Postmenopausal women represent the highest-risk population for osteoporosis (OP), with a prevalence exceeding 32.5%. The resultant fragility fractures are associated with devastating disability, mortality, and a substantial socioeconomic burden. Dual-energy X-ray absorptiometry (DXA), the diagnostic gold standard, is insufficient for large-scale screening due to limited equipment availability, low screening coverage, and poor awareness. Opportunistic screening using CT attenuation values (Hounsfield Units, HU) from routine scans has emerged as a promising alternative, offering the potential for widespread without additional radiation or cost. However, translating this strategy to the core target population of postmenopausal women reveals three critical evidence gaps: (1) a lack of genetic causal evidence specific to postmenopausal women, making it difficult to establish a definitive link between HU decline and osteoporosis; (2) high heterogeneity in diagnostic studies, with a lack of pooled diagnostic parameters exclusive to this group, potentially leading to misclassification with existing general-population thresholds; and (3) the absence of a screening model built entirely on literature parameters from postmenopausal women, hindering individualized risk stratification. This review systematically examines the disease burden of OP in postmenopausal women, the limitations of DXA screening, the principles and progress of opportunistic CT, and critically analyzes these three key gaps to underscore the necessity and urgency for a comprehensive chain of evidence, from causal mechanisms to clinical application.