# 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)

## TL;DR

This study compares different CT-based methods to assess bone quality in the proximal humerus of elderly donors, finding that CT-OAM shows stronger consistency across imaging modalities.

## Contribution

The study introduces a systematic cross-modality evaluation of CT-OAM and BMA workflows for bone quality assessment in the proximal humerus.

## Key findings

- CT-OAM showed very strong cross-modality agreement (R2 = 0.888) compared to BMA (R2 = 0.502).
- Absolute density values differ systematically between calibration frameworks and are not directly interchangeable.
- Z-standardization eliminated significant differences between the three CT-based approaches.

## Abstract

Background: 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. Methods: 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. Results: 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, p < 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. Conclusions: 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.