263. Evaluation of bone mineral density after instrumented lumbar fusion using computed tomography

BACKGROUND CONTEXT Computed tomography (CT) measurement of Hounsfield Units (HU) has been described as a tool for assessing bone mineral density (BMD). For surgeons considering a revision lumbar fusion, knowledge of the BMD of the upper instrumented verterbra (UIV) is of value for surgical planning. However, the presence of metal artifact from instrumentation presents a potential confounder and prior studies have not validated measurements of HU in this setting. PURPOSE The purpose of this study is to determine if HU can be measured reliably at instrumented levels after a lumbar fusion. STUDY DESIGN/SETTING Retrospective observational cohort at a single multisurgeon spine center. PATIENT SAMPLE Consecutive series of patients who had lumbar CT Scans after an instrumented posterior lumbar fusion. OUTCOME MEASURES Hounsfield Units at the upper instrumented vertebra and levels proximal. METHODS We analyzed pre- and postoperative CT scans of 50 patients who underwent L2 and distal instrumented lumbar fusion whose scans were no greater than 1 year apart, obtaining HU measurements of analogous axial cuts at the upper instrumented level (immediately caudal to the halo of the pedicle screw), as well as additional control levels above the construct. RESULTS The HU at the pre-and postoperative UIV exhibited a strong correlation (r=0.917, p CONCLUSIONS Postoperative HU at the UIV was strongly correlated with and not significantly different from the preoperative HU. Although the HU in the vertebrae proximal to the UIV were slightly lower postoperatively, this change was predictable using a correction factor. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.