Age- and Sex-Dependent Bone Density Decline in the Calcar Region of the Proximal Humerus: A CT-Based Population Analysis

The inferomedial calcar is a key biomechanical region for proximal humerus fracture fixation, yet large-scale data on calcar bone quality across age and sex are lacking. This retrospective imaging study analyzed CT-derived Hounsfield unit (HU) values in 739 adult left proximal humeri from the Stryker Orthopaedic Modeling and Analytics database. Cylindrical regions of interest (30 mm length, 5 mm diameter) were defined along the calcar, and HU values were extracted at 5% depth increments. Individuals were stratified by age (18–40, 41–65, > 65 years) and sex. Multiple regression (adjusted R² = 0.36) identified age (β = −1.97, p < 0.001) and sex (β = 53.4, p = 0.001) as independent predictors of calcar density, with no significant interaction. Young males had the highest density (222.5 ± 81.5 HU); elderly females the lowest (65.8 ± 64.6 HU). At 15 mm depth, over 40% of women > 65 had HU values below 100. The calcar undergoes substantial age- and sex-dependent density decline, with implications for implant anchorage in osteoporotic proximal humerus fractures. The clinical relevance of specific HU thresholds remains to be validated against fixation outcomes.