This study evaluates whether opportunistic osteoporosis screening using routinely acquired computed tomography (CT) scans improves fracture risk prediction compared with guideline-recommended FRAX-based screening from age 50. In current practice, few high-risk individuals identified by FRAX actually receive confirmatory dual-energy X-ray absorptiometry (DXA), despite the growing health and economic burden of osteoporotic fractures. Volumetric bone mineral density (vBMD) and CT-based detection of vertebral fractures can be extracted from existing CT images obtained for other indications, offering a non-invasive way to capture key determinants of fracture and mortality risk, including low BMD, age, and prevalent fractures. The trial therefore compares the diagnostic performance of FRAX major osteoporotic fracture risk versus CT-derived vBMD and CT-identified vertebral fractures for predicting incident vertebral fractures in older adults.

Primary objective: To assess the predictive performance of opportunistic volumetric bone mineral density (vBMD) from routine thoracoabdominal CT scans for incident vertebral fractures over 5 years or longer.

Secondary objectives:

• To compare the performance of vBMD to predict incident vertebral fractures with other predictors, including demographic and clinical risk factors, FRAX algorithm scores for 5-year risk of major osteoporotic fractures (MOF), prevalent vertebral fractures, and prevalent clinical fractures, as well as combinations of these predictors.
• To stratify the analyses based on age decades and sex.
• To compare the predictive performance between CT scans with and without administration of i.v. contrast medium.
• To compare the predictive performance of vBMD (using asynchronous calibration) with Hounsfield units
• To describe the prevalence and incidence (in fractures per person-years) of the study population
• Assessment of the impact of a preventive treatment of patients at high risk of fracture in terms of the number of avoided fractures (simulation study)

Inclusion Criteria:

• Baseline CT and 5 years follow-up CT including parts of the lumbar spine

Exclusion Criteria:

• CT: No sagittal reformations or axial slices ≤3 mm
• CT: No inclusion of at least T6 to L4
• No BMI data available

Consecutive patients from the local imaging database that received a CT scan including at least T6 to L4 (=baseline) and a second CT scan after at least 5 years including at least T6 to L4 (=5 years follow-up)