Comparative Assessment of Proximal Humeral Bone Density Using CT Osteoabsorptiometry, Bone Microarchitecture Analysis, and a HU-Based Calibration Method: A CT and Micro-CT Study in Elderly Body Donors (65–86 Years)

<b>Background</b>: Local bone quality of the proximal humerus is a key determinant of fracture risk and implant stability in osteoporotic bone. Beyond established HU-based calibration, CT-osteoabsorptiometry (CT-OAM)-derived indices and microarchitecture-oriented workflows warrant systematic cross-modality evaluation. <b>Methods</b>: Twelve proximal humeral heads from six body donors (age 65-86 years; bilateral specimens) were analyzed using paired clinical CT and high-resolution micro-CT. Bone quality was quantified by (i) a HU-calibrated cancellous vBMD method (Krappinger et al.), (ii) a CT-OAM-inspired workflow reporting an ROI-averaged mean-intensity index in arbitrary units (a.u.), and (iii) a calibrated Bone Microarchitecture Analysis (BMA) workflow in Analyze 15.0. Paired tests, linear regression, and repeated-measures ANOVA after z-standardization were applied. <b>Results</b>: HU calibration yielded a mean trabecular vBMD of 114.37 ± 35.15 mg/cm³ on clinical CT. The BMA workflow produced higher CT-based values (207.37 ± 23.78 mg/cm³, <i>p</i> < 0.001) and markedly higher micro-CT values (469.34 ± 30.99 a.u.), indicating a systematic level shift between calibration frameworks. The CT-OAM index averaged 166.94 ± 40.12 a.u. on clinical CT and 455.89 ± 132.63 a.u. on micro-CT. Cross-modality agreement was very strong for CT-OAM (R² = 0.888) and moderate for BMA (R² = 0.502). After z-standardization, no significant differences were detected between the three CT-based approaches. <b>Conclusions</b>: A CT-OAM-inspired ROI-mean index and a BMA-based workflow provide complementary, transferable readouts of proximal humeral bone quality across clinical CT and micro-CT, with stronger cross-modality rank consistency for CT-OAM. Absolute density values differ systematically between calibration frameworks and should not be interpreted as directly interchangeable. These approaches support opportunistic, site-specific bone quality assessment from routine CT, but require prospective validation against fixation-related outcomes and robust scanner-independent standardization.