## 3 Results
### Level Gait  
During the stance phase of level walking, for both implant designs, a small inter-subject variability was observed in the ligament elongation patterns, however, with transition to the swing phase, the inter-subject variability started to increase (Figure 2, Figures S1 and S2; Supplementary Information File). During the first half of the gait cycle (GC), the MCL bundles remained close to their reference lengths (with average length changes between -0.2 and 1.2% for the GRAD subjects and from 0 to 1.2% for the DUAL subjects), while the PCL and LCL bundles were slightly lax (with average length changes between \(-\)4.8 and 0.4% for the GRAD subjects and from \(-\)4.5 to 0% for the DUAL subjects) (Figure 2).  
During the second half of the GC, the different bundles started to exhibit distinct elongation patterns (Figure 2); while the PCL and LCL bundles experienced a rapid slackening, the MCL bundles started elongating. Here, the PM portion of the PCL showed lower strains than the AL portion and a local minimum at around 70% of the GC in level gait (GRAD: \(-\)14.07 \(\pm\) 3.4%, DUAL: \(-\)11.59 \(\pm\) 3.76%), while the AL portion of the ligament reached its maximum elongation at around 80% GC (GRAD: 1.96 \(\pm\) 2.88%, DUAL: 3.28 \(\pm\) 2.69%, Figure 2).  
From 30% to 50% of the GC, statistical analysis revealed significant differences in the LCL and MCL elongation patterns between the two implants, indicating slightly larger strains in the MCL and more slackening in the LCL of the knees with the DUAL implant (\(p\) < 0.012; Figures 2 and 3). Moreover, within the last 10% of the GC, significant differences between the GRAD and DUAL implants were observed in the length change patterns of all ligaments (\(p\) < 0.022; Figures 2 and 3).  
Comparing the two implant designs, the flexion-dependent elongation patterns revealed higher strains in the anterior lateral PCL and LCL for the DUAL implant in comparison to the GRAD design for flexion angles above 18\({}^{\circ}\) and 26\({}^{\circ}\), respectively (\(p\) < 0.013; Figures 4 and 5).  
Figure 2: Average elongation patterns throughout the complete level walking cycle. Solid lines represent inter-subject means and shaded area represent \(\pm\) SDs. The vertical dashed lines show the averaged 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; and LCL: lateral collateral ligament. The dotted lines represent the average toe-off times.  
Figure 4: Average elongation patterns of the knee ligaments during level walking throughout the range of knee flexion. Solid lines represent the group average across all subjects. Dashed lines represent the group average when data for more than 6 subjects were available. Shaded areas represent \(\pm\) SDs considering more than 6 subjects. 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; and LCL: lateral collateral ligament.  
Figure 3: SPM plots indicating significant differences between GRAD and DUAL ligament elongation patterns throughout the complete gait cycle of level gait. Red dashed line represents F value corresponding to the level of significance \(\alpha=0.05\). The gray shaded areas represent regions of statistical significance. 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; and LCL: lateral collateral ligament.