BMD-based assessment of local porosity in human femoral cortical bone

Abstract

Cortical pores are determinants of the elastic properties and of the ultimate strength of bone tissue. An increase of the overall cortical porosity (Ct.Po) as well as the local coalescence of large pores cause an impairment of the mechanical competence of bone. Therefore, Ct.Po represents a relevant target for identifying patients with high fracture risk. However, given their small size, the in vivo imaging of cortical pores remains challenging. The advent of modern high-resolution peripheral quantitative computed tomography (HR-pQCT) triggered new methods for the clinical assessment of Ct.Po at the peripheral skeleton, either by pore segmentation or by exploiting local bone mineral density (BMD). In this work, we compared BMD-based Ct.Po estimates with high-resolution reference values measured by scanning acoustic microscopy. A calibration rule to estimate local Ct.Po from BMD as assessed by HR-pQCT was derived experimentally. Within areas of interest smaller than 0.5 mm, our model was able to estimate the local Ct.Po with an error of 3.4%. The incorporation of the BMD inhomogeneity and of one parameter from the BMD distribution of the entire scan volume led to a relative reduction of the estimate error of 30%, if compared to an estimate based on the average BMD. When applied to the assessment of Ct.Po within entire cortical bone cross-sections, the proposed BMD-based method had better accuracy than measurements performed with a conventional threshold-based approach.

Large cortical bone pores in the tibia are associated with proximal femur strength

“…130 μm and 95 μm for 1 st and 2 nd generation HR-pQCT, respectively). HR-pQCT can estimate Ct.Po beyond its nominal resolution by using BMD-based approaches [28], meaning that a measurement of relCt.Po is readily available in vivo from HR-pQCT images. Therefore, future HR-pQCT studies should investigate the relation between fracture risk and the prevalence of large pores in the cortical bone of the distal skeleton.…”

“…Volumes were further coarsened to an isotropic voxel size of 2.7 mm (Fig 1A), and gray values converted first to vBMD and then to bone volume fraction. For this, a linear calibration rule was derived for the specific set of samples using 3D registered scanning acoustic microscopy (SAM) and HR-pQCT images of the proximal femur shafts [28]. An elastic-yield constitutive law based on the local bone volume fraction was adapted, as described in [26].…”

Estimation of Cortical Bone Microstructure From Ultrasound Backscatter

“…Nineteen left tibia bones from human cadavers (6 male, 13 female, age: 83.7 ± 8.4 years, range: 69 -94 years) described in previous studies [1,15,35] were used for the ex-vivo measurements. Specimens were received without soft tissue and distal ends (cut off at approximately 50 %) and stored at −20 °C.…”

“…Briefly, aBMD was measured at the femur neck using a Hologic Discovery A scanner (Discovery QDR, Hologic Inc., USA). Non-linear homogenized voxel Finite Element (hvFE) models of the proximal femur were developed from second-generation HR-pQCT datasets [35] of the entire proximal femur to estimate stiffness (hvFE_S) and ultimate force (hvFE_Fu) under stance and side-ways fall conditions. Whereas individual hvFE models have been developed for left and right proximal femora of the 19 donors, only the properties from the left side will be compared with the corresponding left tibia properties hereinafter.…”

“…2a). The estimations of tissue impedance and structural parameters from SAM images has been described in detail in previous studies [30,35,37]. Briefly, the bone matrix was segmented from the background using an adaptive threshold [38].…”