True Differences in Poor Outcome Risks Between Revision and Primary Lumbar Spine Surgeries

Background: Previous studies have shown that the rates of complications associated with revision spine surgery are higher than those of primary spine surgery. However, there is a lack of research exploring the difference in magnitude of risk of poor outcomes between primary and revision lumbar spine surgeries. Purposes: We sought to compare the risks of poor outcomes for primary and revision lumbar spine surgeries and to analyze different measures of risk to better understand the true differences between the 2 forms of surgery. Methods: This retrospective observational study used data from the Quality Outcomes Database Lumbar Spine Surgical Registry from 2012 to 2018. We included individuals who received primary or revision surgery due to degenerative lumbar disorders. Outcome variables collected were complications within 30 days of surgery and 3 destination variables, specifically, (1) 30-day hospital readmission, (2) 30-day return to operating room, and (3) revision surgery within 3 months. Measures of risk considered were odds ratio (OR), relative risk (RR), relative risk increase (RRI), and absolute risk increase (ARI). Results: There were 31,843 individuals who received primary surgery and 7889 who received revision surgery. After controlling for baseline descriptive variables and comorbidities, revision surgery increased the odds of 4 complications and all 3 destination variables. Risk ratios reflected smaller magnitudes but similar findings as the statistically significant ORs. Conclusion: Revision surgery is related to higher overall risks than primary surgery, but the true magnitudes of these risks are very small. RRI and ARI should be included when reporting ORs to better clarify the significance.