Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P36. Influence of lumbar spine pathology on bone mineral density measurement by quantitative computed tomography (QCT)

Abstract

BACKGROUND CONTEXT Quantitative computed tomography (QCT) is increasingly used for clinically diagnosing osteopenia and osteoporosis. In contrast to dual X-ray absorptiometry (DXA) which uses a two-dimensional projection, QCT provides a true volumetric bone mineral density (BMD) measurement. Certain conditions like spinal degeneration, abdominal aortic calcification, and other sclerotic lesions can lead to an overestimation of BMD by DXA. Similarly, QCT measurements can be affected by degenerative or sclerotic vertebral body changes if inadvertently included in the field during the measurement process. It remains unclear if excluding pathologic bone regions in the selected field allows for more accurate BMD measurements. PURPOSE The aim of this study was to assess whether BMD measured from pathologic levels is different than BMD derived from nonpathologic levels in paired, matched controls. STUDY DESIGN/SETTING Case-control study. PATIENT SAMPLE A total of 296 consecutive patients undergoing posterior lumbar spinal fusion from 2014 to 2017 at a single, academic institution. OUTCOME MEASURES Bone mineral density. METHODS Patients undergoing posterior lumbar spinal fusion from 2014 to 2017 at a single, academic institution with available preoperative lumbar spine CT imaging were included. QCT measurements of all lumbar and the first sacral vertebra were performed on all patients. Pathologic levels were defined by referencing operated levels from surgical records. Degenerative or sclerotic bone regions at pathologic levels were avoided during the measurement process to minimize overestimation of bone density in the vertebral body. Due to known differences in BMD at different levels in the lumbosacral spine, comparisons between pathologic and normal levels within the same patient are not possible. To overcome this limitation, matched normal-pathologic measurements at the same lumbosacral level were identified in matched patient-pairs. Patients were matched 1:1 based on gender, age (+/−5yrs), BMI (+/−5), and race. One or more normal-pathologic matched levels were identified from each patient pair. Differences between normal and pathologic levels were assessed using two-tailed paired t-tests with significance set at P RESULTS Seventy-seven matched patient pairs (154 patients) were isolated from a cohort of 296 patients treated surgically for lumbar spine pathology. Patients not matched were excluded due to inability to match on all four matching criteria. From the 77 patient pairs, 152 matched normal-pathologic levels were identified for analysis. The mean (SD) for normal and pathologic levels was 140.4 mg/cm3 (54.13) and 143.0 mg/cm3 (49.04), respectively. Paired statistical analyses revealed no significant difference between groups (P=.563). CONCLUSIONS Our data demonstrates no difference in BMD measured at pathologic and nonpathologic vertebra at the same lumbar or sacral levels in paired patients matched based on age, gender, BMI and race. When using the recommended methodology for QCT measurements including the avoidance of degenerative and/or sclerotic regions, BMD can be accurately measured at pathologic levels. Lumbar degenerative changes are known to adversely impact the sensitivity and specificity of DXA for diagnosing osteopenia and osteoporosis. Our findings suggest that unlike DXA BMD measurements, lumbar QCT measurements may not be affected by degenerative changes and may more accurately represent volumetric bone density in the lumbar spine.