DXA Interpretation and Pitfalls

Dual-energy X-ray absorptiometry measures areal bone mineral density (g/cm²) via soft tissue attenuation subtraction, rendering it susceptible to artifact-driven overestimation from lumbar degenerative sclerosis, aortic calcifications, and structural deformities. The spine captures rapid trabecular remodeling during therapy or acute metabolic bone loss, whereas the proximal femur anchored in FRAX serves as the gold-standard predictor of hip fracture risk. The 1/3 radius provides critical evaluation in primary hyperparathyroidism due to PTH-mediated cortical bone resorption. Advanced modalities like volumetric quantitative CT eliminate 2D areal artifacts using absolute mg/cm³ thresholds (under 80 mg/cm³ for osteoporosis), while Trabecular Bone Score and Vertebral Fracture Assessment uncover microarchitectural degradation and clinically silent vertebral compression fractures to recalibrate true fracture risk.