Variations in Data Collection Methods Between National Databases Affect Study Results: A Comparison of the Nationwide Inpatient Sample and National Surgical Quality Improvement Program Databases for Lumbar Spine Fusion Procedures

Background: There has been an increasing use of national databases to conduct orthopaedic research. Questions regarding the validity and consistency of these studies have not been fully addressed. The purpose of this study was to test for similarity in reported measures between two national databases commonly used for orthopaedic research. Methods: A retrospective cohort study of patients undergoing lumbar spinal fusion procedures during 2009 to 2011 was performed in two national databases: the Nationwide Inpatient Sample and the National Surgical Quality Improvement Program. Demographic characteristics, comorbidities, and inpatient adverse events were directly compared between databases. Results: The total numbers of patients included were 144,098 from the Nationwide Inpatient Sample and 8434 from the National Surgical Quality Improvement Program. There were only small differences in demographic characteristics between the two databases. There were large differences between databases in the rates at which specific comorbidities were documented. Non-morbid obesity was documented at rates of 9.33% in the Nationwide Inpatient Sample and 36.93% in the National Surgical Quality Improvement Program (relative risk, 0.25; p < 0.05). Peripheral vascular disease was documented at rates of 2.35% in the Nationwide Inpatient Sample and 0.60% in the National Surgical Quality Improvement Program (relative risk, 3.89; p < 0.05). Similarly, there were large differences between databases in the rates at which specific inpatient adverse events were documented. Sepsis was documented at rates of 0.38% in the Nationwide Inpatient Sample and 0.81% in the National Surgical Quality Improvement Program (relative risk, 0.47; p < 0.05). Acute kidney injury was documented at rates of 1.79% in the Nationwide Inpatient Sample and 0.21% in the National Surgical Quality Improvement Program (relative risk, 8.54; p < 0.05). Conclusions: As database studies become more prevalent in orthopaedic surgery, authors, reviewers, and readers should view these studies with caution. This study shows that two commonly used databases can identify demographically similar patients undergoing a common orthopaedic procedure; however, the databases document markedly different rates of comorbidities and inpatient adverse events. The differences are likely the result of the very different mechanisms through which the databases collect their comorbidity and adverse event data. Findings highlight concerns regarding the validity of orthopaedic database research.