Fractal lacunarity of trabecular bone in vertebral MRI to predict osteoporotic fracture risk in over-fifties women. The LOTO study

Background. Osteoporotic fractures are a major cause of morbidity in the elderly. Menopausal women represent the population with the highest risk of early osteoporosis onset, often accompanied by vertebral fractures (VF). Bone mineral density (BMD) is commonly assessed by dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnosis; however, BMD alone does not represent a significant predictor of fracture risk. Bone microarchitecture, instead, arises as a determinant of bone fragility independent of BMD. High-resolution magnetic resonance imaging (MRI) is an effective noninvasive/nonionizing tool for in vivo characterisation of trabecular bone microarchitecture (TBA). We have previously set up an MRI method able to characterise TBA changes in aging and osteoporosis by one parameter, trabecular bone lacunarity parameter beta (TBL beta). Fractal lacunarity was used for TBA texture analysis as it describes discontinuity of bone network and size of bone marrow spaces, changes of which increase the risk of bone fracture. This study aims to assess the potential of TBL beta method as a tool for osteoporotic fracture risk. Methods. An observational, cross-sectional, and prospective study on over-50s women at risk for VF was designed. TBL beta, our index of osteoporotic fracture risk, is the main outcome measure. It was calculated on lumbar vertebra axial images, acquired by 1.5T MRI spin-echo technique, from 279 osteopenic/osteoporotic women with/without prior VF. Diagnostic power of TBL beta method, by Receiver Operating Characteristics (ROC) curve and other diagnostic accuracy measurements were compared with lumbar spine DXA-BMD. Results. Baseline results show that TBL beta is able to discriminate patients with/without prevalent VF (p=0.003). AUC (area under the curve from ROC) is 0.63 for TBL beta, statistically higher (p=0.012) than BMD one (0.53). Contribution of TBL beta to prevalent VF is statistically higher (p<0.001) than BMD (sensitivity: 66% vs. 52% respectively; OR: 3.20, p<0.0001 for TBL beta vs. 1.31, p=0.297 for BMD). Preliminary 1-year prospective results suggest that TBA contribution to incident VF is even higher (sensitivity: 73% for TBL beta vs. 55% for BMD; RR: 3.00, p=0.002 for TBL beta vs. 1.31, p=0.380 for BMD). Conclusion. Results from this study further highlight the usefulness of TBL beta as a biomarker of TBA degeneration and an index of osteoporotic fracture risk.