## 4 Discussion  
This parametric simulation study assessed the effect of impact velocity, conventional flooring materials, and trochanteric soft-tissue stiffness on the incidence, severity, and type of acetabular fracture. While the effect of the body configuration on the acetabular fracture was studied previously [9], to the best of our knowledge, this is the first study evaluating the effect of \(\mathrm{V_{Impact}}\), flooring material, and TST stiffness on acetabular bone failure. Since this parametric study aimed to investigate the effect of \(\mathrm{V_{Impact}}\), flooring material, and TST quality alterations on the relative incidence and type of acetabular fracture and no direct empirical validation was available, the model was validated against previous experimental studies. Previously, [PERSON] et al. [75] and [PERSON] et al. [13] used cadaveric testing to validate their finite element models of the femur, predicting the crack initiation and propagation. The GRF responses predicted by our models in terms of GRF\({}_{\mathrm{max}}\), \(t_{\mathrm{max}}\), and shape of the curves were in good agreement with the previous studies with similar impact velocities [27; 45; 72]. Also, as discussed in the following paragraphs, the results obtained regarding the type of acetabular fracture and the effect of conventional flooring material were consistent with the clinical findings. Previous studies [10; 30; 32; 76] have hypothesized that a greater height of the center of mass in taller persons results in a higher impact velocity, and consequently, an elevated risk of proximal femur fracture. [PERSON] et al. [32] showed that by increasing the \(\mathrm{V_{Impact}}\) from 1200 to 3170 mm/s, the strain ratio (\(\mathrm{\varepsilon_{max}}/\mathrm{\varepsilon_{ultimate}}\)) increases gradually and that by a further increase to 4790 mm/s, the strain ratio jumps up (more than two times in comparison with 3170 mm/s). The significant effect of \(\mathrm{V_{Impact}}\) was also demonstrated by our study for the acetabular fracture. In the current study, a substantial change in the pattern and intensity of compressive bone failure within the acetabulum was observed for \(\mathrm{V_{Impact}}>3170\) mm/s (Figure 2a). Also, [PERSON] et al. [32] stated that for \(\mathrm{V_{Impact}}\leq 1200\) mm/s, the strain ratio would be less than one (0.77), which is consistent with our finding indicating no compressive bone failure for \(\mathrm{V_{Impact}}=580\) mm/s (Figure 5). Through another study on the lateral compressive failure of the pelvis, [PERSON] and [PERSON] [77] introduced 8000 N as the threshold impact force for the incidence of obvious pelvic fracture, close to the corresponding GRF\({}_{\mathrm{max}}\) (8835 N) of the \(\mathrm{V_{Impact}}=3170\) mm/s in the present study (Figure 2a). Also, the \(\mathrm{I_{GRFmax}}\) for \(\mathrm{V_{Impact}}>3170\) mm/s was more than two times that of \(\mathrm{V_{Impact}}\leq 3170\) mm/s (43.63-62.24 vs. 91.38-111.94 N.s) (Figure 2a). Not only was GRF affected greatly by the impact velocity, but the IRF was increased and \(\mathrm{t_{REFmax}}\) decreased for all joints (including hip) by increasing \(\mathrm{V_{Impact}}\). This can explain why a higher \(\mathrm{V_{Impact}}\) can change the incidence and type of acetabular fracture. A higher \(\mathrm{V_{Impact}}\) is associated with a bigger impact force exerted in a shorter time (a higher strain rate), which makes the bone prone to fracture during falls [78]. In a recent study, [PERSON] et al. [79] concluded that by increasing the impact energy (velocity), the type of acetabular fracture changes. Also, they stated that the anterior wall fracture is common among elderly people who experience low-energy event trauma.