## 4 Discussion
A comparison of the regions with concentrated bone failure (Figure 5) with the fractured regions depicted in [PERSON]'s acetabular fracture classification [80] (Appendix A, Figure A5) showed that the type of acetabular fracture is the anterior wall at low velocities (\(\mathrm{V_{Impact}}\leq 3170\) mm/s), whereas at higher velocities it changes to both associated columns, representing one of the most prevalent types of acetabular fracture in the senior population [4; 81]. Overall, it seems that \(\mathrm{V_{Impact}}\cong 3170\) mm/s can be considered as the threshold value for the incidence of acetabular bone failure. By assuming the body as a lumped falling object and the law of conservation of energy, the corresponding height to this impact velocity would be equal to 51.2 cm. \(\mathrm{V_{Impact}}=3170\) mm/s was reported by [PERSON] [82] as the average value for hip impact velocity. This can explain why a sideways fall from a standing height among healthy young adults who have healthy bone remodeling rarely ends up in an acetabular fracture [83]. This study showed that, unlike impact velocity, conventional flooring materials did not affect the acetabular fracture remarkably. Only in the case of compliant surfaces such as agglomerated cork and linoleum GRF was slightly lower and \(\mathrm{I_{GRFmax}}\) was slightly higher than for the stiffer flooring (Figure 2b). Also, flooring material affected the IRF\({}_{\mathrm{max}}\) within thejoints, and the bone failure pattern negligibly. These findings are consistent with [PERSON] et al. [21], who concluded that while novel compliant flooring materials such as SmartCells and Sorbashock can attenuate the impact force considerably, conventional surfaces cannot notably reduce the exerting force to the hip during a fall. Similarly, [PERSON] et al. [84] concluded that conventional flooring can only provide negligible impact on the force attenuation, and novel flooring materials such as rubber with a honeycomb structure can attenuate the impact force up to 25%. Also, [PERSON] et al. [26] stated that there is not an obvious difference in terms of trend, magnitude, and maximum GRF resulting from running on different flooring materials, and [PERSON] et al. [25] reported that GRF\({}_{\text{max}}\) ranges from 11.9 to 12.4 kN for four different flooring materials. This is explained by the fact that the deceleration during impact is influenced by the initial conditions, viscoelastic properties of the ground, and the soft tissue. In terms of impact force attenuation, changing the conventional flooring material may not be as effective as previously thought with regard to the protection of elderly individuals from bone fractures in nursing facilities. The dissipative role of trochanteric soft tissue can be attributed to its thickness or quality. [PERSON] et al. [31] and [PERSON] et al. [32] concluded that TST thinning increases the risk of proximal femur fracture, but they did not consider TST stiffness changes due to aging, as reported by [PERSON] and [PERSON] [50] and [PERSON] et al. [34]. The current study revealed that TST stiffness mostly affects the post-impact phase. Also, it is strongly correlated with GRF\({}_{\text{max}}\) and IRF\({}_{\text{max}}\) within the sacroiliac joint, although this is not the case for t\({}_{\text{max}}\), I\({}_{\text{RFPmax}}\), and IRF\({}_{\text{max}}\) within the hip or pubic symphysis joints. This shows that soft-tissue stiffening due to aging leads to a loss of the tissue's inherent ability to dissipate impact force; therefore, the tissue transfers a higher amount of force toward the sacroiliac joint. In combination with osteoporosis, this can explain to some extent why a low-energy sacroiliac fracture is more common among elderly people [85]. This study showed that changes in TST stiffness do not alter the type of acetabular fracture substantially and do not remarkably affect the bone failure within the acetabulum in comparison with TST thickness as reported by [PERSON] et al. [32].