Stress strain index

The Stress-Strain-Index  (abbreviated  SSI ; in German: Deformation - Stress -Index) of a bone is a better measure of its strength or flexural strength than it can be calculated using the area moment of inertia . The stress strain index enables the comparison of in vivo measurement results (cross-sectional scans using QCT / pQCT ) with the results of typical material testing tests such as B. the three-point bending test .

definition

The SSI is calculated as follows:

${\displaystyle SSI=\sum _{i=0}^{n}{\frac {r_{i}^{2}\cdot A\cdot {\frac {CD}{ND}}}{r_{\mathrm {max} }}}}$

With

• ${\displaystyle r_{i}}$: Distance of the pixel from the center
• ${\displaystyle A}$: Area of the pixel
• ${\displaystyle CD}$: apparent (mean) bone density of the voxel
• ${\displaystyle ND}$: typical density of bone as a material ( cortical bone )
• ${\displaystyle r_{\mathrm {max} }}$: Distance of the voxel from the center.

Individual evidence

1. ↑ Ward K., Roberts S., Adams J., Mughal M .: Bone geometry and density in the skeleton of pre-pubertal gymnasts and school children . In: Bone . 36, No. 6, 2005, pp. 1012-1018. PMID 15876561 .
2. ↑ ^{a b} Hasegawa Y., Schneider P., Reiners C .: Age, sex, and grip strength determine architectural bone parameters assessed by peripheral quantitative computed tomography (pQCT) at the human radius. . In: J Biomech . 34, No. 4, 2001, pp. 497-503. PMID 11266673 .