Stress-strain index
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The stress-strain index (SSI), of a bone, is a surrogate measure of bone strength[1] determined from a cross-sectional scan by QCT or pQCT (radiological scan). The Stress-Strain Index is used to compare the strucural parameters determined by analysis of QCT/pQCT cross-sectional scans to the results of three point bending test.
[edit] Definition
It is calculated using the following formula:[2]
Where:
- rmax is the distance of voxel from centre
- CD is the apparent cortical (bone) density
- ND is the normal (cortical bone) density
- ri is the pixel position from the centre
- a is the area of a pixel
[edit] History and relation to moments of inertia
It was developed by the manufacturer of a peripheral quantitative CT (pQCT) scanner,[2] and is considered to be by some an improvement over the information provided by calculating the area moments of inertia and polar moments of inertia.
[edit] References
- ^ Ward K, Roberts S, Adams J, Mughal M (2005). "Bone geometry and density in the skeleton of pre-pubertal gymnasts and school children.". Bone 36 (6): 1012–8. doi: . PMID 15876561.
- ^ a b Hasegawa Y, Schneider P, Reiners C (2001). "Age, sex, and grip strength determine architectural bone parameters assessed by peripheral quantitative computed tomography (pQCT) at the human radius.". J Biomech 34 (4): 497–503. doi: . PMID 11266673.