Dual-Energy X-Ray Absorptiometry vs Computed Tomography: Comparison of Bone Mineral Density Measurements in Predicting Postoperative Spinal Fusion Outcomes

INTRODUCTION: Diminished bone mineral density (BMD) places patients at increased risk for complications from lumbar fusion procedures. Dual-energy X-Ray absorptiometry (DEXA) scanners have been used as the gold standard in measuring BMD. More recently, various studies have suggested that Hounsfield unit measurements from computed tomography (CT) scans may be more accurate. METHODS: After obtaining IRB approval, we retrospectively reviewed all patients aged 18 and older who underwent lumbar fusion procedures between 01/01/2010 and 12/31/2016 at our institution. We used linear regression to assess for a correlation between CT Hounsfield units and DEXA t scores. Student's t-test was used to compare CT Hounsfield units, lumbar spine t score and hip t scores for patients with and without pseudoarthrosis as well as those with and without hardware failure. RESULTS: A total of 167 patients with lumbar fusion procedures met inclusion criteria. Ages ranged 24 to 88 yr old with a mean of 64. Using linear regression there was no correlation between CT Hounsfield units and Dexa T scores. There was no difference between the groups with respect to CT Hounsfield units or DEXA T scores when comparing patients with and without pseudoarthrosis and when comparing patients with or without hardware failure. CONCLUSION: Diminished BMD is an important factor to consider when contemplating lumbar spine fusion procedures as this has been associated with increased risk of hardware failure or pseudoarthrosis. Traditionally DEXA scans and more recently CT Hounsfield units have used to screen patients for decreased BMD, however, in this relatively large retrospective series we found that neither correlate well with complications from lumbar spine fusion procedures. CT and DEXA scans may not be as reliable as once thought in assessing BMD.