Discrepancy between DXA and CT-based assessment of spine bone mineral density

Purpose Adequate bone mineral density (BMD) is necessary for success in spine surgery. Dual-energy X-ray absorptiometry (DXA) is the gold standard in determining BMD but may give spuriously high values. Hounsfield units (HU) from computed tomography (CT) may provide a more accurate depiction of the focal BMD encountered during spine surgery. Our objective is to determine the discrepancy rate between DXA and CT BMD determinations and how often DXA overestimates BMD compared to CT. Methods We retrospectively reviewed 93 patients with both DXA and CT within 6 months. DXA lumbar spine and overall T scores were classified as osteoporotic ( T Score ≤ − 2.5) or non-osteoporotic ( T Score > −2.5). L1 vertebral body HU were classified as osteoporotic or non-osteoporotic using cutoff thresholds of either ≤ 135 HU or ≤ 110 HU. Corresponding DXA and HU classifications were compared to determine disagreement and overestimation rates. Results Using lumbar T scores, the CT vs DXA disagreement rate was 40–54% depending on the HU threshold. DXA overestimated BMD 97–100% of the time compared to CT. Using overall DXA T scores, the disagreement rate was 33–47% with DXA greater than CT 74–87% of the time. In the sub-cohort of 10 patients with very low HU (HU