## 4 Discussion
The ROM for bone-to-bone impingement, which is known as a major cause of limited ROM of the hip joint, was lower compared to implant-to-implant impingement, which is in line with the literature [23; 32; 71]. However, it should be carefully noted that the virtual ROMs during external rotation exceeded the clinical expectations [35; 55; 57], most likely due to the neglected active and passive parts of the soft-tissue structures, which are known to limit the ROM. This is also supported by the study of [PERSON] et al. [64], where they have investigated the impingement on cadaver specimens and reported that computational assessment of ROM tended to overestimate the values due to the absence of soft-tissue structures. Moreover, our results are in excellent agreement with a recent study conducted by [PERSON] et al. [54], where they reported that neglecting soft-tissue structures in computer simulations led to significant overestimation of hip ROM up to 68.1\({}^{\circ}\) for external rotation at 90\({}^{\circ}\) flexion (more than 60\({}^{\circ}\) in our results). Therefore, the ROM for such movement is not only controlled by bone-to-bone or implant-to-implant impingement but also limited by the surrounding soft-tissue structures of the hip joint, i.e., muscles, capsule, labrum, and ligaments [54; 64]. Hence, the results for external rotation at 90\({}^{\circ}\) flexion should not be taken for direct comparison with data from clinical examinations of patients. Regarding the influence of THR design parameters, we observed a minor influence of the CCD angle on ROM for all movements, which is in accordance to the study by [PERSON] et al. [51]. It is also known that a change in CCD angles requires adaption of cup anteversion, to overcome the reduction of ROM caused by increased CCD angle [41], which we also observed during flexion movement. However, inaccuracy of the manually performed alignment of the femoral hip stem is a factor that influences the ROM as a function of the CCD angle. Considering the acetabular cup, increasing the cup size led to higher ROM in the flexion and internal rotation movements. Since prosthetic impingement was mostly between the neck and the liner, the cross-interference of other parameters can influence the ROM. The underlying factor in the increased ROM may be the prosthetic head diameter because the patients with a larger cup also received a larger head (Table 1). Therefore, the increase of ROM is most likely caused by the resulting higher head-to-neck ratio. Additionally, there is no systematic methodology available to assess stem antertorsion from radiographs, which also complicates the efforts to reconstruct postoperative alignment. A second limitation is the fact that the bone geometries of 19 patients were used for this investigation, which leads to the additional cross-interference of varying bone geometry. With respect to parameter studies, our MRI-based framework could be used for analyzing the interplay between implant positioning and design parameters, such as head-to-neck ratio, CCD angle, head size, and stem antertorsion as well as cup anteversion and inclination as previously shown in the comprehensive computational study conducted by [PERSON] et al. [41]. Moreover, our framework may contribute to an improved preoperative planning in the future by virtually testing off-the-shelf endoprosthetic designs, thus assisting an orthopedic surgeon to select a proper implant design in terms of personalized component positioning based on the patient's requirements, i.e., to maximize the impingement-freeROM. Another limitation was that the hip joint was assumed to have a fixed center of rotation during motion. In fact, the prosthetic head and liner are not perfectly congruent due to the clearance between head and acetabular cup, allowing translational degrees of freedom [27].