Large databases are commonly used to analyze surgical outcomes. Recent studies have suggested that there are differences in complication rates between databases across certain procedures, but the reasons for these differences are not fully understood. The goal of this study was to compare complications of shoulder arthroplasty across databases as well as to interpret the causes of any differences. The authors compared complication rates for shoulder arthroplasty as reported by the Healthcare Cost and Utilization Project Nationwide Inpatient Sample (NIS) and the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) from 2006 to 2010. The authors then restricted NIS data solely to hospitals that also contributed to NSQIP to provide a more direct comparison of the patient populations. The authors identified 48,287 discharges reported in NIS and 1679 discharges reported in NSQIP for patients who underwent shoulder arthroplasty. The complication rate for shoulder arthroplasty was significantly higher in the NIS population (12.6%; 95% confidence interval, 12.0%-13.2%) than in the NSQIP population (5.60%; 95% confidence interval, 4.59%-6.81%). When NIS data were restricted solely to hospitals that also participated in NSQIP, the rate of complications remained higher, at 13.4% (95% confidence interval, 11.2%-15.8%), and the rate increased relative to the nonrestricted data. The databases compared in this study had statistically significant differences in reported complication rates for shoulder arthroplasty. This difference persisted when NIS data were restricted to hospitals that also participated in NSQIP, suggesting that differences in database design contribute to important differences in data. Orthopedic surgeons and administrators must use caution when using complication rates derived from large database studies. [Orthopedics. 2020;43(2):113-118.].
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