## 4 Discussion
Here, the impact of slight differences in ligament reference lengths, arising from variations in subjects' anthropometry between the two groups, on the final strain patterns is expected to be minimal, as the ligament length changes were normalised to their respective reference lengths defined at heel strike during level walking. Moreover, the kinematics obtained by the means of single-plane video-fluoroscopy used as input motion data are limited by the out-of-plane inaccuracy. However, the effect of varying the input kinematics and TKA implantation on the ligament elongation was previously assessed by a sensitivity analysis, reporting only minor influences of medio-lateral translation on ligament elongation patterns [20; 26]. In this project, the ligament bundles were modelled as one-dimensional curvilinear fibres connecting the femoral and tibial attachment sites. In vivo lengthening of ligament bundles may be considered as a more complex three-dimensional motion consisting of interfacial sliding and fibre twisting [58]. Finally, the small range of overlap between the flexion angles experienced by different subjects, especially in the stance phase of gait activities, precluded a complete analysis of inter-implant differences that may be highlighted at larger flexion angles. In conclusion, we demonstrated that ligament elongation patterns and, more specifically, those of the PCL clearly differ between dual-radii and gradually reducing radius implants. In addition, this project underscores the significance of the MCL and PCL in attaining mid-flexion stability following PCR-TKA. It further emphasises the critical requirement for achieving an optimal balance between implant design and ligament length change patterns to ensure satisfactory outcomes after joint replacement. Future studies with larger cohorts and a variety of implant designs are needed to gain a deeper understanding of how implant geometry influences post-TKA ligament function. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14219910/s1](https://www.mdpi.com/article/10.3390/app14219910/s1)]([https://www.mdpi.com/article/10.3390/app14219910/s1](https://www.mdpi.com/article/10.3390/app14219910/s1)). Table S1. Comparison of bone lengths derived from X-ray images with those obtained through scaling of the generic multibody model. Note: This comparison was conducted exclusively for the six subjects with available frontal X-ray images. Figure S1. Subject-specific elongation patterns along the complete level walking cycle for 15 subjects with DUAL implant. Different colours represent individual subjects, solid lines represent intra-subject mean while shaded area represent \(\pm\) SDs. Vertical lines indicate individual toe-off times. PCLal and PCLpm: anterolateral and posteromedial bundles of the posterior cruciate ligament; aMCL, iMCL, and pMCL, anterior, intermediate, and posterior bundles of the medial collateral ligament; LCL, iMCL, anterior, intermediate, and posterior bundles of the medial collateral ligament; LCL, lateral collateral ligament. Figure S2. Subject-specific elongation patterns along the complete level walking cycle for 15 subjects with GRAD implant. Different colours represent individual subjects, solid lines represent intra-subject mean while shaded area represent \(\pm\) SDs. Vertical lines indicate individual toe-off times. PCLal and PCLpm: anterolateral and posteromedial bundles of the posterior cruciate ligament; aMCL, iMCL, and pMCL, anterior, intermediate, and posterior bundles of the medial collateral ligament; LCL, lateral collateral ligament. Figure S3. Subject-specific elongation patterns along the complete cycle during sit-to-stand-to-sit activity for 15 DUAL subjects. Different colours represent individual subjects, solid lines represent intra-subject means and shadings represent \(\pm\) SDs.