Stress-strain index
Jump to navigation
Jump to search
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.
Definition
It is calculated using the following formula:[2]
<math>SSI = \sum_{i=0}^n {{r_i^2 a ({{CD} \over {ND}})} \over {r_{max}}}</math>
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
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.
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. PMID 15876561.
- ↑ 2.0 2.1 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. PMID 11266673.