## 3 Search Results  
### Bone and Implant Features  
#### 3.1.1 Geometry  
Bone  
Most 3D FE models have been developed by directly segmenting the bone geometry from computed tomography (CT) scan datasets of the patients and reducing the length of the original femur by resecting the distal part of the bone to reduce the computational cost (Table 1). Medical image processing software such as MIMICS(r) (Materialise, Leuven, Belgium) was typically used in most of the selected works to process CT scan data and distinguish bone from soft tissue using CT number threshold values [28; 34]. In some cases, the three dimensional geometry of a composite femur was used as a standard reference for the FE model (Table 1) [26; 29; 30; 31; 32]. Instead of the intact bone-implant model, few studies solely mimic the local adjacent region of bone-implant interfaces based on a cubic 3D CAD model [36; 39; 47] or a plane 2D model [48]. In addition, simplified cylindrical 3D models were reconstructed in [33; 40].  
Implant  
As shown in Table 1, only a few studies used simplified cylindrical or truncated cone shapes to model the femoral stem implant [33; 49], while cubic and planar geometries were considered only for local models that include the adjacent regions of the bone-implant interface [36; 39; 47]. The majority of FE models of the implant were derived from commercial stem designs. Implants with different outline structures and surface morphologies have been tested as comparative characteristics to investigate whether implant geometries affect stability [27; 28; 30; 32; 34; 36; 39; 50]. For example, [PERSON] et al. investigated osseointegration and bone remodelling performance using two fully coated cementless hip stems, one obtained from a generic TriLock ([PERSON], USA) design and the other derived from a shape optimisation study [27]. [PERSON] et al. [30] compared two commercial stems: the tapered stem (Trilock by [PERSON]) and a cylindrical cross-sectioned stem (AML by [PERSON]). The tapered stem was found to be intrinsically more stable than the cylindrical stem with a similar fit and material. [PERSON] et al. [35] focused on the short-stemmed implants and found that more bone formation occurred in the short stem with the lateral flare present compared to when the flare was absent.  
Few studies have demonstrated that the implant surface texture might significantly improve bone ingrowth, while non-textured implants might promote fibrous tissue forma  
Figure 1: Flowchart of article selection.  
tion [34; 36; 39]. Specifically, three types of stem surface macro-textures were compared in [36; 44]: softer connective tissues and relatively less bone growth were observed at the edges of the grooves/ribs, where high-stress concentration occurs. In addition, some authors simulated the coating surface based on a porous microstructure [33; 48; 51]. [PERSON] et al. [33] compared the functionally graded porous with two diameters of homogenous porous microstructures on implant stability. Models with larger pore sizes predicted fewer chances of bone ingrowth, and functionally graded porous surfaces promoted stability and reduced the failure chance.  
A few implant shape optimisation studies were also conducted in [27; 32]. [PERSON] et al. used a three-dimensional shape optimisation computational tool to obtain a hip stem with improved stability and reduced stress shielding. Various design variables were considered to define the geometric parameterisation of the stem, starting from the Tri-Lock (DePuy) stem geometry. By minimising three single objective functions targeting tangential displacement on the stem-bone interface, normal contact stress, and stress shielding, they obtained seven optimised stems, which were then used to evaluate long-term performance [32].