Bone Strain Index: preliminary distributional characteristics in a population of women with normal bone mass, osteopenia and osteoporosis

Purpose Bone Strain Index (BSI) is a recently developed dual-energy X-ray absorptiometry (DXA) software, applying a finite element analysis on lumbar spine and femoral DXA scans. BSI is a parameter of bone deformation, providing information on bone resistance to applied loads. BSI values indicate the average bone strain in the explored site, where a higher strain (higher BSI values) suggests a higher fracture risk. This study reports the distributional characteristics of lumbar BSI (L-BSI) in women with normal bone mass, osteopenia or osteoporosis and their relationships with BMD, weight, height and BMI. Material and methods Two-hundred-fifty-nine consecutive unfractured women who performed DXA were divided into three groups based on BMD T-score: normal bone mass (n = 43, 16.6%), osteopenia (n = 82, 31.7%) and osteoporosis (n = 134, 51.7%). The distribution of L-BSI was evaluated with conventional statistical methods, histograms and by calculating parametric and nonparametric 95% confidence intervals, together with the 90%, 95% and 99% bilateral tolerance limits with a 95% confidence. Results Ninety percent bilateral tolerance limits with 95% confidence for L-BSI distribution are 1.0-2.40, 0.95-2.63 and 0.84-3.15 in the group of patients with normal bone mass, 1.34-2.78, 1.24-2.95 and 1.05-3.32 in the osteopenic group and 1.68-3.79, 1.58-4.15 and 1.40-4.96 in the osteoporotic group. Conclusion In women without vertebral fractures at baseline, L-BSI values from 1.68 (osteoporotic group) and 2.40 (upper of the normal bone mass group) can be tentatively chosen as a lower and upper threshold to stratify postmenopausal women according to their bone resistance to loads.