Validation of distal radius failure load predictions by homogenized- and micro-finite element analyses based on second-generation high-resolution peripheral quantitative CT images

Abstract

This study developed a well-standardized and reproducible approach for micro-finite element (mFE) and homogenized-FE (hFE) analyses that can accurately predict the distal radius failure load using either mFE or hFE models when using the approaches and parameters developed in this study.

Introduction: Micro-FE analyses based on high-resolution peripheral quantitative CT (HR-pQCT) images are frequently used to predict distal radius failure load. With the introduction of a second-generation HR-pQCT device, however, the default modelling approach no longer provides accurate results. The aim of this study was to develop a well-standardized and reproducible approach for mFE and hFE analyses that can provide precise and accurate results for distal radius failure load predictions based on second-generation HR-pQCT images.

Methods: Second-generation HR-pQCT was used to scan the distal 20-mm section of 22 cadaver radii. The sections were excised and mechanically tested afterwards. For these sections, mFE and hFE models were made that were used to identify required material parameters by comparing predicted and measured results. Using these parameters, the models were cropped to represent the 10-mm region recommended for clinical studies to test their performance for failure load prediction.

Results: After identification of material parameters, the measured failure load of the 20-mm segments was in good agreement with the results of mFE models (R2 = 0.969, slope = 1.035) and hFE models (R2 = 0.966, slope = 0.890). When the models were restricted to the clinical region, mFE still accurately predicted the measured failure load (R2 = 0.955, slope = 1.021), while hFE predictions were precise but tended to overpredict the failure load (R2 = 0.952, slope = 0.780).

Conclusions: It was concluded that it is possible to accurately predict the distal radius failure load using either mFE or hFE models when using the approaches and parameters developed in this study.

Keywords: Bone strength; Distal radius; Finite element analysis; HR-pQCT; Micro-FE; Osteoporosis.

Conflict of interest statement

Bert van Rietbergen is a consultant for Scanco Medical AG.

Andrés Julián Arias-Moreno, Hadi S. Hosseini, Melissa Bevers, Keita Ito, and Philippe Zysset declare that they have no conflict of interest.

Figures

Fig. 1

The downscaled full mask (red) overlaid with the original full mask (dark blue). Note that the downscaled mask includes the full mask completely

Fig. 2

Top row: Density homogenization of the cancellous region for a radius cross section with green lines delineating the periosteal and endosteal contours. The blue square represents a brick element and the blue circle the spherical region around the element centroid that is used for homogenization. Depending on the element location, different approaches are used: a If the spherical region was completely within the cancellous compartment, the element trabecular density (ρtrab) was evaluated for the full sphere and assigned to the full element (ftrab = 1). b If the sphere was only partly inside the cancellous compartment, the element trabecular density (ρtrab) was evaluated only for the part of the sphere within the cancellous region which was assigned to the full element (ftrab = 1). c If the sphere and the element were only partly within the cancellous compartment, the element trabecular density (ρtrab) was evaluated only for the part of the sphere within the cancellous region which was assigned to the part of the element (ftrab < 1) that was within the cancellous compartment. Bottom row: Density homogenization of the cortical region. The blue square represents a brick element, which for the cortical bone also represents the region used for homogenization. Depending on the element location, different approaches were used: d If the element was completely within the cortical compartment, the element cortical density (ρcort) was evaluated for the full element region and assigned to the full element (fcort = 1). e, f If the element was only partly within the cortical compartment, the element cortical density (ρcort) was evaluated only for the part of the element that was within the cortical compartment which was assigned to the part of the element (fcort < 1) that was within the cortical compartment

Fig. 3

Schematic representation of the homogenization procedure. In a first step, a “full mask” was generated representing the volume within the periosteal contour. In a second step, this mask was downscaled and segmented to obtain a 1.7-mm brick element representation. In a third step, the homogenized density and fabric were calculated for each brick element and assigned to the element

Fig. 4

Regression of the FE-predicted stiffness (left) and failure load (right) with the experimentally measured values for the 20-mm segments

Fig. 5

Regression of the FE-calculated failure load based on the 10-mm segments (horizontal axis) and the experimentally measured failure load for the 20-mm segments (vertical axis)

Fig. 6

Bland-Altman plots to compare the failure load calculated for the 20-mm segments with the failure load calculated for the 10-mm segments (top), the failure load calculated for the 20-mm segments with the experimentally measured failure load (bottom left), and the failure load calculated for the 10-mm segments with the experimentally measured failure load (bottom right)