A 7T MRI Study of Fibular Bone Thickness and Density: Impact of Age, Sex and Body Weight, and Correlation with Bone Marrow Expansion and Muscle Fat Infiltration

<b>Background:</b> Reduced bone mass and density, hallmark features of osteopenia and osteoporosis, significantly increase the risk of fractures, falls, and loss of mobility, especially in post-menopausal women and the elderly. <b>Methods:</b> This quantitative 7T MRI study examines the features of fibular bone thinning and bone mineral density loss (BMD) in 107 individuals (43F/64M) across various ages, body mass indices (BMIs), and ethnicities. <b>Results:</b> Women had significantly lower cross-sectional bone wall thickness (BT) and bone tissue area (BA), along with greater BMD loss compared to men in those over age 50 (<i>n</i> = 77), but not in the younger group (<i>n</i> = 30). The bone g-factor, defined as the ratio of inner-to-outer bone diameters, increased with bone thinning, bone marrow expansion (BME), and muscle fat infiltration (MFI) but was independent of subcutaneous fat thickness (SFT). Bone thinning and BMD loss both tend to increase with BME and MFI. Additionally, bone density decrease correlated with bone mass loss, with a stronger association observed with BT than BA. <b>Conclusions:</b> These findings offer insights into the effects of aging and sex on skeletomuscular health, with implications for strategies to mitigate bone loss in osteoporosis and osteosarcopenia.