## 4 Discussion
### Comparison of Quality and Mechanical Tests  
Figure 9 compares all our results on the cube samples: BMD, porosity, Tb.Th, Tb.Sp, \(\sigma_{\text{max}}\), \(\sigma_{\text{r}}\), and \(E\). In Figure 10, we show the quality parameters compared against age and gender. Again, all scales are spanned by their corresponding lower and higher values to facilitate comparisons. Moreover, the values for these parameters fall within the range of published human values (see, e.g., [40; 41; 42]).  
From our results, we can note that BMD for the 57-year-old male donor (Donor 4 shown in orange) got one of the highest values for our osteoporotic donors, but its porosity was also the second-highest, only placed after our oldest donor. On the other hand, the porosity of the 50-year-old male donor (Donor 2 displayed in navy-blue), whose BMD was one of the lowest, does not show a dramatically high porosity. These results seem counter-intuitive and suggest that BMD could not be considered as the sole criteria for defining the bone strength. In that sense, studying bone quality in more extensive detail could prove complementary in bone assessment for clinical applications.  
Even when our results put our control sample in the osteopenia group, we have to remember that clinical diagnosis criteria consider total bone, which contains not only trabecular bone, but also the denser and more compact cortical bone. Based on this, our BMD values were expected to be lower; hence, we consider our control donor to be healthy.  
The stiffness is related to the bone mineralization or the BMD value. This relationship can be examined more deeply by comparing BMD and \(E\). In that sense, \(E\) showed a higher dispersion over the minimum-maximum range. This behavior in \(E\) allows for better discrimination of our sample cubes based on mineralization. Such an enhanced capacity of discrimination could be an important asset in the development of future diagnosis techniques.  
Our inter-individual variations show the need for performing a larger number of experiments to generate consistent statistics of the quality parameters before these can be used in other areas such as mathematical modeling or future clinical diagnosis. Nevertheless, the results obtained up to this point show promising potential, especially when compared to other studies such as [40], in which the trabecular thickness and space re  
Figure 9: Comparison of all the measurements made on our cube samples. Color coding is the same as in Figure 8. Note that scales in porosity and Tb.Sp go in opposite direction with respect to others (decreasing from left to right) for comparison purposes.  
mained fairly constant despite the strength of the bone, hence leading to the conclusion that trabecular data were poor indicators of bone quality. Here, we show that Tb.Th and Tb.Sp are inversely correlated (as expected) while the first one is directly correlated to \(\sigma_{\text{max}}\) and \(E\). Therefore, we show that trabecular data may be used as indicators of bone quality, especially when signs of osteoporosis are present.  
Figure 10: Comparison of quality parameters against age and gender. All graphs show raw data from female donors in red dots and those from male donors in blue. Dashed lines correspond to the linear regression of the corresponding data. Significant differences among genders were found in the case of trabecular space (\(t\)-test, \(p=0.0017\)).