Osteoporosis and Hip Fracture Risk From Routine Computed Tomography Scans: The Fracture, Osteoporosis, and CT Utilization Study (FOCUS)

Abstract

Methods now exist for analyzing previously taken clinical computed tomography (CT) scans to measure a dual-energy X-ray absorptiometry (DXA)-equivalent bone mineral density (BMD) at the hip and a finite element analysis-derived femoral strength. We assessed the efficacy of this "biomechanical CT" (BCT) approach for identifying patients at high risk of incident hip fracture in a large clinical setting. Using a case-cohort design sampled from 111,694 women and men aged 65 or older who had a prior hip CT scan, a DXA within 3 years of the CT, and no prior hip fracture, we compared those with subsequent hip fracture (n = 1959) with randomly selected sex-stratified controls (n = 1979) and analyzed their CT scans blinded to all other data. We found that the age-, race-, and body mass index (BMI)-adjusted hazard ratio (HR; per standard deviation) for femoral strength was significant before (women: HR = 2.8, 95% confidence interval [CI] 2.2-3.5; men: 2.8, 2.1-3.7) and after adjusting also for the (lowest) hip BMD T-score by BCT (women: 2.1, 1.4-3.2; men: 2.7, 1.6-4.6). The hazard ratio for the hip BMD T-score was similar between BCT and DXA for both sexes (women: 2.1, 1.8-2.5 BCT versus 2.1, 1.7-2.5 DXA; men: 2.8, 2.1-3.8 BCT versus 2.5, 2.0-3.2 DXA) and was higher than for the (lowest) spine/hip BMD T-score by DXA (women: 1.6, 1.4-1.9; men: 2.1, 1.6-2.7). Compared with the latter as a clinical-practice reference and using both femoral strength and the hip BMD T-score from BCT, sensitivity for predicting hip fracture was higher for BCT (women: 0.66 versus 0.59; men: 0.56 versus 0.48), with comparable respective specificity (women: 0.66 versus 0.67; men: 0.76 versus 0.78). We conclude that BCT analysis of previously acquired routine abdominal or pelvic CT scans is at least as effective as DXA testing for identifying patients at high risk of hip fracture. © 2018 American Society for Bone and Mineral Research.

Cost-Effectiveness of Osteoporosis Screening Using Biomechanical Computed Tomography for Patients With a Previous Abdominal CT

“…The improved sensitivity of BCT compared to traditional DXA is a unique feature of BCT, providing confidence that, as an adjunct to DXA, BCT is at least as good as the clinical standard. In addition, women who test positive with BCT are at significantly higher risk of hip fracture due to low bone strength than are women who test positive with traditional DXA . Because alendronate is thought to be more effective in patients having lower bone strength, BCT‐positive patients may be more responsive to alendronate than are DXA‐positive patients, a possible effect that was not explored in our analysis.…”

“…), the program is set up so that all 1000 patients undergo the BCT test in year 1, which would be feasible in a managed care setting because no new patient procedure is needed and the screen is medically indicated. Typically, 90% of those CT scans yield diagnostic‐quality BCT results . Patients who tested positive were classified at high risk and were eligible for 2 years of alendronate treatment, whereas patients who tested negative were not offered any treatment.…”

“…First, and especially for men, the screening rate for DXA is low—only 9.5% of women and 1.7% of men in the US Medicare population aged 65 years and older . Second, the sensitivity of traditional DXA for predicting fracture is modest . Thus, any adjunct approaches to DXA that have higher screening rates and sensitivity, even if only for a subset of patients, could improve osteoporosis management.…”

“…One recently validated test for diagnostic screening of osteoporosis is “biomechanical computed tomography” (BCT) as applied to abdominal CT scans previously obtained for any medical indication . The general BCT approach, ie, finite element analysis of clinical‐resolution CT scans, provides noninvasive estimates of the breaking strength of the hip and spine.…”

“…Combining that measurement with a CT‐based measurement of a DXA‐equivalent hip BMD T ‐score, BCT provides a more comprehensive diagnostic assessment of osteoporosis than using either bone strength or BMD alone. For example, because femoral strength predicts hip fracture independently of hip BMD, BCT has higher sensitivity for hip fracture than traditional DXA, and patients who test positive with BCT are at higher risk of hip fracture than are patients who test positive with traditional DXA . When applied to previously obtained CT scans —an ancillary approach—no extra procedure or office visit is required by the patient to undergo an osteoporosis screen, and no change is required in the clinical imaging protocol.…”