## 1 Introduction  
The incidence of low-energy fractures (e.g., falling from standing height) of the acetabulum has increased substantially (2.4-fold) in developed countries during recent decades [1; 2; 3]. Low-energy acetabular fractures are common among the geriatric population, and in most cases, they happen due to sideways falling [4; 5], when the trochanteric soft tissue (TST) hits the ground and the impact force is transmitted through the femoral neck and head to the acetabulum [6; 7]. Many factors such as bone and soft-tissue quality and body configuration during impact can affect the incidence, severity, and type of low-energy acetabular fractures [2; 8; 9]. Owing to the higher incidence, the mechanism of proximal femur fractures resulting from low-energy falls has been studied widely [10; 11; 12; 13; 14]. Through different computational and experimental methods (e.g., mass-spring-damper system, inverse pendulum, pelvis release, and free-fall from standing height), the range of force applied to the femur and its corresponding impact velocities were reported as 1004-9990 N and 580-6070 mm/s, respectively [15]. Also, [PERSON] et al. [16] reported that the whole-body kinetic energy range varies from 160 to 387 J in backward and from 6 to 291 J in forward rotation during sideways falls. These force and impact velocity ranges do not necessarily imply the femoral fracture incidence. The typical range of the force that can cause a fracture in a femur during a sideways fall was reported from 1500 to 4000 N [15], although much smaller (573 N) [17] and much bigger forces (15,304 N) [18] have been reported. Even if the mortality rate of geriatric acetabular fractures is higher than that of proximal femur fracture [19], low-energy acetabular fractures have rarely been investigated [9; 20]. [PERSON] et al. [20] studied the acetabular fracture for standing and seating positions and reported the corresponding fracture loads as 3200 and 2300 N. Our previous study [9] showed that whereas the ground reaction force equal to 2600 N may cause a femoral fracture, it does not lead to acetabular fracture. Whereas the effect of body configuration at the impact on the acetabular fracture was studied previously [9], the effect of other variables such as impact velocity (V\({}_{\text{Impact}}\)), flooring material, and TST stiffness on low-energy acetabular fractures has remained underexplored. V\({}_{\text{Impact}}\) is positively correlated with the body weight and height and, therefore, it can be speculated that taller and heavier individuals are at higher risk of fracture during a low-energy sideways fall [15]. Compliant flooring may decrease the incidence and severity of the injuries resulted from low-energy falls [21]. The role of flooring material in the prevention of bone fractures reflects in its shock-absorbent properties and ability in the attenuation of the force [22]. The effect of flooring material in low-energy fractures is somewhat unclear. Previous studies on low-energy fractures have indicated that compliant flooring might contribute to fracture prevention within the proximal femur (up to a 76.6% reduction in the peak force in the femoral neck) [22; 23; 24], whereas it has also been suggested that changing the flooring material does not notably affect the impact force [25; 26]. Some studies [27; 28] showed that novel compliant flooring systems can reduce the risk of proximal fracture substantially in comparison with conventional flooring materials. The role of TST thickness and mechanical properties in the attenuation and distribution of the impact load is critical. It was shown that a lower body mass index is correlated with an elevated risk of hip fracture [29; 30] and [PERSON] et al. [31] suggested that the persons with a lower body mass index have a thinner TST too and their TST is unable to attenuate the impact force properly. Also, [PERSON] et al. investigated the effects of TST thickness and hip impact velocity on low-energy proximal femur fractures [32; 33].