# Aspect-Related Mechanical Properties of the Cortical Bone in the Third Metacarpal Bone of Mares
## 3 Results  
### Aspect-Related Properties of the MC III  
Cortical bone thickness differed between aspects of the MC III (\(p<0.0001\)). In the mid-length of the MC III diaphysis, the medial aspect (13.9 mm) was thicker than the dorsal (10.9 mm), lateral (10.9 mm), and palmar (6.6 mm) aspects, while the palmar aspect was thinner than the dorsal, lateral, and medial aspects. No significant difference in cortical bone thickness was found between the dorsal and lateral aspects of the MC III (Figure 3A). Moreover, cortical bone relative density did not vary significantly between aspects of the MC III (dorsal aspect, 1731 HU; lateral aspect, 1771 HU; medial aspect, 1724 HU; palmar aspect, 1698 HU; \(p=0.15\); Figure 3B).  
Figure 3: Aspect-related properties of the metacarpal bone III (MC III) include: (**A**) cortical bone thickness, (**B**) cortical bone relative density, and (**C–F**) the elastic modulus calculated based on the  
results of mechanical tests. (**C**) The 3-point bending test in the external-internal direction; (**D**) uniaxial compression test in the proximo-distal direction; (**E**) uniaxial compression test in the external-internal direction; and (**F**) uniaxial compression test in the latero-lateral direction. Boxes represent lower quartile, median, and upper quartile, whereas whiskers represent minimum and maximum values. Lowercase letters (a, b, c) indicate significant differences between MC III aspects for \(p\) < 0.05.  
The elastic modulus, calculated based on the sample reaction force from a 3-point bending test performed in the external-internal direction, differed between aspects of the MC III (_p_ = 0.002). The sample reaction force-based elastic modulus was higher for the dorsal aspect (16.0 GPa) than for the palmar aspect (10.0 GPa), with no differences observed between the dorsal, lateral (18.1 GPa), and medial (16.0 GPa) aspects, or between the lateral, medial, and palmar aspects (Figure 3C).  
The elastic modulus, calculated based on the axial compression force from the uniaxial compression test, differed between aspects of the MC III when tested in the proximo-distal direction (_p_ = 0.02; Figure 3D) and the externo-internal direction (_p_ = 0.002; Figure 3E) but not in the latero-lateral direction (dorsal aspect, 11.1 GPa; lateral aspect, 13.5 GPa; medial aspect, 8.9 GPa; palmar aspect, 7.9 GPa; \(p\) = 0.1; Figure 3F). In the proximo-distal direction, the axial compression force-based elastic modulus was higher for the dorsal aspect (57.5 GPa) than for the palmar aspect (32.4 GPa), with no differences observed between the dorsal, lateral (21.0 GPa), and medial (34.6 GPa) aspects, or between the lateral, medial, and palmar aspects. In the externo-internal direction, the axial compression force-based elastic modulus was higher for the dorsal (24.6 GPa) and palmar (22.7 GPa) aspects than for the lateral (8.3 GPa) and medial (6.2 GPa) aspects, with no differences observed between the dorsal and palmar aspects, or between the lateral and medial aspects.  
It is notable that across all tested samples, the mean sample reaction force-based elastic modulus was 15.1 GPa (ranging from 9.4 to 21.9 GPa). However, due to the observed differences between MC III aspects, this value should not be generalized to the entire diaphysis.