Feasibility of opportunistic osteoporosis screening using ankle CT Hounsfield units in older adults with ankle fractures

BACKGROUND: Fragility fractures reveal osteoporosis, but ankle fractures are not consistently defined as fragility fractures. CT-derived Hounsfield unit measurements may provide an opportunistic method to identify patients at risk for osteoporosis. PURPOSE: This study investigated the relationship between Hounsfield units (HU) from ankle CT scans and bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DEXA), with the aim of determining whether sufficient signal exists between ankle HU and DEXA-derived BMD to justify a larger prospective validation study, rather than to establish a definitive diagnostic tool. STUDY DESIGN/LEVEL OF EVIDENCE: Retrospective correlation study. Level III. METHODS: Patients aged 55 years or older, who underwent open reduction and internal fixation for OTA/AO 44 A-C ankle fractures between 2012 and 2024 and had both a preoperative ankle CT and a DEXA scan within 1 year of injury, were reviewed. HU values of the distal tibia and fibula were measured using standardized elliptical regions of interest. Multivariate linear regression was performed with the lowest DEXA T-score as the dependent variable, with HU values, and BMI as independent variables. RESULTS: A total of 57 patients (87.7% female, mean age 69.67 ± 9.24 years) were included. The average ankle HU was 192.43 ± 60.04, and the mean T-score was -1.73 ± 0.96. Regression analysis demonstrated that HU values (B = 0.005, P = .021) and BMI (B = 0.064, P = .007) were positively correlated with the T-score.The regression model was lowest T-score = 0.005*Ankle HU + 0.064*BMI-4.422.Based on this equation, an HU measurement of 106.64 or less, assuming a BMI of 21.7, correlated with osteoporosis. CONCLUSIONS: Ankle HU values from CT scans demonstrated a positive association with DEXA-derived BMD, supporting proof-of-concept for ankle HU as a preliminary screening tool and providing methodological groundwork for future prospective validation. Given the high prevalence of osteopenia or osteoporosis in this population, ankle fractures should prompt formal bone health evaluation.