Predisposing Characteristics of Adjacent Segment Disease After Lumbar Fusion.

STUDY DESIGN Retrospective Review. OBJECTIVE The aim of this study was to determine medical, radiographic, and surgical risk factors for the development of adjacent segment disease (ASD) after lumbar fusion. SUMMARY OF BACKGROUND DATA ASD is a recognized outcome of spinal fusion that leads to increased costs and debilitating symptoms for patients. However, a comprehensive understanding of risk factors for the development of this surgical outcome does not exist. METHODS The medical records of patients who received their first lumbar fusion for any indication were retrospectively examined for preoperative medical comorbidities and medications, as well as surgical approach and perioperative complications. A blinded reviewer assessed radiographs for each patient to examine sagittal alignment after fusion. Multivariable logistic regression was used to model the risk of developing ASD on the basis of one or more predictors. RESULTS A total of 137 patients fit the inclusion criteria; 9% required a follow-up operation for degeneration at segments adjacent to the fusion. The ASD group had a mean follow-up of 21.1 months prior to revision surgery and an overall follow-up of 41.0 months. The average follow-up in the control group was 14.0 months. Statistically significant independent predictors of developing ASD included antidepressant use [odds ratio (OR) = 5.4], diagnosis of degenerative scoliosis (OR = 34.2), fusion of L4-S1 (OR = 56.5), having no decompressions adjacent to the fusion, and low sacral slope (OR = 0.9). No patient who developed ASD received a decompression adjacent to the fusion such that an OR could not be generated for this independent predictor. CONCLUSION This study is the first to use a combination of medical, surgical, and postoperative sagittal balance as risk factors for the development of adjacent segment disease after lumbar fusion. The awareness of these risk factors may allow for better patient selection and surgical technique to decrease the probability of acquiring this adverse outcome. LEVEL OF EVIDENCE 4.