## 3 Search Results
### Boundary Conditions  
A distinction between macroscale, microscale, and hybrid techniques has been made when detailing the boundary conditions for the selected FE modelling studies (Table 2). In particular, macroscale techniques are referred to for those studies where the level of modelling concerns the overall behaviour of the implant-femur structure, while all the works that considered a model that only included the adjacent regions of the bone-implant interface were classified as microscale models (highlighted rows in Table 1). In macroscale models (Figure 2a), loading conditions are typically determined based on the subject's body weight and applied as hip contact forces and muscular loads (Table 2). Muscle loads are distributed over the respective attachment areas [51] or considered rigid plates attached to the stem and femur to avoid stress concentration [37], while the hip contact forces are usually applied as a concentrated load to the centre of the head of the femoral stem [34; 37]. Torsional loading applied to the superior part of the implant was considered in [40]. The femur is usually constrained at the distal part after defining a specific distance \(h\) below the implant tip (e.g., 45 or 50 mm) (Figure 2) [34; 51]. The conditions prescribed by [PERSON]'s principle were checked by [50; 52]. Forces and moments extracted from daily activities such as normal walking, stair climbing, standing up, and sitting down are considered in the majority of the selected studies with reference to the work conducted by [PERSON] et al. [62], [PERSON] et al. [63; 64] and [PERSON] et al. [65]. Most of the studies considered static loading scenarios [26; 27; 28; 29; 30; 31; 32; 34; 35; 37; 38; 39; 40; 42] or solved a quasi-static problem by discretizing the load history into sub-steps of static loading [50; 52]. Some authors have proposed adding a less-loaded phase to mimic the resting period or walking with a walking aid after the operation [34; 37; 38; 41]. For example, in [41], an unloading phase was included in each loading cycle with a compressive force of 50 N considered for stability purposes. In the study conducted by [34; 37], both muscle and hip forces were reduced in the first simulation period (e.g., 1-8 iterations) considering 80% of the patient's BW and swing phase of the gait cycle. [PERSON] et al. [38] introduced a one-week period of no loading before simulating 25 weeks of healthy activities, where four different loading cases, including resting, were considered. In addition, the frequency of various activities has been taken into account in a few studies [35; 38]. The microscale models are usually solved under loading conditions, in terms of both loads and displacements, applied to the implant part while constraining the bone [36; 39; 47]. In [48], the fixed part was the bottom surface of the implant. Shear load or tangential displacements were typically used to impose relative motion between the bone and the implant, while compressive force or normal displacement were applied to simulate gap distance and press-fit conditions at the bone-implant interface [36; 39]. A hybrid approach was adopted in [37; 51], where loading conditions applied to the microscale model were obtained by first solving the macroscale analysis (Table 2). Some authors investigated how different loading conditions could influence the simulation results in terms of osseointegration [34; 38; 39; 52]. [PERSON] et al. [34] examined the influence of two typical loading scenarios (i.e., normal walking and stair climbing) on the growth of the connective tissue phenotypes (i.e., mesenchymal stem cells, fibrous tissue, cartilage, and bone) around the stem. The results demonstrated a higher occurrence of fibrous tissue during stair climbing in comparison to normal walking. This suggests an increased risk of early AL during stair climbing, potentially attributed to elevated torsional moments at the bone-implant interface.