future Outlier Status for Total Hip Arthroplasty Surgeons

Introduction The New Zealand Joint Registry monitors surgeon-level arthroplasty outcomes using funnel plots. If future outlier status could be predicted, this would provide an opportunity to intervene and potentially improve performance prior to exceeding the outlier threshold. The purpose of this study was to evaluate the predictive value of revision rate trend and exceeding a lower “alert” threshold for subsequent identification as an outlier. Methods For the revision at two years reporting timeframe, trend in revision rate prior to exceeding the outlier threshold was evaluated for 2021 outliers. This analysis included ten reporting years. The predictive value of exceeding the 80% control limit for being identified as an outlier (exceeding the 95% control limit) within the subsequent three years was then evaluated using McNemar's test. The likelihood of outliers exceeding the 80% control limit in the three years preceding identification as an outlier was also evaluated. These analyses identified surgeons from the five most recent reporting years available in 2021. Results Five of six outliers who could have their longitudinal performance tracked had an upward trend in revision rate, relative to the control limit, prior to exceeding the outlier threshold. Twenty-two surgeons exceeded the 80% control limit in the five included reporting years (2014 to 2018). Six of these surgeons became outliers within three years of first exceeding the lower threshold; a significantly higher proportion than for surgeons remaining below the 80% control limit (p <0.001). Five of nine surgeons identified as outliers from 2017 to 2021 were outside the 80% control limit in at least one of the three years prior to exceeding the outlier threshold. Conclusion Trend in revision rate and exceeding the 80% control limit have predictive value for future outlier status. Including this information in reports could facilitate earlier changes to practice and avoidance of future outlier status.