Measurement of cortical porosity of the proximal femur improves identification of women with nonvertebral fragility fractures

Summary: We tested whether cortical porosity of the proximal femur measured using StrAx1.0 software provides additional information to areal bone mineral density (aBMD) or Fracture Risk Assessment Tool (FRAX) in differentiating women with and without fracture. Porosity was associated with fracture independent of aBMD and FRAX and identified additional women with fractures than by osteoporosis or FRAX thresholds. Introduction: Neither aBMD nor the FRAX captures cortical porosity, a major determinant of bone strength. We therefore tested whether combining porosity with aBMD or FRAX improves identification of women with fractures. Methods: We quantified femoral neck (FN) aBMD using dual-energy X-ray absorptiometry, FRAX score, and femoral subtrochanteric cortical porosity using StrAx1.0 software in 211 postmenopausal women aged 54–94 years with nonvertebral fractures and 232 controls in Tromsø, Norway. Odds ratios (ORs) were calculated using logistic regression analysis. Results: Women with fractures had lower FN aBMD, higher FRAX score, and higher cortical porosity than controls (all p < 0.001). Each standard deviation higher porosity was associated with fracture independent of FN aBMD (OR 1.39; 95 % confidence interval 1.11–1.74) and FRAX score (OR 1.58; 1.27–1.97) in all women combined. Porosity was also associated with fracture independent of FRAX score in subgroups with normal FN aBMD (OR 1.88; 1.21–2.94), osteopenia (OR 1.40; 1.06–1.85), but not significantly in those with osteoporosis (OR 1.48; 0.68–3.23). Of the 211 fracture cases, only 18 women (9 %) were identified using FN aBMD T-score < −2.5, 45 women (21 %) using FRAX threshold >20 %, whereas porosity >80th percentile identified 61 women (29 %). Porosity identified 26 % additional women with fractures than identified by the osteoporosis threshold and 21 % additional women with fractures than by this FRAX threshold. Conclusions: Cortical porosity is a risk factor for fracture independent of aBMD and FRAX and improves identification of women with fracture.