Bone Abstracts

High resolution peripheral quantitative computed tomography (HR-pQCT) in combination with micro finite element analysis (μFEA) is a promising tool to assess longitudinal changes in bone mechanical properties during the fracture healing process in the distal radius. In the present study we investigate if these changes can be detected as well when using images with lower resolutions, comparable to clinical QCT images.

Postmenopausal women with a stable distal radius fracture (n=17) were scanned by a HR-pQCT system at four visits during a 12 week follow-up period. HR-pQCT scans (isotropic voxel size 82 μm) were downscaled, mimicking QCT resolutions. Downscaled voxel sizes were 164×164×164, 328×328×328, 656×656×656, 1312×1312×1312 and 328×328×656 μm, respectively. Stiffness in compression, torsion and bending were assessed by μFEA based on HR-pQCT scans and by FEA based on downscaled scans, both using grey-level dependent material properties. μFEA outcomes and FEA outcomes based on the downscaled images were compared by assessment of Spearman’s correlation coefficient and Bland-Altman plots. A linear mixed effect model was used to identify significant changes in stiffness from baseline. When similar significant longitudinal changes were found for μFEA and downscaled FEA, the resolution was considered sufficient to assess bone stiffness in the fracture healing process.

All correlations were significant (P<0.05), however decreased when a larger downscaling factor was applied. FEA outcomes with voxel sizes of 328×328×656 μm and smaller deviated approximately 13, 7 and 9% from μFEA outcomes for stiffness in compression, torsion and bending, respectively. μFEA outcomes all showed significant changes from baseline at 12 weeks post-fracture (P<0.05). The largest downscaled voxel size with significant longitudinal changes in stiffness was 328×328×656 μm (P<0.1).

Concluding, FEA based on scans with clinically feasible voxel sizes could lead to similar conclusions for torsional and bending stiffness as μFEA based on HR-pQCT images during the fracture healing process.