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.