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Magnetic resonance imaging as an instrument to assess the association between femoral neck bone geometry and strength of the proximal femur Manske, Sarah Lynn
Introduction: Hip fractures are an increasing health and economic burden. Dual energy x-ray absorptiometry (DXA) is the instrument currently used to diagnose osteoporosis, however, there are limitations associated with using DXA to predict fracture risk and to measure response to therapeutic interventions. Magnetic resonance imaging (MRI) is an emerging instrument to assess bone, however the ability of MRI measurements of femoral neck geometry to predict bone strength has not been previously assessed. Objectives: To evaluate the association of femoral neck cross-sectional geometry measured with MRI with failure load in cadaveric femora, and to compare this association with DXA and Hip Structural Analysis (HSA). The secondary objective was to compare reliability of femoral neck geometry measured with 3 Tesla (T) MRI and 1.5 T MRI systems. Methods: Thirty-six human cadaveric proximal femora underwent DXA and MRI imaging. DXA images were also analyzed with HSA. Areal BMD (aBMD) was evaluated with DXA and HSA. Cross-sectional geometry (area, second area moment of inertia - Ix, and section modulus) were evaluated with MRI (femoral neck region) and HSA (narrow neck and intertrochanteric regions). Inter-analysis and inter-acquisition reliability were compared between measurements with 1.5 T and 3 T MRI systems. The femora were loaded to failure in a fall configuration. Results: Femoral neck cortical cross-sectional area and Ix, measured with MRI, were strongly associated with failure load (R² = 0.47 for both measures, p < 0.001). The predictive ability of Ix was lower than trochanteric aBMD (R² = 0.70), p = 0.10. Ix significantly contributed to the variance explained in failure load after accounting for femoral neck aBMD (R2-change = 0.14, p = 0.01), but not after accounting for trochanteric aBMD (R²-change = 0.03, p = 0.23). Crosssectional geometry, e.g. Ix, measured with MRI explained similar variance in failure load (R² = 0.47) as cross-sectional geometry estimated with HSA (R² = 0.31). Inter-acquisition and interanalysis reliability were similar for 3 T and 1.5 T MRI systems. Summary and Conclusion: Femoral neck cross-sectional geometry assessed with MRI and HSA, and aBMD by DXA were similarly associated with failure load ex vivo. MRI holds promise for the in vivo assessment of cortical bone geometry at the proximal femur, as neither DXA nor HSA are capable of measuring these parameters without major assumptions. However, a targeted program of research that aims to improve and standardize MRI image acquisition and analysis is warranted.
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