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

Abstract

SummaryWe 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.IntroductionNeither 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.MethodsWe 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.ResultsWomen 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.ConclusionsCortical porosity is a risk factor for fracture independent of aBMD and FRAX and improves identification of women with fracture.

The clinical contribution of cortical porosity to fragility fractures

“…Moreover, StrAx includes porosity of both the completely empty voxels, as well as voxels containing void and mineralized bone matrix. 11 Conversely, porosity quantified using this software for analysis of HR-pQCT images 24,25 or lowresolution CT images, 26 is higher than porosity reported with other methods. 11 Porosity of the compact-appearing cortex is B35% and that of the transitional zones is B60%, and the average porosity of the total cortex (compact-appearing plus transitional zones) is 43%, respectively.…”

“…26,27 The coefficients of variation for porosity of each cortical compartment were between 0.3 and 2.3%. 26 Thus, StrAx1.0 software provides accurate and reliable measurements of cortical porosity.…”

“…26,27 Bone is segmented by analyzing B3600 consecutive overlapping profiles around the perimeter of each cross-sectional slice.…”

“…11 Porosity of the compact-appearing cortex is B35% and that of the transitional zones is B60%, and the average porosity of the total cortex (compact-appearing plus transitional zones) is 43%, respectively. 26 StrAx software does not quantify the size and number of pores, but the proportion of porosity (emptiness) regardless of the size of the pores.…”

“…26,27 The agreement (R 2 ) between CT and HR-pQCT for quantification of porosity at the same femoral subtrochanter site ranged from 0.86 to 0.96. 26,27 The coefficients of variation for porosity of each cortical compartment were between 0.3 and 2.3%. 26 Thus, StrAx1.0 software provides accurate and reliable measurements of cortical porosity.…”