1366. Assessing the Differences in Characteristics of Patients Lost to Follow-up at 2 years: Results from the Multi-Site Quality Outcomes Database (QOD) Study of Impact of Fusion on Outcomes of Grade 1 Spondylolisthesis

Authors: Mohamad Bydon, MD, FAANS ; Praveen Mummaneni, MD; John Knightly, MD; Kevin Foley, MD; Jonathan Slotkin, MD; Eric Potts, MD; Mark Shaffrey; Christopher Shaffrey, MD; Michael Wang, MD; Paul Park, MD; Erica Bisson, MD; Anthony Asher, MD (Rochester, MN)

Introduction: Loss to follow up has been shown to bias outcome assessment among studies utilizing clinical registries. Previous studies has investigated the reasons why patients are lost to follow up; however, little is known about characteristics of patients that are lost to follow up and how they compare to patients who are captured. Herein, we analyzed patients enrolled in a national surgical registry and compared the baseline characteristics of patients captured with those lost to follow up at 2 years. Methods: We queried the Quality Outcomes Database for patients with grade 1 lumbar degenerative spondylolisthesis undergoing a surgical intervention between July 2014 and June 2016. Only those patients enrolled in a multi-side study investigating the impact of fusion on clinical and Patient Reported Outcomes (PROs) among patients with grade 1 spondylolisthesis were evaluated. Results: Of the 608 patients undergoing enrolled in the study, 84% (n=511) were successfully followed for 2 years. Patients who were captured were more likely to be unemployed (50.5%,n=258 vs 40.2%,n=39,p=0.04) and at baseline had lower back-pain (VAS-BP 6.5±2.7 vs 7.3±2.4, p=0.021), lower leg-pain (VAS-LP 6.4±2.8 vs 7.3±2.6, p=0.006), lower ODI-score (45.86±16.8 vs 51.04±18.1, p=0.007) and higher EQ-5D-score (0.54±0.22 vs 0.41±0.24, p=0.004) but longer operative time (180.2 minutes±87.3 vs 157.8±78, p=0.020). Patients lost to follow-up were more likely to be smokers (16.5%,n=16 vs 10.6%, n=54, p=0.032) and have a history of depression (26.8%,n=26 vs 19%,n=97, p=0.05). Proportion of patients undergoing a fusion surgery did not differ between the two groups (78.4%,n=134 vs 80.5%,n=504). Conclusion: To execute future, high-quality study, it is important to identify patients undergoing surgery for spondylolisthesis who might be lost to follow up after surgical intervention. In a large, prospective registry, we found that those who were lost to follow up were more likely to be smokers and depressed