## 2 Materials and Methods
### Biomechanical Test Setup  
Biomechanical tests of custom-made implant 1 and reference implant 1 were performed on a hydraulic axial testing system (585 MiniBionix, MTS, Eden Prairie, MN, USA) (Figure 3a,b). Off-the-shelf stems were mounted torque-controlled to reference implant 1 as well as to custom-made implant 1 with 27 Nm. The stems were embedded in casting resin, such that the femoral components were tilted to 7\({}^{\circ}\) in the sagittal plane and 9\({}^{\circ}\) in the frontal plane. The load was applied via an off-the-shelf meniscus component with a height of 10 mm. In order to avoid shear stress, the interface between load actuator and meniscus component was lubricated with silicone oil such that the meniscus component was able to move freely in horizontal direction. The loading protocol consists of force controlled, sinusoidal compression with a peak load of 2.6 kN and a minimum load of 260 N. This cyclic load was applied with a frequency of 15 Hz for 10,000,000 cycles. The number of cycles is based on well-established standards of orthopedic implants to investigate high cycle fatigue phenomena of metallic components under dynamic loading [23]. In order to analyze the failure mechanism and the safety reserves, both assemblies were tested in addition according to the Locati method. After 10,000,000 cycles, the peak load was increased every 1,000,000 cycles for 500 N, whereby the ratio of minimum to \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Custom-Made Implant 1** & **Custom-Made Implant 2** \\ \hline Clinical case and pre-operative planning & & \\ \hline Implant components & & \\ Main failure mechanisms & Mechanical fatigue of proximal-anterior box area & \\ Corresponding FEA measure & Maximum tensile stress & \\ Post-operative image & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Overview of the custom-made implants. maximum load of 0.1 remained constant. The procedure was stopped at completion of load level 4.6 kN. The biomechanical tests of custom-made implant 2 and reference implant 2 were performed in two different setups (Figure 3c,d). The investigation was focused on the clinical acceptance of the taper junction itself. This taper junction was developed and tested within a hip assembly, consisting of a trochanteric module and a stem (Figure 3c). Custom-made implant 2 relies on the identical taper junction, yet in a knee assembly (Figure 3d). A biomechanical off-the-shelf knee assembly test with this taper junction was not available. Therefore, the results of the hip assembly test were compared to the results of the knee assembly test. The taper junctions in both biomechanical applications are exposed to combined bending load, such that this comparison was considered acceptable. In accordance with the clinical practice, in the hip assembly the stem was mounted to the Trochanteric module with a hammer punch in the axial direction. The locking screw was mounted using 10 Nm torque-controlled. The stem was embedded in casting resin with a tilt of 10\({}^{\circ}\) in the frontal plane and 9\({}^{\circ}\) in the sagittal plane. A load-controlled hydraulic axial testing system was used to apply a sinusoidal compression load with a maximum load of 2.3 kN and a minimum load of 230 N with a test frequency of 5 Hz. After 5,000,000 cycles, the load was increased every 1,000,000 cycles by 500 N, whereby the ratio between minimum and maximum load of 0.1 remained constant. The procedure was stopped after completion of load level 4.8 kN. The biomechanical test setup of custom-made implant 2 in the knee assembly (Figure 3d) is analog to the test setup of custom-made implant 1. The mounting of custom-made implant 2 to the stem was performed in accordance with reference implant 2 using a hammer punch and the locking screw was mounted (10 Nm torque controlled). The stem was embedded in casting resin at the proximal end such that a distance between joint line and embedding level of 132 mm resulted.