Screening for Low Bone Mineral Density Using Opportunistic Foot Radiographs

Background: The gold standard for low bone mineral density (BMD) screening is dual-energy X-ray absorptiometry (DXA) scanning, which has declined in use in recent years for a variety of reasons. This decline warrants alternative screening mechanisms. This study aimed to determine if opportunistic foot radiographs can serve as a screening tool for predicting low BMD as measured by DXA scan. Methods: The fifth metatarsal index (5MI), a novel measurement made using the oblique foot radiograph to evaluate cortical thickness, was calculated for patients 50 years and older who underwent a DXA scan and a foot radiograph within 1 year. T scores and BMD were documented for each patient. Receiver operating characteristic curves were generated, and areas under the curves were calculated to determine which 5MI had optimized sensitivity and specificity for identifying osteoporosis. Results: A total of 89 patients were included in the study cohort. The average 5MI in patients with normal BMD, osteopenia, and osteoporosis was 52.6%, 44.6%, and 35.2%, respectively. The optimal 5MI for identifying osteoporosis based on the DXA-derived T scores was 46.8%, which correlated with an area under the curve of 0.977. This optimal cutoff for identifying osteoporosis had a sensitivity of 93.3% (95% CI, 70.2%-99.7%) and a specificity of 95.0% (95% CI, 76.4%-99.7%) ( P < .001). Conclusion: This study describes a potential screening method using low-cost foot radiographs to identify patients with low BMD, which may support earlier detection and referral for bone health evaluation. Level of Evidence: Level III, retrospective case series.